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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
 /*
  * linux/fs/seq_file.c
  *
  * helper functions for making synthetic files from sequences of records.
  * initial implementation -- AV, Oct 2001.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/cache.h>
 #include <linux/fs.h>
 #include <linux/export.h>
 #include <linux/seq_file.h>
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
 #include <linux/cred.h>
 #include <linux/mm.h>
 #include <linux/printk.h>
 #include <linux/string_helpers.h>
 #include <linux/uio.h>
 
 #include <linux/uaccess.h>
 #include <asm/page.h>
 
 static struct kmem_cache *seq_file_cache __ro_after_init;
 
 static void seq_set_overflow(struct seq_file *m)
 {
     m->count = m->size;
 }
 
 static void *seq_buf_alloc(unsigned long size)
 {
     if (unlikely(size > MAX_RW_COUNT))
         return NULL;
 
     return kvmalloc(size, GFP_KERNEL_ACCOUNT);
 }
 
 /**
  *  seq_open -  initialize sequential file
  *  @file: file we initialize
  *  @op: method table describing the sequence
  *
  *  seq_open() sets @file, associating it with a sequence described
  *  by @op.  @op->start() sets the iterator up and returns the first
  *  element of sequence. @op->stop() shuts it down.  @op->next()
  *  returns the next element of sequence.  @op->show() prints element
  *  into the buffer.  In case of error ->start() and ->next() return
  *  ERR_PTR(error).  In the end of sequence they return %NULL. ->show()
  *  returns 0 in case of success and negative number in case of error.
  *  Returning SEQ_SKIP means "discard this element and move on".
  *  Note: seq_open() will allocate a struct seq_file and store its
  *  pointer in @file->private_data. This pointer should not be modified.
  */
 int seq_open(struct file *file, const struct seq_operations *op)
 {
     struct seq_file *p;
 
     WARN_ON(file->private_data);
 
     p = kmem_cache_zalloc(seq_file_cache, GFP_KERNEL);
     if (!p)
         return -ENOMEM;
 
     file->private_data = p;
 
     mutex_init(&p->lock);
     p->op = op;
 
     // No refcounting: the lifetime of 'p' is constrained
     // to the lifetime of the file.
     p->file = file;
 
     /*
      * seq_files support lseek() and pread().  They do not implement
      * write() at all, but we clear FMODE_PWRITE here for historical
      * reasons.
      *
      * If a client of seq_files a) implements file.write() and b) wishes to
      * support pwrite() then that client will need to implement its own
      * file.open() which calls seq_open() and then sets FMODE_PWRITE.
      */
     file->f_mode &= ~FMODE_PWRITE;
     return 0;
 }
 EXPORT_SYMBOL(seq_open);
 
 static int traverse(struct seq_file *m, loff_t offset)
 {
     loff_t pos = 0;
     int error = 0;
     void *p;
 
     m->index = 0;
     m->count = m->from = 0;
     if (!offset)
         return 0;
 
     if (!m->buf) {
         m->buf = seq_buf_alloc(m->size = PAGE_SIZE);
         if (!m->buf)
             return -ENOMEM;
     }
     p = m->op->start(m, &m->index);
     while (p) {
         error = PTR_ERR(p);
         if (IS_ERR(p))
             break;
         error = m->op->show(m, p);
         if (error < 0)
             break;
         if (unlikely(error)) {
             error = 0;
             m->count = 0;
         }
         if (seq_has_overflowed(m))
             goto Eoverflow;
         p = m->op->next(m, p, &m->index);
         if (pos + m->count > offset) {
             m->from = offset - pos;
             m->count -= m->from;
             break;
         }
         pos += m->count;
         m->count = 0;
         if (pos == offset)
             break;
     }
     m->op->stop(m, p);
     return error;
 
 Eoverflow:
     m->op->stop(m, p);
     kvfree(m->buf);
     m->count = 0;
     m->buf = seq_buf_alloc(m->size <<= 1);
     return !m->buf ? -ENOMEM : -EAGAIN;
 }
 
