/*
   *  scsi_lib.c Copyright (C) 1999 Eric Youngdale
   *
   *  SCSI queueing library.
   *      Initial versions: Eric Youngdale (eric@andante.org).
   *                        Based upon conversations with large numbers
   *                        of people at Linux Expo.
   */
  
  #include <linux/bio.h>

  #include <linux/bitops.h>

  #include <linux/blkdev.h>
  #include <linux/completion.h>
  #include <linux/kernel.h>

  #include <linux/export.h>

  #include <linux/mempool.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/pci.h>
  #include <linux/delay.h>

  #include <linux/hardirq.h>

  #include <linux/scatterlist.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_priv.h"
  #include "scsi_logging.h"

  #define SG_MEMPOOL_NR		ARRAY_SIZE(scsi_sg_pools)

  #define SG_MEMPOOL_SIZE		2

  
  struct scsi_host_sg_pool {
  	size_t		size;

  	char		*name;

  	struct kmem_cache	*slab;

  	mempool_t	*pool;
  };

  #define SP(x) { x, "sgpool-" __stringify(x) }
  #if (SCSI_MAX_SG_SEGMENTS < 32)
  #error SCSI_MAX_SG_SEGMENTS is too small (must be 32 or greater)
  #endif

  static struct scsi_host_sg_pool scsi_sg_pools[] = {

  	SP(8),
  	SP(16),

  #if (SCSI_MAX_SG_SEGMENTS > 32)

  	SP(32),

  #if (SCSI_MAX_SG_SEGMENTS > 64)

  	SP(64),
  #if (SCSI_MAX_SG_SEGMENTS > 128)

  	SP(128),

  #if (SCSI_MAX_SG_SEGMENTS > 256)
  #error SCSI_MAX_SG_SEGMENTS is too large (256 MAX)

  #endif
  #endif
  #endif

  #endif
  	SP(SCSI_MAX_SG_SEGMENTS)

  };

  #undef SP

  struct kmem_cache *scsi_sdb_cache;

  /*
   * When to reinvoke queueing after a resource shortage. It's 3 msecs to
   * not change behaviour from the previous unplug mechanism, experimentation
   * may prove this needs changing.
   */
  #define SCSI_QUEUE_DELAY	3

  /*
   * Function:	scsi_unprep_request()
   *
   * Purpose:	Remove all preparation done for a request, including its
   *		associated scsi_cmnd, so that it can be requeued.
   *
   * Arguments:	req	- request to unprepare
   *
   * Lock status:	Assumed that no locks are held upon entry.
   *
   * Returns:	Nothing.
   */
  static void scsi_unprep_request(struct request *req)
  {
  	struct scsi_cmnd *cmd = req->special;

  	blk_unprep_request(req);

  	req->special = NULL;

  	scsi_put_command(cmd);
  }

  /**
   * __scsi_queue_insert - private queue insertion
   * @cmd: The SCSI command being requeued
   * @reason:  The reason for the requeue
   * @unbusy: Whether the queue should be unbusied

   *

   * This is a private queue insertion.  The public interface
   * scsi_queue_insert() always assumes the queue should be unbusied
   * because it's always called before the completion.  This function is
   * for a requeue after completion, which should only occur in this
   * file.

   */

  static int __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)

  {
  	struct Scsi_Host *host = cmd->device->host;
  	struct scsi_device *device = cmd->device;

  	struct scsi_target *starget = scsi_target(device);

  	struct request_queue *q = device->request_queue;
  	unsigned long flags;

  
  	SCSI_LOG_MLQUEUE(1,
  		 printk("Inserting command %p into mlqueue
  ", cmd));
  
  	/*

  	 * Set the appropriate busy bit for the device/host.

