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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  linux/kernel/printk.c
  *
  *  Copyright (C) 1991, 1992  Linus Torvalds
  *
  * Modified to make sys_syslog() more flexible: added commands to
  * return the last 4k of kernel messages, regardless of whether
  * they've been read or not.  Added option to suppress kernel printk's
  * to the console.  Added hook for sending the console messages
  * elsewhere, in preparation for a serial line console (someday).
  * Ted Ts'o, 2/11/93.
  * Modified for sysctl support, 1/8/97, Chris Horn.
  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
  *     manfred@colorfullife.com
  * Rewrote bits to get rid of console_lock
  *  01Mar01 Andrew Morton
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
 #include <linux/console.h>
 #include <linux/init.h>
 #include <linux/jiffies.h>
 #include <linux/nmi.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/delay.h>
 #include <linux/smp.h>
 #include <linux/security.h>
 #include <linux/memblock.h>
 #include <linux/syscalls.h>
 #include <linux/crash_core.h>
 #include <linux/ratelimit.h>
 #include <linux/kmsg_dump.h>
 #include <linux/syslog.h>
 #include <linux/cpu.h>
 #include <linux/rculist.h>
 #include <linux/poll.h>
 #include <linux/irq_work.h>
 #include <linux/ctype.h>
 #include <linux/uio.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/task_stack.h>
 
 #include <linux/uaccess.h>
 #include <asm/sections.h>
 
 #include <trace/events/initcall.h>
 #define CREATE_TRACE_POINTS
 #include <trace/events/printk.h>
 
 #include "printk_ringbuffer.h"
 #include "console_cmdline.h"
 #include "braille.h"
 #include "internal.h"
 
 int console_printk[4] = {
     CONSOLE_LOGLEVEL_DEFAULT,   /* console_loglevel */
     MESSAGE_LOGLEVEL_DEFAULT,   /* default_message_loglevel */
     CONSOLE_LOGLEVEL_MIN,       /* minimum_console_loglevel */
     CONSOLE_LOGLEVEL_DEFAULT,   /* default_console_loglevel */
 };
 EXPORT_SYMBOL_GPL(console_printk);
 
 atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
 EXPORT_SYMBOL(ignore_console_lock_warning);
 
 /*
  * Low level drivers may need that to know if they can schedule in
  * their unblank() callback or not. So let's export it.
  */
 int oops_in_progress;
 EXPORT_SYMBOL(oops_in_progress);
 
 /*
  * console_sem protects the console_drivers list, and also
  * provides serialisation for access to the entire console
  * driver system.
  */
 static DEFINE_SEMAPHORE(console_sem);
 struct console *console_drivers;
 EXPORT_SYMBOL_GPL(console_drivers);
 
 /*
  * System may need to suppress printk message under certain
  * circumstances, like after kernel panic happens.
  */
 int __read_mostly suppress_printk;
 
 /*
  * During panic, heavy printk by other CPUs can delay the
  * panic and risk deadlock on console resources.
  */
 static int __read_mostly suppress_panic_printk;
 
 #ifdef CONFIG_LOCKDEP
 static struct lockdep_map console_lock_dep_map = {
     .name = "console_lock"
 };
 #endif
 
 enum devkmsg_log_bits {
     __DEVKMSG_LOG_BIT_ON = 0,
     __DEVKMSG_LOG_BIT_OFF,
     __DEVKMSG_LOG_BIT_LOCK,
 };
 
 enum devkmsg_log_masks {
     DEVKMSG_LOG_MASK_ON             = BIT(__DEVKMSG_LOG_BIT_ON),
     DEVKMSG_LOG_MASK_OFF            = BIT(__DEVKMSG_LOG_BIT_OFF),
     DEVKMSG_LOG_MASK_LOCK           = BIT(__DEVKMSG_LOG_BIT_LOCK),
 };
 
 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
 #define DEVKMSG_LOG_MASK_DEFAULT    0
 
 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
 
 static int __control_devkmsg(char *str)
 {
     size_t len;
 
     if (!str)
         return -EINVAL;
 
     len = str_has_prefix(str, "on");
     if (len) {
         devkmsg_log = DEVKMSG_LOG_MASK_ON;
         return len;
     }
 
     len = str_has_prefix(str, "off");
     if (len) {
         devkmsg_log = DEVKMSG_LOG_MASK_OFF;
         return len;
     }
 
     len = str_has_prefix(str, "ratelimit");
     if (len) {
         devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
         return len;
     }
 
     return -EINVAL;
 }
 
 static int __init control_devkmsg(char *str)
 {
     if (__control_devkmsg(str) < 0) {
         pr_warn("printk.devkmsg: bad option string '%s'\n", str);
         return 1;
     }
 
     /*
      * Set sysctl string accordingly:
      */
     if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
         strcpy(devkmsg_log_str, "on");
     else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
         strcpy(devkmsg_log_str, "off");
     /* else "ratelimit" which is set by default. */
 
     /*
      * Sysctl cannot change it anymore. The kernel command line setting of
      * this parameter is to force the setting to be permanent throughout the
      * runtime of the system. This is a precation measure against userspace
      * trying to be a smarta** and attempting to change it up on us.
      */
     devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
 
     return 1;
 }
 __setup("printk.devkmsg=", control_devkmsg);
 
 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
 int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
                   void *buffer, size_t *lenp, loff_t *ppos)
 {
     char old_str[DEVKMSG_STR_MAX_SIZE];
     unsigned int old;
     int err;
 
     if (write) {
         if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
             return -EINVAL;
 
         old = devkmsg_log;
         strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
     }
 
     err = proc_dostring(table, write, buffer, lenp, ppos);
     if (err)
         return err;
 
     if (write) {
         err = __control_devkmsg(devkmsg_log_str);
 
         /*
          * Do not accept an unknown string OR a known string with
          * trailing crap...
          */
         if (err < 0 || (err + 1 != *lenp)) {
 
             /* ... and restore old setting. */
             devkmsg_log = old;
             strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
 
             return -EINVAL;
         }
     }
 
     return 0;
 }
 #endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
 
 /* Number of registered extended console drivers. */
 static int nr_ext_console_drivers;
 
 /*
  * Helper macros to handle lockdep when locking/unlocking console_sem. We use
  * macros instead of functions so that _RET_IP_ contains useful information.
  */
 #define down_console_sem() do { \
     down(&console_sem);\
     mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
 } while (0)
 
 static int __down_trylock_console_sem(unsigned long ip)
 {
     int lock_failed;
     unsigned long flags;
 
     /*
      * Here and in __up_console_sem() we need to be in safe mode,
      * because spindump/WARN/etc from under console ->lock will
      * deadlock in printk()->down_trylock_console_sem() otherwise.
      */
     printk_safe_enter_irqsave(flags);
     lock_failed = down_trylock(&console_sem);
     printk_safe_exit_irqrestore(flags);
 
     if (lock_failed)
         return 1;
     mutex_acquire(&console_lock_dep_map, 0, 1, ip);
     return 0;
 }
 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
 
 static void __up_console_sem(unsigned long ip)
 {
     unsigned long flags;
 
     mutex_release(&console_lock_dep_map, ip);
 
     printk_safe_enter_irqsave(flags);
     up(&console_sem);
     printk_safe_exit_irqrestore(flags);
 }
 #define up_console_sem() __up_console_sem(_RET_IP_)
 
 static bool panic_in_progress(void)
 {
     return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
 }
 
 /*
  * This is used for debugging the mess that is the VT code by
  * keeping track if we have the console semaphore held. It's
  * definitely not the perfect debug tool (we don't know if _WE_
  * hold it and are racing, but it helps tracking those weird code
  * paths in the console code where we end up in places I want
  * locked without the console semaphore held).
  */
 static int console_locked, console_suspended;
 
 /*
  *  Array of consoles built from command line options (console=)
  */
 
 #define MAX_CMDLINECONSOLES 8
 
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 
 static int preferred_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
 
 /* Flag: console code may call schedule() */
 static int console_may_schedule;
 
 enum con_msg_format_flags {
     MSG_FORMAT_DEFAULT  = 0,
     MSG_FORMAT_SYSLOG   = (1 << 0),
 };
 
 static int console_msg_format = MSG_FORMAT_DEFAULT;
 
 /*
  * The printk log buffer consists of a sequenced collection of records, each
  * containing variable length message text. Every record also contains its
  * own meta-data (@info).
  *
  * Every record meta-data carries the timestamp in microseconds, as well as
  * the standard userspace syslog level and syslog facility. The usual kernel
  * messages use LOG_KERN; userspace-injected messages always carry a matching
  * syslog facility, by default LOG_USER. The origin of every message can be
  * reliably determined that way.
  *
  * The human readable log message of a record is available in @text, the
  * length of the message text in @text_len. The stored message is not
  * terminated.
  *
  * Optionally, a record can carry a dictionary of properties (key/value
  * pairs), to provide userspace with a machine-readable message context.
  *
  * Examples for well-defined, commonly used property names are:
  *   DEVICE=b12:8               device identifier
  *                                b12:8         block dev_t
  *                                c127:3        char dev_t
  *                                n8            netdev ifindex
  *                                +sound:card0  subsystem:devname
  *   SUBSYSTEM=pci              driver-core subsystem name
  *
  * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
  * and values are terminated by a '\0' character.
  *
  * Example of record values:
  *   record.text_buf                = "it's a line" (unterminated)
  *   record.info.seq                = 56
  *   record.info.ts_nsec            = 36863
  *   record.info.text_len           = 11
  *   record.info.facility           = 0 (LOG_KERN)
  *   record.info.flags              = 0
  *   record.info.level              = 3 (LOG_ERR)
  *   record.info.caller_id          = 299 (task 299)
  *   record.info.dev_info.subsystem = "pci" (terminated)
  *   record.info.dev_info.device    = "+pci:0000:00:01.0" (terminated)
  *
  * The 'struct printk_info' buffer must never be directly exported to
  * userspace, it is a kernel-private implementation detail that might
  * need to be changed in the future, when the requirements change.
  *
  * /dev/kmsg exports the structured data in the following line format:
  *   "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
  *
  * Users of the export format should ignore possible additional values
  * separated by ',', and find the message after the ';' character.
  *
  * The optional key/value pairs are attached as continuation lines starting
  * with a space character and terminated by a newline. All possible
  * non-prinatable characters are escaped in the "\xff" notation.
  */
 
 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
 static DEFINE_MUTEX(syslog_lock);
 
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
 /* All 3 protected by @syslog_lock. */
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
 static u64 syslog_seq;
 static size_t syslog_partial;
 static bool syslog_time;
 
 struct latched_seq {
     seqcount_latch_t    latch;
     u64         val[2];
 };
 
 /*
  * The next printk record to read after the last 'clear' command. There are
  * two copies (updated with seqcount_latch) so that reads can locklessly
  * access a valid value. Writers are synchronized by @syslog_lock.
  */
 static struct latched_seq clear_seq = {
     .latch      = SEQCNT_LATCH_ZERO(clear_seq.latch),
     .val[0]     = 0,
     .val[1]     = 0,
 };
 
 #ifdef CONFIG_PRINTK_CALLER
 #define PREFIX_MAX      48
 #else
 #define PREFIX_MAX      32
 #endif
 
 /* the maximum size of a formatted record (i.e. with prefix added per line) */
 #define CONSOLE_LOG_MAX     1024
 
 /* the maximum size for a dropped text message */
 #define DROPPED_TEXT_MAX    64
 
 /* the maximum size allowed to be reserved for a record */
 #define LOG_LINE_MAX        (CONSOLE_LOG_MAX - PREFIX_MAX)
 
 #define LOG_LEVEL(v)        ((v) & 0x07)
 #define LOG_FACILITY(v)     ((v) >> 3 & 0xff)
 
 /* record buffer */
 #define LOG_ALIGN __alignof__(unsigned long)
 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
 static char *log_buf = __log_buf;
 static u32 log_buf_len = __LOG_BUF_LEN;
 
 /*
  * Define the average message size. This only affects the number of
  * descriptors that will be available. Underestimating is better than
  * overestimating (too many available descriptors is better than not enough).
  */
 #define PRB_AVGBITS 5   /* 32 character average length */
 
 #if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
 #error CONFIG_LOG_BUF_SHIFT value too small.
 #endif
 _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
          PRB_AVGBITS, &__log_buf[0]);
 
 static struct printk_ringbuffer printk_rb_dynamic;
 
 static struct printk_ringbuffer *prb = &printk_rb_static;
 
 /*
  * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
  * per_cpu_areas are initialised. This variable is set to true when
  * it's safe to access per-CPU data.
  */
 static bool __printk_percpu_data_ready __read_mostly;
 
 bool printk_percpu_data_ready(void)
 {
     return __printk_percpu_data_ready;
 }
 
 /* Must be called under syslog_lock. */
 static void latched_seq_write(struct latched_seq *ls, u64 val)
 {
     raw_write_seqcount_latch(&ls->latch);
     ls->val[0] = val;
     raw_write_seqcount_latch(&ls->latch);
     ls->val[1] = val;
 }
 
