/*
   *  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"

  #define CREATE_TRACE_POINTS
  #include <trace/events/scsi.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)
  
  /*

   * 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 ",

  };

  /**
   * scsi_device_type - Return 17 char string indicating device type.
   * @type: type number to look up
   */

  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	*cmd_slab;
  	struct kmem_cache	*sense_slab;
  	unsigned int		users;
  	char			*cmd_name;
  	char			*sense_name;
  	unsigned int		slab_flags;
  	gfp_t			gfp_mask;

  };
  
  static struct scsi_host_cmd_pool scsi_cmd_pool = {

  	.cmd_name	= "scsi_cmd_cache",
  	.sense_name	= "scsi_sense_cache",

  	.slab_flags	= SLAB_HWCACHE_ALIGN,
  };
  
  static struct scsi_host_cmd_pool scsi_cmd_dma_pool = {

  	.cmd_name	= "scsi_cmd_cache(DMA)",
  	.sense_name	= "scsi_sense_cache(DMA)",

  	.slab_flags	= SLAB_HWCACHE_ALIGN|SLAB_CACHE_DMA,
  	.gfp_mask	= __GFP_DMA,
  };

  static DEFINE_MUTEX(host_cmd_pool_mutex);

  /**

   * scsi_pool_alloc_command - internal function to get a fully allocated command
   * @pool:	slab pool to allocate the command from
   * @gfp_mask:	mask for the allocation
   *
   * Returns a fully allocated command (with the allied sense buffer) or
   * NULL on failure
   */
  static struct scsi_cmnd *
  scsi_pool_alloc_command(struct scsi_host_cmd_pool *pool, gfp_t gfp_mask)
  {
  	struct scsi_cmnd *cmd;

  	cmd = kmem_cache_zalloc(pool->cmd_slab, gfp_mask | pool->gfp_mask);

  	if (!cmd)
  		return NULL;

  	cmd->sense_buffer = kmem_cache_alloc(pool->sense_slab,
  					     gfp_mask | pool->gfp_mask);
  	if (!cmd->sense_buffer) {
  		kmem_cache_free(pool->cmd_slab, cmd);
  		return NULL;
  	}
  
  	return cmd;
  }
  
  /**
   * scsi_pool_free_command - internal function to release a command
   * @pool:	slab pool to allocate the command from
   * @cmd:	command to release
   *
   * the command must previously have been allocated by
   * scsi_pool_alloc_command.
   */
  static void
  scsi_pool_free_command(struct scsi_host_cmd_pool *pool,
  			 struct scsi_cmnd *cmd)
  {

  	if (cmd->prot_sdb)
  		kmem_cache_free(scsi_sdb_cache, cmd->prot_sdb);

  	kmem_cache_free(pool->sense_slab, cmd->sense_buffer);
  	kmem_cache_free(pool->cmd_slab, cmd);
  }
  
  /**

   * scsi_host_alloc_command - internal function to allocate command
   * @shost:	SCSI host whose pool to allocate from
   * @gfp_mask:	mask for the allocation
   *
   * Returns a fully allocated command with sense buffer and protection
   * data buffer (where applicable) or NULL on failure
   */
  static struct scsi_cmnd *
  scsi_host_alloc_command(struct Scsi_Host *shost, gfp_t gfp_mask)
  {
  	struct scsi_cmnd *cmd;
  
  	cmd = scsi_pool_alloc_command(shost->cmd_pool, gfp_mask);
  	if (!cmd)
  		return NULL;
  
  	if (scsi_host_get_prot(shost) >= SHOST_DIX_TYPE0_PROTECTION) {
  		cmd->prot_sdb = kmem_cache_zalloc(scsi_sdb_cache, gfp_mask);
  
  		if (!cmd->prot_sdb) {
  			scsi_pool_free_command(shost->cmd_pool, cmd);
  			return NULL;
  		}
  	}
  
  	return cmd;
  }
  
  /**

   * __scsi_get_command - Allocate a struct scsi_cmnd
   * @shost: host to transmit command
   * @gfp_mask: allocation mask
   *
   * Description: allocate a struct scsi_cmd from host's slab, recycling from the
   *              host's free_list if necessary.
   */

  struct scsi_cmnd *__scsi_get_command(struct Scsi_Host *shost, gfp_t gfp_mask)