 /**
  *  seq_read -  ->read() method for sequential files.
  *  @file: the file to read from
  *  @buf: the buffer to read to
  *  @size: the maximum number of bytes to read
  *  @ppos: the current position in the file
  *
  *  Ready-made ->f_op->read()
  */
 ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 {
     struct iovec iov = { .iov_base = buf, .iov_len = size};
     struct kiocb kiocb;
     struct iov_iter iter;
     ssize_t ret;
 
     init_sync_kiocb(&kiocb, file);
     iov_iter_init(&iter, READ, &iov, 1, size);
 
     kiocb.ki_pos = *ppos;
     ret = seq_read_iter(&kiocb, &iter);
     *ppos = kiocb.ki_pos;
     return ret;
 }
 EXPORT_SYMBOL(seq_read);
 
 /*
  * Ready-made ->f_op->read_iter()
  */
 ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
     struct seq_file *m = iocb->ki_filp->private_data;
     size_t copied = 0;
     size_t n;
     void *p;
     int err = 0;
 
     if (!iov_iter_count(iter))
         return 0;
 
     mutex_lock(&m->lock);
 
     /*
      * if request is to read from zero offset, reset iterator to first
      * record as it might have been already advanced by previous requests
      */
     if (iocb->ki_pos == 0) {
         m->index = 0;
         m->count = 0;
     }
 
     /* Don't assume ki_pos is where we left it */
     if (unlikely(iocb->ki_pos != m->read_pos)) {
         while ((err = traverse(m, iocb->ki_pos)) == -EAGAIN)
             ;
         if (err) {
             /* With prejudice... */
             m->read_pos = 0;
             m->index = 0;
             m->count = 0;
             goto Done;
         } else {
             m->read_pos = iocb->ki_pos;
         }
     }
 
     /* grab buffer if we didn't have one */
     if (!m->buf) {
         m->buf = seq_buf_alloc(m->size = PAGE_SIZE);
         if (!m->buf)
             goto Enomem;
     }
     // something left in the buffer - copy it out first
     if (m->count) {
         n = copy_to_iter(m->buf + m->from, m->count, iter);
         m->count -= n;
         m->from += n;
         copied += n;
         if (m->count)   // hadn't managed to copy everything
             goto Done;
     }
     // get a non-empty record in the buffer
     m->from = 0;
     p = m->op->start(m, &m->index);
     while (1) {
         err = PTR_ERR(p);
         if (!p || IS_ERR(p))    // EOF or an error
             break;
         err = m->op->show(m, p);
         if (err < 0)        // hard error
             break;
         if (unlikely(err))  // ->show() says "skip it"
             m->count = 0;
         if (unlikely(!m->count)) { // empty record
             p = m->op->next(m, p, &m->index);
             continue;
         }
         if (!seq_has_overflowed(m)) // got it
             goto Fill;
         // need a bigger buffer
         m->op->stop(m, p);
         kvfree(m->buf);
         m->count = 0;
         m->buf = seq_buf_alloc(m->size <<= 1);
         if (!m->buf)
             goto Enomem;
         p = m->op->start(m, &m->index);
     }
     // EOF or an error
     m->op->stop(m, p);
     m->count = 0;
     goto Done;
 Fill:
     // one non-empty record is in the buffer; if they want more,
     // try to fit more in, but in any case we need to advance
     // the iterator once for every record shown.
     while (1) {
         size_t offs = m->count;
         loff_t pos = m->index;
 
         p = m->op->next(m, p, &m->index);
         if (pos == m->index) {
             pr_info_ratelimited("buggy .next function %ps did not update position index\n",
                         m->op->next);
             m->index++;
         }
         if (!p || IS_ERR(p))    // no next record for us
             break;
         if (m->count >= iov_iter_count(iter))
             break;
         err = m->op->show(m, p);
         if (err > 0) {      // ->show() says "skip it"
             m->count = offs;
         } else if (err || seq_has_overflowed(m)) {
             m->count = offs;
             break;
         }
     }
     m->op->stop(m, p);
     n = copy_to_iter(m->buf, m->count, iter);
     copied += n;
     m->count -= n;
     m->from = n;
 Done:
     if (unlikely(!copied)) {
         copied = m->count ? -EFAULT : err;
     } else {
         iocb->ki_pos += copied;
         m->read_pos += copied;
     }
     mutex_unlock(&m->lock);
     return copied;
 Enomem:
     err = -ENOMEM;
     goto Done;
 }
 EXPORT_SYMBOL(seq_read_iter);
 