  	 *
  	 * If the host/device isn't busy, assume that something actually
  	 * completed, and that we should be able to queue a command now.
  	 *
  	 * Note that the prior mid-layer assumption that any host could
  	 * always queue at least one command is now broken.  The mid-layer
  	 * will implement a user specifiable stall (see
  	 * scsi_host.max_host_blocked and scsi_device.max_device_blocked)
  	 * if a command is requeued with no other commands outstanding
  	 * either for the device or for the host.
  	 */

  	switch (reason) {
  	case SCSI_MLQUEUE_HOST_BUSY:

  		host->host_blocked = host->max_host_blocked;

  		break;
  	case SCSI_MLQUEUE_DEVICE_BUSY:

  	case SCSI_MLQUEUE_EH_RETRY:

  		device->device_blocked = device->max_device_blocked;

  		break;
  	case SCSI_MLQUEUE_TARGET_BUSY:
  		starget->target_blocked = starget->max_target_blocked;
  		break;
  	}

  
  	/*

  	 * Decrement the counters, since these commands are no longer
  	 * active on the host/device.
  	 */

  	if (unbusy)
  		scsi_device_unbusy(device);

  
  	/*

  	 * Requeue this command.  It will go before all other commands
  	 * that are already in the queue.

  	 */

  	spin_lock_irqsave(q->queue_lock, flags);

  	blk_requeue_request(q, cmd->request);

  	spin_unlock_irqrestore(q->queue_lock, flags);

  	kblockd_schedule_work(q, &device->requeue_work);

  	return 0;
  }

  /*
   * Function:    scsi_queue_insert()
   *
   * Purpose:     Insert a command in the midlevel queue.
   *
   * Arguments:   cmd    - command that we are adding to queue.
   *              reason - why we are inserting command to queue.
   *
   * Lock status: Assumed that lock is not held upon entry.
   *
   * Returns:     Nothing.
   *
   * Notes:       We do this for one of two cases.  Either the host is busy
   *              and it cannot accept any more commands for the time being,
   *              or the device returned QUEUE_FULL and can accept no more
   *              commands.
   * Notes:       This could be called either from an interrupt context or a
   *              normal process context.
   */
  int scsi_queue_insert(struct scsi_cmnd *cmd, int reason)
  {
  	return __scsi_queue_insert(cmd, reason, 1);
  }

  /**

   * scsi_execute - insert request and wait for the result

   * @sdev:	scsi device
   * @cmd:	scsi command
   * @data_direction: data direction
   * @buffer:	data buffer
   * @bufflen:	len of buffer
   * @sense:	optional sense buffer
   * @timeout:	request timeout in seconds
   * @retries:	number of times to retry request

   * @flags:	or into request flags;

   * @resid:	optional residual length

   *

   * returns the req->errors value which is the scsi_cmnd result

   * field.

   */

  int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
  		 int data_direction, void *buffer, unsigned bufflen,

  		 unsigned char *sense, int timeout, int retries, int flags,
  		 int *resid)

  {
  	struct request *req;
  	int write = (data_direction == DMA_TO_DEVICE);
  	int ret = DRIVER_ERROR << 24;
  
  	req = blk_get_request(sdev->request_queue, write, __GFP_WAIT);

  	if (!req)
  		return ret;

  
  	if (bufflen &&	blk_rq_map_kern(sdev->request_queue, req,
  					buffer, bufflen, __GFP_WAIT))
  		goto out;
  
  	req->cmd_len = COMMAND_SIZE(cmd[0]);
  	memcpy(req->cmd, cmd, req->cmd_len);
  	req->sense = sense;
  	req->sense_len = 0;

  	req->retries = retries;

  	req->timeout = timeout;

  	req->cmd_type = REQ_TYPE_BLOCK_PC;
  	req->cmd_flags |= flags | REQ_QUIET | REQ_PREEMPT;

  
  	/*
  	 * head injection *required* here otherwise quiesce won't work
  	 */
  	blk_execute_rq(req->q, NULL, req, 1);

  	/*
  	 * Some devices (USB mass-storage in particular) may transfer
  	 * garbage data together with a residue indicating that the data
  	 * is invalid.  Prevent the garbage from being misinterpreted
  	 * and prevent security leaks by zeroing out the excess data.
  	 */

  	if (unlikely(req->resid_len > 0 && req->resid_len <= bufflen))
  		memset(buffer + (bufflen - req->resid_len), 0, req->resid_len);

  	if (resid)

