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 // SPDX-License-Identifier: GPL-2.0+
 /*
  * IBM eServer Hypervisor Virtual Console Server Device Driver
  * Copyright (C) 2003, 2004 IBM Corp.
  *  Ryan S. Arnold (rsa@us.ibm.com)
  *
  * Author(s) :  Ryan S. Arnold <rsa@us.ibm.com>
  *
  * This is the device driver for the IBM Hypervisor Virtual Console Server,
  * "hvcs".  The IBM hvcs provides a tty driver interface to allow Linux
  * user space applications access to the system consoles of logically
  * partitioned operating systems, e.g. Linux, running on the same partitioned
  * Power5 ppc64 system.  Physical hardware consoles per partition are not
  * practical on this hardware so system consoles are accessed by this driver
  * using inter-partition firmware interfaces to virtual terminal devices.
  *
  * A vty is known to the HMC as a "virtual serial server adapter".  It is a
  * virtual terminal device that is created by firmware upon partition creation
  * to act as a partitioned OS's console device.
  *
  * Firmware dynamically (via hotplug) exposes vty-servers to a running ppc64
  * Linux system upon their creation by the HMC or their exposure during boot.
  * The non-user interactive backend of this driver is implemented as a vio
  * device driver so that it can receive notification of vty-server lifetimes
  * after it registers with the vio bus to handle vty-server probe and remove
  * callbacks.
  *
  * Many vty-servers can be configured to connect to one vty, but a vty can
  * only be actively connected to by a single vty-server, in any manner, at one
  * time.  If the HMC is currently hosting the console for a target Linux
  * partition; attempts to open the tty device to the partition's console using
  * the hvcs on any partition will return -EBUSY with every open attempt until
  * the HMC frees the connection between its vty-server and the desired
  * partition's vty device.  Conversely, a vty-server may only be connected to
  * a single vty at one time even though it may have several configured vty
  * partner possibilities.
  *
  * Firmware does not provide notification of vty partner changes to this
  * driver.  This means that an HMC Super Admin may add or remove partner vtys
  * from a vty-server's partner list but the changes will not be signaled to
  * the vty-server.  Firmware only notifies the driver when a vty-server is
  * added or removed from the system.  To compensate for this deficiency, this
  * driver implements a sysfs update attribute which provides a method for
  * rescanning partner information upon a user's request.
  *
  * Each vty-server, prior to being exposed to this driver is reference counted
  * using the 2.6 Linux kernel kref construct.
  *
  * For direction on installation and usage of this driver please reference
  * Documentation/powerpc/hvcs.rst.
  */
 
 #include <linux/device.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/kref.h>
 #include <linux/kthread.h>
 #include <linux/list.h>
 #include <linux/major.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/stat.h>
 #include <linux/tty.h>
 #include <linux/tty_flip.h>
 #include <asm/hvconsole.h>
 #include <asm/hvcserver.h>
 #include <linux/uaccess.h>
 #include <asm/vio.h>
 
 /*
  * 1.3.0 -> 1.3.1 In hvcs_open memset(..,0x00,..) instead of memset(..,0x3F,00).
  * Removed braces around single statements following conditionals.  Removed '=
  * 0' after static int declarations since these default to zero.  Removed
  * list_for_each_safe() and replaced with list_for_each_entry() in
  * hvcs_get_by_index().  The 'safe' version is un-needed now that the driver is
  * using spinlocks.  Changed spin_lock_irqsave() to spin_lock() when locking
  * hvcs_structs_lock and hvcs_pi_lock since these are not touched in an int
  * handler.  Initialized hvcs_structs_lock and hvcs_pi_lock to
  * SPIN_LOCK_UNLOCKED at declaration time rather than in hvcs_module_init().
  * Added spin_lock around list_del() in destroy_hvcs_struct() to protect the
  * list traversals from a deletion.  Removed '= NULL' from pointer declaration
  * statements since they are initialized NULL by default.  Removed wmb()
  * instances from hvcs_try_write().  They probably aren't needed with locking in
  * place.  Added check and cleanup for hvcs_pi_buff = kmalloc() in
  * hvcs_module_init().  Exposed hvcs_struct.index via a sysfs attribute so that
  * the coupling between /dev/hvcs* and a vty-server can be automatically
  * determined.  Moved kobject_put() in hvcs_open outside of the
  * spin_unlock_irqrestore().
  *
  * 1.3.1 -> 1.3.2 Changed method for determining hvcs_struct->index and had it
  * align with how the tty layer always assigns the lowest index available.  This
  * change resulted in a list of ints that denotes which indexes are available.
  * Device additions and removals use the new hvcs_get_index() and
  * hvcs_return_index() helper functions.  The list is created with
  * hvsc_alloc_index_list() and it is destroyed with hvcs_free_index_list().
  * Without these fixes hotplug vty-server adapter support goes crazy with this
  * driver if the user removes a vty-server adapter.  Moved free_irq() outside of
  * the hvcs_final_close() function in order to get it out of the spinlock.
  * Rearranged hvcs_close().  Cleaned up some printks and did some housekeeping
  * on the changelog.  Removed local CLC_LENGTH and used HVCS_CLC_LENGTH from
  * arch/powerepc/include/asm/hvcserver.h
  *
  * 1.3.2 -> 1.3.3 Replaced yield() in hvcs_close() with tty_wait_until_sent() to
  * prevent possible lockup with realtime scheduling as similarly pointed out by
  * akpm in hvc_console.  Changed resulted in the removal of hvcs_final_close()
  * to reorder cleanup operations and prevent discarding of pending data during
  * an hvcs_close().  Removed spinlock protection of hvcs_struct data members in
  * hvcs_write_room() and hvcs_chars_in_buffer() because they aren't needed.
  */
 
 #define HVCS_DRIVER_VERSION "1.3.3"
 
 MODULE_AUTHOR("Ryan S. Arnold <rsa@us.ibm.com>");
 MODULE_DESCRIPTION("IBM hvcs (Hypervisor Virtual Console Server) Driver");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(HVCS_DRIVER_VERSION);
 
 /*
  * Wait this long per iteration while trying to push buffered data to the
  * hypervisor before allowing the tty to complete a close operation.
  */
 #define HVCS_CLOSE_WAIT (HZ/100) /* 1/10 of a second */
 
 /*
  * Since the Linux TTY code does not currently (2-04-2004) support dynamic
  * addition of tty derived devices and we shouldn't allocate thousands of
  * tty_device pointers when the number of vty-server & vty partner connections
  * will most often be much lower than this, we'll arbitrarily allocate
  * HVCS_DEFAULT_SERVER_ADAPTERS tty_structs and cdev's by default when we
  * register the tty_driver. This can be overridden using an insmod parameter.
  */
 #define HVCS_DEFAULT_SERVER_ADAPTERS    64
 