 /**
  *  seq_lseek - ->llseek() method for sequential files.
  *  @file: the file in question
  *  @offset: new position
  *  @whence: 0 for absolute, 1 for relative position
  *
  *  Ready-made ->f_op->llseek()
  */
 loff_t seq_lseek(struct file *file, loff_t offset, int whence)
 {
     struct seq_file *m = file->private_data;
     loff_t retval = -EINVAL;
 
     mutex_lock(&m->lock);
     switch (whence) {
     case SEEK_CUR:
         offset += file->f_pos;
         fallthrough;
     case SEEK_SET:
         if (offset < 0)
             break;
         retval = offset;
         if (offset != m->read_pos) {
             while ((retval = traverse(m, offset)) == -EAGAIN)
                 ;
             if (retval) {
                 /* with extreme prejudice... */
                 file->f_pos = 0;
                 m->read_pos = 0;
                 m->index = 0;
                 m->count = 0;
             } else {
                 m->read_pos = offset;
                 retval = file->f_pos = offset;
             }
         } else {
             file->f_pos = offset;
         }
     }
     mutex_unlock(&m->lock);
     return retval;
 }
 EXPORT_SYMBOL(seq_lseek);
 
 /**
  *  seq_release -   free the structures associated with sequential file.
  *  @file: file in question
  *  @inode: its inode
  *
  *  Frees the structures associated with sequential file; can be used
  *  as ->f_op->release() if you don't have private data to destroy.
  */
 int seq_release(struct inode *inode, struct file *file)
 {
     struct seq_file *m = file->private_data;
     kvfree(m->buf);
     kmem_cache_free(seq_file_cache, m);
     return 0;
 }
 EXPORT_SYMBOL(seq_release);
 
 /**
  * seq_escape_mem - print data into buffer, escaping some characters
  * @m: target buffer
  * @src: source buffer
  * @len: size of source buffer
  * @flags: flags to pass to string_escape_mem()
  * @esc: set of characters that need escaping
  *
  * Puts data into buffer, replacing each occurrence of character from
  * given class (defined by @flags and @esc) with printable escaped sequence.
  *
  * Use seq_has_overflowed() to check for errors.
  */
 void seq_escape_mem(struct seq_file *m, const char *src, size_t len,
             unsigned int flags, const char *esc)
 {
     char *buf;
     size_t size = seq_get_buf(m, &buf);
     int ret;
 
     ret = string_escape_mem(src, len, buf, size, flags, esc);
     seq_commit(m, ret < size ? ret : -1);
 }
 EXPORT_SYMBOL(seq_escape_mem);
 
 void seq_vprintf(struct seq_file *m, const char *f, va_list args)
 {
     int len;
 
     if (m->count < m->size) {
         len = vsnprintf(m->buf + m->count, m->size - m->count, f, args);
         if (m->count + len < m->size) {
             m->count += len;
             return;
         }
     }
     seq_set_overflow(m);
 }
 EXPORT_SYMBOL(seq_vprintf);
 
 void seq_printf(struct seq_file *m, const char *f, ...)
 {
     va_list args;
 
     va_start(args, f);
     seq_vprintf(m, f, args);
     va_end(args);
 }
 EXPORT_SYMBOL(seq_printf);
 
 #ifdef CONFIG_BINARY_PRINTF
 void seq_bprintf(struct seq_file *m, const char *f, const u32 *binary)
 {
     int len;
 
     if (m->count < m->size) {
         len = bstr_printf(m->buf + m->count, m->size - m->count, f,
                   binary);
         if (m->count + len < m->size) {
             m->count += len;
             return;
         }
     }
     seq_set_overflow(m);
 }
 EXPORT_SYMBOL(seq_bprintf);
 #endif /* CONFIG_BINARY_PRINTF */
 