  		*resid = req->resid_len;

  	ret = req->errors;
   out:
  	blk_put_request(req);
  
  	return ret;
  }

  EXPORT_SYMBOL(scsi_execute);

  
  int scsi_execute_req(struct scsi_device *sdev, const unsigned char *cmd,
  		     int data_direction, void *buffer, unsigned bufflen,

  		     struct scsi_sense_hdr *sshdr, int timeout, int retries,
  		     int *resid)

  {
  	char *sense = NULL;

  	int result;
  	

  	if (sshdr) {

  		sense = kzalloc(SCSI_SENSE_BUFFERSIZE, GFP_NOIO);

  		if (!sense)
  			return DRIVER_ERROR << 24;

  	}

  	result = scsi_execute(sdev, cmd, data_direction, buffer, bufflen,

  			      sense, timeout, retries, 0, resid);

  	if (sshdr)

  		scsi_normalize_sense(sense, SCSI_SENSE_BUFFERSIZE, sshdr);

  
  	kfree(sense);
  	return result;
  }
  EXPORT_SYMBOL(scsi_execute_req);

  /*
   * Function:    scsi_init_cmd_errh()
   *
   * Purpose:     Initialize cmd fields related to error handling.
   *
   * Arguments:   cmd	- command that is ready to be queued.
   *

   * Notes:       This function has the job of initializing a number of
   *              fields related to error handling.   Typically this will
   *              be called once for each command, as required.
   */

  static void scsi_init_cmd_errh(struct scsi_cmnd *cmd)

  {

  	cmd->serial_number = 0;

  	scsi_set_resid(cmd, 0);

  	memset(cmd->sense_buffer, 0, SCSI_SENSE_BUFFERSIZE);

  	if (cmd->cmd_len == 0)

  		cmd->cmd_len = scsi_command_size(cmd->cmnd);

  }
  
  void scsi_device_unbusy(struct scsi_device *sdev)
  {
  	struct Scsi_Host *shost = sdev->host;

  	struct scsi_target *starget = scsi_target(sdev);

  	unsigned long flags;
  
  	spin_lock_irqsave(shost->host_lock, flags);
  	shost->host_busy--;

  	starget->target_busy--;

  	if (unlikely(scsi_host_in_recovery(shost) &&

  		     (shost->host_failed || shost->host_eh_scheduled)))

  		scsi_eh_wakeup(shost);
  	spin_unlock(shost->host_lock);

  	spin_lock(sdev->request_queue->queue_lock);

  	sdev->device_busy--;

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

  }
  
  /*
   * Called for single_lun devices on IO completion. Clear starget_sdev_user,
   * and call blk_run_queue for all the scsi_devices on the target -
   * including current_sdev first.
   *
   * Called with *no* scsi locks held.
   */
  static void scsi_single_lun_run(struct scsi_device *current_sdev)
  {
  	struct Scsi_Host *shost = current_sdev->host;
  	struct scsi_device *sdev, *tmp;
  	struct scsi_target *starget = scsi_target(current_sdev);
  	unsigned long flags;
  
  	spin_lock_irqsave(shost->host_lock, flags);
  	starget->starget_sdev_user = NULL;
  	spin_unlock_irqrestore(shost->host_lock, flags);
  
  	/*
  	 * Call blk_run_queue for all LUNs on the target, starting with
  	 * current_sdev. We race with others (to set starget_sdev_user),
  	 * but in most cases, we will be first. Ideally, each LU on the
  	 * target would get some limited time or requests on the target.
  	 */
  	blk_run_queue(current_sdev->request_queue);
  
  	spin_lock_irqsave(shost->host_lock, flags);
  	if (starget->starget_sdev_user)
  		goto out;
  	list_for_each_entry_safe(sdev, tmp, &starget->devices,
  			same_target_siblings) {
  		if (sdev == current_sdev)
  			continue;
  		if (scsi_device_get(sdev))
  			continue;
  
  		spin_unlock_irqrestore(shost->host_lock, flags);
  		blk_run_queue(sdev->request_queue);
  		spin_lock_irqsave(shost->host_lock, flags);
  	
  		scsi_device_put(sdev);
  	}
   out:
  	spin_unlock_irqrestore(shost->host_lock, flags);
  }

  static inline int scsi_device_is_busy(struct scsi_device *sdev)
  {
  	if (sdev->device_busy >= sdev->queue_depth || sdev->device_blocked)
  		return 1;
  