 /*
  * The user can't insmod with more than HVCS_MAX_SERVER_ADAPTERS hvcs device
  * nodes as a sanity check.  Theoretically there can be over 1 Billion
  * vty-server & vty partner connections.
  */
 #define HVCS_MAX_SERVER_ADAPTERS    1024
 
 /*
  * We let Linux assign us a major number and we start the minors at zero.  There
  * is no intuitive mapping between minor number and the target vty-server
  * adapter except that each new vty-server adapter is always assigned to the
  * smallest minor number available.
  */
 #define HVCS_MINOR_START    0
 
 /*
  * The hcall interface involves putting 8 chars into each of two registers.
  * We load up those 2 registers (in arch/powerpc/platforms/pseries/hvconsole.c)
  * by casting char[16] to long[2].  It would work without __ALIGNED__, but a 
  * little (tiny) bit slower because an unaligned load is slower than aligned 
  * load.
  */
 #define __ALIGNED__ __attribute__((__aligned__(8)))
 
 /*
  * How much data can firmware send with each hvc_put_chars()?  Maybe this
  * should be moved into an architecture specific area.
  */
 #define HVCS_BUFF_LEN   16
 
 /*
  * This is the maximum amount of data we'll let the user send us (hvcs_write) at
  * once in a chunk as a sanity check.
  */
 #define HVCS_MAX_FROM_USER  4096
 
 /*
  * Be careful when adding flags to this line discipline.  Don't add anything
  * that will cause echoing or we'll go into recursive loop echoing chars back
  * and forth with the console drivers.
  */
 static const struct ktermios hvcs_tty_termios = {
     .c_iflag = IGNBRK | IGNPAR,
     .c_oflag = OPOST,
     .c_cflag = B38400 | CS8 | CREAD | HUPCL,
     .c_cc = INIT_C_CC,
     .c_ispeed = 38400,
     .c_ospeed = 38400
 };
 
 /*
  * This value is used to take the place of a command line parameter when the
  * module is inserted.  It starts as -1 and stays as such if the user doesn't
  * specify a module insmod parameter.  If they DO specify one then it is set to
  * the value of the integer passed in.
  */
 static int hvcs_parm_num_devs = -1;
 module_param(hvcs_parm_num_devs, int, 0);
 
 static const char hvcs_driver_name[] = "hvcs";
 static const char hvcs_device_node[] = "hvcs";
 
 /* Status of partner info rescan triggered via sysfs. */
 static int hvcs_rescan_status;
 
 static struct tty_driver *hvcs_tty_driver;
 
 /*
  * In order to be somewhat sane this driver always associates the hvcs_struct
  * index element with the numerically equal tty->index.  This means that a
  * hotplugged vty-server adapter will always map to the lowest index valued
  * device node.  If vty-servers were hotplug removed from the system and then
  * new ones added the new vty-server may have the largest slot number of all
  * the vty-server adapters in the partition but it may have the lowest dev node
  * index of all the adapters due to the hole left by the hotplug removed
  * adapter.  There are a set of functions provided to get the lowest index for
  * a new device as well as return the index to the list.  This list is allocated
  * with a number of elements equal to the number of device nodes requested when
  * the module was inserted.
  */
 static int *hvcs_index_list;
 
 /*
  * How large is the list?  This is kept for traversal since the list is
  * dynamically created.
  */
 static int hvcs_index_count;
 
 /*
  * Used by the khvcsd to pick up I/O operations when the kernel_thread is
  * already awake but potentially shifted to TASK_INTERRUPTIBLE state.
  */
 static int hvcs_kicked;
 
 /*
  * Use by the kthread construct for task operations like waking the sleeping
  * thread and stopping the kthread.
  */
 static struct task_struct *hvcs_task;
 
 /*
  * We allocate this for the use of all of the hvcs_structs when they fetch
  * partner info.
  */
 static unsigned long *hvcs_pi_buff;
 
 /* Only allow one hvcs_struct to use the hvcs_pi_buff at a time. */
 static DEFINE_SPINLOCK(hvcs_pi_lock);
 
 /* One vty-server per hvcs_struct */
 struct hvcs_struct {
     struct tty_port port;
     spinlock_t lock;
 
     /*
      * This index identifies this hvcs device as the complement to a
      * specific tty index.
      */
     unsigned int index;
 
     /*
      * Used to tell the driver kernel_thread what operations need to take
      * place upon this hvcs_struct instance.
      */
     int todo_mask;
 
     /*
      * This buffer is required so that when hvcs_write_room() reports that
      * it can send HVCS_BUFF_LEN characters that it will buffer the full
      * HVCS_BUFF_LEN characters if need be.  This is essential for opost
      * writes since they do not do high level buffering and expect to be
      * able to send what the driver commits to sending buffering
      * [e.g. tab to space conversions in n_tty.c opost()].
      */
     char buffer[HVCS_BUFF_LEN];
     int chars_in_buffer;
 
     /*
      * Any variable below is valid before a tty is connected and
      * stays valid after the tty is disconnected.  These shouldn't be
      * whacked until the kobject refcount reaches zero though some entries
      * may be changed via sysfs initiatives.
      */
     int connected; /* is the vty-server currently connected to a vty? */
     uint32_t p_unit_address; /* partner unit address */
     uint32_t p_partition_ID; /* partner partition ID */
     char p_location_code[HVCS_CLC_LENGTH + 1]; /* CLC + Null Term */
     struct list_head next; /* list management */
     struct vio_dev *vdev;
 };
 
 static LIST_HEAD(hvcs_structs);
 static DEFINE_SPINLOCK(hvcs_structs_lock);
 static DEFINE_MUTEX(hvcs_init_mutex);
 
 static int hvcs_get_pi(struct hvcs_struct *hvcsd);
 static int hvcs_rescan_devices_list(void);
 
 static void hvcs_partner_free(struct hvcs_struct *hvcsd);
 
 static int hvcs_initialize(void);
 