 /**
  *  mangle_path -   mangle and copy path to buffer beginning
  *  @s: buffer start
  *  @p: beginning of path in above buffer
  *  @esc: set of characters that need escaping
  *
  *      Copy the path from @p to @s, replacing each occurrence of character from
  *      @esc with usual octal escape.
  *      Returns pointer past last written character in @s, or NULL in case of
  *      failure.
  */
 char *mangle_path(char *s, const char *p, const char *esc)
 {
     while (s <= p) {
         char c = *p++;
         if (!c) {
             return s;
         } else if (!strchr(esc, c)) {
             *s++ = c;
         } else if (s + 4 > p) {
             break;
         } else {
             *s++ = '\\';
             *s++ = '0' + ((c & 0300) >> 6);
             *s++ = '0' + ((c & 070) >> 3);
             *s++ = '0' + (c & 07);
         }
     }
     return NULL;
 }
 EXPORT_SYMBOL(mangle_path);
 
 /**
  * seq_path - seq_file interface to print a pathname
  * @m: the seq_file handle
  * @path: the struct path to print
  * @esc: set of characters to escape in the output
  *
  * return the absolute path of 'path', as represented by the
  * dentry / mnt pair in the path parameter.
  */
 int seq_path(struct seq_file *m, const struct path *path, const char *esc)
 {
     char *buf;
     size_t size = seq_get_buf(m, &buf);
     int res = -1;
 
     if (size) {
         char *p = d_path(path, buf, size);
         if (!IS_ERR(p)) {
             char *end = mangle_path(buf, p, esc);
             if (end)
                 res = end - buf;
         }
     }
     seq_commit(m, res);
 
     return res;
 }
 EXPORT_SYMBOL(seq_path);
 
 /**
  * seq_file_path - seq_file interface to print a pathname of a file
  * @m: the seq_file handle
  * @file: the struct file to print
  * @esc: set of characters to escape in the output
  *
  * return the absolute path to the file.
  */
 int seq_file_path(struct seq_file *m, struct file *file, const char *esc)
 {
     return seq_path(m, &file->f_path, esc);
 }
 EXPORT_SYMBOL(seq_file_path);
 
 /*
  * Same as seq_path, but relative to supplied root.
  */
 int seq_path_root(struct seq_file *m, const struct path *path,
           const struct path *root, const char *esc)
 {
     char *buf;
     size_t size = seq_get_buf(m, &buf);
     int res = -ENAMETOOLONG;
 
     if (size) {
         char *p;
 
         p = __d_path(path, root, buf, size);
         if (!p)
             return SEQ_SKIP;
         res = PTR_ERR(p);
         if (!IS_ERR(p)) {
             char *end = mangle_path(buf, p, esc);
             if (end)
                 res = end - buf;
             else
                 res = -ENAMETOOLONG;
         }
     }
     seq_commit(m, res);
 
     return res < 0 && res != -ENAMETOOLONG ? res : 0;
 }
 
 /*
  * returns the path of the 'dentry' from the root of its filesystem.
  */
 int seq_dentry(struct seq_file *m, struct dentry *dentry, const char *esc)
 {
     char *buf;
     size_t size = seq_get_buf(m, &buf);
     int res = -1;
 
     if (size) {
         char *p = dentry_path(dentry, buf, size);
         if (!IS_ERR(p)) {
             char *end = mangle_path(buf, p, esc);
             if (end)
                 res = end - buf;
         }
     }
     seq_commit(m, res);
 
     return res;
 }
 EXPORT_SYMBOL(seq_dentry);
 
 void *single_start(struct seq_file *p, loff_t *pos)
 {
     return *pos ? NULL : SEQ_START_TOKEN;
 }
 
 static void *single_next(struct seq_file *p, void *v, loff_t *pos)
 {
     ++*pos;
     return NULL;
 }
 