 /* Can be called from any context. */
 static u64 latched_seq_read_nolock(struct latched_seq *ls)
 {
     unsigned int seq;
     unsigned int idx;
     u64 val;
 
     do {
         seq = raw_read_seqcount_latch(&ls->latch);
         idx = seq & 0x1;
         val = ls->val[idx];
     } while (read_seqcount_latch_retry(&ls->latch, seq));
 
     return val;
 }
 
 /* Return log buffer address */
 char *log_buf_addr_get(void)
 {
     return log_buf;
 }
 
 /* Return log buffer size */
 u32 log_buf_len_get(void)
 {
     return log_buf_len;
 }
 
 /*
  * Define how much of the log buffer we could take at maximum. The value
  * must be greater than two. Note that only half of the buffer is available
  * when the index points to the middle.
  */
 #define MAX_LOG_TAKE_PART 4
 static const char trunc_msg[] = "<truncated>";
 
 static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
 {
     /*
      * The message should not take the whole buffer. Otherwise, it might
      * get removed too soon.
      */
     u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
 
     if (*text_len > max_text_len)
         *text_len = max_text_len;
 
     /* enable the warning message (if there is room) */
     *trunc_msg_len = strlen(trunc_msg);
     if (*text_len >= *trunc_msg_len)
         *text_len -= *trunc_msg_len;
     else
         *trunc_msg_len = 0;
 }
 
 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
 
 static int syslog_action_restricted(int type)
 {
     if (dmesg_restrict)
         return 1;
     /*
      * Unless restricted, we allow "read all" and "get buffer size"
      * for everybody.
      */
     return type != SYSLOG_ACTION_READ_ALL &&
            type != SYSLOG_ACTION_SIZE_BUFFER;
 }
 
 static int check_syslog_permissions(int type, int source)
 {
     /*
      * If this is from /proc/kmsg and we've already opened it, then we've
      * already done the capabilities checks at open time.
      */
     if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
         goto ok;
 
     if (syslog_action_restricted(type)) {
         if (capable(CAP_SYSLOG))
             goto ok;
         /*
          * For historical reasons, accept CAP_SYS_ADMIN too, with
          * a warning.
          */
         if (capable(CAP_SYS_ADMIN)) {
             pr_warn_once("%s (%d): Attempt to access syslog with "
                      "CAP_SYS_ADMIN but no CAP_SYSLOG "
                      "(deprecated).\n",
                  current->comm, task_pid_nr(current));
             goto ok;
         }
         return -EPERM;
     }
 ok:
     return security_syslog(type);
 }
 
 static void append_char(char **pp, char *e, char c)
 {
     if (*pp < e)
         *(*pp)++ = c;
 }
 
 static ssize_t info_print_ext_header(char *buf, size_t size,
                      struct printk_info *info)
 {
     u64 ts_usec = info->ts_nsec;
     char caller[20];
 #ifdef CONFIG_PRINTK_CALLER
     u32 id = info->caller_id;
 
     snprintf(caller, sizeof(caller), ",caller=%c%u",
          id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
 #else
     caller[0] = '\0';
 #endif
 
     do_div(ts_usec, 1000);
 
     return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
              (info->facility << 3) | info->level, info->seq,
              ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
 }
 
 static ssize_t msg_add_ext_text(char *buf, size_t size,
                 const char *text, size_t text_len,
                 unsigned char endc)
 {
     char *p = buf, *e = buf + size;
     size_t i;
 
     /* escape non-printable characters */
     for (i = 0; i < text_len; i++) {
         unsigned char c = text[i];
 
         if (c < ' ' || c >= 127 || c == '\\')
             p += scnprintf(p, e - p, "\\x%02x", c);
         else
             append_char(&p, e, c);
     }
     append_char(&p, e, endc);
 
     return p - buf;
 }
 
 static ssize_t msg_add_dict_text(char *buf, size_t size,
                  const char *key, const char *val)
 {
     size_t val_len = strlen(val);
     ssize_t len;
 
     if (!val_len)
         return 0;
 
     len = msg_add_ext_text(buf, size, "", 0, ' ');  /* dict prefix */
     len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
     len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
 
     return len;
 }
 
 static ssize_t msg_print_ext_body(char *buf, size_t size,
                   char *text, size_t text_len,
                   struct dev_printk_info *dev_info)
 {
     ssize_t len;
 
     len = msg_add_ext_text(buf, size, text, text_len, '\n');
 
     if (!dev_info)
         goto out;
 
     len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
                  dev_info->subsystem);
     len += msg_add_dict_text(buf + len, size - len, "DEVICE",
                  dev_info->device);
 out:
     return len;
 }
 
 /* /dev/kmsg - userspace message inject/listen interface */
 struct devkmsg_user {
     atomic64_t seq;
     struct ratelimit_state rs;
     struct mutex lock;
     char buf[CONSOLE_EXT_LOG_MAX];
 
     struct printk_info info;
     char text_buf[CONSOLE_EXT_LOG_MAX];
     struct printk_record record;
 };
 
 static __printf(3, 4) __cold
 int devkmsg_emit(int facility, int level, const char *fmt, ...)
 {
     va_list args;
     int r;
 
     va_start(args, fmt);
     r = vprintk_emit(facility, level, NULL, fmt, args);
     va_end(args);
 
     return r;
 }
 
 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
 {
     char *buf, *line;
     int level = default_message_loglevel;
     int facility = 1;   /* LOG_USER */
     struct file *file = iocb->ki_filp;
     struct devkmsg_user *user = file->private_data;
     size_t len = iov_iter_count(from);
     ssize_t ret = len;
 
     if (!user || len > LOG_LINE_MAX)
         return -EINVAL;
 
     /* Ignore when user logging is disabled. */
     if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
         return len;
 
     /* Ratelimit when not explicitly enabled. */
     if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
         if (!___ratelimit(&user->rs, current->comm))
             return ret;
     }
 
     buf = kmalloc(len+1, GFP_KERNEL);
     if (buf == NULL)
         return -ENOMEM;
 
     buf[len] = '\0';
     if (!copy_from_iter_full(buf, len, from)) {
         kfree(buf);
         return -EFAULT;
     }
 
     /*
      * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
      * the decimal value represents 32bit, the lower 3 bit are the log
      * level, the rest are the log facility.
      *
      * If no prefix or no userspace facility is specified, we
      * enforce LOG_USER, to be able to reliably distinguish
      * kernel-generated messages from userspace-injected ones.
      */
     line = buf;
     if (line[0] == '<') {
         char *endp = NULL;
         unsigned int u;
 
         u = simple_strtoul(line + 1, &endp, 10);
         if (endp && endp[0] == '>') {
             level = LOG_LEVEL(u);
             if (LOG_FACILITY(u) != 0)
                 facility = LOG_FACILITY(u);
             endp++;
             line = endp;
         }
     }
 
     devkmsg_emit(facility, level, "%s", line);
     kfree(buf);
     return ret;
 }
 
 static ssize_t devkmsg_read(struct file *file, char __user *buf,
                 size_t count, loff_t *ppos)
 {
     struct devkmsg_user *user = file->private_data;
     struct printk_record *r = &user->record;
     size_t len;
     ssize_t ret;
 
     if (!user)
         return -EBADF;
 
     ret = mutex_lock_interruptible(&user->lock);
     if (ret)
         return ret;
 
     if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
         if (file->f_flags & O_NONBLOCK) {
             ret = -EAGAIN;
             goto out;
         }
 
         /*
          * Guarantee this task is visible on the waitqueue before
          * checking the wake condition.
          *
          * The full memory barrier within set_current_state() of
          * prepare_to_wait_event() pairs with the full memory barrier
          * within wq_has_sleeper().
          *
          * This pairs with __wake_up_klogd:A.
          */
         ret = wait_event_interruptible(log_wait,
                 prb_read_valid(prb,
                     atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
         if (ret)
             goto out;
     }
 
     if (r->info->seq != atomic64_read(&user->seq)) {
         /* our last seen message is gone, return error and reset */
         atomic64_set(&user->seq, r->info->seq);
         ret = -EPIPE;
         goto out;
     }
 
     len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
     len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
                   &r->text_buf[0], r->info->text_len,
                   &r->info->dev_info);
 
     atomic64_set(&user->seq, r->info->seq + 1);
 
     if (len > count) {
         ret = -EINVAL;
         goto out;
     }
 
     if (copy_to_user(buf, user->buf, len)) {
         ret = -EFAULT;
         goto out;
     }
     ret = len;
 out:
     mutex_unlock(&user->lock);
     return ret;
 }
 
 /*
  * Be careful when modifying this function!!!
  *
  * Only few operations are supported because the device works only with the
  * entire variable length messages (records). Non-standard values are
  * returned in the other cases and has been this way for quite some time.
  * User space applications might depend on this behavior.
  */
 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 {
     struct devkmsg_user *user = file->private_data;
     loff_t ret = 0;
 
     if (!user)
         return -EBADF;
     if (offset)
         return -ESPIPE;
 
     switch (whence) {
     case SEEK_SET:
         /* the first record */
         atomic64_set(&user->seq, prb_first_valid_seq(prb));
         break;
     case SEEK_DATA:
         /*
          * The first record after the last SYSLOG_ACTION_CLEAR,
          * like issued by 'dmesg -c'. Reading /dev/kmsg itself
          * changes no global state, and does not clear anything.
          */
         atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
         break;
     case SEEK_END:
         /* after the last record */
         atomic64_set(&user->seq, prb_next_seq(prb));
         break;
     default:
         ret = -EINVAL;
     }
     return ret;
 }
 
 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 {
     struct devkmsg_user *user = file->private_data;
     struct printk_info info;
     __poll_t ret = 0;
 
     if (!user)
         return EPOLLERR|EPOLLNVAL;
 
     poll_wait(file, &log_wait, wait);
 
     if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
         /* return error when data has vanished underneath us */
         if (info.seq != atomic64_read(&user->seq))
             ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
         else
             ret = EPOLLIN|EPOLLRDNORM;
     }
 
     return ret;
 }
 
 static int devkmsg_open(struct inode *inode, struct file *file)
 {
     struct devkmsg_user *user;
     int err;
 
     if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
         return -EPERM;
 
     /* write-only does not need any file context */
     if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
         err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
                            SYSLOG_FROM_READER);
         if (err)
             return err;
     }
 
     user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
     if (!user)
         return -ENOMEM;
 
     ratelimit_default_init(&user->rs);
     ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
 
     mutex_init(&user->lock);
 
     prb_rec_init_rd(&user->record, &user->info,
             &user->text_buf[0], sizeof(user->text_buf));
 
     atomic64_set(&user->seq, prb_first_valid_seq(prb));
 
     file->private_data = user;
     return 0;
 }
 
 static int devkmsg_release(struct inode *inode, struct file *file)
 {
     struct devkmsg_user *user = file->private_data;
 
     if (!user)
         return 0;
 
     ratelimit_state_exit(&user->rs);
 
     mutex_destroy(&user->lock);
     kvfree(user);
     return 0;
 }
 
 const struct file_operations kmsg_fops = {
     .open = devkmsg_open,
     .read = devkmsg_read,
     .write_iter = devkmsg_write,
     .llseek = devkmsg_llseek,
     .poll = devkmsg_poll,
     .release = devkmsg_release,
 };
 
 #ifdef CONFIG_CRASH_CORE
 /*
  * This appends the listed symbols to /proc/vmcore
  *
  * /proc/vmcore is used by various utilities, like crash and makedumpfile to
  * obtain access to symbols that are otherwise very difficult to locate.  These
  * symbols are specifically used so that utilities can access and extract the
  * dmesg log from a vmcore file after a crash.
  */
 void log_buf_vmcoreinfo_setup(void)
 {
     struct dev_printk_info *dev_info = NULL;
 
     VMCOREINFO_SYMBOL(prb);
     VMCOREINFO_SYMBOL(printk_rb_static);
     VMCOREINFO_SYMBOL(clear_seq);
 
     /*
      * Export struct size and field offsets. User space tools can
      * parse it and detect any changes to structure down the line.
      */
 
     VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
     VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
     VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
     VMCOREINFO_OFFSET(printk_ringbuffer, fail);
 
     VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
     VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
     VMCOREINFO_OFFSET(prb_desc_ring, descs);
     VMCOREINFO_OFFSET(prb_desc_ring, infos);
     VMCOREINFO_OFFSET(prb_desc_ring, head_id);
     VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
 
     VMCOREINFO_STRUCT_SIZE(prb_desc);
     VMCOREINFO_OFFSET(prb_desc, state_var);
     VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
 
     VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
     VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
     VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
 
     VMCOREINFO_STRUCT_SIZE(printk_info);
     VMCOREINFO_OFFSET(printk_info, seq);
     VMCOREINFO_OFFSET(printk_info, ts_nsec);
     VMCOREINFO_OFFSET(printk_info, text_len);
     VMCOREINFO_OFFSET(printk_info, caller_id);
     VMCOREINFO_OFFSET(printk_info, dev_info);
 
     VMCOREINFO_STRUCT_SIZE(dev_printk_info);
     VMCOREINFO_OFFSET(dev_printk_info, subsystem);
     VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
     VMCOREINFO_OFFSET(dev_printk_info, device);
     VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
 
     VMCOREINFO_STRUCT_SIZE(prb_data_ring);
     VMCOREINFO_OFFSET(prb_data_ring, size_bits);
     VMCOREINFO_OFFSET(prb_data_ring, data);
     VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
     VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
 
