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scsi.c

/*
 *  scsi.c Copyright (C) 1992 Drew Eckhardt
 *         Copyright (C) 1993, 1994, 1995, 1999 Eric Youngdale
 *         Copyright (C) 2002, 2003 Christoph Hellwig
 *
 *  generic mid-level SCSI driver
 *      Initial versions: Drew Eckhardt
 *      Subsequent revisions: Eric Youngdale
 *
 *  <drew@colorado.edu>
 *
 *  Bug correction thanks go to :
 *      Rik Faith <faith@cs.unc.edu>
 *      Tommy Thorn <tthorn>
 *      Thomas Wuensche <tw@fgb1.fgb.mw.tu-muenchen.de>
 *
 *  Modified by Eric Youngdale eric@andante.org or ericy@gnu.ai.mit.edu to
 *  add scatter-gather, multiple outstanding request, and other
 *  enhancements.
 *
 *  Native multichannel, wide scsi, /proc/scsi and hot plugging
 *  support added by Michael Neuffer <mike@i-connect.net>
 *
 *  Added request_module("scsi_hostadapter") for kerneld:
 *  (Put an "alias scsi_hostadapter your_hostadapter" in /etc/modprobe.conf)
 *  Bjorn Ekwall  <bj0rn@blox.se>
 *  (changed to kmod)
 *
 *  Major improvements to the timeout, abort, and reset processing,
 *  as well as performance modifications for large queue depths by
 *  Leonard N. Zubkoff <lnz@dandelion.com>
 *
 *  Converted cli() code to spinlocks, Ingo Molnar
 *
 *  Jiffies wrap fixes (host->resetting), 3 Dec 1998 Andrea Arcangeli
 *
 *  out_of_space hacks, D. Gilbert (dpg) 990608
 */

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/unistd.h>
#include <linux/spinlock.h>
#include <linux/kmod.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>

#include <scsi/scsi.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_driver.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_tcq.h>

#include "scsi_priv.h"
#include "scsi_logging.h"

static void scsi_done(struct scsi_cmnd *cmd);

/*
 * Definitions and constants.
 */

#define MIN_RESET_DELAY (2*HZ)

/* Do not call reset on error if we just did a reset within 15 sec. */
#define MIN_RESET_PERIOD (15*HZ)

/*
 * Macro to determine the size of SCSI command. This macro takes vendor
 * unique commands into account. SCSI commands in groups 6 and 7 are
 * vendor unique and we will depend upon the command length being
 * supplied correctly in cmd_len.
 */
#define CDB_SIZE(cmd)   (((((cmd)->cmnd[0] >> 5) & 7) < 6) ? \
                        COMMAND_SIZE((cmd)->cmnd[0]) : (cmd)->cmd_len)

/*
 * Note - the initial logging level can be set here to log events at boot time.
 * After the system is up, you may enable logging via the /proc interface.
 */
unsigned int scsi_logging_level;
#if defined(CONFIG_SCSI_LOGGING)
EXPORT_SYMBOL(scsi_logging_level);
#endif

/* NB: These are exposed through /proc/scsi/scsi and form part of the ABI.
 * You may not alter any existing entry (although adding new ones is
 * encouraged once assigned by ANSI/INCITS T10
 */
static const char *const scsi_device_types[] = {
      "Direct-Access    ",
      "Sequential-Access",
      "Printer          ",
      "Processor        ",
      "WORM             ",
      "CD-ROM           ",
      "Scanner          ",
      "Optical Device   ",
      "Medium Changer   ",
      "Communications   ",
      "ASC IT8          ",
      "ASC IT8          ",
      "RAID             ",
      "Enclosure        ",
      "Direct-Access-RBC",
      "Optical card     ",
      "Bridge controller",
      "Object storage   ",
      "Automation/Drive ",
};

const char * scsi_device_type(unsigned type)
{
      if (type == 0x1e)
            return "Well-known LUN   ";
      if (type == 0x1f)
            return "No Device        ";
      if (type >= ARRAY_SIZE(scsi_device_types))
            return "Unknown          ";
      return scsi_device_types[type];
}