 #define HVCS_SCHED_READ 0x00000001
 #define HVCS_QUICK_READ 0x00000002
 #define HVCS_TRY_WRITE  0x00000004
 #define HVCS_READ_MASK  (HVCS_SCHED_READ | HVCS_QUICK_READ)
 
 static inline struct hvcs_struct *from_vio_dev(struct vio_dev *viod)
 {
     return dev_get_drvdata(&viod->dev);
 }
 /* The sysfs interface for the driver and devices */
 
 static ssize_t hvcs_partner_vtys_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
     struct vio_dev *viod = to_vio_dev(dev);
     struct hvcs_struct *hvcsd = from_vio_dev(viod);
     unsigned long flags;
     int retval;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     retval = sprintf(buf, "%X\n", hvcsd->p_unit_address);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     return retval;
 }
 static DEVICE_ATTR(partner_vtys, S_IRUGO, hvcs_partner_vtys_show, NULL);
 
 static ssize_t hvcs_partner_clcs_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
     struct vio_dev *viod = to_vio_dev(dev);
     struct hvcs_struct *hvcsd = from_vio_dev(viod);
     unsigned long flags;
     int retval;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     retval = sprintf(buf, "%s\n", &hvcsd->p_location_code[0]);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     return retval;
 }
 static DEVICE_ATTR(partner_clcs, S_IRUGO, hvcs_partner_clcs_show, NULL);
 
 static ssize_t hvcs_current_vty_store(struct device *dev, struct device_attribute *attr, const char * buf,
         size_t count)
 {
     /*
      * Don't need this feature at the present time because firmware doesn't
      * yet support multiple partners.
      */
     printk(KERN_INFO "HVCS: Denied current_vty change: -EPERM.\n");
     return -EPERM;
 }
 
 static ssize_t hvcs_current_vty_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
     struct vio_dev *viod = to_vio_dev(dev);
     struct hvcs_struct *hvcsd = from_vio_dev(viod);
     unsigned long flags;
     int retval;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     retval = sprintf(buf, "%s\n", &hvcsd->p_location_code[0]);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     return retval;
 }
 
 static DEVICE_ATTR(current_vty,
     S_IRUGO | S_IWUSR, hvcs_current_vty_show, hvcs_current_vty_store);
 
 static ssize_t hvcs_vterm_state_store(struct device *dev, struct device_attribute *attr, const char *buf,
         size_t count)
 {
     struct vio_dev *viod = to_vio_dev(dev);
     struct hvcs_struct *hvcsd = from_vio_dev(viod);
     unsigned long flags;
 
     /* writing a '0' to this sysfs entry will result in the disconnect. */
     if (simple_strtol(buf, NULL, 0) != 0)
         return -EINVAL;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
 
     if (hvcsd->port.count > 0) {
         spin_unlock_irqrestore(&hvcsd->lock, flags);
         printk(KERN_INFO "HVCS: vterm state unchanged.  "
                 "The hvcs device node is still in use.\n");
         return -EPERM;
     }
 
     if (hvcsd->connected == 0) {
         spin_unlock_irqrestore(&hvcsd->lock, flags);
         printk(KERN_INFO "HVCS: vterm state unchanged. The"
                 " vty-server is not connected to a vty.\n");
         return -EPERM;
     }
 
     hvcs_partner_free(hvcsd);
     printk(KERN_INFO "HVCS: Closed vty-server@%X and"
             " partner vty@%X:%d connection.\n",
             hvcsd->vdev->unit_address,
             hvcsd->p_unit_address,
             (uint32_t)hvcsd->p_partition_ID);
 
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     return count;
 }
 
 static ssize_t hvcs_vterm_state_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
     struct vio_dev *viod = to_vio_dev(dev);
     struct hvcs_struct *hvcsd = from_vio_dev(viod);
     unsigned long flags;
     int retval;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     retval = sprintf(buf, "%d\n", hvcsd->connected);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     return retval;
 }
 static DEVICE_ATTR(vterm_state, S_IRUGO | S_IWUSR,
         hvcs_vterm_state_show, hvcs_vterm_state_store);
 
 static ssize_t hvcs_index_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
     struct vio_dev *viod = to_vio_dev(dev);
     struct hvcs_struct *hvcsd = from_vio_dev(viod);
     unsigned long flags;
     int retval;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     retval = sprintf(buf, "%d\n", hvcsd->index);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     return retval;
 }
 
 static DEVICE_ATTR(index, S_IRUGO, hvcs_index_show, NULL);
 
 static struct attribute *hvcs_attrs[] = {
     &dev_attr_partner_vtys.attr,
     &dev_attr_partner_clcs.attr,
     &dev_attr_current_vty.attr,
     &dev_attr_vterm_state.attr,
     &dev_attr_index.attr,
     NULL,
 };
 
 static struct attribute_group hvcs_attr_group = {
     .attrs = hvcs_attrs,
 };
 
 static ssize_t rescan_show(struct device_driver *ddp, char *buf)
 {
     /* A 1 means it is updating, a 0 means it is done updating */
     return snprintf(buf, PAGE_SIZE, "%d\n", hvcs_rescan_status);
 }
 
 static ssize_t rescan_store(struct device_driver *ddp, const char * buf,
         size_t count)
 {
     if ((simple_strtol(buf, NULL, 0) != 1)
         && (hvcs_rescan_status != 0))
         return -EINVAL;
 
     hvcs_rescan_status = 1;
     printk(KERN_INFO "HVCS: rescanning partner info for all"
         " vty-servers.\n");
     hvcs_rescan_devices_list();
     hvcs_rescan_status = 0;
     return count;
 }
 
 static DRIVER_ATTR_RW(rescan);
 
 static void hvcs_kick(void)
 {
     hvcs_kicked = 1;
     wmb();
     wake_up_process(hvcs_task);
 }
 
 static void hvcs_unthrottle(struct tty_struct *tty)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
     unsigned long flags;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     hvcsd->todo_mask |= HVCS_SCHED_READ;
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     hvcs_kick();
 }
 
 static void hvcs_throttle(struct tty_struct *tty)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
     unsigned long flags;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     vio_disable_interrupts(hvcsd->vdev);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 }
 
 /*
  * If the device is being removed we don't have to worry about this interrupt
  * handler taking any further interrupts because they are disabled which means
  * the hvcs_struct will always be valid in this handler.
  */
 static irqreturn_t hvcs_handle_interrupt(int irq, void *dev_instance)
 {
     struct hvcs_struct *hvcsd = dev_instance;
 
     spin_lock(&hvcsd->lock);
     vio_disable_interrupts(hvcsd->vdev);
     hvcsd->todo_mask |= HVCS_SCHED_READ;
     spin_unlock(&hvcsd->lock);
     hvcs_kick();
 
     return IRQ_HANDLED;
 }
 
 /* This function must be called with the hvcsd->lock held */
 static void hvcs_try_write(struct hvcs_struct *hvcsd)
 {
     uint32_t unit_address = hvcsd->vdev->unit_address;
     struct tty_struct *tty = hvcsd->port.tty;
     int sent;
 
     if (hvcsd->todo_mask & HVCS_TRY_WRITE) {
         /* won't send partial writes */
         sent = hvc_put_chars(unit_address,
                 &hvcsd->buffer[0],
                 hvcsd->chars_in_buffer );
         if (sent > 0) {
             hvcsd->chars_in_buffer = 0;
             /* wmb(); */
             hvcsd->todo_mask &= ~(HVCS_TRY_WRITE);
             /* wmb(); */
 