  	return 0;
  }

  static inline int scsi_target_is_busy(struct scsi_target *starget)
  {
  	return ((starget->can_queue > 0 &&
  		 starget->target_busy >= starget->can_queue) ||
  		 starget->target_blocked);
  }

  static inline int scsi_host_is_busy(struct Scsi_Host *shost)
  {
  	if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
  	    shost->host_blocked || shost->host_self_blocked)
  		return 1;
  
  	return 0;
  }

  /*
   * Function:	scsi_run_queue()
   *
   * Purpose:	Select a proper request queue to serve next
   *
   * Arguments:	q	- last request's queue
   *
   * Returns:     Nothing
   *
   * Notes:	The previous command was completely finished, start
   *		a new one if possible.
   */
  static void scsi_run_queue(struct request_queue *q)
  {

  	struct scsi_device *sdev = q->queuedata;

  	struct Scsi_Host *shost;

  	LIST_HEAD(starved_list);

  	unsigned long flags;

  	/* if the device is dead, sdev will be NULL, so no queue to run */
  	if (!sdev)
  		return;
  
  	shost = sdev->host;

  	if (scsi_target(sdev)->single_lun)

  		scsi_single_lun_run(sdev);
  
  	spin_lock_irqsave(shost->host_lock, flags);

  	list_splice_init(&shost->starved_list, &starved_list);
  
  	while (!list_empty(&starved_list)) {

  		/*
  		 * As long as shost is accepting commands and we have
  		 * starved queues, call blk_run_queue. scsi_request_fn
  		 * drops the queue_lock and can add us back to the
  		 * starved_list.
  		 *
  		 * host_lock protects the starved_list and starved_entry.
  		 * scsi_request_fn must get the host_lock before checking
  		 * or modifying starved_list or starved_entry.
  		 */

  		if (scsi_host_is_busy(shost))

  			break;

  		sdev = list_entry(starved_list.next,
  				  struct scsi_device, starved_entry);
  		list_del_init(&sdev->starved_entry);

  		if (scsi_target_is_busy(scsi_target(sdev))) {
  			list_move_tail(&sdev->starved_entry,
  				       &shost->starved_list);
  			continue;
  		}

  		spin_unlock(shost->host_lock);
  		spin_lock(sdev->request_queue->queue_lock);
  		__blk_run_queue(sdev->request_queue);
  		spin_unlock(sdev->request_queue->queue_lock);
  		spin_lock(shost->host_lock);

  	}

  	/* put any unprocessed entries back */
  	list_splice(&starved_list, &shost->starved_list);

  	spin_unlock_irqrestore(shost->host_lock, flags);
  
  	blk_run_queue(q);
  }

  void scsi_requeue_run_queue(struct work_struct *work)
  {
  	struct scsi_device *sdev;
  	struct request_queue *q;
  
  	sdev = container_of(work, struct scsi_device, requeue_work);
  	q = sdev->request_queue;
  	scsi_run_queue(q);
  }

  /*
   * Function:	scsi_requeue_command()
   *
   * Purpose:	Handle post-processing of completed commands.
   *
   * Arguments:	q	- queue to operate on
   *		cmd	- command that may need to be requeued.
   *
   * Returns:	Nothing
   *
   * Notes:	After command completion, there may be blocks left
   *		over which weren't finished by the previous command
   *		this can be for a number of reasons - the main one is
   *		I/O errors in the middle of the request, in which case
   *		we need to request the blocks that come after the bad
   *		sector.

   * Notes:	Upon return, cmd is a stale pointer.