  {

  	struct scsi_cmnd *cmd = scsi_host_alloc_command(shost, 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);

  
  		if (cmd) {

  			void *buf, *prot;

  			buf = cmd->sense_buffer;

  			prot = cmd->prot_sdb;

  			memset(cmd, 0, sizeof(*cmd));

  			cmd->sense_buffer = buf;

  			cmd->prot_sdb = prot;

  		}

  	}
  
  	return cmd;
  }

  EXPORT_SYMBOL_GPL(__scsi_get_command);

  /**
   * scsi_get_command - Allocate and setup a scsi command block
   * @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;

  		cmd->device = dev;

  		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);

  /**
   * __scsi_put_command - Free a struct scsi_cmnd
   * @shost: dev->host
   * @cmd: Command to free
   * @dev: parent scsi device
   */

  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))
  		scsi_pool_free_command(shost->cmd_pool, cmd);

  
  	put_device(dev);
  }
  EXPORT_SYMBOL(__scsi_put_command);

  /**
   * scsi_put_command - Free a scsi command block
   * @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);

  static struct scsi_host_cmd_pool *scsi_get_host_cmd_pool(gfp_t gfp_mask)

  {

  	struct scsi_host_cmd_pool *retval = NULL, *pool;

  	/*
  	 * Select a command slab for this host and create it if not

  	 * yet existent.

  	 */

  	mutex_lock(&host_cmd_pool_mutex);

  	pool = (gfp_mask & __GFP_DMA) ? &scsi_cmd_dma_pool :
  		&scsi_cmd_pool;

  	if (!pool->users) {

  		pool->cmd_slab = kmem_cache_create(pool->cmd_name,
  						   sizeof(struct scsi_cmnd), 0,
  						   pool->slab_flags, NULL);
  		if (!pool->cmd_slab)
  			goto fail;
  
  		pool->sense_slab = kmem_cache_create(pool->sense_name,
  						     SCSI_SENSE_BUFFERSIZE, 0,
  						     pool->slab_flags, NULL);
  		if (!pool->sense_slab) {
  			kmem_cache_destroy(pool->cmd_slab);

  			goto fail;

  		}

  	}
  
  	pool->users++;

  	retval = pool;
   fail:

  	mutex_unlock(&host_cmd_pool_mutex);

  	return retval;
  }
  
  static void scsi_put_host_cmd_pool(gfp_t gfp_mask)
  {
  	struct scsi_host_cmd_pool *pool;

  	mutex_lock(&host_cmd_pool_mutex);
  	pool = (gfp_mask & __GFP_DMA) ? &scsi_cmd_dma_pool :
  		&scsi_cmd_pool;

  	/*

  	 * This may happen if a driver has a mismatched get and put
  	 * of the command pool; the driver should be implicated in
  	 * the stack trace

  	 */

  	BUG_ON(pool->users == 0);

  	if (!--pool->users) {
  		kmem_cache_destroy(pool->cmd_slab);
  		kmem_cache_destroy(pool->sense_slab);
  	}

  	mutex_unlock(&host_cmd_pool_mutex);

  }
  
  /**
   * scsi_allocate_command - get a fully allocated SCSI command
   * @gfp_mask:	allocation mask
   *
   * This function is for use outside of the normal host based pools.
   * It allocates the relevant command and takes an additional reference
   * on the pool it used.  This function *must* be paired with
   * scsi_free_command which also has the identical mask, otherwise the
   * free pool counts will eventually go wrong and you'll trigger a bug.
   *
   * This function should *only* be used by drivers that need a static
   * command allocation at start of day for internal functions.
   */
  struct scsi_cmnd *scsi_allocate_command(gfp_t gfp_mask)
  {
  	struct scsi_host_cmd_pool *pool = scsi_get_host_cmd_pool(gfp_mask);
  
  	if (!pool)
  		return NULL;
  
  	return scsi_pool_alloc_command(pool, gfp_mask);
  }
  EXPORT_SYMBOL(scsi_allocate_command);
  
  /**
   * scsi_free_command - free a command allocated by scsi_allocate_command
   * @gfp_mask:	mask used in the original allocation
   * @cmd:	command to free
   *
   * Note: using the original allocation mask is vital because that's
   * what determines which command pool we use to free the command.  Any
   * mismatch will cause the system to BUG eventually.
   */
  void scsi_free_command(gfp_t gfp_mask, struct scsi_cmnd *cmd)
  {
  	struct scsi_host_cmd_pool *pool = scsi_get_host_cmd_pool(gfp_mask);
  