             /*
              * We are still obligated to deliver the data to the
              * hypervisor even if the tty has been closed because
              * we committed to delivering it.  But don't try to wake
              * a non-existent tty.
              */
             if (tty) {
                 tty_wakeup(tty);
             }
         }
     }
 }
 
 static int hvcs_io(struct hvcs_struct *hvcsd)
 {
     uint32_t unit_address;
     struct tty_struct *tty;
     char buf[HVCS_BUFF_LEN] __ALIGNED__;
     unsigned long flags;
     int got = 0;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
 
     unit_address = hvcsd->vdev->unit_address;
     tty = hvcsd->port.tty;
 
     hvcs_try_write(hvcsd);
 
     if (!tty || tty_throttled(tty)) {
         hvcsd->todo_mask &= ~(HVCS_READ_MASK);
         goto bail;
     } else if (!(hvcsd->todo_mask & (HVCS_READ_MASK)))
         goto bail;
 
     /* remove the read masks */
     hvcsd->todo_mask &= ~(HVCS_READ_MASK);
 
     if (tty_buffer_request_room(&hvcsd->port, HVCS_BUFF_LEN) >= HVCS_BUFF_LEN) {
         got = hvc_get_chars(unit_address,
                 &buf[0],
                 HVCS_BUFF_LEN);
         tty_insert_flip_string(&hvcsd->port, buf, got);
     }
 
     /* Give the TTY time to process the data we just sent. */
     if (got)
         hvcsd->todo_mask |= HVCS_QUICK_READ;
 
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     /* This is synch -- FIXME :js: it is not! */
     if (got)
         tty_flip_buffer_push(&hvcsd->port);
     else {
         /* Do this _after_ the flip_buffer_push */
         spin_lock_irqsave(&hvcsd->lock, flags);
         vio_enable_interrupts(hvcsd->vdev);
         spin_unlock_irqrestore(&hvcsd->lock, flags);
     }
 
     return hvcsd->todo_mask;
 
  bail:
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     return hvcsd->todo_mask;
 }
 
 static int khvcsd(void *unused)
 {
     struct hvcs_struct *hvcsd;
     int hvcs_todo_mask;
 
     __set_current_state(TASK_RUNNING);
 
     do {
         hvcs_todo_mask = 0;
         hvcs_kicked = 0;
         wmb();
 
         spin_lock(&hvcs_structs_lock);
         list_for_each_entry(hvcsd, &hvcs_structs, next) {
             hvcs_todo_mask |= hvcs_io(hvcsd);
         }
         spin_unlock(&hvcs_structs_lock);
 
         /*
          * If any of the hvcs adapters want to try a write or quick read
          * don't schedule(), yield a smidgen then execute the hvcs_io
          * thread again for those that want the write.
          */
          if (hvcs_todo_mask & (HVCS_TRY_WRITE | HVCS_QUICK_READ)) {
             yield();
             continue;
         }
 
         set_current_state(TASK_INTERRUPTIBLE);
         if (!hvcs_kicked)
             schedule();
         __set_current_state(TASK_RUNNING);
     } while (!kthread_should_stop());
 
     return 0;
 }
 
 static const struct vio_device_id hvcs_driver_table[] = {
     {"serial-server", "hvterm2"},
     { "", "" }
 };
 MODULE_DEVICE_TABLE(vio, hvcs_driver_table);
 
 static void hvcs_return_index(int index)
 {
     /* Paranoia check */
     if (!hvcs_index_list)
         return;
     if (index < 0 || index >= hvcs_index_count)
         return;
     if (hvcs_index_list[index] == -1)
         return;
     else
         hvcs_index_list[index] = -1;
 }
 
 static void hvcs_destruct_port(struct tty_port *p)
 {
     struct hvcs_struct *hvcsd = container_of(p, struct hvcs_struct, port);
     struct vio_dev *vdev;
     unsigned long flags;
 
     spin_lock(&hvcs_structs_lock);
     spin_lock_irqsave(&hvcsd->lock, flags);
 
     /* the list_del poisons the pointers */
     list_del(&(hvcsd->next));
 
     if (hvcsd->connected == 1) {
         hvcs_partner_free(hvcsd);
         printk(KERN_INFO "HVCS: Closed vty-server@%X and"
                 " partner vty@%X:%d connection.\n",
                 hvcsd->vdev->unit_address,
                 hvcsd->p_unit_address,
                 (uint32_t)hvcsd->p_partition_ID);
     }
     printk(KERN_INFO "HVCS: Destroyed hvcs_struct for vty-server@%X.\n",
             hvcsd->vdev->unit_address);
 
     vdev = hvcsd->vdev;
     hvcsd->vdev = NULL;
 
     hvcsd->p_unit_address = 0;
     hvcsd->p_partition_ID = 0;
     hvcs_return_index(hvcsd->index);
     memset(&hvcsd->p_location_code[0], 0x00, HVCS_CLC_LENGTH + 1);
 
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     spin_unlock(&hvcs_structs_lock);
 
     sysfs_remove_group(&vdev->dev.kobj, &hvcs_attr_group);
 
     kfree(hvcsd);
 }
 
 static const struct tty_port_operations hvcs_port_ops = {
     .destruct = hvcs_destruct_port,
 };
 
 static int hvcs_get_index(void)
 {
     int i;
     /* Paranoia check */
     if (!hvcs_index_list) {
         printk(KERN_ERR "HVCS: hvcs_index_list NOT valid!.\n");
         return -EFAULT;
     }
     /* Find the numerically lowest first free index. */
     for(i = 0; i < hvcs_index_count; i++) {
         if (hvcs_index_list[i] == -1) {
             hvcs_index_list[i] = 0;
             return i;
         }
     }
     return -1;
 }
 
 static int hvcs_probe(
     struct vio_dev *dev,
     const struct vio_device_id *id)
 {
     struct hvcs_struct *hvcsd;
     int index, rc;
     int retval;
 
     if (!dev || !id) {
         printk(KERN_ERR "HVCS: probed with invalid parameter.\n");
         return -EPERM;
     }
 