   */
  static void scsi_requeue_command(struct request_queue *q, struct scsi_cmnd *cmd)
  {

  	struct request *req = cmd->request;

  	unsigned long flags;

  	spin_lock_irqsave(q->queue_lock, flags);

  	scsi_unprep_request(req);

  	blk_requeue_request(q, req);

  	spin_unlock_irqrestore(q->queue_lock, flags);

  
  	scsi_run_queue(q);
  }
  
  void scsi_next_command(struct scsi_cmnd *cmd)
  {

  	struct scsi_device *sdev = cmd->device;
  	struct request_queue *q = sdev->request_queue;
  
  	/* need to hold a reference on the device before we let go of the cmd */
  	get_device(&sdev->sdev_gendev);

  
  	scsi_put_command(cmd);
  	scsi_run_queue(q);

  
  	/* ok to remove device now */
  	put_device(&sdev->sdev_gendev);

  }
  
  void scsi_run_host_queues(struct Scsi_Host *shost)
  {
  	struct scsi_device *sdev;
  
  	shost_for_each_device(sdev, shost)
  		scsi_run_queue(sdev->request_queue);
  }

  static void __scsi_release_buffers(struct scsi_cmnd *, int);

  /*
   * Function:    scsi_end_request()
   *
   * Purpose:     Post-processing of completed commands (usually invoked at end
   *		of upper level post-processing and scsi_io_completion).
   *
   * Arguments:   cmd	 - command that is complete.

   *              error    - 0 if I/O indicates success, < 0 for I/O error.

   *              bytes    - number of bytes of completed I/O
   *		requeue  - indicates whether we should requeue leftovers.
   *
   * Lock status: Assumed that lock is not held upon entry.
   *

   * Returns:     cmd if requeue required, NULL otherwise.

   *
   * Notes:       This is called for block device requests in order to
   *              mark some number of sectors as complete.
   * 
   *		We are guaranteeing that the request queue will be goosed
   *		at some point during this call.

   * Notes:	If cmd was requeued, upon return it will be a stale pointer.

   */

  static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int error,

  					  int bytes, int requeue)
  {

  	struct request_queue *q = cmd->device->request_queue;

  	struct request *req = cmd->request;

  
  	/*
  	 * If there are blocks left over at the end, set up the command
  	 * to queue the remainder of them.
  	 */

  	if (blk_end_request(req, error, bytes)) {

  		/* kill remainder if no retrys */

  		if (error && scsi_noretry_cmd(cmd))

  			blk_end_request_all(req, error);

  		else {

  			if (requeue) {

  				/*
  				 * Bleah.  Leftovers again.  Stick the
  				 * leftovers in the front of the
  				 * queue, and goose the queue again.
  				 */

  				scsi_release_buffers(cmd);

  				scsi_requeue_command(q, cmd);

  				cmd = NULL;
  			}

  			return cmd;
  		}
  	}

  	/*
  	 * This will goose the queue request function at the end, so we don't
  	 * need to worry about launching another command.
  	 */

  	__scsi_release_buffers(cmd, 0);

  	scsi_next_command(cmd);
  	return NULL;
  }

  static inline unsigned int scsi_sgtable_index(unsigned short nents)
  {
  	unsigned int index;

  	BUG_ON(nents > SCSI_MAX_SG_SEGMENTS);
  
  	if (nents <= 8)

  		index = 0;

  	else
  		index = get_count_order(nents) - 3;

  	return index;
  }

  static void scsi_sg_free(struct scatterlist *sgl, unsigned int nents)

  {
  	struct scsi_host_sg_pool *sgp;

  	sgp = scsi_sg_pools + scsi_sgtable_index(nents);
  	mempool_free(sgl, sgp->pool);
  }

  static struct scatterlist *scsi_sg_alloc(unsigned int nents, gfp_t gfp_mask)
  {
  	struct scsi_host_sg_pool *sgp;

  	sgp = scsi_sg_pools + scsi_sgtable_index(nents);
  	return mempool_alloc(sgp->pool, gfp_mask);
  }

  static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
  			      gfp_t gfp_mask)

  {
  	int ret;

  	BUG_ON(!nents);

  	ret = __sg_alloc_table(&sdb->table, nents, SCSI_MAX_SG_SEGMENTS,
  			       gfp_mask, scsi_sg_alloc);

  	if (unlikely(ret))

  		__sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS,

  				scsi_sg_free);

  	return ret;

  }

  static void scsi_free_sgtable(struct scsi_data_buffer *sdb)