     VMCOREINFO_SIZE(atomic_long_t);
     VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
 
     VMCOREINFO_STRUCT_SIZE(latched_seq);
     VMCOREINFO_OFFSET(latched_seq, val);
 }
 #endif
 
 /* requested log_buf_len from kernel cmdline */
 static unsigned long __initdata new_log_buf_len;
 
 /* we practice scaling the ring buffer by powers of 2 */
 static void __init log_buf_len_update(u64 size)
 {
     if (size > (u64)LOG_BUF_LEN_MAX) {
         size = (u64)LOG_BUF_LEN_MAX;
         pr_err("log_buf over 2G is not supported.\n");
     }
 
     if (size)
         size = roundup_pow_of_two(size);
     if (size > log_buf_len)
         new_log_buf_len = (unsigned long)size;
 }
 
 /* save requested log_buf_len since it's too early to process it */
 static int __init log_buf_len_setup(char *str)
 {
     u64 size;
 
     if (!str)
         return -EINVAL;
 
     size = memparse(str, &str);
 
     log_buf_len_update(size);
 
     return 0;
 }
 early_param("log_buf_len", log_buf_len_setup);
 
 #ifdef CONFIG_SMP
 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
 
 static void __init log_buf_add_cpu(void)
 {
     unsigned int cpu_extra;
 
     /*
      * archs should set up cpu_possible_bits properly with
      * set_cpu_possible() after setup_arch() but just in
      * case lets ensure this is valid.
      */
     if (num_possible_cpus() == 1)
         return;
 
     cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
 
     /* by default this will only continue through for large > 64 CPUs */
     if (cpu_extra <= __LOG_BUF_LEN / 2)
         return;
 
     pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
         __LOG_CPU_MAX_BUF_LEN);
     pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
         cpu_extra);
     pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
 
     log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
 }
 #else /* !CONFIG_SMP */
 static inline void log_buf_add_cpu(void) {}
 #endif /* CONFIG_SMP */
 
 static void __init set_percpu_data_ready(void)
 {
     __printk_percpu_data_ready = true;
 }
 
 static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
                      struct printk_record *r)
 {
     struct prb_reserved_entry e;
     struct printk_record dest_r;
 
     prb_rec_init_wr(&dest_r, r->info->text_len);
 
     if (!prb_reserve(&e, rb, &dest_r))
         return 0;
 
     memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
     dest_r.info->text_len = r->info->text_len;
     dest_r.info->facility = r->info->facility;
     dest_r.info->level = r->info->level;
     dest_r.info->flags = r->info->flags;
     dest_r.info->ts_nsec = r->info->ts_nsec;
     dest_r.info->caller_id = r->info->caller_id;
     memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
 
     prb_final_commit(&e);
 
     return prb_record_text_space(&e);
 }
 
 static char setup_text_buf[LOG_LINE_MAX] __initdata;
 
 void __init setup_log_buf(int early)
 {
     struct printk_info *new_infos;
     unsigned int new_descs_count;
     struct prb_desc *new_descs;
     struct printk_info info;
     struct printk_record r;
     unsigned int text_size;
     size_t new_descs_size;
     size_t new_infos_size;
     unsigned long flags;
     char *new_log_buf;
     unsigned int free;
     u64 seq;
 
     /*
      * Some archs call setup_log_buf() multiple times - first is very
      * early, e.g. from setup_arch(), and second - when percpu_areas
      * are initialised.
      */
     if (!early)
         set_percpu_data_ready();
 
     if (log_buf != __log_buf)
         return;
 
     if (!early && !new_log_buf_len)
         log_buf_add_cpu();
 
     if (!new_log_buf_len)
         return;
 
     new_descs_count = new_log_buf_len >> PRB_AVGBITS;
     if (new_descs_count == 0) {
         pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
         return;
     }
 
     new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
     if (unlikely(!new_log_buf)) {
         pr_err("log_buf_len: %lu text bytes not available\n",
                new_log_buf_len);
         return;
     }
 
     new_descs_size = new_descs_count * sizeof(struct prb_desc);
     new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
     if (unlikely(!new_descs)) {
         pr_err("log_buf_len: %zu desc bytes not available\n",
                new_descs_size);
         goto err_free_log_buf;
     }
 
     new_infos_size = new_descs_count * sizeof(struct printk_info);
     new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
     if (unlikely(!new_infos)) {
         pr_err("log_buf_len: %zu info bytes not available\n",
                new_infos_size);
         goto err_free_descs;
     }
 
     prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
 
     prb_init(&printk_rb_dynamic,
          new_log_buf, ilog2(new_log_buf_len),
          new_descs, ilog2(new_descs_count),
          new_infos);
 
     local_irq_save(flags);
 
     log_buf_len = new_log_buf_len;
     log_buf = new_log_buf;
     new_log_buf_len = 0;
 
     free = __LOG_BUF_LEN;
     prb_for_each_record(0, &printk_rb_static, seq, &r) {
         text_size = add_to_rb(&printk_rb_dynamic, &r);
         if (text_size > free)
             free = 0;
         else
             free -= text_size;
     }
 
     prb = &printk_rb_dynamic;
 
     local_irq_restore(flags);
 
     /*
      * Copy any remaining messages that might have appeared from
      * NMI context after copying but before switching to the
      * dynamic buffer.
      */
     prb_for_each_record(seq, &printk_rb_static, seq, &r) {
         text_size = add_to_rb(&printk_rb_dynamic, &r);
         if (text_size > free)
             free = 0;
         else
             free -= text_size;
     }
 
     if (seq != prb_next_seq(&printk_rb_static)) {
         pr_err("dropped %llu messages\n",
                prb_next_seq(&printk_rb_static) - seq);
     }
 
     pr_info("log_buf_len: %u bytes\n", log_buf_len);
     pr_info("early log buf free: %u(%u%%)\n",
         free, (free * 100) / __LOG_BUF_LEN);
     return;
 
 err_free_descs:
     memblock_free(new_descs, new_descs_size);
 err_free_log_buf:
     memblock_free(new_log_buf, new_log_buf_len);
 }
 
 static bool __read_mostly ignore_loglevel;
 
 static int __init ignore_loglevel_setup(char *str)
 {
     ignore_loglevel = true;
     pr_info("debug: ignoring loglevel setting.\n");
 
     return 0;
 }
 
 early_param("ignore_loglevel", ignore_loglevel_setup);
 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(ignore_loglevel,
          "ignore loglevel setting (prints all kernel messages to the console)");
 
 static bool suppress_message_printing(int level)
 {
     return (level >= console_loglevel && !ignore_loglevel);
 }
 
 #ifdef CONFIG_BOOT_PRINTK_DELAY
 
 static int boot_delay; /* msecs delay after each printk during bootup */
 static unsigned long long loops_per_msec;   /* based on boot_delay */
 
 static int __init boot_delay_setup(char *str)
 {
     unsigned long lpj;
 
     lpj = preset_lpj ? preset_lpj : 1000000;    /* some guess */
     loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 
     get_option(&str, &boot_delay);
     if (boot_delay > 10 * 1000)
         boot_delay = 0;
 
     pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
         "HZ: %d, loops_per_msec: %llu\n",
         boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
     return 0;
 }
 early_param("boot_delay", boot_delay_setup);
 
 static void boot_delay_msec(int level)
 {
     unsigned long long k;
     unsigned long timeout;
 
     if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
         || suppress_message_printing(level)) {
         return;
     }
 
     k = (unsigned long long)loops_per_msec * boot_delay;
 
     timeout = jiffies + msecs_to_jiffies(boot_delay);
     while (k) {
         k--;
         cpu_relax();
         /*
          * use (volatile) jiffies to prevent
          * compiler reduction; loop termination via jiffies
          * is secondary and may or may not happen.
          */
         if (time_after(jiffies, timeout))
             break;
         touch_nmi_watchdog();
     }
 }
 #else
 static inline void boot_delay_msec(int level)
 {
 }
 #endif
 
 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 
 static size_t print_syslog(unsigned int level, char *buf)
 {
     return sprintf(buf, "<%u>", level);
 }
 
 static size_t print_time(u64 ts, char *buf)
 {
     unsigned long rem_nsec = do_div(ts, 1000000000);
 
     return sprintf(buf, "[%5lu.%06lu]",
                (unsigned long)ts, rem_nsec / 1000);
 }
 
 #ifdef CONFIG_PRINTK_CALLER
 static size_t print_caller(u32 id, char *buf)
 {
     char caller[12];
 
     snprintf(caller, sizeof(caller), "%c%u",
          id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
     return sprintf(buf, "[%6s]", caller);
 }
 #else
 #define print_caller(id, buf) 0
 #endif
 
 static size_t info_print_prefix(const struct printk_info  *info, bool syslog,
                 bool time, char *buf)
 {
     size_t len = 0;
 
     if (syslog)
         len = print_syslog((info->facility << 3) | info->level, buf);
 
     if (time)
         len += print_time(info->ts_nsec, buf + len);
 
     len += print_caller(info->caller_id, buf + len);
 
     if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
         buf[len++] = ' ';
         buf[len] = '\0';
     }
 
     return len;
 }
 
 /*
  * Prepare the record for printing. The text is shifted within the given
  * buffer to avoid a need for another one. The following operations are
  * done:
  *
  *   - Add prefix for each line.
  *   - Drop truncated lines that no longer fit into the buffer.
  *   - Add the trailing newline that has been removed in vprintk_store().
  *   - Add a string terminator.
  *
  * Since the produced string is always terminated, the maximum possible
  * return value is @r->text_buf_size - 1;
  *
  * Return: The length of the updated/prepared text, including the added
  * prefixes and the newline. The terminator is not counted. The dropped
  * line(s) are not counted.
  */
 static size_t record_print_text(struct printk_record *r, bool syslog,
                 bool time)
 {
     size_t text_len = r->info->text_len;
     size_t buf_size = r->text_buf_size;
     char *text = r->text_buf;
     char prefix[PREFIX_MAX];
     bool truncated = false;
     size_t prefix_len;
     size_t line_len;
     size_t len = 0;
     char *next;
 
     /*
      * If the message was truncated because the buffer was not large
      * enough, treat the available text as if it were the full text.
      */
     if (text_len > buf_size)
         text_len = buf_size;
 
     prefix_len = info_print_prefix(r->info, syslog, time, prefix);
 
     /*
      * @text_len: bytes of unprocessed text
      * @line_len: bytes of current line _without_ newline
      * @text:     pointer to beginning of current line
      * @len:      number of bytes prepared in r->text_buf
      */
     for (;;) {
         next = memchr(text, '\n', text_len);
         if (next) {
             line_len = next - text;
         } else {
             /* Drop truncated line(s). */
             if (truncated)
                 break;
             line_len = text_len;
         }
 
         /*
          * Truncate the text if there is not enough space to add the
          * prefix and a trailing newline and a terminator.
          */
         if (len + prefix_len + text_len + 1 + 1 > buf_size) {
             /* Drop even the current line if no space. */
             if (len + prefix_len + line_len + 1 + 1 > buf_size)
                 break;
 
             text_len = buf_size - len - prefix_len - 1 - 1;
             truncated = true;
         }
 
         memmove(text + prefix_len, text, text_len);
         memcpy(text, prefix, prefix_len);
 
         /*
          * Increment the prepared length to include the text and
          * prefix that were just moved+copied. Also increment for the
          * newline at the end of this line. If this is the last line,
          * there is no newline, but it will be added immediately below.
          */
         len += prefix_len + line_len + 1;
         if (text_len == line_len) {
             /*
              * This is the last line. Add the trailing newline
              * removed in vprintk_store().
              */
             text[prefix_len + line_len] = '\n';
             break;
         }
 
         /*
          * Advance beyond the added prefix and the related line with
          * its newline.
          */
         text += prefix_len + line_len + 1;
 
         /*
          * The remaining text has only decreased by the line with its
          * newline.
          *
          * Note that @text_len can become zero. It happens when @text
          * ended with a newline (either due to truncation or the
          * original string ending with "\n\n"). The loop is correctly
          * repeated and (if not truncated) an empty line with a prefix
          * will be prepared.
          */
         text_len -= line_len + 1;
     }
 
     /*
      * If a buffer was provided, it will be terminated. Space for the
      * string terminator is guaranteed to be available. The terminator is
      * not counted in the return value.
      */
     if (buf_size > 0)
         r->text_buf[len] = 0;
 
     return len;
 }
 
 static size_t get_record_print_text_size(struct printk_info *info,
                      unsigned int line_count,
                      bool syslog, bool time)
 {
     char prefix[PREFIX_MAX];
     size_t prefix_len;
 
     prefix_len = info_print_prefix(info, syslog, time, prefix);
 
     /*
      * Each line will be preceded with a prefix. The intermediate
      * newlines are already within the text, but a final trailing
      * newline will be added.
      */
     return ((prefix_len * line_count) + info->text_len + 1);
 }
 
 /*
  * Beginning with @start_seq, find the first record where it and all following
  * records up to (but not including) @max_seq fit into @size.
  *
  * @max_seq is simply an upper bound and does not need to exist. If the caller
  * does not require an upper bound, -1 can be used for @max_seq.
  */
 static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
                   bool syslog, bool time)
 {
     struct printk_info info;
     unsigned int line_count;
     size_t len = 0;
     u64 seq;
 