EXPORT_SYMBOL(scsi_device_type);

struct scsi_host_cmd_pool {
      struct kmem_cache *slab;
      unsigned int      users;
      char        *name;
      unsigned int      slab_flags;
      gfp_t       gfp_mask;
};

static struct scsi_host_cmd_pool scsi_cmd_pool = {
      .name       = "scsi_cmd_cache",
      .slab_flags = SLAB_HWCACHE_ALIGN,
};

static struct scsi_host_cmd_pool scsi_cmd_dma_pool = {
      .name       = "scsi_cmd_cache(DMA)",
      .slab_flags = SLAB_HWCACHE_ALIGN|SLAB_CACHE_DMA,
      .gfp_mask   = __GFP_DMA,
};

static DEFINE_MUTEX(host_cmd_pool_mutex);

struct scsi_cmnd *__scsi_get_command(struct Scsi_Host *shost, gfp_t gfp_mask)
{
      struct scsi_cmnd *cmd;

      cmd = kmem_cache_alloc(shost->cmd_pool->slab,
                  gfp_mask | shost->cmd_pool->gfp_mask);

      if (unlikely(!cmd)) {
            unsigned long flags;

            spin_lock_irqsave(&shost->free_list_lock, flags);
            if (likely(!list_empty(&shost->free_list))) {
                  cmd = list_entry(shost->free_list.next,
                               struct scsi_cmnd, list);
                  list_del_init(&cmd->list);
            }
            spin_unlock_irqrestore(&shost->free_list_lock, flags);
      }

      return cmd;
}
EXPORT_SYMBOL_GPL(__scsi_get_command);

/*
 * Function:      scsi_get_command()
 *
 * Purpose: Allocate and setup a scsi command block
 *
 * Arguments:     dev   - parent scsi device
 *          gfp_mask- allocator flags
 *
 * Returns: The allocated scsi command structure.
 */
struct scsi_cmnd *scsi_get_command(struct scsi_device *dev, gfp_t gfp_mask)
{
      struct scsi_cmnd *cmd;

      /* Bail if we can't get a reference to the device */
      if (!get_device(&dev->sdev_gendev))
            return NULL;

      cmd = __scsi_get_command(dev->host, gfp_mask);

      if (likely(cmd != NULL)) {
            unsigned long flags;

            memset(cmd, 0, sizeof(*cmd));
            cmd->device = dev;
            init_timer(&cmd->eh_timeout);
            INIT_LIST_HEAD(&cmd->list);
            spin_lock_irqsave(&dev->list_lock, flags);
            list_add_tail(&cmd->list, &dev->cmd_list);
            spin_unlock_irqrestore(&dev->list_lock, flags);
            cmd->jiffies_at_alloc = jiffies;
      } else
            put_device(&dev->sdev_gendev);

      return cmd;
}
EXPORT_SYMBOL(scsi_get_command);

void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd,
                  struct device *dev)
{
      unsigned long flags;

      /* changing locks here, don't need to restore the irq state */
      spin_lock_irqsave(&shost->free_list_lock, flags);
      if (unlikely(list_empty(&shost->free_list))) {
            list_add(&cmd->list, &shost->free_list);
            cmd = NULL;
      }
      spin_unlock_irqrestore(&shost->free_list_lock, flags);

      if (likely(cmd != NULL))
            kmem_cache_free(shost->cmd_pool->slab, cmd);

      put_device(dev);
}
EXPORT_SYMBOL(__scsi_put_command);

/*
 * Function:      scsi_put_command()
 *
 * Purpose: Free a scsi command block
 *
 * Arguments:     cmd   - command block to free
 *
 * Returns: Nothing.
 *
 * Notes:   The command must not belong to any lists.
 */
void scsi_put_command(struct scsi_cmnd *cmd)
{
      struct scsi_device *sdev = cmd->device;
      unsigned long flags;

      /* serious error if the command hasn't come from a device list */
      spin_lock_irqsave(&cmd->device->list_lock, flags);
      BUG_ON(list_empty(&cmd->list));
      list_del_init(&cmd->list);
      spin_unlock_irqrestore(&cmd->device->list_lock, flags);

      __scsi_put_command(cmd->device->host, cmd, &sdev->sdev_gendev);
}
EXPORT_SYMBOL(scsi_put_command);

/*
 * Function:      scsi_setup_command_freelist()
 *
 * Purpose: Setup the command freelist for a scsi host.
 *
 * Arguments:     shost - host to allocate the freelist for.
 *
 * Returns: Nothing.
 */
int scsi_setup_command_freelist(struct Scsi_Host *shost)
{
      struct scsi_host_cmd_pool *pool;
      struct scsi_cmnd *cmd;

      spin_lock_init(&shost->free_list_lock);
      INIT_LIST_HEAD(&shost->free_list);