  {

  	__sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, scsi_sg_free);

  }

  static void __scsi_release_buffers(struct scsi_cmnd *cmd, int do_bidi_check)
  {
  
  	if (cmd->sdb.table.nents)
  		scsi_free_sgtable(&cmd->sdb);
  
  	memset(&cmd->sdb, 0, sizeof(cmd->sdb));
  
  	if (do_bidi_check && scsi_bidi_cmnd(cmd)) {
  		struct scsi_data_buffer *bidi_sdb =
  			cmd->request->next_rq->special;
  		scsi_free_sgtable(bidi_sdb);
  		kmem_cache_free(scsi_sdb_cache, bidi_sdb);
  		cmd->request->next_rq->special = NULL;
  	}
  
  	if (scsi_prot_sg_count(cmd))
  		scsi_free_sgtable(cmd->prot_sdb);
  }

  /*
   * Function:    scsi_release_buffers()
   *
   * Purpose:     Completion processing for block device I/O requests.
   *
   * Arguments:   cmd	- command that we are bailing.
   *
   * Lock status: Assumed that no lock is held upon entry.
   *
   * Returns:     Nothing
   *
   * Notes:       In the event that an upper level driver rejects a
   *		command, we must release resources allocated during
   *		the __init_io() function.  Primarily this would involve
   *		the scatter-gather table, and potentially any bounce
   *		buffers.
   */

  void scsi_release_buffers(struct scsi_cmnd *cmd)

  {

  	__scsi_release_buffers(cmd, 1);

  }

  EXPORT_SYMBOL(scsi_release_buffers);

  static int __scsi_error_from_host_byte(struct scsi_cmnd *cmd, int result)
  {
  	int error = 0;
  
  	switch(host_byte(result)) {
  	case DID_TRANSPORT_FAILFAST:
  		error = -ENOLINK;
  		break;
  	case DID_TARGET_FAILURE:
  		cmd->result |= (DID_OK << 16);
  		error = -EREMOTEIO;
  		break;
  	case DID_NEXUS_FAILURE:
  		cmd->result |= (DID_OK << 16);
  		error = -EBADE;
  		break;
  	default:
  		error = -EIO;
  		break;
  	}
  
  	return error;
  }

  /*
   * Function:    scsi_io_completion()
   *
   * Purpose:     Completion processing for block device I/O requests.
   *
   * Arguments:   cmd   - command that is finished.
   *
   * Lock status: Assumed that no lock is held upon entry.
   *
   * Returns:     Nothing
   *
   * Notes:       This function is matched in terms of capabilities to
   *              the function that created the scatter-gather list.
   *              In other words, if there are no bounce buffers
   *              (the normal case for most drivers), we don't need
   *              the logic to deal with cleaning up afterwards.
   *

   *		We must call scsi_end_request().  This will finish off
   *		the specified number of sectors.  If we are done, the
   *		command block will be released and the queue function
   *		will be goosed.  If we are not done then we have to
   *		figure out what to do next:

   *

   *		a) We can call scsi_requeue_command().  The request
   *		   will be unprepared and put back on the queue.  Then
   *		   a new command will be created for it.  This should
   *		   be used if we made forward progress, or if we want
   *		   to switch from READ(10) to READ(6) for example.

   *

   *		b) We can call scsi_queue_insert().  The request will
   *		   be put back on the queue and retried using the same
   *		   command as before, possibly after a delay.
   *
   *		c) We can call blk_end_request() with -EIO to fail
   *		   the remainder of the request.

   */

  void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)

  {
  	int result = cmd->result;

  	struct request_queue *q = cmd->device->request_queue;

  	struct request *req = cmd->request;

  	int error = 0;

  	struct scsi_sense_hdr sshdr;
  	int sense_valid = 0;
  	int sense_deferred = 0;

  	enum {ACTION_FAIL, ACTION_REPREP, ACTION_RETRY,
  	      ACTION_DELAYED_RETRY} action;
  	char *description = NULL;

  	if (result) {
  		sense_valid = scsi_command_normalize_sense(cmd, &sshdr);
  		if (sense_valid)
  			sense_deferred = scsi_sense_is_deferred(&sshdr);
  	}

  	if (req->cmd_type == REQ_TYPE_BLOCK_PC) { /* SG_IO ioctl from block level */

  		req->errors = result;
  		if (result) {

  			if (sense_valid && req->sense) {
  				/*
  				 * SG_IO wants current and deferred errors
  				 */
  				int len = 8 + cmd->sense_buffer[7];
  
  				if (len > SCSI_SENSE_BUFFERSIZE)
  					len = SCSI_SENSE_BUFFERSIZE;
  				memcpy(req->sense, cmd->sense_buffer,  len);
  				req->sense_len = len;
  			}

  			if (!sense_deferred)

  				error = __scsi_error_from_host_byte(cmd, result);