     /* Make sure we are properly initialized */
     rc = hvcs_initialize();
     if (rc) {
         pr_err("HVCS: Failed to initialize core driver.\n");
         return rc;
     }
 
     /* early to avoid cleanup on failure */
     index = hvcs_get_index();
     if (index < 0) {
         return -EFAULT;
     }
 
     hvcsd = kzalloc(sizeof(*hvcsd), GFP_KERNEL);
     if (!hvcsd)
         return -ENODEV;
 
     tty_port_init(&hvcsd->port);
     hvcsd->port.ops = &hvcs_port_ops;
     spin_lock_init(&hvcsd->lock);
 
     hvcsd->vdev = dev;
     dev_set_drvdata(&dev->dev, hvcsd);
 
     hvcsd->index = index;
 
     /* hvcsd->index = ++hvcs_struct_count; */
     hvcsd->chars_in_buffer = 0;
     hvcsd->todo_mask = 0;
     hvcsd->connected = 0;
 
     /*
      * This will populate the hvcs_struct's partner info fields for the
      * first time.
      */
     if (hvcs_get_pi(hvcsd)) {
         printk(KERN_ERR "HVCS: Failed to fetch partner"
             " info for vty-server@%X on device probe.\n",
             hvcsd->vdev->unit_address);
     }
 
     /*
      * If a user app opens a tty that corresponds to this vty-server before
      * the hvcs_struct has been added to the devices list then the user app
      * will get -ENODEV.
      */
     spin_lock(&hvcs_structs_lock);
     list_add_tail(&(hvcsd->next), &hvcs_structs);
     spin_unlock(&hvcs_structs_lock);
 
     retval = sysfs_create_group(&dev->dev.kobj, &hvcs_attr_group);
     if (retval) {
         printk(KERN_ERR "HVCS: Can't create sysfs attrs for vty-server@%X\n",
                hvcsd->vdev->unit_address);
         return retval;
     }
 
     printk(KERN_INFO "HVCS: vty-server@%X added to the vio bus.\n", dev->unit_address);
 
     /*
      * DON'T enable interrupts here because there is no user to receive the
      * data.
      */
     return 0;
 }
 
 static void hvcs_remove(struct vio_dev *dev)
 {
     struct hvcs_struct *hvcsd = dev_get_drvdata(&dev->dev);
     unsigned long flags;
     struct tty_struct *tty;
 
     /* By this time the vty-server won't be getting any more interrupts */
 
     spin_lock_irqsave(&hvcsd->lock, flags);
 
     tty = hvcsd->port.tty;
 
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 
     /*
      * Let the last holder of this object cause it to be removed, which
      * would probably be tty_hangup below.
      */
     tty_port_put(&hvcsd->port);
 
     /*
      * The hangup is a scheduled function which will auto chain call
      * hvcs_hangup.  The tty should always be valid at this time unless a
      * simultaneous tty close already cleaned up the hvcs_struct.
      */
     if (tty)
         tty_hangup(tty);
 
     printk(KERN_INFO "HVCS: vty-server@%X removed from the"
             " vio bus.\n", dev->unit_address);
 };
 
 static struct vio_driver hvcs_vio_driver = {
     .id_table   = hvcs_driver_table,
     .probe      = hvcs_probe,
     .remove     = hvcs_remove,
     .name       = hvcs_driver_name,
 };
 
 /* Only called from hvcs_get_pi please */
 static void hvcs_set_pi(struct hvcs_partner_info *pi, struct hvcs_struct *hvcsd)
 {
     hvcsd->p_unit_address = pi->unit_address;
     hvcsd->p_partition_ID  = pi->partition_ID;
 
     /* copy the null-term char too */
     strlcpy(hvcsd->p_location_code, pi->location_code,
         sizeof(hvcsd->p_location_code));
 }
 
 /*
  * Traverse the list and add the partner info that is found to the hvcs_struct
  * struct entry. NOTE: At this time I know that partner info will return a
  * single entry but in the future there may be multiple partner info entries per
  * vty-server and you'll want to zero out that list and reset it.  If for some
  * reason you have an old version of this driver but there IS more than one
  * partner info then hvcsd->p_* will hold the last partner info data from the
  * firmware query.  A good way to update this code would be to replace the three
  * partner info fields in hvcs_struct with a list of hvcs_partner_info
  * instances.
  *
  * This function must be called with the hvcsd->lock held.
  */
 static int hvcs_get_pi(struct hvcs_struct *hvcsd)
 {
     struct hvcs_partner_info *pi;
     uint32_t unit_address = hvcsd->vdev->unit_address;
     struct list_head head;
     int retval;
 
     spin_lock(&hvcs_pi_lock);
     if (!hvcs_pi_buff) {
         spin_unlock(&hvcs_pi_lock);
         return -EFAULT;
     }
     retval = hvcs_get_partner_info(unit_address, &head, hvcs_pi_buff);
     spin_unlock(&hvcs_pi_lock);
     if (retval) {
         printk(KERN_ERR "HVCS: Failed to fetch partner"
             " info for vty-server@%x.\n", unit_address);
         return retval;
     }
 
     /* nixes the values if the partner vty went away */
     hvcsd->p_unit_address = 0;
     hvcsd->p_partition_ID = 0;
 
     list_for_each_entry(pi, &head, node)
         hvcs_set_pi(pi, hvcsd);
 
     hvcs_free_partner_info(&head);
     return 0;
 }
 
 /*
  * This function is executed by the driver "rescan" sysfs entry.  It shouldn't
  * be executed elsewhere, in order to prevent deadlock issues.
  */
 static int hvcs_rescan_devices_list(void)
 {
     struct hvcs_struct *hvcsd;
     unsigned long flags;
 
     spin_lock(&hvcs_structs_lock);
 
     list_for_each_entry(hvcsd, &hvcs_structs, next) {
         spin_lock_irqsave(&hvcsd->lock, flags);
         hvcs_get_pi(hvcsd);
         spin_unlock_irqrestore(&hvcsd->lock, flags);
     }
 
     spin_unlock(&hvcs_structs_lock);
 
     return 0;
 }
 
 /*
  * Farm this off into its own function because it could be more complex once
  * multiple partners support is added. This function should be called with
  * the hvcsd->lock held.
  */
 static int hvcs_has_pi(struct hvcs_struct *hvcsd)
 {
     if ((!hvcsd->p_unit_address) || (!hvcsd->p_partition_ID))
         return 0;
     return 1;
 }
 
 /*
  * NOTE: It is possible that the super admin removed a partner vty and then
  * added a different vty as the new partner.
  *
  * This function must be called with the hvcsd->lock held.
  */
 static int hvcs_partner_connect(struct hvcs_struct *hvcsd)
 {
     int retval;
     unsigned int unit_address = hvcsd->vdev->unit_address;
 