     /* Determine the size of the records up to @max_seq. */
     prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
         if (info.seq >= max_seq)
             break;
         len += get_record_print_text_size(&info, line_count, syslog, time);
     }
 
     /*
      * Adjust the upper bound for the next loop to avoid subtracting
      * lengths that were never added.
      */
     if (seq < max_seq)
         max_seq = seq;
 
     /*
      * Move first record forward until length fits into the buffer. Ignore
      * newest messages that were not counted in the above cycle. Messages
      * might appear and get lost in the meantime. This is a best effort
      * that prevents an infinite loop that could occur with a retry.
      */
     prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
         if (len <= size || info.seq >= max_seq)
             break;
         len -= get_record_print_text_size(&info, line_count, syslog, time);
     }
 
     return seq;
 }
 
 /* The caller is responsible for making sure @size is greater than 0. */
 static int syslog_print(char __user *buf, int size)
 {
     struct printk_info info;
     struct printk_record r;
     char *text;
     int len = 0;
     u64 seq;
 
     text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
     if (!text)
         return -ENOMEM;
 
     prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
     mutex_lock(&syslog_lock);
 
     /*
      * Wait for the @syslog_seq record to be available. @syslog_seq may
      * change while waiting.
      */
     do {
         seq = syslog_seq;
 
         mutex_unlock(&syslog_lock);
         /*
          * Guarantee this task is visible on the waitqueue before
          * checking the wake condition.
          *
          * The full memory barrier within set_current_state() of
          * prepare_to_wait_event() pairs with the full memory barrier
          * within wq_has_sleeper().
          *
          * This pairs with __wake_up_klogd:A.
          */
         len = wait_event_interruptible(log_wait,
                 prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
         mutex_lock(&syslog_lock);
 
         if (len)
             goto out;
     } while (syslog_seq != seq);
 
     /*
      * Copy records that fit into the buffer. The above cycle makes sure
      * that the first record is always available.
      */
     do {
         size_t n;
         size_t skip;
         int err;
 
         if (!prb_read_valid(prb, syslog_seq, &r))
             break;
 
         if (r.info->seq != syslog_seq) {
             /* message is gone, move to next valid one */
             syslog_seq = r.info->seq;
             syslog_partial = 0;
         }
 
         /*
          * To keep reading/counting partial line consistent,
          * use printk_time value as of the beginning of a line.
          */
         if (!syslog_partial)
             syslog_time = printk_time;
 
         skip = syslog_partial;
         n = record_print_text(&r, true, syslog_time);
         if (n - syslog_partial <= size) {
             /* message fits into buffer, move forward */
             syslog_seq = r.info->seq + 1;
             n -= syslog_partial;
             syslog_partial = 0;
         } else if (!len){
             /* partial read(), remember position */
             n = size;
             syslog_partial += n;
         } else
             n = 0;
 
         if (!n)
             break;
 
         mutex_unlock(&syslog_lock);
         err = copy_to_user(buf, text + skip, n);
         mutex_lock(&syslog_lock);
 
         if (err) {
             if (!len)
                 len = -EFAULT;
             break;
         }
 
         len += n;
         size -= n;
         buf += n;
     } while (size);
 out:
     mutex_unlock(&syslog_lock);
     kfree(text);
     return len;
 }
 
 static int syslog_print_all(char __user *buf, int size, bool clear)
 {
     struct printk_info info;
     struct printk_record r;
     char *text;
     int len = 0;
     u64 seq;
     bool time;
 
     text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
     if (!text)
         return -ENOMEM;
 
     time = printk_time;
     /*
      * Find first record that fits, including all following records,
      * into the user-provided buffer for this dump.
      */
     seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
                      size, true, time);
 
     prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
     len = 0;
     prb_for_each_record(seq, prb, seq, &r) {
         int textlen;
 
         textlen = record_print_text(&r, true, time);
 
         if (len + textlen > size) {
             seq--;
             break;
         }
 
         if (copy_to_user(buf + len, text, textlen))
             len = -EFAULT;
         else
             len += textlen;
 
         if (len < 0)
             break;
     }
 
     if (clear) {
         mutex_lock(&syslog_lock);
         latched_seq_write(&clear_seq, seq);
         mutex_unlock(&syslog_lock);
     }
 
     kfree(text);
     return len;
 }
 
 static void syslog_clear(void)
 {
     mutex_lock(&syslog_lock);
     latched_seq_write(&clear_seq, prb_next_seq(prb));
     mutex_unlock(&syslog_lock);
 }
 
 int do_syslog(int type, char __user *buf, int len, int source)
 {
     struct printk_info info;
     bool clear = false;
     static int saved_console_loglevel = LOGLEVEL_DEFAULT;
     int error;
 
     error = check_syslog_permissions(type, source);
     if (error)
         return error;
 
     switch (type) {
     case SYSLOG_ACTION_CLOSE:   /* Close log */
         break;
     case SYSLOG_ACTION_OPEN:    /* Open log */
         break;
     case SYSLOG_ACTION_READ:    /* Read from log */
         if (!buf || len < 0)
             return -EINVAL;
         if (!len)
             return 0;
         if (!access_ok(buf, len))
             return -EFAULT;
         error = syslog_print(buf, len);
         break;
     /* Read/clear last kernel messages */
     case SYSLOG_ACTION_READ_CLEAR:
         clear = true;
         fallthrough;
     /* Read last kernel messages */
     case SYSLOG_ACTION_READ_ALL:
         if (!buf || len < 0)
             return -EINVAL;
         if (!len)
             return 0;
         if (!access_ok(buf, len))
             return -EFAULT;
         error = syslog_print_all(buf, len, clear);
         break;
     /* Clear ring buffer */
     case SYSLOG_ACTION_CLEAR:
         syslog_clear();
         break;
     /* Disable logging to console */
     case SYSLOG_ACTION_CONSOLE_OFF:
         if (saved_console_loglevel == LOGLEVEL_DEFAULT)
             saved_console_loglevel = console_loglevel;
         console_loglevel = minimum_console_loglevel;
         break;
     /* Enable logging to console */
     case SYSLOG_ACTION_CONSOLE_ON:
         if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
             console_loglevel = saved_console_loglevel;
             saved_console_loglevel = LOGLEVEL_DEFAULT;
         }
         break;
     /* Set level of messages printed to console */
     case SYSLOG_ACTION_CONSOLE_LEVEL:
         if (len < 1 || len > 8)
             return -EINVAL;
         if (len < minimum_console_loglevel)
             len = minimum_console_loglevel;
         console_loglevel = len;
         /* Implicitly re-enable logging to console */
         saved_console_loglevel = LOGLEVEL_DEFAULT;
         break;
     /* Number of chars in the log buffer */
     case SYSLOG_ACTION_SIZE_UNREAD:
         mutex_lock(&syslog_lock);
         if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
             /* No unread messages. */
             mutex_unlock(&syslog_lock);
             return 0;
         }
         if (info.seq != syslog_seq) {
             /* messages are gone, move to first one */
             syslog_seq = info.seq;
             syslog_partial = 0;
         }
         if (source == SYSLOG_FROM_PROC) {
             /*
              * Short-cut for poll(/"proc/kmsg") which simply checks
              * for pending data, not the size; return the count of
              * records, not the length.
              */
             error = prb_next_seq(prb) - syslog_seq;
         } else {
             bool time = syslog_partial ? syslog_time : printk_time;
             unsigned int line_count;
             u64 seq;
 
             prb_for_each_info(syslog_seq, prb, seq, &info,
                       &line_count) {
                 error += get_record_print_text_size(&info, line_count,
                                     true, time);
                 time = printk_time;
             }
             error -= syslog_partial;
         }
         mutex_unlock(&syslog_lock);
         break;
     /* Size of the log buffer */
     case SYSLOG_ACTION_SIZE_BUFFER:
         error = log_buf_len;
         break;
     default:
         error = -EINVAL;
         break;
     }
 
     return error;
 }
 
 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 {
     return do_syslog(type, buf, len, SYSLOG_FROM_READER);
 }
 
 /*
  * Special console_lock variants that help to reduce the risk of soft-lockups.
  * They allow to pass console_lock to another printk() call using a busy wait.
  */
 
 #ifdef CONFIG_LOCKDEP
 static struct lockdep_map console_owner_dep_map = {
     .name = "console_owner"
 };
 #endif
 
 static DEFINE_RAW_SPINLOCK(console_owner_lock);
 static struct task_struct *console_owner;
 static bool console_waiter;
 
 /**
  * console_lock_spinning_enable - mark beginning of code where another
  *  thread might safely busy wait
  *
  * This basically converts console_lock into a spinlock. This marks
  * the section where the console_lock owner can not sleep, because
  * there may be a waiter spinning (like a spinlock). Also it must be
  * ready to hand over the lock at the end of the section.
  */
 static void console_lock_spinning_enable(void)
 {
     raw_spin_lock(&console_owner_lock);
     console_owner = current;
     raw_spin_unlock(&console_owner_lock);
 
     /* The waiter may spin on us after setting console_owner */
     spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
 }
 
 /**
  * console_lock_spinning_disable_and_check - mark end of code where another
  *  thread was able to busy wait and check if there is a waiter
  *
  * This is called at the end of the section where spinning is allowed.
  * It has two functions. First, it is a signal that it is no longer
  * safe to start busy waiting for the lock. Second, it checks if
  * there is a busy waiter and passes the lock rights to her.
  *
  * Important: Callers lose the lock if there was a busy waiter.
  *  They must not touch items synchronized by console_lock
  *  in this case.
  *
  * Return: 1 if the lock rights were passed, 0 otherwise.
  */
 static int console_lock_spinning_disable_and_check(void)
 {
     int waiter;
 
     raw_spin_lock(&console_owner_lock);
     waiter = READ_ONCE(console_waiter);
     console_owner = NULL;
     raw_spin_unlock(&console_owner_lock);
 
     if (!waiter) {
         spin_release(&console_owner_dep_map, _THIS_IP_);
         return 0;
     }
 
     /* The waiter is now free to continue */
     WRITE_ONCE(console_waiter, false);
 
     spin_release(&console_owner_dep_map, _THIS_IP_);
 
     /*
      * Hand off console_lock to waiter. The waiter will perform
      * the up(). After this, the waiter is the console_lock owner.
      */
     mutex_release(&console_lock_dep_map, _THIS_IP_);
     return 1;
 }
 
 /**
  * console_trylock_spinning - try to get console_lock by busy waiting
  *
  * This allows to busy wait for the console_lock when the current
  * owner is running in specially marked sections. It means that
  * the current owner is running and cannot reschedule until it
  * is ready to lose the lock.
  *
  * Return: 1 if we got the lock, 0 othrewise
  */
 static int console_trylock_spinning(void)
 {
     struct task_struct *owner = NULL;
     bool waiter;
     bool spin = false;
     unsigned long flags;
 
     if (console_trylock())
         return 1;
 
     /*
      * It's unsafe to spin once a panic has begun. If we are the
      * panic CPU, we may have already halted the owner of the
      * console_sem. If we are not the panic CPU, then we should
      * avoid taking console_sem, so the panic CPU has a better
      * chance of cleanly acquiring it later.
      */
     if (panic_in_progress())
         return 0;
 
     printk_safe_enter_irqsave(flags);
 
     raw_spin_lock(&console_owner_lock);
     owner = READ_ONCE(console_owner);
     waiter = READ_ONCE(console_waiter);
     if (!waiter && owner && owner != current) {
         WRITE_ONCE(console_waiter, true);
         spin = true;
     }
     raw_spin_unlock(&console_owner_lock);
 
     /*
      * If there is an active printk() writing to the
      * consoles, instead of having it write our data too,
      * see if we can offload that load from the active
      * printer, and do some printing ourselves.
      * Go into a spin only if there isn't already a waiter
      * spinning, and there is an active printer, and
      * that active printer isn't us (recursive printk?).
      */
     if (!spin) {
         printk_safe_exit_irqrestore(flags);
         return 0;
     }
 
     /* We spin waiting for the owner to release us */
     spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
     /* Owner will clear console_waiter on hand off */
     while (READ_ONCE(console_waiter))
         cpu_relax();
     spin_release(&console_owner_dep_map, _THIS_IP_);
 
     printk_safe_exit_irqrestore(flags);
     /*
      * The owner passed the console lock to us.
      * Since we did not spin on console lock, annotate
      * this as a trylock. Otherwise lockdep will
      * complain.
      */
     mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
 
     return 1;
 }
 
 /*
  * Call the specified console driver, asking it to write out the specified
  * text and length. If @dropped_text is non-NULL and any records have been
  * dropped, a dropped message will be written out first.
  */
 static void call_console_driver(struct console *con, const char *text, size_t len,
                 char *dropped_text)
 {
     size_t dropped_len;
 
     if (con->dropped && dropped_text) {
         dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX,
                        "** %lu printk messages dropped **\n",
                        con->dropped);
         con->dropped = 0;
         con->write(con, dropped_text, dropped_len);
     }
 
     con->write(con, text, len);
 }
 
 /*
  * Recursion is tracked separately on each CPU. If NMIs are supported, an
  * additional NMI context per CPU is also separately tracked. Until per-CPU
  * is available, a separate "early tracking" is performed.
  */
 static DEFINE_PER_CPU(u8, printk_count);
 static u8 printk_count_early;
 #ifdef CONFIG_HAVE_NMI
 static DEFINE_PER_CPU(u8, printk_count_nmi);
 static u8 printk_count_nmi_early;
 #endif
 