      /*
       * Select a command slab for this host and create it if not
       * yet existant.
       */
      mutex_lock(&host_cmd_pool_mutex);
      pool = (shost->unchecked_isa_dma ? &scsi_cmd_dma_pool : &scsi_cmd_pool);
      if (!pool->users) {
            pool->slab = kmem_cache_create(pool->name,
                        sizeof(struct scsi_cmnd), 0,
                        pool->slab_flags, NULL);
            if (!pool->slab)
                  goto fail;
      }

      pool->users++;
      shost->cmd_pool = pool;
      mutex_unlock(&host_cmd_pool_mutex);

      /*
       * Get one backup command for this host.
       */
      cmd = kmem_cache_alloc(shost->cmd_pool->slab,
                  GFP_KERNEL | shost->cmd_pool->gfp_mask);
      if (!cmd)
            goto fail2;
      list_add(&cmd->list, &shost->free_list);        
      return 0;

 fail2:
      if (!--pool->users)
            kmem_cache_destroy(pool->slab);
      return -ENOMEM;
 fail:
      mutex_unlock(&host_cmd_pool_mutex);
      return -ENOMEM;

}

/*
 * Function:      scsi_destroy_command_freelist()
 *
 * Purpose: Release the command freelist for a scsi host.
 *
 * Arguments:     shost - host that's freelist is going to be destroyed
 */
void scsi_destroy_command_freelist(struct Scsi_Host *shost)
{
      while (!list_empty(&shost->free_list)) {
            struct scsi_cmnd *cmd;

            cmd = list_entry(shost->free_list.next, struct scsi_cmnd, list);
            list_del_init(&cmd->list);
            kmem_cache_free(shost->cmd_pool->slab, cmd);
      }

      mutex_lock(&host_cmd_pool_mutex);
      if (!--shost->cmd_pool->users)
            kmem_cache_destroy(shost->cmd_pool->slab);
      mutex_unlock(&host_cmd_pool_mutex);
}

#ifdef CONFIG_SCSI_LOGGING
void scsi_log_send(struct scsi_cmnd *cmd)
{
      unsigned int level;

      /*
       * If ML QUEUE log level is greater than or equal to:
       *
       * 1: nothing (match completion)
       *
       * 2: log opcode + command of all commands
       *
       * 3: same as 2 plus dump cmd address
       *
       * 4: same as 3 plus dump extra junk
       */
      if (unlikely(scsi_logging_level)) {
            level = SCSI_LOG_LEVEL(SCSI_LOG_MLQUEUE_SHIFT,
                               SCSI_LOG_MLQUEUE_BITS);
            if (level > 1) {
                  scmd_printk(KERN_INFO, cmd, "Send: ");
                  if (level > 2)
                        printk("0x%p ", cmd);
                  printk("\n");
                  scsi_print_command(cmd);
                  if (level > 3) {
                        printk(KERN_INFO "buffer = 0x%p, bufflen = %d,"
                               " queuecommand 0x%p\n",
                              scsi_sglist(cmd), scsi_bufflen(cmd),
                              cmd->device->host->hostt->queuecommand);

                  }
            }
      }
}

void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
{
      unsigned int level;

      /*
       * If ML COMPLETE log level is greater than or equal to:
       *
       * 1: log disposition, result, opcode + command, and conditionally
       * sense data for failures or non SUCCESS dispositions.
       *
       * 2: same as 1 but for all command completions.
       *
       * 3: same as 2 plus dump cmd address
       *
       * 4: same as 3 plus dump extra junk
       */
      if (unlikely(scsi_logging_level)) {
            level = SCSI_LOG_LEVEL(SCSI_LOG_MLCOMPLETE_SHIFT,
                               SCSI_LOG_MLCOMPLETE_BITS);
            if (((level > 0) && (cmd->result || disposition != SUCCESS)) ||
                (level > 1)) {
                  scmd_printk(KERN_INFO, cmd, "Done: ");
                  if (level > 2)
                        printk("0x%p ", cmd);
                  /*
                   * Dump truncated values, so we usually fit within
                   * 80 chars.
                   */
                  switch (disposition) {
                  case SUCCESS:
                        printk("SUCCESS\n");
                        break;
                  case NEEDS_RETRY:
                        printk("RETRY\n");
                        break;
                  case ADD_TO_MLQUEUE:
                        printk("MLQUEUE\n");
                        break;
                  case FAILED:
                        printk("FAILED\n");
                        break;
                  case TIMEOUT_ERROR:
                        /* 
                         * If called via scsi_times_out.
                         */
                        printk("TIMEOUT\n");
                        break;
                  default:
                        printk("UNKNOWN\n");
                  }
                  scsi_print_result(cmd);
                  scsi_print_command(cmd);
                  if (status_byte(cmd->result) & CHECK_CONDITION)
                        scsi_print_sense("", cmd);
                  if (level > 3)
                        scmd_printk(KERN_INFO, cmd,
                                  "scsi host busy %d failed %d\n",
                                  cmd->device->host->host_busy,
                                  cmd->device->host->host_failed);
            }
      }
}
#endif