     /*
      * If there wasn't any pi when the device was added it doesn't meant
      * there isn't any now.  This driver isn't notified when a new partner
      * vty is added to a vty-server so we discover changes on our own.
      * Please see comments in hvcs_register_connection() for justification
      * of this bizarre code.
      */
     retval = hvcs_register_connection(unit_address,
             hvcsd->p_partition_ID,
             hvcsd->p_unit_address);
     if (!retval) {
         hvcsd->connected = 1;
         return 0;
     } else if (retval != -EINVAL)
         return retval;
 
     /*
      * As per the spec re-get the pi and try again if -EINVAL after the
      * first connection attempt.
      */
     if (hvcs_get_pi(hvcsd))
         return -ENOMEM;
 
     if (!hvcs_has_pi(hvcsd))
         return -ENODEV;
 
     retval = hvcs_register_connection(unit_address,
             hvcsd->p_partition_ID,
             hvcsd->p_unit_address);
     if (retval != -EINVAL) {
         hvcsd->connected = 1;
         return retval;
     }
 
     /*
      * EBUSY is the most likely scenario though the vty could have been
      * removed or there really could be an hcall error due to the parameter
      * data but thanks to ambiguous firmware return codes we can't really
      * tell.
      */
     printk(KERN_INFO "HVCS: vty-server or partner"
             " vty is busy.  Try again later.\n");
     return -EBUSY;
 }
 
 /* This function must be called with the hvcsd->lock held */
 static void hvcs_partner_free(struct hvcs_struct *hvcsd)
 {
     int retval;
     do {
         retval = hvcs_free_connection(hvcsd->vdev->unit_address);
     } while (retval == -EBUSY);
     hvcsd->connected = 0;
 }
 
 /* This helper function must be called WITHOUT the hvcsd->lock held */
 static int hvcs_enable_device(struct hvcs_struct *hvcsd, uint32_t unit_address,
         unsigned int irq, struct vio_dev *vdev)
 {
     unsigned long flags;
     int rc;
 
     /*
      * It is possible that the vty-server was removed between the time that
      * the conn was registered and now.
      */
     rc = request_irq(irq, &hvcs_handle_interrupt, 0, "ibmhvcs", hvcsd);
     if (!rc) {
         /*
          * It is possible the vty-server was removed after the irq was
          * requested but before we have time to enable interrupts.
          */
         if (vio_enable_interrupts(vdev) == H_SUCCESS)
             return 0;
         else {
             printk(KERN_ERR "HVCS: int enable failed for"
                     " vty-server@%X.\n", unit_address);
             free_irq(irq, hvcsd);
         }
     } else
         printk(KERN_ERR "HVCS: irq req failed for"
                 " vty-server@%X.\n", unit_address);
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     hvcs_partner_free(hvcsd);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 
     return rc;
 
 }
 
 /*
  * This always increments the kref ref count if the call is successful.
  * Please remember to dec when you are done with the instance.
  *
  * NOTICE: Do NOT hold either the hvcs_struct.lock or hvcs_structs_lock when
  * calling this function or you will get deadlock.
  */
 static struct hvcs_struct *hvcs_get_by_index(int index)
 {
     struct hvcs_struct *hvcsd;
     unsigned long flags;
 
     spin_lock(&hvcs_structs_lock);
     list_for_each_entry(hvcsd, &hvcs_structs, next) {
         spin_lock_irqsave(&hvcsd->lock, flags);
         if (hvcsd->index == index) {
             tty_port_get(&hvcsd->port);
             spin_unlock_irqrestore(&hvcsd->lock, flags);
             spin_unlock(&hvcs_structs_lock);
             return hvcsd;
         }
         spin_unlock_irqrestore(&hvcsd->lock, flags);
     }
     spin_unlock(&hvcs_structs_lock);
 
     return NULL;
 }
 
 static int hvcs_install(struct tty_driver *driver, struct tty_struct *tty)
 {
     struct hvcs_struct *hvcsd;
     struct vio_dev *vdev;
     unsigned long unit_address, flags;
     unsigned int irq;
     int retval;
 
     /*
      * Is there a vty-server that shares the same index?
      * This function increments the kref index.
      */
     hvcsd = hvcs_get_by_index(tty->index);
     if (!hvcsd) {
         printk(KERN_WARNING "HVCS: open failed, no device associated"
                 " with tty->index %d.\n", tty->index);
         return -ENODEV;
     }
 
     spin_lock_irqsave(&hvcsd->lock, flags);
 
     if (hvcsd->connected == 0) {
         retval = hvcs_partner_connect(hvcsd);
         if (retval) {
             spin_unlock_irqrestore(&hvcsd->lock, flags);
             printk(KERN_WARNING "HVCS: partner connect failed.\n");
             goto err_put;
         }
     }
 
     hvcsd->port.count = 0;
     hvcsd->port.tty = tty;
     tty->driver_data = hvcsd;
 
     memset(&hvcsd->buffer[0], 0x00, HVCS_BUFF_LEN);
 
     /*
      * Save these in the spinlock for the enable operations that need them
      * outside of the spinlock.
      */
     irq = hvcsd->vdev->irq;
     vdev = hvcsd->vdev;
     unit_address = hvcsd->vdev->unit_address;
 
     hvcsd->todo_mask |= HVCS_SCHED_READ;
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 
     /*
      * This must be done outside of the spinlock because it requests irqs
      * and will grab the spinlock and free the connection if it fails.
      */
     retval = hvcs_enable_device(hvcsd, unit_address, irq, vdev);
     if (retval) {
         printk(KERN_WARNING "HVCS: enable device failed.\n");
         goto err_put;
     }
 
     retval = tty_port_install(&hvcsd->port, driver, tty);
     if (retval)
         goto err_irq;
 
     return 0;
 err_irq:
     spin_lock_irqsave(&hvcsd->lock, flags);
     vio_disable_interrupts(hvcsd->vdev);
     spin_unlock_irqrestore(&hvcsd->lock, flags);
     free_irq(irq, hvcsd);
 err_put:
     tty_port_put(&hvcsd->port);
 
     return retval;
 }
 
 /*
  * This is invoked via the tty_open interface when a user app connects to the
  * /dev node.
  */
 static int hvcs_open(struct tty_struct *tty, struct file *filp)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
     unsigned long flags;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     hvcsd->port.count++;
     hvcsd->todo_mask |= HVCS_SCHED_READ;
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 
     hvcs_kick();
 
     printk(KERN_INFO "HVCS: vty-server@%X connection opened.\n",
         hvcsd->vdev->unit_address );
 
     return 0;
 }
 
 static void hvcs_close(struct tty_struct *tty, struct file *filp)
 {
     struct hvcs_struct *hvcsd;
     unsigned long flags;
     int irq;
 