 /*
  * Recursion is limited to keep the output sane. printk() should not require
  * more than 1 level of recursion (allowing, for example, printk() to trigger
  * a WARN), but a higher value is used in case some printk-internal errors
  * exist, such as the ringbuffer validation checks failing.
  */
 #define PRINTK_MAX_RECURSION 3
 
 /*
  * Return a pointer to the dedicated counter for the CPU+context of the
  * caller.
  */
 static u8 *__printk_recursion_counter(void)
 {
 #ifdef CONFIG_HAVE_NMI
     if (in_nmi()) {
         if (printk_percpu_data_ready())
             return this_cpu_ptr(&printk_count_nmi);
         return &printk_count_nmi_early;
     }
 #endif
     if (printk_percpu_data_ready())
         return this_cpu_ptr(&printk_count);
     return &printk_count_early;
 }
 
 /*
  * Enter recursion tracking. Interrupts are disabled to simplify tracking.
  * The caller must check the boolean return value to see if the recursion is
  * allowed. On failure, interrupts are not disabled.
  *
  * @recursion_ptr must be a variable of type (u8 *) and is the same variable
  * that is passed to printk_exit_irqrestore().
  */
 #define printk_enter_irqsave(recursion_ptr, flags)  \
 ({                          \
     bool success = true;                \
                             \
     typecheck(u8 *, recursion_ptr);         \
     local_irq_save(flags);              \
     (recursion_ptr) = __printk_recursion_counter(); \
     if (*(recursion_ptr) > PRINTK_MAX_RECURSION) {  \
         local_irq_restore(flags);       \
         success = false;            \
     } else {                    \
         (*(recursion_ptr))++;           \
     }                       \
     success;                    \
 })
 
 /* Exit recursion tracking, restoring interrupts. */
 #define printk_exit_irqrestore(recursion_ptr, flags)    \
     do {                        \
         typecheck(u8 *, recursion_ptr);     \
         (*(recursion_ptr))--;           \
         local_irq_restore(flags);       \
     } while (0)
 
 int printk_delay_msec __read_mostly;
 
 static inline void printk_delay(int level)
 {
     boot_delay_msec(level);
 
     if (unlikely(printk_delay_msec)) {
         int m = printk_delay_msec;
 
         while (m--) {
             mdelay(1);
             touch_nmi_watchdog();
         }
     }
 }
 
 static inline u32 printk_caller_id(void)
 {
     return in_task() ? task_pid_nr(current) :
         0x80000000 + smp_processor_id();
 }
 
 /**
  * printk_parse_prefix - Parse level and control flags.
  *
  * @text:     The terminated text message.
  * @level:    A pointer to the current level value, will be updated.
  * @flags:    A pointer to the current printk_info flags, will be updated.
  *
  * @level may be NULL if the caller is not interested in the parsed value.
  * Otherwise the variable pointed to by @level must be set to
  * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
  *
  * @flags may be NULL if the caller is not interested in the parsed value.
  * Otherwise the variable pointed to by @flags will be OR'd with the parsed
  * value.
  *
  * Return: The length of the parsed level and control flags.
  */
 u16 printk_parse_prefix(const char *text, int *level,
             enum printk_info_flags *flags)
 {
     u16 prefix_len = 0;
     int kern_level;
 
     while (*text) {
         kern_level = printk_get_level(text);
         if (!kern_level)
             break;
 
         switch (kern_level) {
         case '0' ... '7':
             if (level && *level == LOGLEVEL_DEFAULT)
                 *level = kern_level - '0';
             break;
         case 'c':   /* KERN_CONT */
             if (flags)
                 *flags |= LOG_CONT;
         }
 
         prefix_len += 2;
         text += 2;
     }
 
     return prefix_len;
 }
 
 __printf(5, 0)
 static u16 printk_sprint(char *text, u16 size, int facility,
              enum printk_info_flags *flags, const char *fmt,
              va_list args)
 {
     u16 text_len;
 
     text_len = vscnprintf(text, size, fmt, args);
 
     /* Mark and strip a trailing newline. */
     if (text_len && text[text_len - 1] == '\n') {
         text_len--;
         *flags |= LOG_NEWLINE;
     }
 
     /* Strip log level and control flags. */
     if (facility == 0) {
         u16 prefix_len;
 
         prefix_len = printk_parse_prefix(text, NULL, NULL);
         if (prefix_len) {
             text_len -= prefix_len;
             memmove(text, text + prefix_len, text_len);
         }
     }
 
     trace_console_rcuidle(text, text_len);
 
     return text_len;
 }
 
 __printf(4, 0)
 int vprintk_store(int facility, int level,
           const struct dev_printk_info *dev_info,
           const char *fmt, va_list args)
 {
     struct prb_reserved_entry e;
     enum printk_info_flags flags = 0;
     struct printk_record r;
     unsigned long irqflags;
     u16 trunc_msg_len = 0;
     char prefix_buf[8];
     u8 *recursion_ptr;
     u16 reserve_size;
     va_list args2;
     u32 caller_id;
     u16 text_len;
     int ret = 0;
     u64 ts_nsec;
 
     if (!printk_enter_irqsave(recursion_ptr, irqflags))
         return 0;
 
     /*
      * Since the duration of printk() can vary depending on the message
      * and state of the ringbuffer, grab the timestamp now so that it is
      * close to the call of printk(). This provides a more deterministic
      * timestamp with respect to the caller.
      */
     ts_nsec = local_clock();
 
     caller_id = printk_caller_id();
 
     /*
      * The sprintf needs to come first since the syslog prefix might be
      * passed in as a parameter. An extra byte must be reserved so that
      * later the vscnprintf() into the reserved buffer has room for the
      * terminating '\0', which is not counted by vsnprintf().
      */
     va_copy(args2, args);
     reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
     va_end(args2);
 
     if (reserve_size > LOG_LINE_MAX)
         reserve_size = LOG_LINE_MAX;
 
     /* Extract log level or control flags. */
     if (facility == 0)
         printk_parse_prefix(&prefix_buf[0], &level, &flags);
 
     if (level == LOGLEVEL_DEFAULT)
         level = default_message_loglevel;
 
     if (dev_info)
         flags |= LOG_NEWLINE;
 
     if (flags & LOG_CONT) {
         prb_rec_init_wr(&r, reserve_size);
         if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
             text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
                          facility, &flags, fmt, args);
             r.info->text_len += text_len;
 
             if (flags & LOG_NEWLINE) {
                 r.info->flags |= LOG_NEWLINE;
                 prb_final_commit(&e);
             } else {
                 prb_commit(&e);
             }
 
             ret = text_len;
             goto out;
         }
     }
 
     /*
      * Explicitly initialize the record before every prb_reserve() call.
      * prb_reserve_in_last() and prb_reserve() purposely invalidate the
      * structure when they fail.
      */
     prb_rec_init_wr(&r, reserve_size);
     if (!prb_reserve(&e, prb, &r)) {
         /* truncate the message if it is too long for empty buffer */
         truncate_msg(&reserve_size, &trunc_msg_len);
 
         prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
         if (!prb_reserve(&e, prb, &r))
             goto out;
     }
 
     /* fill message */
     text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
     if (trunc_msg_len)
         memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
     r.info->text_len = text_len + trunc_msg_len;
     r.info->facility = facility;
     r.info->level = level & 7;
     r.info->flags = flags & 0x1f;
     r.info->ts_nsec = ts_nsec;
     r.info->caller_id = caller_id;
     if (dev_info)
         memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
 
     /* A message without a trailing newline can be continued. */
     if (!(flags & LOG_NEWLINE))
         prb_commit(&e);
     else
         prb_final_commit(&e);
 
     ret = text_len + trunc_msg_len;
 out:
     printk_exit_irqrestore(recursion_ptr, irqflags);
     return ret;
 }
 
 asmlinkage int vprintk_emit(int facility, int level,
                 const struct dev_printk_info *dev_info,
                 const char *fmt, va_list args)
 {
     int printed_len;
     bool in_sched = false;
 
     /* Suppress unimportant messages after panic happens */
     if (unlikely(suppress_printk))
         return 0;
 
     if (unlikely(suppress_panic_printk) &&
         atomic_read(&panic_cpu) != raw_smp_processor_id())
         return 0;
 
     if (level == LOGLEVEL_SCHED) {
         level = LOGLEVEL_DEFAULT;
         in_sched = true;
     }
 
     printk_delay(level);
 
     printed_len = vprintk_store(facility, level, dev_info, fmt, args);
 
     /* If called from the scheduler, we can not call up(). */
     if (!in_sched) {
         /*
          * The caller may be holding system-critical or
          * timing-sensitive locks. Disable preemption during
          * printing of all remaining records to all consoles so that
          * this context can return as soon as possible. Hopefully
          * another printk() caller will take over the printing.
          */
         preempt_disable();
         /*
          * Try to acquire and then immediately release the console
          * semaphore. The release will print out buffers. With the
          * spinning variant, this context tries to take over the
          * printing from another printing context.
          */
         if (console_trylock_spinning())
             console_unlock();
         preempt_enable();
     }
 
     wake_up_klogd();
     return printed_len;
 }
 EXPORT_SYMBOL(vprintk_emit);
 
 int vprintk_default(const char *fmt, va_list args)
 {
     return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
 }
 EXPORT_SYMBOL_GPL(vprintk_default);
 
 asmlinkage __visible int _printk(const char *fmt, ...)
 {
     va_list args;
     int r;
 
     va_start(args, fmt);
     r = vprintk(fmt, args);
     va_end(args);
 
     return r;
 }
 EXPORT_SYMBOL(_printk);
 
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
 
 #else /* CONFIG_PRINTK */
 
 #define CONSOLE_LOG_MAX     0
 #define DROPPED_TEXT_MAX    0
 #define printk_time     false
 
 #define prb_read_valid(rb, seq, r)  false
 #define prb_first_valid_seq(rb)     0
 #define prb_next_seq(rb)        0
 
 static u64 syslog_seq;
 
 static size_t record_print_text(const struct printk_record *r,
                 bool syslog, bool time)
 {
     return 0;
 }
 static ssize_t info_print_ext_header(char *buf, size_t size,
                      struct printk_info *info)
 {
     return 0;
 }
 static ssize_t msg_print_ext_body(char *buf, size_t size,
                   char *text, size_t text_len,
                   struct dev_printk_info *dev_info) { return 0; }
 static void console_lock_spinning_enable(void) { }
 static int console_lock_spinning_disable_and_check(void) { return 0; }
 static void call_console_driver(struct console *con, const char *text, size_t len,
                 char *dropped_text)
 {
 }
 static bool suppress_message_printing(int level) { return false; }
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
 
 #endif /* CONFIG_PRINTK */
 
 #ifdef CONFIG_EARLY_PRINTK
 struct console *early_console;
 
 asmlinkage __visible void early_printk(const char *fmt, ...)
 {
     va_list ap;
     char buf[512];
     int n;
 
     if (!early_console)
         return;
 
     va_start(ap, fmt);
     n = vscnprintf(buf, sizeof(buf), fmt, ap);
     va_end(ap);
 
     early_console->write(early_console, buf, n);
 }
 #endif
 
 static void set_user_specified(struct console_cmdline *c, bool user_specified)
 {
     if (!user_specified)
         return;
 
     /*
      * @c console was defined by the user on the command line.
      * Do not clear when added twice also by SPCR or the device tree.
      */
     c->user_specified = true;
     /* At least one console defined by the user on the command line. */
     console_set_on_cmdline = 1;
 }
 
 static int __add_preferred_console(char *name, int idx, char *options,
                    char *brl_options, bool user_specified)
 {
     struct console_cmdline *c;
     int i;
 
     /*
      *  See if this tty is not yet registered, and
      *  if we have a slot free.
      */
     for (i = 0, c = console_cmdline;
          i < MAX_CMDLINECONSOLES && c->name[0];
          i++, c++) {
         if (strcmp(c->name, name) == 0 && c->index == idx) {
             if (!brl_options)
                 preferred_console = i;
             set_user_specified(c, user_specified);
             return 0;
         }
     }
     if (i == MAX_CMDLINECONSOLES)
         return -E2BIG;
     if (!brl_options)
         preferred_console = i;
     strlcpy(c->name, name, sizeof(c->name));
     c->options = options;
     set_user_specified(c, user_specified);
     braille_set_options(c, brl_options);
 
     c->index = idx;
     return 0;
 }
 
 static int __init console_msg_format_setup(char *str)
 {
     if (!strcmp(str, "syslog"))
         console_msg_format = MSG_FORMAT_SYSLOG;
     if (!strcmp(str, "default"))
         console_msg_format = MSG_FORMAT_DEFAULT;
     return 1;
 }
 __setup("console_msg_format=", console_msg_format_setup);
 
 /*
  * Set up a console.  Called via do_early_param() in init/main.c
  * for each "console=" parameter in the boot command line.
  */
 static int __init console_setup(char *str)
 {
     char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
     char *s, *options, *brl_options = NULL;
     int idx;
 