/* 
 * Assign a serial number to the request for error recovery
 * and debugging purposes.  Protected by the Host_Lock of host.
 */
static inline void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd *cmd)
{
      cmd->serial_number = host->cmd_serial_number++;
      if (cmd->serial_number == 0) 
            cmd->serial_number = host->cmd_serial_number++;
}

/*
 * Function:    scsi_dispatch_command
 *
 * Purpose:     Dispatch a command to the low-level driver.
 *
 * Arguments:   cmd - command block we are dispatching.
 *
 * Notes:
 */
int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
{
      struct Scsi_Host *host = cmd->device->host;
      unsigned long flags = 0;
      unsigned long timeout;
      int rtn = 0;

      /* check if the device is still usable */
      if (unlikely(cmd->device->sdev_state == SDEV_DEL)) {
            /* in SDEV_DEL we error all commands. DID_NO_CONNECT
             * returns an immediate error upwards, and signals
             * that the device is no longer present */
            cmd->result = DID_NO_CONNECT << 16;
            atomic_inc(&cmd->device->iorequest_cnt);
            __scsi_done(cmd);
            /* return 0 (because the command has been processed) */
            goto out;
      }

      /* Check to see if the scsi lld put this device into state SDEV_BLOCK. */
      if (unlikely(cmd->device->sdev_state == SDEV_BLOCK)) {
            /* 
             * in SDEV_BLOCK, the command is just put back on the device
             * queue.  The suspend state has already blocked the queue so
             * future requests should not occur until the device 
             * transitions out of the suspend state.
             */
            scsi_queue_insert(cmd, SCSI_MLQUEUE_DEVICE_BUSY);

            SCSI_LOG_MLQUEUE(3, printk("queuecommand : device blocked \n"));

            /*
             * NOTE: rtn is still zero here because we don't need the
             * queue to be plugged on return (it's already stopped)
             */
            goto out;
      }

      /* 
       * If SCSI-2 or lower, store the LUN value in cmnd.
       */
      if (cmd->device->scsi_level <= SCSI_2 &&
          cmd->device->scsi_level != SCSI_UNKNOWN) {
            cmd->cmnd[1] = (cmd->cmnd[1] & 0x1f) |
                         (cmd->device->lun << 5 & 0xe0);
      }

      /*
       * We will wait MIN_RESET_DELAY clock ticks after the last reset so
       * we can avoid the drive not being ready.
       */
      timeout = host->last_reset + MIN_RESET_DELAY;

      if (host->resetting && time_before(jiffies, timeout)) {
            int ticks_remaining = timeout - jiffies;
            /*
             * NOTE: This may be executed from within an interrupt
             * handler!  This is bad, but for now, it'll do.  The irq
             * level of the interrupt handler has been masked out by the
             * platform dependent interrupt handling code already, so the
             * sti() here will not cause another call to the SCSI host's
             * interrupt handler (assuming there is one irq-level per
             * host).
             */
            while (--ticks_remaining >= 0)
                  mdelay(1 + 999 / HZ);
            host->resetting = 0;
      }

      /* 
       * AK: unlikely race here: for some reason the timer could
       * expire before the serial number is set up below.
       */
      scsi_add_timer(cmd, cmd->timeout_per_command, scsi_times_out);

      scsi_log_send(cmd);

      /*
       * We will use a queued command if possible, otherwise we will
       * emulate the queuing and calling of completion function ourselves.
       */
      atomic_inc(&cmd->device->iorequest_cnt);