     /*
      * Is someone trying to close the file associated with this device after
      * we have hung up?  If so tty->driver_data wouldn't be valid.
      */
     if (tty_hung_up_p(filp))
         return;
 
     /*
      * No driver_data means that this close was probably issued after a
      * failed hvcs_open by the tty layer's release_dev() api and we can just
      * exit cleanly.
      */
     if (!tty->driver_data)
         return;
 
     hvcsd = tty->driver_data;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     if (--hvcsd->port.count == 0) {
 
         vio_disable_interrupts(hvcsd->vdev);
 
         /*
          * NULL this early so that the kernel_thread doesn't try to
          * execute any operations on the TTY even though it is obligated
          * to deliver any pending I/O to the hypervisor.
          */
         hvcsd->port.tty = NULL;
 
         irq = hvcsd->vdev->irq;
         spin_unlock_irqrestore(&hvcsd->lock, flags);
 
         tty_wait_until_sent(tty, HVCS_CLOSE_WAIT);
 
         free_irq(irq, hvcsd);
         return;
     } else if (hvcsd->port.count < 0) {
         printk(KERN_ERR "HVCS: vty-server@%X open_count: %d is mismanaged.\n",
         hvcsd->vdev->unit_address, hvcsd->port.count);
     }
 
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 }
 
 static void hvcs_cleanup(struct tty_struct * tty)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
 
     /*
      * This line is important because it tells hvcs_open that this
      * device needs to be re-configured the next time hvcs_open is
      * called.
      */
     tty->driver_data = NULL;
 
     tty_port_put(&hvcsd->port);
 }
 
 static void hvcs_hangup(struct tty_struct * tty)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
     unsigned long flags;
     int temp_open_count;
     int irq;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
     /* Preserve this so that we know how many kref refs to put */
     temp_open_count = hvcsd->port.count;
 
     /*
      * Don't kref put inside the spinlock because the destruction
      * callback may use the spinlock and it may get called before the
      * spinlock has been released.
      */
     vio_disable_interrupts(hvcsd->vdev);
 
     hvcsd->todo_mask = 0;
 
     /* I don't think the tty needs the hvcs_struct pointer after a hangup */
     tty->driver_data = NULL;
     hvcsd->port.tty = NULL;
 
     hvcsd->port.count = 0;
 
     /* This will drop any buffered data on the floor which is OK in a hangup
      * scenario. */
     memset(&hvcsd->buffer[0], 0x00, HVCS_BUFF_LEN);
     hvcsd->chars_in_buffer = 0;
 
     irq = hvcsd->vdev->irq;
 
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 
     free_irq(irq, hvcsd);
 
     /*
      * We need to kref_put() for every open_count we have since the
      * tty_hangup() function doesn't invoke a close per open connection on a
      * non-console device.
      */
     while(temp_open_count) {
         --temp_open_count;
         /*
          * The final put will trigger destruction of the hvcs_struct.
          * NOTE:  If this hangup was signaled from user space then the
          * final put will never happen.
          */
         tty_port_put(&hvcsd->port);
     }
 }
 
 /*
  * NOTE: This is almost always from_user since user level apps interact with the
  * /dev nodes. I'm trusting that if hvcs_write gets called and interrupted by
  * hvcs_remove (which removes the target device and executes tty_hangup()) that
  * tty_hangup will allow hvcs_write time to complete execution before it
  * terminates our device.
  */
 static int hvcs_write(struct tty_struct *tty,
         const unsigned char *buf, int count)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
     unsigned int unit_address;
     const unsigned char *charbuf;
     unsigned long flags;
     int total_sent = 0;
     int tosend = 0;
     int result = 0;
 
     /*
      * If they don't check the return code off of their open they may
      * attempt this even if there is no connected device.
      */
     if (!hvcsd)
         return -ENODEV;
 
     /* Reasonable size to prevent user level flooding */
     if (count > HVCS_MAX_FROM_USER) {
         printk(KERN_WARNING "HVCS write: count being truncated to"
                 " HVCS_MAX_FROM_USER.\n");
         count = HVCS_MAX_FROM_USER;
     }
 
     charbuf = buf;
 
     spin_lock_irqsave(&hvcsd->lock, flags);
 
     /*
      * Somehow an open succeeded but the device was removed or the
      * connection terminated between the vty-server and partner vty during
      * the middle of a write operation?  This is a crummy place to do this
      * but we want to keep it all in the spinlock.
      */
     if (hvcsd->port.count <= 0) {
         spin_unlock_irqrestore(&hvcsd->lock, flags);
         return -ENODEV;
     }
 
     unit_address = hvcsd->vdev->unit_address;
 
     while (count > 0) {
         tosend = min(count, (HVCS_BUFF_LEN - hvcsd->chars_in_buffer));
         /*
          * No more space, this probably means that the last call to
          * hvcs_write() didn't succeed and the buffer was filled up.
          */
         if (!tosend)
             break;
 
         memcpy(&hvcsd->buffer[hvcsd->chars_in_buffer],
                 &charbuf[total_sent],
                 tosend);
 
         hvcsd->chars_in_buffer += tosend;
 
         result = 0;
 
         /*
          * If this is true then we don't want to try writing to the
          * hypervisor because that is the kernel_threads job now.  We'll
          * just add to the buffer.
          */
         if (!(hvcsd->todo_mask & HVCS_TRY_WRITE))
             /* won't send partial writes */
             result = hvc_put_chars(unit_address,
                     &hvcsd->buffer[0],
                     hvcsd->chars_in_buffer);
 