     /*
      * console="" or console=null have been suggested as a way to
      * disable console output. Use ttynull that has been created
      * for exactly this purpose.
      */
     if (str[0] == 0 || strcmp(str, "null") == 0) {
         __add_preferred_console("ttynull", 0, NULL, NULL, true);
         return 1;
     }
 
     if (_braille_console_setup(&str, &brl_options))
         return 1;
 
     /*
      * Decode str into name, index, options.
      */
     if (str[0] >= '0' && str[0] <= '9') {
         strcpy(buf, "ttyS");
         strncpy(buf + 4, str, sizeof(buf) - 5);
     } else {
         strncpy(buf, str, sizeof(buf) - 1);
     }
     buf[sizeof(buf) - 1] = 0;
     options = strchr(str, ',');
     if (options)
         *(options++) = 0;
 #ifdef __sparc__
     if (!strcmp(str, "ttya"))
         strcpy(buf, "ttyS0");
     if (!strcmp(str, "ttyb"))
         strcpy(buf, "ttyS1");
 #endif
     for (s = buf; *s; s++)
         if (isdigit(*s) || *s == ',')
             break;
     idx = simple_strtoul(s, NULL, 10);
     *s = 0;
 
     __add_preferred_console(buf, idx, options, brl_options, true);
     return 1;
 }
 __setup("console=", console_setup);
 
 /**
  * add_preferred_console - add a device to the list of preferred consoles.
  * @name: device name
  * @idx: device index
  * @options: options for this console
  *
  * The last preferred console added will be used for kernel messages
  * and stdin/out/err for init.  Normally this is used by console_setup
  * above to handle user-supplied console arguments; however it can also
  * be used by arch-specific code either to override the user or more
  * commonly to provide a default console (ie from PROM variables) when
  * the user has not supplied one.
  */
 int add_preferred_console(char *name, int idx, char *options)
 {
     return __add_preferred_console(name, idx, options, NULL, false);
 }
 
 bool console_suspend_enabled = true;
 EXPORT_SYMBOL(console_suspend_enabled);
 
 static int __init console_suspend_disable(char *str)
 {
     console_suspend_enabled = false;
     return 1;
 }
 __setup("no_console_suspend", console_suspend_disable);
 module_param_named(console_suspend, console_suspend_enabled,
         bool, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
     " and hibernate operations");
 
 static bool printk_console_no_auto_verbose;
 
 void console_verbose(void)
 {
     if (console_loglevel && !printk_console_no_auto_verbose)
         console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
 }
 EXPORT_SYMBOL_GPL(console_verbose);
 
 module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
 
 /**
  * suspend_console - suspend the console subsystem
  *
  * This disables printk() while we go into suspend states
  */
 void suspend_console(void)
 {
     if (!console_suspend_enabled)
         return;
     pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
     pr_flush(1000, true);
     console_lock();
     console_suspended = 1;
     up_console_sem();
 }
 
 void resume_console(void)
 {
     if (!console_suspend_enabled)
         return;
     down_console_sem();
     console_suspended = 0;
     console_unlock();
     pr_flush(1000, true);
 }
 
 /**
  * console_cpu_notify - print deferred console messages after CPU hotplug
  * @cpu: unused
  *
  * If printk() is called from a CPU that is not online yet, the messages
  * will be printed on the console only if there are CON_ANYTIME consoles.
  * This function is called when a new CPU comes online (or fails to come
  * up) or goes offline.
  */
 static int console_cpu_notify(unsigned int cpu)
 {
     if (!cpuhp_tasks_frozen) {
         /* If trylock fails, someone else is doing the printing */
         if (console_trylock())
             console_unlock();
     }
     return 0;
 }
 
 /**
  * console_lock - lock the console system for exclusive use.
  *
  * Acquires a lock which guarantees that the caller has
  * exclusive access to the console system and the console_drivers list.
  *
  * Can sleep, returns nothing.
  */
 void console_lock(void)
 {
     might_sleep();
 
     down_console_sem();
     if (console_suspended)
         return;
     console_locked = 1;
     console_may_schedule = 1;
 }
 EXPORT_SYMBOL(console_lock);
 
 /**
  * console_trylock - try to lock the console system for exclusive use.
  *
  * Try to acquire a lock which guarantees that the caller has exclusive
  * access to the console system and the console_drivers list.
  *
  * returns 1 on success, and 0 on failure to acquire the lock.
  */
 int console_trylock(void)
 {
     if (down_trylock_console_sem())
         return 0;
     if (console_suspended) {
         up_console_sem();
         return 0;
     }
     console_locked = 1;
     console_may_schedule = 0;
     return 1;
 }
 EXPORT_SYMBOL(console_trylock);
 
 int is_console_locked(void)
 {
     return console_locked;
 }
 EXPORT_SYMBOL(is_console_locked);
 
 /*
  * Return true when this CPU should unlock console_sem without pushing all
  * messages to the console. This reduces the chance that the console is
  * locked when the panic CPU tries to use it.
  */
 static bool abandon_console_lock_in_panic(void)
 {
     if (!panic_in_progress())
         return false;
 
     /*
      * We can use raw_smp_processor_id() here because it is impossible for
      * the task to be migrated to the panic_cpu, or away from it. If
      * panic_cpu has already been set, and we're not currently executing on
      * that CPU, then we never will be.
      */
     return atomic_read(&panic_cpu) != raw_smp_processor_id();
 }
 
 /*
  * Check if the given console is currently capable and allowed to print
  * records.
  *
  * Requires the console_lock.
  */
 static inline bool console_is_usable(struct console *con)
 {
     if (!(con->flags & CON_ENABLED))
         return false;
 
     if (!con->write)
         return false;
 
     /*
      * Console drivers may assume that per-cpu resources have been
      * allocated. So unless they're explicitly marked as being able to
      * cope (CON_ANYTIME) don't call them until this CPU is officially up.
      */
     if (!cpu_online(raw_smp_processor_id()) &&
         !(con->flags & CON_ANYTIME))
         return false;
 
     return true;
 }
 
 static void __console_unlock(void)
 {
     console_locked = 0;
     up_console_sem();
 }
 
 /*
  * Print one record for the given console. The record printed is whatever
  * record is the next available record for the given console.
  *
  * @text is a buffer of size CONSOLE_LOG_MAX.
  *
  * If extended messages should be printed, @ext_text is a buffer of size
  * CONSOLE_EXT_LOG_MAX. Otherwise @ext_text must be NULL.
  *
  * If dropped messages should be printed, @dropped_text is a buffer of size
  * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
  *
  * @handover will be set to true if a printk waiter has taken over the
  * console_lock, in which case the caller is no longer holding the
  * console_lock. Otherwise it is set to false.
  *
  * Returns false if the given console has no next record to print, otherwise
  * true.
  *
  * Requires the console_lock.
  */
 static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
                      char *dropped_text, bool *handover)
 {
     static int panic_console_dropped;
     struct printk_info info;
     struct printk_record r;
     unsigned long flags;
     char *write_text;
     size_t len;
 
     prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
     *handover = false;
 
     if (!prb_read_valid(prb, con->seq, &r))
         return false;
 
     if (con->seq != r.info->seq) {
         con->dropped += r.info->seq - con->seq;
         con->seq = r.info->seq;
         if (panic_in_progress() && panic_console_dropped++ > 10) {
             suppress_panic_printk = 1;
             pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
         }
     }
 
     /* Skip record that has level above the console loglevel. */
     if (suppress_message_printing(r.info->level)) {
         con->seq++;
         goto skip;
     }
 
     if (ext_text) {
         write_text = ext_text;
         len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info);
         len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len,
                       &r.text_buf[0], r.info->text_len, &r.info->dev_info);
     } else {
         write_text = text;
         len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
     }
 
     /*
      * While actively printing out messages, if another printk()
      * were to occur on another CPU, it may wait for this one to
      * finish. This task can not be preempted if there is a
      * waiter waiting to take over.
      *
      * Interrupts are disabled because the hand over to a waiter
      * must not be interrupted until the hand over is completed
      * (@console_waiter is cleared).
      */
     printk_safe_enter_irqsave(flags);
     console_lock_spinning_enable();
 
     stop_critical_timings();    /* don't trace print latency */
     call_console_driver(con, write_text, len, dropped_text);
     start_critical_timings();
 
     con->seq++;
 
     *handover = console_lock_spinning_disable_and_check();
     printk_safe_exit_irqrestore(flags);
 skip:
     return true;
 }
 
 /*
  * Print out all remaining records to all consoles.
  *
  * @do_cond_resched is set by the caller. It can be true only in schedulable
  * context.
  *
  * @next_seq is set to the sequence number after the last available record.
  * The value is valid only when this function returns true. It means that all
  * usable consoles are completely flushed.
  *
  * @handover will be set to true if a printk waiter has taken over the
  * console_lock, in which case the caller is no longer holding the
  * console_lock. Otherwise it is set to false.
  *
  * Returns true when there was at least one usable console and all messages
  * were flushed to all usable consoles. A returned false informs the caller
  * that everything was not flushed (either there were no usable consoles or
  * another context has taken over printing or it is a panic situation and this
  * is not the panic CPU). Regardless the reason, the caller should assume it
  * is not useful to immediately try again.
  *
  * Requires the console_lock.
  */
 static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
 {
     static char dropped_text[DROPPED_TEXT_MAX];
     static char ext_text[CONSOLE_EXT_LOG_MAX];
     static char text[CONSOLE_LOG_MAX];
     bool any_usable = false;
     struct console *con;
     bool any_progress;
 
     *next_seq = 0;
     *handover = false;
 
     do {
         any_progress = false;
 
         for_each_console(con) {
             bool progress;
 
             if (!console_is_usable(con))
                 continue;
             any_usable = true;
 
             if (con->flags & CON_EXTENDED) {
                 /* Extended consoles do not print "dropped messages". */
                 progress = console_emit_next_record(con, &text[0],
                                     &ext_text[0], NULL,
                                     handover);
             } else {
                 progress = console_emit_next_record(con, &text[0],
                                     NULL, &dropped_text[0],
                                     handover);
             }
             if (*handover)
                 return false;
 
             /* Track the next of the highest seq flushed. */
             if (con->seq > *next_seq)
                 *next_seq = con->seq;
 
             if (!progress)
                 continue;
             any_progress = true;
 
             /* Allow panic_cpu to take over the consoles safely. */
             if (abandon_console_lock_in_panic())
                 return false;
 
             if (do_cond_resched)
                 cond_resched();
         }
     } while (any_progress);
 
     return any_usable;
 }
 
 /**
  * console_unlock - unlock the console system
  *
  * Releases the console_lock which the caller holds on the console system
  * and the console driver list.
  *
  * While the console_lock was held, console output may have been buffered
  * by printk().  If this is the case, console_unlock(); emits
  * the output prior to releasing the lock.
  *
  * console_unlock(); may be called from any context.
  */
 void console_unlock(void)
 {
     bool do_cond_resched;
     bool handover;
     bool flushed;
     u64 next_seq;
 
     if (console_suspended) {
         up_console_sem();
         return;
     }
 
     /*
      * Console drivers are called with interrupts disabled, so
      * @console_may_schedule should be cleared before; however, we may
      * end up dumping a lot of lines, for example, if called from
      * console registration path, and should invoke cond_resched()
      * between lines if allowable.  Not doing so can cause a very long
      * scheduling stall on a slow console leading to RCU stall and
      * softlockup warnings which exacerbate the issue with more
      * messages practically incapacitating the system. Therefore, create
      * a local to use for the printing loop.
      */
     do_cond_resched = console_may_schedule;
 
     do {
         console_may_schedule = 0;
 
         flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
         if (!handover)
             __console_unlock();
 
         /*
          * Abort if there was a failure to flush all messages to all
          * usable consoles. Either it is not possible to flush (in
          * which case it would be an infinite loop of retrying) or
          * another context has taken over printing.
          */
         if (!flushed)
             break;
 
         /*
          * Some context may have added new records after
          * console_flush_all() but before unlocking the console.
          * Re-check if there is a new record to flush. If the trylock
          * fails, another context is already handling the printing.
          */
     } while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
 }
 EXPORT_SYMBOL(console_unlock);
 
 /**
  * console_conditional_schedule - yield the CPU if required
  *
  * If the console code is currently allowed to sleep, and
  * if this CPU should yield the CPU to another task, do
  * so here.
  *
  * Must be called within console_lock();.
  */
 void __sched console_conditional_schedule(void)
 {
     if (console_may_schedule)
         cond_resched();
 }
 EXPORT_SYMBOL(console_conditional_schedule);
 
 void console_unblank(void)
 {
     struct console *c;
 
     /*
      * console_unblank can no longer be called in interrupt context unless
      * oops_in_progress is set to 1..
      */
     if (oops_in_progress) {
         if (down_trylock_console_sem() != 0)
             return;
     } else
         console_lock();
 
     console_locked = 1;
     console_may_schedule = 0;
     for_each_console(c)
         if ((c->flags & CON_ENABLED) && c->unblank)
             c->unblank();
     console_unlock();
 
     if (!oops_in_progress)
         pr_flush(1000, true);
 }
 
 /**
  * console_flush_on_panic - flush console content on panic
  * @mode: flush all messages in buffer or just the pending ones
  *
  * Immediately output all pending messages no matter what.
  */
 void console_flush_on_panic(enum con_flush_mode mode)
 {
     /*
      * If someone else is holding the console lock, trylock will fail
      * and may_schedule may be set.  Ignore and proceed to unlock so
      * that messages are flushed out.  As this can be called from any
      * context and we don't want to get preempted while flushing,
      * ensure may_schedule is cleared.
      */
     console_trylock();
     console_may_schedule = 0;
 
     if (mode == CONSOLE_REPLAY_ALL) {
         struct console *c;
         u64 seq;
 
         seq = prb_first_valid_seq(prb);
         for_each_console(c)
             c->seq = seq;
     }
     console_unlock();
 }
 