      /*
       * Before we queue this command, check if the command
       * length exceeds what the host adapter can handle.
       */
      if (CDB_SIZE(cmd) > cmd->device->host->max_cmd_len) {
            SCSI_LOG_MLQUEUE(3,
                        printk("queuecommand : command too long.\n"));
            cmd->result = (DID_ABORT << 16);

            scsi_done(cmd);
            goto out;
      }

      spin_lock_irqsave(host->host_lock, flags);
      scsi_cmd_get_serial(host, cmd); 

      if (unlikely(host->shost_state == SHOST_DEL)) {
            cmd->result = (DID_NO_CONNECT << 16);
            scsi_done(cmd);
      } else {
            rtn = host->hostt->queuecommand(cmd, scsi_done);
      }
      spin_unlock_irqrestore(host->host_lock, flags);
      if (rtn) {
            if (scsi_delete_timer(cmd)) {
                  atomic_inc(&cmd->device->iodone_cnt);
                  scsi_queue_insert(cmd,
                                (rtn == SCSI_MLQUEUE_DEVICE_BUSY) ?
                                rtn : SCSI_MLQUEUE_HOST_BUSY);
            }
            SCSI_LOG_MLQUEUE(3,
                printk("queuecommand : request rejected\n"));
      }

 out:
      SCSI_LOG_MLQUEUE(3, printk("leaving scsi_dispatch_cmnd()\n"));
      return rtn;
}

/**
 * scsi_req_abort_cmd -- Request command recovery for the specified command
 * cmd: pointer to the SCSI command of interest
 *
 * This function requests that SCSI Core start recovery for the
 * command by deleting the timer and adding the command to the eh
 * queue.  It can be called by either LLDDs or SCSI Core.  LLDDs who
 * implement their own error recovery MAY ignore the timeout event if
 * they generated scsi_req_abort_cmd.
 */
void scsi_req_abort_cmd(struct scsi_cmnd *cmd)
{
      if (!scsi_delete_timer(cmd))
            return;
      scsi_times_out(cmd);
}
EXPORT_SYMBOL(scsi_req_abort_cmd);

/**
 * scsi_done - Enqueue the finished SCSI command into the done queue.
 * @cmd: The SCSI Command for which a low-level device driver (LLDD) gives
 * ownership back to SCSI Core -- i.e. the LLDD has finished with it.
 *
 * This function is the mid-level's (SCSI Core) interrupt routine, which
 * regains ownership of the SCSI command (de facto) from a LLDD, and enqueues
 * the command to the done queue for further processing.
 *
 * This is the producer of the done queue who enqueues at the tail.
 *
 * This function is interrupt context safe.
 */
static void scsi_done(struct scsi_cmnd *cmd)
{
      /*
       * We don't have to worry about this one timing out any more.
       * If we are unable to remove the timer, then the command
       * has already timed out.  In which case, we have no choice but to
       * let the timeout function run, as we have no idea where in fact
       * that function could really be.  It might be on another processor,
       * etc, etc.
       */
      if (!scsi_delete_timer(cmd))
            return;
      __scsi_done(cmd);
}

/* Private entry to scsi_done() to complete a command when the timer
 * isn't running --- used by scsi_times_out */
void __scsi_done(struct scsi_cmnd *cmd)
{
      struct request *rq = cmd->request;

      /*
       * Set the serial numbers back to zero
       */
      cmd->serial_number = 0;

      atomic_inc(&cmd->device->iodone_cnt);
      if (cmd->result)
            atomic_inc(&cmd->device->ioerr_cnt);

      BUG_ON(!rq);

      /*
       * The uptodate/nbytes values don't matter, as we allow partial
       * completes and thus will check this in the softirq callback
       */
      rq->completion_data = cmd;
      blk_complete_request(rq);
}

/* Move this to a header if it becomes more generally useful */
static struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
{
      return *(struct scsi_driver **)cmd->request->rq_disk->private_data;
}

/*
 * Function:    scsi_finish_command
 *
 * Purpose:     Pass command off to upper layer for finishing of I/O
 *              request, waking processes that are waiting on results,
 *              etc.
 */
void scsi_finish_command(struct scsi_cmnd *cmd)
{
      struct scsi_device *sdev = cmd->device;
      struct Scsi_Host *shost = sdev->host;
      struct scsi_driver *drv;
      unsigned int good_bytes;

      scsi_device_unbusy(sdev);

        /*
         * Clear the flags which say that the device/host is no longer
         * capable of accepting new commands.  These are set in scsi_queue.c
         * for both the queue full condition on a device, and for a
         * host full condition on the host.
       *
       * XXX(hch): What about locking?
         */
        shost->host_blocked = 0;
        sdev->device_blocked = 0;