 static void single_stop(struct seq_file *p, void *v)
 {
 }
 
 int single_open(struct file *file, int (*show)(struct seq_file *, void *),
         void *data)
 {
     struct seq_operations *op = kmalloc(sizeof(*op), GFP_KERNEL_ACCOUNT);
     int res = -ENOMEM;
 
     if (op) {
         op->start = single_start;
         op->next = single_next;
         op->stop = single_stop;
         op->show = show;
         res = seq_open(file, op);
         if (!res)
             ((struct seq_file *)file->private_data)->private = data;
         else
             kfree(op);
     }
     return res;
 }
 EXPORT_SYMBOL(single_open);
 
 int single_open_size(struct file *file, int (*show)(struct seq_file *, void *),
         void *data, size_t size)
 {
     char *buf = seq_buf_alloc(size);
     int ret;
     if (!buf)
         return -ENOMEM;
     ret = single_open(file, show, data);
     if (ret) {
         kvfree(buf);
         return ret;
     }
     ((struct seq_file *)file->private_data)->buf = buf;
     ((struct seq_file *)file->private_data)->size = size;
     return 0;
 }
 EXPORT_SYMBOL(single_open_size);
 
 int single_release(struct inode *inode, struct file *file)
 {
     const struct seq_operations *op = ((struct seq_file *)file->private_data)->op;
     int res = seq_release(inode, file);
     kfree(op);
     return res;
 }
 EXPORT_SYMBOL(single_release);
 
 int seq_release_private(struct inode *inode, struct file *file)
 {
     struct seq_file *seq = file->private_data;
 
     kfree(seq->private);
     seq->private = NULL;
     return seq_release(inode, file);
 }
 EXPORT_SYMBOL(seq_release_private);
 
 void *__seq_open_private(struct file *f, const struct seq_operations *ops,
         int psize)
 {
     int rc;
     void *private;
     struct seq_file *seq;
 
     private = kzalloc(psize, GFP_KERNEL_ACCOUNT);
     if (private == NULL)
         goto out;
 
     rc = seq_open(f, ops);
     if (rc < 0)
         goto out_free;
 
     seq = f->private_data;
     seq->private = private;
     return private;
 
 out_free:
     kfree(private);
 out:
     return NULL;
 }
 EXPORT_SYMBOL(__seq_open_private);
 
 int seq_open_private(struct file *filp, const struct seq_operations *ops,
         int psize)
 {
     return __seq_open_private(filp, ops, psize) ? 0 : -ENOMEM;
 }
 EXPORT_SYMBOL(seq_open_private);
 
 void seq_putc(struct seq_file *m, char c)
 {
     if (m->count >= m->size)
         return;
 
     m->buf[m->count++] = c;
 }
 EXPORT_SYMBOL(seq_putc);
 
 void seq_puts(struct seq_file *m, const char *s)
 {
     int len = strlen(s);
 
     if (m->count + len >= m->size) {
         seq_set_overflow(m);
         return;
     }
     memcpy(m->buf + m->count, s, len);
     m->count += len;
 }
 EXPORT_SYMBOL(seq_puts);
 
 /**
  * seq_put_decimal_ull_width - A helper routine for putting decimal numbers
  *                 without rich format of printf().
  * only 'unsigned long long' is supported.
  * @m: seq_file identifying the buffer to which data should be written
  * @delimiter: a string which is printed before the number
  * @num: the number
  * @width: a minimum field width
  *
  * This routine will put strlen(delimiter) + number into seq_filed.
  * This routine is very quick when you show lots of numbers.
  * In usual cases, it will be better to use seq_printf(). It's easier to read.
  */
 void seq_put_decimal_ull_width(struct seq_file *m, const char *delimiter,
              unsigned long long num, unsigned int width)
 {
     int len;
 
     if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
         goto overflow;
 
     if (delimiter && delimiter[0]) {
         if (delimiter[1] == 0)
             seq_putc(m, delimiter[0]);
         else
             seq_puts(m, delimiter);
     }
 