 /*
  * Return the console tty driver structure and its associated index
  */
 struct tty_driver *console_device(int *index)
 {
     struct console *c;
     struct tty_driver *driver = NULL;
 
     console_lock();
     for_each_console(c) {
         if (!c->device)
             continue;
         driver = c->device(c, index);
         if (driver)
             break;
     }
     console_unlock();
     return driver;
 }
 
 /*
  * Prevent further output on the passed console device so that (for example)
  * serial drivers can disable console output before suspending a port, and can
  * re-enable output afterwards.
  */
 void console_stop(struct console *console)
 {
     __pr_flush(console, 1000, true);
     console_lock();
     console->flags &= ~CON_ENABLED;
     console_unlock();
 }
 EXPORT_SYMBOL(console_stop);
 
 void console_start(struct console *console)
 {
     console_lock();
     console->flags |= CON_ENABLED;
     console_unlock();
     __pr_flush(console, 1000, true);
 }
 EXPORT_SYMBOL(console_start);
 
 static int __read_mostly keep_bootcon;
 
 static int __init keep_bootcon_setup(char *str)
 {
     keep_bootcon = 1;
     pr_info("debug: skip boot console de-registration.\n");
 
     return 0;
 }
 
 early_param("keep_bootcon", keep_bootcon_setup);
 
 /*
  * This is called by register_console() to try to match
  * the newly registered console with any of the ones selected
  * by either the command line or add_preferred_console() and
  * setup/enable it.
  *
  * Care need to be taken with consoles that are statically
  * enabled such as netconsole
  */
 static int try_enable_preferred_console(struct console *newcon,
                     bool user_specified)
 {
     struct console_cmdline *c;
     int i, err;
 
     for (i = 0, c = console_cmdline;
          i < MAX_CMDLINECONSOLES && c->name[0];
          i++, c++) {
         if (c->user_specified != user_specified)
             continue;
         if (!newcon->match ||
             newcon->match(newcon, c->name, c->index, c->options) != 0) {
             /* default matching */
             BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
             if (strcmp(c->name, newcon->name) != 0)
                 continue;
             if (newcon->index >= 0 &&
                 newcon->index != c->index)
                 continue;
             if (newcon->index < 0)
                 newcon->index = c->index;
 
             if (_braille_register_console(newcon, c))
                 return 0;
 
             if (newcon->setup &&
                 (err = newcon->setup(newcon, c->options)) != 0)
                 return err;
         }
         newcon->flags |= CON_ENABLED;
         if (i == preferred_console)
             newcon->flags |= CON_CONSDEV;
         return 0;
     }
 
     /*
      * Some consoles, such as pstore and netconsole, can be enabled even
      * without matching. Accept the pre-enabled consoles only when match()
      * and setup() had a chance to be called.
      */
     if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
         return 0;
 
     return -ENOENT;
 }
 
 /* Try to enable the console unconditionally */
 static void try_enable_default_console(struct console *newcon)
 {
     if (newcon->index < 0)
         newcon->index = 0;
 
     if (newcon->setup && newcon->setup(newcon, NULL) != 0)
         return;
 
     newcon->flags |= CON_ENABLED;
 
     if (newcon->device)
         newcon->flags |= CON_CONSDEV;
 }
 
 #define con_printk(lvl, con, fmt, ...)          \
     printk(lvl pr_fmt("%sconsole [%s%d] " fmt), \
            (con->flags & CON_BOOT) ? "boot" : "",   \
            con->name, con->index, ##__VA_ARGS__)
 
 /*
  * The console driver calls this routine during kernel initialization
  * to register the console printing procedure with printk() and to
  * print any messages that were printed by the kernel before the
  * console driver was initialized.
  *
  * This can happen pretty early during the boot process (because of
  * early_printk) - sometimes before setup_arch() completes - be careful
  * of what kernel features are used - they may not be initialised yet.
  *
  * There are two types of consoles - bootconsoles (early_printk) and
  * "real" consoles (everything which is not a bootconsole) which are
  * handled differently.
  *  - Any number of bootconsoles can be registered at any time.
  *  - As soon as a "real" console is registered, all bootconsoles
  *    will be unregistered automatically.
  *  - Once a "real" console is registered, any attempt to register a
  *    bootconsoles will be rejected
  */
 void register_console(struct console *newcon)
 {
     struct console *con;
     bool bootcon_enabled = false;
     bool realcon_enabled = false;
     int err;
 
     for_each_console(con) {
         if (WARN(con == newcon, "console '%s%d' already registered\n",
                      con->name, con->index))
             return;
     }
 
     for_each_console(con) {
         if (con->flags & CON_BOOT)
             bootcon_enabled = true;
         else
             realcon_enabled = true;
     }
 
     /* Do not register boot consoles when there already is a real one. */
     if (newcon->flags & CON_BOOT && realcon_enabled) {
         pr_info("Too late to register bootconsole %s%d\n",
             newcon->name, newcon->index);
         return;
     }
 
     /*
      * See if we want to enable this console driver by default.
      *
      * Nope when a console is preferred by the command line, device
      * tree, or SPCR.
      *
      * The first real console with tty binding (driver) wins. More
      * consoles might get enabled before the right one is found.
      *
      * Note that a console with tty binding will have CON_CONSDEV
      * flag set and will be first in the list.
      */
     if (preferred_console < 0) {
         if (!console_drivers || !console_drivers->device ||
             console_drivers->flags & CON_BOOT) {
             try_enable_default_console(newcon);
         }
     }
 
     /* See if this console matches one we selected on the command line */
     err = try_enable_preferred_console(newcon, true);
 
     /* If not, try to match against the platform default(s) */
     if (err == -ENOENT)
         err = try_enable_preferred_console(newcon, false);
 
     /* printk() messages are not printed to the Braille console. */
     if (err || newcon->flags & CON_BRL)
         return;
 
     /*
      * If we have a bootconsole, and are switching to a real console,
      * don't print everything out again, since when the boot console, and
      * the real console are the same physical device, it's annoying to
      * see the beginning boot messages twice
      */
     if (bootcon_enabled &&
         ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
         newcon->flags &= ~CON_PRINTBUFFER;
     }
 
     /*
      *  Put this console in the list - keep the
      *  preferred driver at the head of the list.
      */
     console_lock();
     if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
         newcon->next = console_drivers;
         console_drivers = newcon;
         if (newcon->next)
             newcon->next->flags &= ~CON_CONSDEV;
         /* Ensure this flag is always set for the head of the list */
         newcon->flags |= CON_CONSDEV;
     } else {
         newcon->next = console_drivers->next;
         console_drivers->next = newcon;
     }
 
     if (newcon->flags & CON_EXTENDED)
         nr_ext_console_drivers++;
 
     newcon->dropped = 0;
     if (newcon->flags & CON_PRINTBUFFER) {
         /* Get a consistent copy of @syslog_seq. */
         mutex_lock(&syslog_lock);
         newcon->seq = syslog_seq;
         mutex_unlock(&syslog_lock);
     } else {
         /* Begin with next message. */
         newcon->seq = prb_next_seq(prb);
     }
     console_unlock();
     console_sysfs_notify();
 
     /*
      * By unregistering the bootconsoles after we enable the real console
      * we get the "console xxx enabled" message on all the consoles -
      * boot consoles, real consoles, etc - this is to ensure that end
      * users know there might be something in the kernel's log buffer that
      * went to the bootconsole (that they do not see on the real console)
      */
     con_printk(KERN_INFO, newcon, "enabled\n");
     if (bootcon_enabled &&
         ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
         !keep_bootcon) {
         /* We need to iterate through all boot consoles, to make
          * sure we print everything out, before we unregister them.
          */
         for_each_console(con)
             if (con->flags & CON_BOOT)
                 unregister_console(con);
     }
 }
 EXPORT_SYMBOL(register_console);
 
 int unregister_console(struct console *console)
 {
     struct console *con;
     int res;
 
     con_printk(KERN_INFO, console, "disabled\n");
 
     res = _braille_unregister_console(console);
     if (res < 0)
         return res;
     if (res > 0)
         return 0;
 
     res = -ENODEV;
     console_lock();
     if (console_drivers == console) {
         console_drivers=console->next;
         res = 0;
     } else {
         for_each_console(con) {
             if (con->next == console) {
                 con->next = console->next;
                 res = 0;
                 break;
             }
         }
     }
 
     if (res)
         goto out_disable_unlock;
 
     if (console->flags & CON_EXTENDED)
         nr_ext_console_drivers--;
 
     /*
      * If this isn't the last console and it has CON_CONSDEV set, we
      * need to set it on the next preferred console.
      */
     if (console_drivers != NULL && console->flags & CON_CONSDEV)
         console_drivers->flags |= CON_CONSDEV;
 
     console->flags &= ~CON_ENABLED;
     console_unlock();
     console_sysfs_notify();
 
     if (console->exit)
         res = console->exit(console);
 
     return res;
 
 out_disable_unlock:
     console->flags &= ~CON_ENABLED;
     console_unlock();
 
     return res;
 }
 EXPORT_SYMBOL(unregister_console);
 
 /*
  * Initialize the console device. This is called *early*, so
  * we can't necessarily depend on lots of kernel help here.
  * Just do some early initializations, and do the complex setup
  * later.
  */
 void __init console_init(void)
 {
     int ret;
     initcall_t call;
     initcall_entry_t *ce;
 
     /* Setup the default TTY line discipline. */
     n_tty_init();
 
     /*
      * set up the console device so that later boot sequences can
      * inform about problems etc..
      */
     ce = __con_initcall_start;
     trace_initcall_level("console");
     while (ce < __con_initcall_end) {
         call = initcall_from_entry(ce);
         trace_initcall_start(call);
         ret = call();
         trace_initcall_finish(call, ret);
         ce++;
     }
 }
 
 /*
  * Some boot consoles access data that is in the init section and which will
  * be discarded after the initcalls have been run. To make sure that no code
  * will access this data, unregister the boot consoles in a late initcall.
  *
  * If for some reason, such as deferred probe or the driver being a loadable
  * module, the real console hasn't registered yet at this point, there will
  * be a brief interval in which no messages are logged to the console, which
  * makes it difficult to diagnose problems that occur during this time.
  *
  * To mitigate this problem somewhat, only unregister consoles whose memory
  * intersects with the init section. Note that all other boot consoles will
  * get unregistered when the real preferred console is registered.
  */
 static int __init printk_late_init(void)
 {
     struct console *con;
     int ret;
 
     for_each_console(con) {
         if (!(con->flags & CON_BOOT))
             continue;
 
         /* Check addresses that might be used for enabled consoles. */
         if (init_section_intersects(con, sizeof(*con)) ||
             init_section_contains(con->write, 0) ||
             init_section_contains(con->read, 0) ||
             init_section_contains(con->device, 0) ||
             init_section_contains(con->unblank, 0) ||
             init_section_contains(con->data, 0)) {
             /*
              * Please, consider moving the reported consoles out
              * of the init section.
              */
             pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
                 con->name, con->index);
             unregister_console(con);
         }
     }
     ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
                     console_cpu_notify);
     WARN_ON(ret < 0);
     ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
                     console_cpu_notify, NULL);
     WARN_ON(ret < 0);
     printk_sysctl_init();
     return 0;
 }
 late_initcall(printk_late_init);
 
 #if defined CONFIG_PRINTK
 /* If @con is specified, only wait for that console. Otherwise wait for all. */
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
 {
     int remaining = timeout_ms;
     struct console *c;
     u64 last_diff = 0;
     u64 printk_seq;
     u64 diff;
     u64 seq;
 
     might_sleep();
 
     seq = prb_next_seq(prb);
 
     for (;;) {
         diff = 0;
 
         console_lock();
 
         for_each_console(c) {
             if (con && con != c)
                 continue;
             if (!console_is_usable(c))
                 continue;
             printk_seq = c->seq;
             if (printk_seq < seq)
                 diff += seq - printk_seq;
         }
 
         /*
          * If consoles are suspended, it cannot be expected that they
          * make forward progress, so timeout immediately. @diff is
          * still used to return a valid flush status.
          */
         if (console_suspended)
             remaining = 0;
         else if (diff != last_diff && reset_on_progress)
             remaining = timeout_ms;
 
         console_unlock();
 
         if (diff == 0 || remaining == 0)
             break;
 
         if (remaining < 0) {
             /* no timeout limit */
             msleep(100);
         } else if (remaining < 100) {
             msleep(remaining);
             remaining = 0;
         } else {
             msleep(100);
             remaining -= 100;
         }
 
         last_diff = diff;
     }
 
     return (diff == 0);
 }
 
 /**
  * pr_flush() - Wait for printing threads to catch up.
  *
  * @timeout_ms:        The maximum time (in ms) to wait.
  * @reset_on_progress: Reset the timeout if forward progress is seen.
  *
  * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
  * represents infinite waiting.
  *
  * If @reset_on_progress is true, the timeout will be reset whenever any
  * printer has been seen to make some forward progress.
  *
  * Context: Process context. May sleep while acquiring console lock.
  * Return: true if all enabled printers are caught up.
  */
 bool pr_flush(int timeout_ms, bool reset_on_progress)
 {
     return __pr_flush(NULL, timeout_ms, reset_on_progress);
 }
 EXPORT_SYMBOL(pr_flush);
 