      /*
       * If we have valid sense information, then some kind of recovery
       * must have taken place.  Make a note of this.
       */
      if (SCSI_SENSE_VALID(cmd))
            cmd->result |= (DRIVER_SENSE << 24);

      SCSI_LOG_MLCOMPLETE(4, sdev_printk(KERN_INFO, sdev,
                        "Notifying upper driver of completion "
                        "(result %x)\n", cmd->result));

      good_bytes = cmd->request_bufflen;
        if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {
            drv = scsi_cmd_to_driver(cmd);
            if (drv->done)
                  good_bytes = drv->done(cmd);
      }
      scsi_io_completion(cmd, good_bytes);
}
EXPORT_SYMBOL(scsi_finish_command);

/*
 * Function:      scsi_adjust_queue_depth()
 *
 * Purpose: Allow low level drivers to tell us to change the queue depth
 *          on a specific SCSI device
 *
 * Arguments:     sdev  - SCSI Device in question
 *          tagged      - Do we use tagged queueing (non-0) or do we treat
 *                  this device as an untagged device (0)
 *          tags  - Number of tags allowed if tagged queueing enabled,
 *                  or number of commands the low level driver can
 *                  queue up in non-tagged mode (as per cmd_per_lun).
 *
 * Returns: Nothing
 *
 * Lock Status:   None held on entry
 *
 * Notes:   Low level drivers may call this at any time and we will do
 *          the right thing depending on whether or not the device is
 *          currently active and whether or not it even has the
 *          command blocks built yet.
 */
void scsi_adjust_queue_depth(struct scsi_device *sdev, int tagged, int tags)
{
      unsigned long flags;

      /*
       * refuse to set tagged depth to an unworkable size
       */
      if (tags <= 0)
            return;

      spin_lock_irqsave(sdev->request_queue->queue_lock, flags);

      /* Check to see if the queue is managed by the block layer
       * if it is, and we fail to adjust the depth, exit */
      if (blk_queue_tagged(sdev->request_queue) &&
          blk_queue_resize_tags(sdev->request_queue, tags) != 0)
            goto out;

      sdev->queue_depth = tags;
      switch (tagged) {
            case MSG_ORDERED_TAG:
                  sdev->ordered_tags = 1;
                  sdev->simple_tags = 1;
                  break;
            case MSG_SIMPLE_TAG:
                  sdev->ordered_tags = 0;
                  sdev->simple_tags = 1;
                  break;
            default:
                  sdev_printk(KERN_WARNING, sdev,
                            "scsi_adjust_queue_depth, bad queue type, "
                            "disabled\n");
            case 0:
                  sdev->ordered_tags = sdev->simple_tags = 0;
                  sdev->queue_depth = tags;
                  break;
      }
 out:
      spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
}
EXPORT_SYMBOL(scsi_adjust_queue_depth);

/*
 * Function:      scsi_track_queue_full()
 *
 * Purpose: This function will track successive QUEUE_FULL events on a
 *          specific SCSI device to determine if and when there is a
 *          need to adjust the queue depth on the device.
 *
 * Arguments:     sdev  - SCSI Device in question
 *          depth - Current number of outstanding SCSI commands on
 *                  this device, not counting the one returned as
 *                  QUEUE_FULL.
 *
 * Returns: 0 - No change needed
 *          >0 - Adjust queue depth to this new depth
 *          -1 - Drop back to untagged operation using host->cmd_per_lun
 *                as the untagged command depth
 *
 * Lock Status:   None held on entry
 *
 * Notes:   Low level drivers may call this at any time and we will do
 *          "The Right Thing."  We are interrupt context safe.
 */
int scsi_track_queue_full(struct scsi_device *sdev, int depth)
{
      if ((jiffies >> 4) == sdev->last_queue_full_time)
            return 0;

      sdev->last_queue_full_time = (jiffies >> 4);
      if (sdev->last_queue_full_depth != depth) {
            sdev->last_queue_full_count = 1;
            sdev->last_queue_full_depth = depth;
      } else {
            sdev->last_queue_full_count++;
      }

      if (sdev->last_queue_full_count <= 10)
            return 0;
      if (sdev->last_queue_full_depth < 8) {
            /* Drop back to untagged */
            scsi_adjust_queue_depth(sdev, 0, sdev->host->cmd_per_lun);
            return -1;
      }
      
      if (sdev->ordered_tags)
            scsi_adjust_queue_depth(sdev, MSG_ORDERED_TAG, depth);
      else
            scsi_adjust_queue_depth(sdev, MSG_SIMPLE_TAG, depth);
      return depth;
}
EXPORT_SYMBOL(scsi_track_queue_full);