     if (!width)
         width = 1;
 
     if (m->count + width >= m->size)
         goto overflow;
 
     len = num_to_str(m->buf + m->count, m->size - m->count, num, width);
     if (!len)
         goto overflow;
 
     m->count += len;
     return;
 
 overflow:
     seq_set_overflow(m);
 }
 
 void seq_put_decimal_ull(struct seq_file *m, const char *delimiter,
              unsigned long long num)
 {
     return seq_put_decimal_ull_width(m, delimiter, num, 0);
 }
 EXPORT_SYMBOL(seq_put_decimal_ull);
 
 /**
  * seq_put_hex_ll - put a number in hexadecimal notation
  * @m: seq_file identifying the buffer to which data should be written
  * @delimiter: a string which is printed before the number
  * @v: the number
  * @width: a minimum field width
  *
  * seq_put_hex_ll(m, "", v, 8) is equal to seq_printf(m, "%08llx", v)
  *
  * This routine is very quick when you show lots of numbers.
  * In usual cases, it will be better to use seq_printf(). It's easier to read.
  */
 void seq_put_hex_ll(struct seq_file *m, const char *delimiter,
                 unsigned long long v, unsigned int width)
 {
     unsigned int len;
     int i;
 
     if (delimiter && delimiter[0]) {
         if (delimiter[1] == 0)
             seq_putc(m, delimiter[0]);
         else
             seq_puts(m, delimiter);
     }
 
     /* If x is 0, the result of __builtin_clzll is undefined */
     if (v == 0)
         len = 1;
     else
         len = (sizeof(v) * 8 - __builtin_clzll(v) + 3) / 4;
 
     if (len < width)
         len = width;
 
     if (m->count + len > m->size) {
         seq_set_overflow(m);
         return;
     }
 
     for (i = len - 1; i >= 0; i--) {
         m->buf[m->count + i] = hex_asc[0xf & v];
         v = v >> 4;
     }
     m->count += len;
 }
 
 void seq_put_decimal_ll(struct seq_file *m, const char *delimiter, long long num)
 {
     int len;
 
     if (m->count + 3 >= m->size) /* we'll write 2 bytes at least */
         goto overflow;
 
     if (delimiter && delimiter[0]) {
         if (delimiter[1] == 0)
             seq_putc(m, delimiter[0]);
         else
             seq_puts(m, delimiter);
     }
 
     if (m->count + 2 >= m->size)
         goto overflow;
 
     if (num < 0) {
         m->buf[m->count++] = '-';
         num = -num;
     }
 
     if (num < 10) {
         m->buf[m->count++] = num + '0';
         return;
     }
 
     len = num_to_str(m->buf + m->count, m->size - m->count, num, 0);
     if (!len)
         goto overflow;
 
     m->count += len;
     return;
 
 overflow:
     seq_set_overflow(m);
 }
 EXPORT_SYMBOL(seq_put_decimal_ll);
 
 /**
  * seq_write - write arbitrary data to buffer
  * @seq: seq_file identifying the buffer to which data should be written
  * @data: data address
  * @len: number of bytes
  *
  * Return 0 on success, non-zero otherwise.
  */
 int seq_write(struct seq_file *seq, const void *data, size_t len)
 {
     if (seq->count + len < seq->size) {
         memcpy(seq->buf + seq->count, data, len);
         seq->count += len;
         return 0;
     }
     seq_set_overflow(seq);
     return -1;
 }
 EXPORT_SYMBOL(seq_write);
 
 /**
  * seq_pad - write padding spaces to buffer
  * @m: seq_file identifying the buffer to which data should be written
  * @c: the byte to append after padding if non-zero
  */
 void seq_pad(struct seq_file *m, char c)
 {
     int size = m->pad_until - m->count;
     if (size > 0) {
         if (size + m->count > m->size) {
             seq_set_overflow(m);
             return;
         }
         memset(m->buf + m->count, ' ', size);
         m->count += size;
     }
     if (c)
         seq_putc(m, c);
 }
 EXPORT_SYMBOL(seq_pad);
 