 /*
  * Delayed printk version, for scheduler-internal messages:
  */
 #define PRINTK_PENDING_WAKEUP   0x01
 #define PRINTK_PENDING_OUTPUT   0x02
 
 static DEFINE_PER_CPU(int, printk_pending);
 
 static void wake_up_klogd_work_func(struct irq_work *irq_work)
 {
     int pending = this_cpu_xchg(printk_pending, 0);
 
     if (pending & PRINTK_PENDING_OUTPUT) {
         /* If trylock fails, someone else is doing the printing */
         if (console_trylock())
             console_unlock();
     }
 
     if (pending & PRINTK_PENDING_WAKEUP)
         wake_up_interruptible(&log_wait);
 }
 
 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
     IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
 
 static void __wake_up_klogd(int val)
 {
     if (!printk_percpu_data_ready())
         return;
 
     preempt_disable();
     /*
      * Guarantee any new records can be seen by tasks preparing to wait
      * before this context checks if the wait queue is empty.
      *
      * The full memory barrier within wq_has_sleeper() pairs with the full
      * memory barrier within set_current_state() of
      * prepare_to_wait_event(), which is called after ___wait_event() adds
      * the waiter but before it has checked the wait condition.
      *
      * This pairs with devkmsg_read:A and syslog_print:A.
      */
     if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
         (val & PRINTK_PENDING_OUTPUT)) {
         this_cpu_or(printk_pending, val);
         irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
     }
     preempt_enable();
 }
 
 void wake_up_klogd(void)
 {
     __wake_up_klogd(PRINTK_PENDING_WAKEUP);
 }
 
 void defer_console_output(void)
 {
     /*
      * New messages may have been added directly to the ringbuffer
      * using vprintk_store(), so wake any waiters as well.
      */
     __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
 }
 
 void printk_trigger_flush(void)
 {
     defer_console_output();
 }
 
 int vprintk_deferred(const char *fmt, va_list args)
 {
     int r;
 
     r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
     defer_console_output();
 
     return r;
 }
 
 int _printk_deferred(const char *fmt, ...)
 {
     va_list args;
     int r;
 
     va_start(args, fmt);
     r = vprintk_deferred(fmt, args);
     va_end(args);
 
     return r;
 }
 
 /*
  * printk rate limiting, lifted from the networking subsystem.
  *
  * This enforces a rate limit: not more than 10 kernel messages
  * every 5s to make a denial-of-service attack impossible.
  */
 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
 
 int __printk_ratelimit(const char *func)
 {
     return ___ratelimit(&printk_ratelimit_state, func);
 }
 EXPORT_SYMBOL(__printk_ratelimit);
 
 /**
  * printk_timed_ratelimit - caller-controlled printk ratelimiting
  * @caller_jiffies: pointer to caller's state
  * @interval_msecs: minimum interval between prints
  *
  * printk_timed_ratelimit() returns true if more than @interval_msecs
  * milliseconds have elapsed since the last time printk_timed_ratelimit()
  * returned true.
  */
 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
             unsigned int interval_msecs)
 {
     unsigned long elapsed = jiffies - *caller_jiffies;
 
     if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
         return false;
 
     *caller_jiffies = jiffies;
     return true;
 }
 EXPORT_SYMBOL(printk_timed_ratelimit);
 
 static DEFINE_SPINLOCK(dump_list_lock);
 static LIST_HEAD(dump_list);
 
 /**
  * kmsg_dump_register - register a kernel log dumper.
  * @dumper: pointer to the kmsg_dumper structure
  *
  * Adds a kernel log dumper to the system. The dump callback in the
  * structure will be called when the kernel oopses or panics and must be
  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
  */
 int kmsg_dump_register(struct kmsg_dumper *dumper)
 {
     unsigned long flags;
     int err = -EBUSY;
 
     /* The dump callback needs to be set */
     if (!dumper->dump)
         return -EINVAL;
 
     spin_lock_irqsave(&dump_list_lock, flags);
     /* Don't allow registering multiple times */
     if (!dumper->registered) {
         dumper->registered = 1;
         list_add_tail_rcu(&dumper->list, &dump_list);
         err = 0;
     }
     spin_unlock_irqrestore(&dump_list_lock, flags);
 
     return err;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_register);
 
 /**
  * kmsg_dump_unregister - unregister a kmsg dumper.
  * @dumper: pointer to the kmsg_dumper structure
  *
  * Removes a dump device from the system. Returns zero on success and
  * %-EINVAL otherwise.
  */
 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
 {
     unsigned long flags;
     int err = -EINVAL;
 
     spin_lock_irqsave(&dump_list_lock, flags);
     if (dumper->registered) {
         dumper->registered = 0;
         list_del_rcu(&dumper->list);
         err = 0;
     }
     spin_unlock_irqrestore(&dump_list_lock, flags);
     synchronize_rcu();
 
     return err;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
 
 static bool always_kmsg_dump;
 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
 
 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
 {
     switch (reason) {
     case KMSG_DUMP_PANIC:
         return "Panic";
     case KMSG_DUMP_OOPS:
         return "Oops";
     case KMSG_DUMP_EMERG:
         return "Emergency";
     case KMSG_DUMP_SHUTDOWN:
         return "Shutdown";
     default:
         return "Unknown";
     }
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 
 /**
  * kmsg_dump - dump kernel log to kernel message dumpers.
  * @reason: the reason (oops, panic etc) for dumping
  *
  * Call each of the registered dumper's dump() callback, which can
  * retrieve the kmsg records with kmsg_dump_get_line() or
  * kmsg_dump_get_buffer().
  */
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
     struct kmsg_dumper *dumper;
 
     rcu_read_lock();
     list_for_each_entry_rcu(dumper, &dump_list, list) {
         enum kmsg_dump_reason max_reason = dumper->max_reason;
 
         /*
          * If client has not provided a specific max_reason, default
          * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
          */
         if (max_reason == KMSG_DUMP_UNDEF) {
             max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
                             KMSG_DUMP_OOPS;
         }
         if (reason > max_reason)
             continue;
 
         /* invoke dumper which will iterate over records */
         dumper->dump(dumper, reason);
     }
     rcu_read_unlock();
 }
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
  * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
  * @len: length of line placed into buffer
  *
  * Start at the beginning of the kmsg buffer, with the oldest kmsg
  * record, and copy one record into the provided buffer.
  *
  * Consecutive calls will return the next available record moving
  * towards the end of the buffer with the youngest messages.
  *
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
             char *line, size_t size, size_t *len)
 {
     u64 min_seq = latched_seq_read_nolock(&clear_seq);
     struct printk_info info;
     unsigned int line_count;
     struct printk_record r;
     size_t l = 0;
     bool ret = false;
 
     if (iter->cur_seq < min_seq)
         iter->cur_seq = min_seq;
 
     prb_rec_init_rd(&r, &info, line, size);
 
     /* Read text or count text lines? */
     if (line) {
         if (!prb_read_valid(prb, iter->cur_seq, &r))
             goto out;
         l = record_print_text(&r, syslog, printk_time);
     } else {
         if (!prb_read_valid_info(prb, iter->cur_seq,
                      &info, &line_count)) {
             goto out;
         }
         l = get_record_print_text_size(&info, line_count, syslog,
                            printk_time);
 
     }
 
     iter->cur_seq = r.info->seq + 1;
     ret = true;
 out:
     if (len)
         *len = l;
     return ret;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
  * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
  * @len_out: length of line placed into buffer
  *
  * Start at the end of the kmsg buffer and fill the provided buffer
  * with as many of the *youngest* kmsg records that fit into it.
  * If the buffer is large enough, all available kmsg records will be
  * copied with a single call.
  *
  * Consecutive calls will fill the buffer with the next block of
  * available older records, not including the earlier retrieved ones.
  *
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
               char *buf, size_t size, size_t *len_out)
 {
     u64 min_seq = latched_seq_read_nolock(&clear_seq);
     struct printk_info info;
     struct printk_record r;
     u64 seq;
     u64 next_seq;
     size_t len = 0;
     bool ret = false;
     bool time = printk_time;
 
     if (!buf || !size)
         goto out;
 
     if (iter->cur_seq < min_seq)
         iter->cur_seq = min_seq;
 
     if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
         if (info.seq != iter->cur_seq) {
             /* messages are gone, move to first available one */
             iter->cur_seq = info.seq;
         }
     }
 
     /* last entry */
     if (iter->cur_seq >= iter->next_seq)
         goto out;
 
     /*
      * Find first record that fits, including all following records,
      * into the user-provided buffer for this dump. Pass in size-1
      * because this function (by way of record_print_text()) will
      * not write more than size-1 bytes of text into @buf.
      */
     seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
                      size - 1, syslog, time);
 
     /*
      * Next kmsg_dump_get_buffer() invocation will dump block of
      * older records stored right before this one.
      */
     next_seq = seq;
 
     prb_rec_init_rd(&r, &info, buf, size);
 
     len = 0;
     prb_for_each_record(seq, prb, seq, &r) {
         if (r.info->seq >= iter->next_seq)
             break;
 
         len += record_print_text(&r, syslog, time);
 
         /* Adjust record to store to remaining buffer space. */
         prb_rec_init_rd(&r, &info, buf + len, size - len);
     }
 
     iter->next_seq = next_seq;
     ret = true;
 out:
     if (len_out)
         *len_out = len;
     return ret;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind - reset the iterator
  * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
  * times within the same dumper.dump() callback.
  */
 void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
     iter->cur_seq = latched_seq_read_nolock(&clear_seq);
     iter->next_seq = prb_next_seq(prb);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
 
 #endif
 
 #ifdef CONFIG_SMP
 static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
 static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
 
 /**
  * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
  *                            spinning lock is not owned by any CPU.
  *
  * Context: Any context.
  */
 void __printk_cpu_sync_wait(void)
 {
     do {
         cpu_relax();
     } while (atomic_read(&printk_cpu_sync_owner) != -1);
 }
 EXPORT_SYMBOL(__printk_cpu_sync_wait);
 
 /**
  * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
  *                               spinning lock.
  *
  * If no processor has the lock, the calling processor takes the lock and
  * becomes the owner. If the calling processor is already the owner of the
  * lock, this function succeeds immediately.
  *
  * Context: Any context. Expects interrupts to be disabled.
  * Return: 1 on success, otherwise 0.
  */
 int __printk_cpu_sync_try_get(void)
 {
     int cpu;
     int old;
 
     cpu = smp_processor_id();
 
     /*
      * Guarantee loads and stores from this CPU when it is the lock owner
      * are _not_ visible to the previous lock owner. This pairs with
      * __printk_cpu_sync_put:B.
      *
      * Memory barrier involvement:
      *
      * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
      * then __printk_cpu_sync_put:A can never read from
      * __printk_cpu_sync_try_get:B.
      *
      * Relies on:
      *
      * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
      * of the previous CPU
      *    matching
      * ACQUIRE from __printk_cpu_sync_try_get:A to
      * __printk_cpu_sync_try_get:B of this CPU
      */
     old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
                      cpu); /* LMM(__printk_cpu_sync_try_get:A) */
     if (old == -1) {
         /*
          * This CPU is now the owner and begins loading/storing
          * data: LMM(__printk_cpu_sync_try_get:B)
          */
         return 1;
 
     } else if (old == cpu) {
         /* This CPU is already the owner. */
         atomic_inc(&printk_cpu_sync_nested);
         return 1;
     }
 
     return 0;
 }
 EXPORT_SYMBOL(__printk_cpu_sync_try_get);
 
 /**
  * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
  *
  * The calling processor must be the owner of the lock.
  *
  * Context: Any context. Expects interrupts to be disabled.
  */
 void __printk_cpu_sync_put(void)
 {
     if (atomic_read(&printk_cpu_sync_nested)) {
         atomic_dec(&printk_cpu_sync_nested);
         return;
     }
 
     /*
      * This CPU is finished loading/storing data:
      * LMM(__printk_cpu_sync_put:A)
      */
 
     /*
      * Guarantee loads and stores from this CPU when it was the
      * lock owner are visible to the next lock owner. This pairs
      * with __printk_cpu_sync_try_get:A.
      *
      * Memory barrier involvement:
      *
      * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
      * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
      *
      * Relies on:
      *
      * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
      * of this CPU
      *    matching
      * ACQUIRE from __printk_cpu_sync_try_get:A to
      * __printk_cpu_sync_try_get:B of the next CPU
      */
     atomic_set_release(&printk_cpu_sync_owner,
                -1); /* LMM(__printk_cpu_sync_put:B) */
 }
 EXPORT_SYMBOL(__printk_cpu_sync_put);
 #endif /* CONFIG_SMP */