/**
 * scsi_device_get  -  get an addition reference to a scsi_device
 * @sdev:   device to get a reference to
 *
 * Gets a reference to the scsi_device and increments the use count
 * of the underlying LLDD module.  You must hold host_lock of the
 * parent Scsi_Host or already have a reference when calling this.
 */
int scsi_device_get(struct scsi_device *sdev)
{
      if (sdev->sdev_state == SDEV_DEL)
            return -ENXIO;
      if (!get_device(&sdev->sdev_gendev))
            return -ENXIO;
      /* We can fail this if we're doing SCSI operations
       * from module exit (like cache flush) */
      try_module_get(sdev->host->hostt->module);

      return 0;
}
EXPORT_SYMBOL(scsi_device_get);

/**
 * scsi_device_put  -  release a reference to a scsi_device
 * @sdev:   device to release a reference on.
 *
 * Release a reference to the scsi_device and decrements the use count
 * of the underlying LLDD module.  The device is freed once the last
 * user vanishes.
 */
void scsi_device_put(struct scsi_device *sdev)
{
#ifdef CONFIG_MODULE_UNLOAD
      struct module *module = sdev->host->hostt->module;

      /* The module refcount will be zero if scsi_device_get()
       * was called from a module removal routine */
      if (module && module_refcount(module) != 0)
            module_put(module);
#endif
      put_device(&sdev->sdev_gendev);
}
EXPORT_SYMBOL(scsi_device_put);

/* helper for shost_for_each_device, thus not documented */
struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
                                 struct scsi_device *prev)
{
      struct list_head *list = (prev ? &prev->siblings : &shost->__devices);
      struct scsi_device *next = NULL;
      unsigned long flags;

      spin_lock_irqsave(shost->host_lock, flags);
      while (list->next != &shost->__devices) {
            next = list_entry(list->next, struct scsi_device, siblings);
            /* skip devices that we can't get a reference to */
            if (!scsi_device_get(next))
                  break;
            next = NULL;
            list = list->next;
      }
      spin_unlock_irqrestore(shost->host_lock, flags);

      if (prev)
            scsi_device_put(prev);
      return next;
}
EXPORT_SYMBOL(__scsi_iterate_devices);

/**
 * starget_for_each_device  -  helper to walk all devices of a target
 * @starget:      target whose devices we want to iterate over.
 *
 * This traverses over each device of @starget.  The devices have
 * a reference that must be released by scsi_host_put when breaking
 * out of the loop.
 */
void starget_for_each_device(struct scsi_target *starget, void *data,
                 void (*fn)(struct scsi_device *, void *))
{
      struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
      struct scsi_device *sdev;

      shost_for_each_device(sdev, shost) {
            if ((sdev->channel == starget->channel) &&
                (sdev->id == starget->id))
                  fn(sdev, data);
      }
}
EXPORT_SYMBOL(starget_for_each_device);

/**
 * __starget_for_each_device  -  helper to walk all devices of a target
 *                       (UNLOCKED)
 * @starget:      target whose devices we want to iterate over.
 *
 * This traverses over each device of @starget.  It does _not_
 * take a reference on the scsi_device, so the whole loop must be
 * protected by shost->host_lock.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they need to access the device list in irq context.  Otherwise you
 * really want to use starget_for_each_device instead.
 **/
void __starget_for_each_device(struct scsi_target *starget, void *data,
                         void (*fn)(struct scsi_device *, void *))
{
      struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
      struct scsi_device *sdev;

      __shost_for_each_device(sdev, shost) {
            if ((sdev->channel == starget->channel) &&
                (sdev->id == starget->id))
                  fn(sdev, data);
      }
}
EXPORT_SYMBOL(__starget_for_each_device);

/**
 * __scsi_device_lookup_by_target - find a device given the target (UNLOCKED)
 * @starget:      SCSI target pointer
 * @lun:    SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @lun for a give
 * @starget. The returned scsi_device does not have an additional
 * reference.  You must hold the host's host_lock over this call and
 * any access to the returned scsi_device.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they're need to access the device list in irq context.  Otherwise you
 * really want to use scsi_device_lookup_by_target instead.
 **/
struct scsi_device *__scsi_device_lookup_by_target(struct scsi_target *starget,
                                       uint lun)
{
      struct scsi_device *sdev;

      list_for_each_entry(sdev, &starget->devices, same_target_siblings) {
            if (sdev->lun ==lun)
                  return sdev;
      }

      return NULL;
}
EXPORT_SYMBOL(__scsi_device_lookup_by_target);