 /* A complete analogue of print_hex_dump() */
 void seq_hex_dump(struct seq_file *m, const char *prefix_str, int prefix_type,
           int rowsize, int groupsize, const void *buf, size_t len,
           bool ascii)
 {
     const u8 *ptr = buf;
     int i, linelen, remaining = len;
     char *buffer;
     size_t size;
     int ret;
 
     if (rowsize != 16 && rowsize != 32)
         rowsize = 16;
 
     for (i = 0; i < len && !seq_has_overflowed(m); i += rowsize) {
         linelen = min(remaining, rowsize);
         remaining -= rowsize;
 
         switch (prefix_type) {
         case DUMP_PREFIX_ADDRESS:
             seq_printf(m, "%s%p: ", prefix_str, ptr + i);
             break;
         case DUMP_PREFIX_OFFSET:
             seq_printf(m, "%s%.8x: ", prefix_str, i);
             break;
         default:
             seq_printf(m, "%s", prefix_str);
             break;
         }
 
         size = seq_get_buf(m, &buffer);
         ret = hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
                      buffer, size, ascii);
         seq_commit(m, ret < size ? ret : -1);
 
         seq_putc(m, '\n');
     }
 }
 EXPORT_SYMBOL(seq_hex_dump);
 
 struct list_head *seq_list_start(struct list_head *head, loff_t pos)
 {
     struct list_head *lh;
 
     list_for_each(lh, head)
         if (pos-- == 0)
             return lh;
 
     return NULL;
 }
 EXPORT_SYMBOL(seq_list_start);
 
 struct list_head *seq_list_start_head(struct list_head *head, loff_t pos)
 {
     if (!pos)
         return head;
 
     return seq_list_start(head, pos - 1);
 }
 EXPORT_SYMBOL(seq_list_start_head);
 
 struct list_head *seq_list_next(void *v, struct list_head *head, loff_t *ppos)
 {
     struct list_head *lh;
 
     lh = ((struct list_head *)v)->next;
     ++*ppos;
     return lh == head ? NULL : lh;
 }
 EXPORT_SYMBOL(seq_list_next);
 
 struct list_head *seq_list_start_rcu(struct list_head *head, loff_t pos)
 {
     struct list_head *lh;
 
     list_for_each_rcu(lh, head)
         if (pos-- == 0)
             return lh;
 
     return NULL;
 }
 EXPORT_SYMBOL(seq_list_start_rcu);
 
 struct list_head *seq_list_start_head_rcu(struct list_head *head, loff_t pos)
 {
     if (!pos)
         return head;
 
     return seq_list_start_rcu(head, pos - 1);
 }
 EXPORT_SYMBOL(seq_list_start_head_rcu);
 
 struct list_head *seq_list_next_rcu(void *v, struct list_head *head,
                     loff_t *ppos)
 {
     struct list_head *lh;
 
     lh = list_next_rcu((struct list_head *)v);
     ++*ppos;
     return lh == head ? NULL : lh;
 }
 EXPORT_SYMBOL(seq_list_next_rcu);
 
 /**
  * seq_hlist_start - start an iteration of a hlist
  * @head: the head of the hlist
  * @pos:  the start position of the sequence
  *
  * Called at seq_file->op->start().
  */
 struct hlist_node *seq_hlist_start(struct hlist_head *head, loff_t pos)
 {
     struct hlist_node *node;
 
     hlist_for_each(node, head)
         if (pos-- == 0)
             return node;
     return NULL;
 }
 EXPORT_SYMBOL(seq_hlist_start);
 
 /**
  * seq_hlist_start_head - start an iteration of a hlist
  * @head: the head of the hlist
  * @pos:  the start position of the sequence
  *
  * Called at seq_file->op->start(). Call this function if you want to
  * print a header at the top of the output.
  */
 struct hlist_node *seq_hlist_start_head(struct hlist_head *head, loff_t pos)
 {
     if (!pos)
         return SEQ_START_TOKEN;
 
     return seq_hlist_start(head, pos - 1);
 }
 EXPORT_SYMBOL(seq_hlist_start_head);
 