  		}

  
  		req->resid_len = scsi_get_resid(cmd);

  		if (scsi_bidi_cmnd(cmd)) {

  			/*
  			 * Bidi commands Must be complete as a whole,
  			 * both sides at once.
  			 */
  			req->next_rq->resid_len = scsi_in(cmd)->resid;

  			scsi_release_buffers(cmd);

  			blk_end_request_all(req, 0);

  			scsi_next_command(cmd);

  			return;
  		}

  	}

  	/* no bidi support for !REQ_TYPE_BLOCK_PC yet */
  	BUG_ON(blk_bidi_rq(req));

  	/*

  	 * Next deal with any sectors which we were able to correctly
  	 * handle.
  	 */

  	SCSI_LOG_HLCOMPLETE(1, printk("%u sectors total, "

  				      "%d bytes done.
  ",

  				      blk_rq_sectors(req), good_bytes));

  	/*
  	 * Recovered errors need reporting, but they're always treated
  	 * as success, so fiddle the result code here.  For BLOCK_PC
  	 * we already took a copy of the original into rq->errors which
  	 * is what gets returned to the user
  	 */

  	if (sense_valid && (sshdr.sense_key == RECOVERED_ERROR)) {
  		/* if ATA PASS-THROUGH INFORMATION AVAILABLE skip
  		 * print since caller wants ATA registers. Only occurs on
  		 * SCSI ATA PASS_THROUGH commands when CK_COND=1
  		 */
  		if ((sshdr.asc == 0x0) && (sshdr.ascq == 0x1d))
  			;
  		else if (!(req->cmd_flags & REQ_QUIET))

  			scsi_print_sense("", cmd);
  		result = 0;
  		/* BLOCK_PC may have set error */
  		error = 0;
  	}
  
  	/*
  	 * A number of bytes were successfully read.  If there

  	 * are leftovers and there is some kind of error
  	 * (result != 0), retry the rest.
  	 */

  	if (scsi_end_request(cmd, error, good_bytes, result == 0) == NULL)

  		return;

  	error = __scsi_error_from_host_byte(cmd, result);

  	if (host_byte(result) == DID_RESET) {
  		/* Third party bus reset or reset for error recovery
  		 * reasons.  Just retry the command and see what
  		 * happens.
  		 */
  		action = ACTION_RETRY;
  	} else if (sense_valid && !sense_deferred) {

  		switch (sshdr.sense_key) {
  		case UNIT_ATTENTION:
  			if (cmd->device->removable) {

  				/* Detected disc change.  Set a bit

  				 * and quietly refuse further access.
  				 */
  				cmd->device->changed = 1;

  				description = "Media Changed";
  				action = ACTION_FAIL;

  			} else {

  				/* Must have been a power glitch, or a
  				 * bus reset.  Could not have been a
  				 * media change, so we just retry the

  				 * command and see what happens.

  				 */

  				action = ACTION_RETRY;

  			}
  			break;
  		case ILLEGAL_REQUEST:

  			/* If we had an ILLEGAL REQUEST returned, then
  			 * we may have performed an unsupported
  			 * command.  The only thing this should be
  			 * would be a ten byte read where only a six
  			 * byte read was supported.  Also, on a system
  			 * where READ CAPACITY failed, we may have
  			 * read past the end of the disk.
  			 */

  			if ((cmd->device->use_10_for_rw &&
  			    sshdr.asc == 0x20 && sshdr.ascq == 0x00) &&

  			    (cmd->cmnd[0] == READ_10 ||
  			     cmd->cmnd[0] == WRITE_10)) {

  				/* This will issue a new 6-byte command. */

  				cmd->device->use_10_for_rw = 0;

  				action = ACTION_REPREP;