  	/*
  	 * this could trigger if the mask to scsi_allocate_command
  	 * doesn't match this mask.  Otherwise we're guaranteed that this
  	 * succeeds because scsi_allocate_command must have taken a reference
  	 * on the pool
  	 */
  	BUG_ON(!pool);
  
  	scsi_pool_free_command(pool, cmd);
  	/*
  	 * scsi_put_host_cmd_pool is called twice; once to release the
  	 * reference we took above, and once to release the reference
  	 * originally taken by scsi_allocate_command
  	 */
  	scsi_put_host_cmd_pool(gfp_mask);
  	scsi_put_host_cmd_pool(gfp_mask);
  }
  EXPORT_SYMBOL(scsi_free_command);
  
  /**
   * scsi_setup_command_freelist - Setup the command freelist for a scsi host.
   * @shost: host to allocate the freelist for.
   *
   * Description: The command freelist protects against system-wide out of memory
   * deadlock by preallocating one SCSI command structure for each host, so the
   * system can always write to a swap file on a device associated with that host.
   *
   * Returns:	Nothing.
   */
  int scsi_setup_command_freelist(struct Scsi_Host *shost)
  {
  	struct scsi_cmnd *cmd;
  	const gfp_t gfp_mask = shost->unchecked_isa_dma ? GFP_DMA : GFP_KERNEL;
  
  	spin_lock_init(&shost->free_list_lock);
  	INIT_LIST_HEAD(&shost->free_list);
  
  	shost->cmd_pool = scsi_get_host_cmd_pool(gfp_mask);
  
  	if (!shost->cmd_pool)
  		return -ENOMEM;
  
  	/*
  	 * Get one backup command for this host.
  	 */

  	cmd = scsi_host_alloc_command(shost, gfp_mask);

  	if (!cmd) {
  		scsi_put_host_cmd_pool(gfp_mask);

  		shost->cmd_pool = NULL;

  		return -ENOMEM;
  	}
  	list_add(&cmd->list, &shost->free_list);
  	return 0;

  }

  /**
   * scsi_destroy_command_freelist - Release the command freelist for a scsi host.
   * @shost: host whose freelist is going to be destroyed

   */
  void scsi_destroy_command_freelist(struct Scsi_Host *shost)
  {

  	/*
  	 * If cmd_pool is NULL the free list was not initialized, so
  	 * do not attempt to release resources.
  	 */
  	if (!shost->cmd_pool)
  		return;

  	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);

  		scsi_pool_free_command(shost->cmd_pool, cmd);

  	}

  	shost->cmd_pool = NULL;
  	scsi_put_host_cmd_pool(shost->unchecked_isa_dma ? GFP_DMA : GFP_KERNEL);

  }

  #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("
  ");

  			scsi_print_command(cmd);
  			if (level > 3) {
  				printk(KERN_INFO "buffer = 0x%p, bufflen = %d,"

  				       " queuecommand 0x%p
  ",

  					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
  ");

  				break;
  			case NEEDS_RETRY:

  				printk("RETRY
  ");

  				break;
  			case ADD_TO_MLQUEUE:

  				printk("MLQUEUE
  ");

  				break;
  			case FAILED:

  				printk("FAILED
  ");

  				break;
  			case TIMEOUT_ERROR:
  				/* 
  				 * If called via scsi_times_out.
  				 */

  				printk("TIMEOUT
  ");

  				break;
  			default:

  				printk("UNKNOWN
  ");

  			}

  			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
  ",
  					    cmd->device->host->host_busy,
  					    cmd->device->host->host_failed);

  		}
  	}
  }
  #endif

  /**
   * scsi_cmd_get_serial - Assign a serial number to a command
   * @host: the scsi host
   * @cmd: command to assign serial number to
   *
   * Description: a serial number identifies a request for error recovery

   * and debugging purposes.  Protected by the Host_Lock of host.
   */

  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++;

  }

  EXPORT_SYMBOL(scsi_cmd_get_serial);

  /**
   * scsi_dispatch_command - Dispatch a command to the low-level driver.
   * @cmd: command block we are dispatching.

   *

   * Return: nonzero return request was rejected and device's queue needs to be
   * plugged.