 /**
  * seq_hlist_next - move to the next position of the hlist
  * @v:    the current iterator
  * @head: the head of the hlist
  * @ppos: the current position
  *
  * Called at seq_file->op->next().
  */
 struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
                   loff_t *ppos)
 {
     struct hlist_node *node = v;
 
     ++*ppos;
     if (v == SEQ_START_TOKEN)
         return head->first;
     else
         return node->next;
 }
 EXPORT_SYMBOL(seq_hlist_next);
 
 /**
  * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
  * @head: the head of the hlist
  * @pos:  the start position of the sequence
  *
  * Called at seq_file->op->start().
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
 struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
                        loff_t pos)
 {
     struct hlist_node *node;
 
     __hlist_for_each_rcu(node, head)
         if (pos-- == 0)
             return node;
     return NULL;
 }
 EXPORT_SYMBOL(seq_hlist_start_rcu);
 
 /**
  * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
  * @head: the head of the hlist
  * @pos:  the start position of the sequence
  *
  * Called at seq_file->op->start(). Call this function if you want to
  * print a header at the top of the output.
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
 struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
                         loff_t pos)
 {
     if (!pos)
         return SEQ_START_TOKEN;
 
     return seq_hlist_start_rcu(head, pos - 1);
 }
 EXPORT_SYMBOL(seq_hlist_start_head_rcu);
 
 /**
  * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
  * @v:    the current iterator
  * @head: the head of the hlist
  * @ppos: the current position
  *
  * Called at seq_file->op->next().
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
 struct hlist_node *seq_hlist_next_rcu(void *v,
                       struct hlist_head *head,
                       loff_t *ppos)
 {
     struct hlist_node *node = v;
 
     ++*ppos;
     if (v == SEQ_START_TOKEN)
         return rcu_dereference(head->first);
     else
         return rcu_dereference(node->next);
 }
 EXPORT_SYMBOL(seq_hlist_next_rcu);
 
 /**
  * seq_hlist_start_percpu - start an iteration of a percpu hlist array
  * @head: pointer to percpu array of struct hlist_heads
  * @cpu:  pointer to cpu "cursor"
  * @pos:  start position of sequence
  *
  * Called at seq_file->op->start().
  */
 struct hlist_node *
 seq_hlist_start_percpu(struct hlist_head __percpu *head, int *cpu, loff_t pos)
 {
     struct hlist_node *node;
 
     for_each_possible_cpu(*cpu) {
         hlist_for_each(node, per_cpu_ptr(head, *cpu)) {
             if (pos-- == 0)
                 return node;
         }
     }
     return NULL;
 }
 EXPORT_SYMBOL(seq_hlist_start_percpu);
 
 /**
  * seq_hlist_next_percpu - move to the next position of the percpu hlist array
  * @v:    pointer to current hlist_node
  * @head: pointer to percpu array of struct hlist_heads
  * @cpu:  pointer to cpu "cursor"
  * @pos:  start position of sequence
  *
  * Called at seq_file->op->next().
  */
 struct hlist_node *
 seq_hlist_next_percpu(void *v, struct hlist_head __percpu *head,
             int *cpu, loff_t *pos)
 {
     struct hlist_node *node = v;
 
     ++*pos;
 
     if (node->next)
         return node->next;
 
     for (*cpu = cpumask_next(*cpu, cpu_possible_mask); *cpu < nr_cpu_ids;
          *cpu = cpumask_next(*cpu, cpu_possible_mask)) {
         struct hlist_head *bucket = per_cpu_ptr(head, *cpu);
 
         if (!hlist_empty(bucket))
             return bucket->first;
     }
     return NULL;
 }
 EXPORT_SYMBOL(seq_hlist_next_percpu);
 
 void __init seq_file_init(void)
 {
     seq_file_cache = KMEM_CACHE(seq_file, SLAB_ACCOUNT|SLAB_PANIC);
 }

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