/**
 * scsi_device_lookup_by_target - find a device given the target
 * @starget:      SCSI target pointer
 * @lun:    SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @channel, @id, @lun for a
 * give host.  The returned scsi_device has an additional reference that
 * needs to be release with scsi_host_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup_by_target(struct scsi_target *starget,
                                     uint lun)
{
      struct scsi_device *sdev;
      struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
      unsigned long flags;

      spin_lock_irqsave(shost->host_lock, flags);
      sdev = __scsi_device_lookup_by_target(starget, lun);
      if (sdev && scsi_device_get(sdev))
            sdev = NULL;
      spin_unlock_irqrestore(shost->host_lock, flags);

      return sdev;
}
EXPORT_SYMBOL(scsi_device_lookup_by_target);

/**
 * scsi_device_lookup - find a device given the host (UNLOCKED)
 * @shost:  SCSI host pointer
 * @channel:      SCSI channel (zero if only one channel)
 * @pun:    SCSI target number (physical unit number)
 * @lun:    SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @channel, @id, @lun for a
 * give host. The returned scsi_device does not have an additional reference.
 * You must hold the host's host_lock over this call and any access to the
 * returned scsi_device.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they're need to access the device list in irq context.  Otherwise you
 * really want to use scsi_device_lookup instead.
 **/
struct scsi_device *__scsi_device_lookup(struct Scsi_Host *shost,
            uint channel, uint id, uint lun)
{
      struct scsi_device *sdev;

      list_for_each_entry(sdev, &shost->__devices, siblings) {
            if (sdev->channel == channel && sdev->id == id &&
                        sdev->lun ==lun)
                  return sdev;
      }

      return NULL;
}
EXPORT_SYMBOL(__scsi_device_lookup);

/**
 * scsi_device_lookup - find a device given the host
 * @shost:  SCSI host pointer
 * @channel:      SCSI channel (zero if only one channel)
 * @id:           SCSI target number (physical unit number)
 * @lun:    SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @channel, @id, @lun for a
 * give host.  The returned scsi_device has an additional reference that
 * needs to be release with scsi_host_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup(struct Scsi_Host *shost,
            uint channel, uint id, uint lun)
{
      struct scsi_device *sdev;
      unsigned long flags;

      spin_lock_irqsave(shost->host_lock, flags);
      sdev = __scsi_device_lookup(shost, channel, id, lun);
      if (sdev && scsi_device_get(sdev))
            sdev = NULL;
      spin_unlock_irqrestore(shost->host_lock, flags);

      return sdev;
}
EXPORT_SYMBOL(scsi_device_lookup);

MODULE_DESCRIPTION("SCSI core");
MODULE_LICENSE("GPL");

module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");

static int __init init_scsi(void)
{
      int error;

      error = scsi_init_queue();
      if (error)
            return error;
      error = scsi_init_procfs();
      if (error)
            goto cleanup_queue;
      error = scsi_init_devinfo();
      if (error)
            goto cleanup_procfs;
      error = scsi_init_hosts();
      if (error)
            goto cleanup_devlist;
      error = scsi_init_sysctl();
      if (error)
            goto cleanup_hosts;
      error = scsi_sysfs_register();
      if (error)
            goto cleanup_sysctl;

      scsi_netlink_init();

      printk(KERN_NOTICE "SCSI subsystem initialized\n");
      return 0;

cleanup_sysctl:
      scsi_exit_sysctl();
cleanup_hosts:
      scsi_exit_hosts();
cleanup_devlist:
      scsi_exit_devinfo();
cleanup_procfs:
      scsi_exit_procfs();
cleanup_queue:
      scsi_exit_queue();
      printk(KERN_ERR "SCSI subsystem failed to initialize, error = %d\n",
             -error);
      return error;
}

static void __exit exit_scsi(void)
{
      scsi_netlink_exit();
      scsi_sysfs_unregister();
      scsi_exit_sysctl();
      scsi_exit_hosts();
      scsi_exit_devinfo();
      scsi_exit_procfs();
      scsi_exit_queue();
}

subsys_initcall(init_scsi);
module_exit(exit_scsi);

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