         /*
          * Since we know we have enough room in hvcsd->buffer for
          * tosend we record that it was sent regardless of whether the
          * hypervisor actually took it because we have it buffered.
          */
         total_sent+=tosend;
         count-=tosend;
         if (result == 0) {
             hvcsd->todo_mask |= HVCS_TRY_WRITE;
             hvcs_kick();
             break;
         }
 
         hvcsd->chars_in_buffer = 0;
         /*
          * Test after the chars_in_buffer reset otherwise this could
          * deadlock our writes if hvc_put_chars fails.
          */
         if (result < 0)
             break;
     }
 
     spin_unlock_irqrestore(&hvcsd->lock, flags);
 
     if (result == -1)
         return -EIO;
     else
         return total_sent;
 }
 
 /*
  * This is really asking how much can we guarantee that we can send or that we
  * absolutely WILL BUFFER if we can't send it.  This driver MUST honor the
  * return value, hence the reason for hvcs_struct buffering.
  */
 static unsigned int hvcs_write_room(struct tty_struct *tty)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
 
     if (!hvcsd || hvcsd->port.count <= 0)
         return 0;
 
     return HVCS_BUFF_LEN - hvcsd->chars_in_buffer;
 }
 
 static unsigned int hvcs_chars_in_buffer(struct tty_struct *tty)
 {
     struct hvcs_struct *hvcsd = tty->driver_data;
 
     return hvcsd->chars_in_buffer;
 }
 
 static const struct tty_operations hvcs_ops = {
     .install = hvcs_install,
     .open = hvcs_open,
     .close = hvcs_close,
     .cleanup = hvcs_cleanup,
     .hangup = hvcs_hangup,
     .write = hvcs_write,
     .write_room = hvcs_write_room,
     .chars_in_buffer = hvcs_chars_in_buffer,
     .unthrottle = hvcs_unthrottle,
     .throttle = hvcs_throttle,
 };
 
 static int hvcs_alloc_index_list(int n)
 {
     int i;
 
     hvcs_index_list = kmalloc_array(n, sizeof(hvcs_index_count),
                     GFP_KERNEL);
     if (!hvcs_index_list)
         return -ENOMEM;
     hvcs_index_count = n;
     for (i = 0; i < hvcs_index_count; i++)
         hvcs_index_list[i] = -1;
     return 0;
 }
 
 static void hvcs_free_index_list(void)
 {
     /* Paranoia check to be thorough. */
     kfree(hvcs_index_list);
     hvcs_index_list = NULL;
     hvcs_index_count = 0;
 }
 
 static int hvcs_initialize(void)
 {
     int rc, num_ttys_to_alloc;
 
     mutex_lock(&hvcs_init_mutex);
     if (hvcs_task) {
         mutex_unlock(&hvcs_init_mutex);
         return 0;
     }
 
     /* Has the user specified an overload with an insmod param? */
     if (hvcs_parm_num_devs <= 0 ||
         (hvcs_parm_num_devs > HVCS_MAX_SERVER_ADAPTERS)) {
         num_ttys_to_alloc = HVCS_DEFAULT_SERVER_ADAPTERS;
     } else
         num_ttys_to_alloc = hvcs_parm_num_devs;
 
     hvcs_tty_driver = tty_alloc_driver(num_ttys_to_alloc,
             TTY_DRIVER_REAL_RAW);
     if (IS_ERR(hvcs_tty_driver)) {
         mutex_unlock(&hvcs_init_mutex);
         return PTR_ERR(hvcs_tty_driver);
     }
 
     if (hvcs_alloc_index_list(num_ttys_to_alloc)) {
         rc = -ENOMEM;
         goto index_fail;
     }
 
     hvcs_tty_driver->driver_name = hvcs_driver_name;
     hvcs_tty_driver->name = hvcs_device_node;
 
     /*
      * We'll let the system assign us a major number, indicated by leaving
      * it blank.
      */
 
     hvcs_tty_driver->minor_start = HVCS_MINOR_START;
     hvcs_tty_driver->type = TTY_DRIVER_TYPE_SYSTEM;
 
     /*
      * We role our own so that we DONT ECHO.  We can't echo because the
      * device we are connecting to already echoes by default and this would
      * throw us into a horrible recursive echo-echo-echo loop.
      */
     hvcs_tty_driver->init_termios = hvcs_tty_termios;
 
     tty_set_operations(hvcs_tty_driver, &hvcs_ops);
 
     /*
      * The following call will result in sysfs entries that denote the
      * dynamically assigned major and minor numbers for our devices.
      */
     if (tty_register_driver(hvcs_tty_driver)) {
         printk(KERN_ERR "HVCS: registration as a tty driver failed.\n");
         rc = -EIO;
         goto register_fail;
     }
 
     hvcs_pi_buff = (unsigned long *) __get_free_page(GFP_KERNEL);
     if (!hvcs_pi_buff) {
         rc = -ENOMEM;
         goto buff_alloc_fail;
     }
 
     hvcs_task = kthread_run(khvcsd, NULL, "khvcsd");
     if (IS_ERR(hvcs_task)) {
         printk(KERN_ERR "HVCS: khvcsd creation failed.\n");
         rc = -EIO;
         goto kthread_fail;
     }
     mutex_unlock(&hvcs_init_mutex);
     return 0;
 
 kthread_fail:
     free_page((unsigned long)hvcs_pi_buff);
 buff_alloc_fail:
     tty_unregister_driver(hvcs_tty_driver);
 register_fail:
     hvcs_free_index_list();
 index_fail:
     tty_driver_kref_put(hvcs_tty_driver);
     hvcs_tty_driver = NULL;
     mutex_unlock(&hvcs_init_mutex);
     return rc;
 }
 
 static int __init hvcs_module_init(void)
 {
     int rc = vio_register_driver(&hvcs_vio_driver);
     if (rc) {
         printk(KERN_ERR "HVCS: can't register vio driver\n");
         return rc;
     }
 
     pr_info("HVCS: Driver registered.\n");
 
     /* This needs to be done AFTER the vio_register_driver() call or else
      * the kobjects won't be initialized properly.
      */
     rc = driver_create_file(&(hvcs_vio_driver.driver), &driver_attr_rescan);
     if (rc)
         pr_warn("HVCS: Failed to create rescan file (err %d)\n", rc);
 
     return 0;
 }
 
 static void __exit hvcs_module_exit(void)
 {
     /*
      * This driver receives hvcs_remove callbacks for each device upon
      * module removal.
      */
     vio_unregister_driver(&hvcs_vio_driver);
     if (!hvcs_task)
         return;
 
     /*
      * This synchronous operation  will wake the khvcsd kthread if it is
      * asleep and will return when khvcsd has terminated.
      */
     kthread_stop(hvcs_task);
 
     spin_lock(&hvcs_pi_lock);
     free_page((unsigned long)hvcs_pi_buff);
     hvcs_pi_buff = NULL;
     spin_unlock(&hvcs_pi_lock);
 
     driver_remove_file(&hvcs_vio_driver.driver, &driver_attr_rescan);
 
     tty_unregister_driver(hvcs_tty_driver);
 
     hvcs_free_index_list();
 
     tty_driver_kref_put(hvcs_tty_driver);
 
     printk(KERN_INFO "HVCS: driver module removed.\n");
 }
 
 module_init(hvcs_module_init);
 module_exit(hvcs_module_exit);

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