   */
  int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
  {
  	struct Scsi_Host *host = cmd->device->host;

  	unsigned long timeout;
  	int rtn = 0;

  	atomic_inc(&cmd->device->iorequest_cnt);

  	/* 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;

  		scsi_done(cmd);

  		/* return 0 (because the command has been processed) */
  		goto out;
  	}

  	/* Check to see if the scsi lld made this device blocked. */
  	if (unlikely(scsi_device_blocked(cmd->device))) {

  		/* 

  		 * in blocked state, 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 
  "));
  
  		/*
  		 * 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;
  	}

  	scsi_log_send(cmd);
  
  	/*

  	 * Before we queue this command, check if the command
  	 * length exceeds what the host adapter can handle.
  	 */

  	if (cmd->cmd_len > cmd->device->host->max_cmd_len) {

  		SCSI_LOG_MLQUEUE(3,

  			printk("queuecommand : command too long. "
  			       "cdb_size=%d host->max_cmd_len=%d
  ",
  			       cmd->cmd_len, cmd->device->host->max_cmd_len));

  		cmd->result = (DID_ABORT << 16);
  
  		scsi_done(cmd);
  		goto out;
  	}

  	if (unlikely(host->shost_state == SHOST_DEL)) {

  		cmd->result = (DID_NO_CONNECT << 16);
  		scsi_done(cmd);
  	} else {

  		trace_scsi_dispatch_cmd_start(cmd);

  		cmd->scsi_done = scsi_done;
  		rtn = host->hostt->queuecommand(host, cmd);

  	}

  	if (rtn) {

  		trace_scsi_dispatch_cmd_error(cmd, rtn);

  		if (rtn != SCSI_MLQUEUE_DEVICE_BUSY &&
  		    rtn != SCSI_MLQUEUE_TARGET_BUSY)
  			rtn = SCSI_MLQUEUE_HOST_BUSY;
  
  		scsi_queue_insert(cmd, rtn);

  		SCSI_LOG_MLQUEUE(3,
  		    printk("queuecommand : request rejected
  "));
  	}
  
   out:
  	SCSI_LOG_MLQUEUE(3, printk("leaving scsi_dispatch_cmnd()
  "));
  	return rtn;
  }

  /**
   * 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.
   *

   * Description: 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)

  {

  	trace_scsi_dispatch_cmd_done(cmd);

  	blk_complete_request(cmd->request);

  }

  /* 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;
  }

  /**
   * scsi_finish_command - cleanup and pass command back to upper layer
   * @cmd: the command

   *

   * Description: 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_target *starget = scsi_target(sdev);

  	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;

  	starget->target_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)
  ", cmd->result));

  	good_bytes = scsi_bufflen(cmd);

          if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {

  		int old_good_bytes = good_bytes;

  		drv = scsi_cmd_to_driver(cmd);
  		if (drv->done)
  			good_bytes = drv->done(cmd);

  		/*
  		 * USB may not give sense identifying bad sector and
  		 * simply return a residue instead, so subtract off the
  		 * residue if drv->done() error processing indicates no
  		 * change to the completion length.
  		 */
  		if (good_bytes == old_good_bytes)
  			good_bytes -= scsi_get_resid(cmd);

  	}
  	scsi_io_completion(cmd, good_bytes);

  }
  EXPORT_SYMBOL(scsi_finish_command);

  /**
   * scsi_adjust_queue_depth - Let low level drivers change a device's queue depth
   * @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.
  	 *
  	 * Do not resize the tag map if it is a host wide share bqt,
  	 * because the size should be the hosts's can_queue. If there
  	 * is more IO than the LLD's can_queue (so there are not enuogh
  	 * tags) request_fn's host queue ready check will handle it.
  	 */
  	if (!sdev->host->bqt) {
  		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
  ");

  		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);

  /**
   * scsi_track_queue_full - track QUEUE_FULL events to adjust queue depth
   * @sdev: SCSI Device in question
   * @depth: Current number of outstanding SCSI commands on this device,
   *         not counting the one returned as QUEUE_FULL.

   *

   * Description:	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.
   *

   * 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)
  {

  
  	/*
  	 * Don't let QUEUE_FULLs on the same
  	 * jiffies count, they could all be from
  	 * same event.
  	 */
  	if ((jiffies >> 4) == (sdev->last_queue_full_time >> 4))

  		return 0;

  	sdev->last_queue_full_time = jiffies;

  	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_vpd_inquiry - Request a device provide us with a VPD page
   * @sdev: The device to ask
   * @buffer: Where to put the result
   * @page: Which Vital Product Data to return
   * @len: The length of the buffer
   *
   * This is an internal helper function.  You probably want to use
   * scsi_get_vpd_page instead.
   *
   * Returns 0 on success or a negative error number.
   */
  static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
  							u8 page, unsigned len)
  {
  	int result;
  	unsigned char cmd[16];
  
  	cmd[0] = INQUIRY;
  	cmd[1] = 1;		/* EVPD */
  	cmd[2] = page;
  	cmd[3] = len >> 8;
  	cmd[4] = len & 0xff;
  	cmd[5] = 0;		/* Control byte */
  
  	/*
  	 * I'm not convinced we need to try quite this hard to get VPD, but
  	 * all the existing users tried this hard.
  	 */
  	result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer,

  				  len, NULL, 30 * HZ, 3, NULL);

  	if (result)
  		return result;
  
  	/* Sanity check that we got the page back that we asked for */
  	if (buffer[1] != page)
  		return -EIO;
  
  	return 0;
  }
  
  /**
   * scsi_get_vpd_page - Get Vital Product Data from a SCSI device
   * @sdev: The device to ask
   * @page: Which Vital Product Data to return

   * @buf: where to store the VPD
   * @buf_len: number of bytes in the VPD buffer area

   *
   * SCSI devices may optionally supply Vital Product Data.  Each 'page'
   * of VPD is defined in the appropriate SCSI document (eg SPC, SBC).
   * If the device supports this VPD page, this routine returns a pointer
   * to a buffer containing the data from that page.  The caller is
   * responsible for calling kfree() on this pointer when it is no longer
   * needed.  If we cannot retrieve the VPD page this routine returns %NULL.
   */

  int scsi_get_vpd_page(struct scsi_device *sdev, u8 page, unsigned char *buf,
  		      int buf_len)

  {
  	int i, result;

  
  	/* Ask for all the pages supported by this device */

  	result = scsi_vpd_inquiry(sdev, buf, 0, buf_len);

  	if (result)
  		goto fail;
  
  	/* If the user actually wanted this page, we can skip the rest */
  	if (page == 0)

  		return 0;

  	for (i = 0; i < min((int)buf[3], buf_len - 4); i++)

  		if (buf[i + 4] == page)
  			goto found;

  	if (i < buf[3] && i >= buf_len - 4)

  		/* ran off the end of the buffer, give us benefit of doubt */
  		goto found;

  	/* The device claims it doesn't support the requested page */
  	goto fail;
  
   found:

  	result = scsi_vpd_inquiry(sdev, buf, page, buf_len);

  	if (result)
  		goto fail;

  	return 0;

  
   fail:

  	return -EINVAL;

  }
  EXPORT_SYMBOL_GPL(scsi_get_vpd_page);
  
  /**

   * scsi_device_get  -  get an additional reference to a scsi_device

   * @sdev:	device to get a reference to
   *

   * Description: 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.
   *

   * Description: 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, see that for documentation */

  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.

   * @data:	Opaque passed to each function call.
   * @fn:		Function to call on each device

   *

   * 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.

   * @data:	parameter for callback @fn()
   * @fn:		callback function that is invoked for each device

   *
   * 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
   *

   * Description: Looks up the scsi_device with the specified @lun for a given
   * @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. A scsi_device in state
   * SDEV_DEL is skipped.

   *

   * Note:  The only reason why drivers should use this is because

   * they 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->sdev_state == SDEV_DEL)
  			continue;

  		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
   *

   * Description: Looks up the scsi_device with the specified @lun for a given
   * @starget.  The returned scsi_device has an additional reference that

   * needs to be released with scsi_device_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)

   * @id:		SCSI target number (physical unit number)

   * @lun:	SCSI Logical Unit Number
   *

   * Description: Looks up the scsi_device with the specified @channel, @id, @lun
   * for a given 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 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
   *

   * Description: Looks up the scsi_device with the specified @channel, @id, @lun
   * for a given host.  The returned scsi_device has an additional reference that
   * needs to be released with scsi_device_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
  ");
  	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
  ",
  	       -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);