  			} else if (sshdr.asc == 0x10) /* DIX */ {
  				description = "Host Data Integrity Failure";
  				action = ACTION_FAIL;
  				error = -EILSEQ;

  			/* INVALID COMMAND OPCODE or INVALID FIELD IN CDB */
  			} else if ((sshdr.asc == 0x20 || sshdr.asc == 0x24) &&
  				   (cmd->cmnd[0] == UNMAP ||
  				    cmd->cmnd[0] == WRITE_SAME_16 ||
  				    cmd->cmnd[0] == WRITE_SAME)) {
  				description = "Discard failure";
  				action = ACTION_FAIL;

  			} else
  				action = ACTION_FAIL;
  			break;

  		case ABORTED_COMMAND:

  			action = ACTION_FAIL;

  			if (sshdr.asc == 0x10) { /* DIF */

  				description = "Target Data Integrity Failure";

  				error = -EILSEQ;

  			}

  			break;
  		case NOT_READY:

  			/* If the device is in the process of becoming

  			 * ready, or has a temporary blockage, retry.

  			 */

  			if (sshdr.asc == 0x04) {
  				switch (sshdr.ascq) {
  				case 0x01: /* becoming ready */
  				case 0x04: /* format in progress */
  				case 0x05: /* rebuild in progress */
  				case 0x06: /* recalculation in progress */
  				case 0x07: /* operation in progress */
  				case 0x08: /* Long write in progress */
  				case 0x09: /* self test in progress */

  				case 0x14: /* space allocation in progress */

  					action = ACTION_DELAYED_RETRY;

  					break;

  				default:
  					description = "Device not ready";
  					action = ACTION_FAIL;
  					break;

  				}

  			} else {
  				description = "Device not ready";
  				action = ACTION_FAIL;

  			}

  			break;

  		case VOLUME_OVERFLOW:

  			/* See SSC3rXX or current. */

  			action = ACTION_FAIL;
  			break;

  		default:

  			description = "Unhandled sense code";
  			action = ACTION_FAIL;

  			break;
  		}

  	} else {
  		description = "Unhandled error code";
  		action = ACTION_FAIL;

  	}

  
  	switch (action) {
  	case ACTION_FAIL:
  		/* Give up and fail the remainder of the request */

  		scsi_release_buffers(cmd);

  		if (!(req->cmd_flags & REQ_QUIET)) {

  			if (description)

  				scmd_printk(KERN_INFO, cmd, "%s
  ",

  					    description);

  			scsi_print_result(cmd);

  			if (driver_byte(result) & DRIVER_SENSE)
  				scsi_print_sense("", cmd);

  			scsi_print_command(cmd);

  		}

  		if (blk_end_request_err(req, error))

  			scsi_requeue_command(q, cmd);
  		else
  			scsi_next_command(cmd);

  		break;
  	case ACTION_REPREP:
  		/* Unprep the request and put it back at the head of the queue.
  		 * A new command will be prepared and issued.
  		 */

  		scsi_release_buffers(cmd);

  		scsi_requeue_command(q, cmd);
  		break;
  	case ACTION_RETRY:
  		/* Retry the same command immediately */

  		__scsi_queue_insert(cmd, SCSI_MLQUEUE_EH_RETRY, 0);

  		break;
  	case ACTION_DELAYED_RETRY:
  		/* Retry the same command after a delay */

  		__scsi_queue_insert(cmd, SCSI_MLQUEUE_DEVICE_BUSY, 0);

  		break;

  	}
  }

  static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb,
  			     gfp_t gfp_mask)

  {

  	int count;

  
  	/*

  	 * If sg table allocation fails, requeue request later.

  	 */

  	if (unlikely(scsi_alloc_sgtable(sdb, req->nr_phys_segments,
  					gfp_mask))) {

  		return BLKPREP_DEFER;

  	}

  	req->buffer = NULL;

  
  	/* 
  	 * Next, walk the list, and fill in the addresses and sizes of
  	 * each segment.
  	 */

  	count = blk_rq_map_sg(req->q, req, sdb->table.sgl);
  	BUG_ON(count > sdb->table.nents);
  	sdb->table.nents = count;

  	sdb->length = blk_rq_bytes(req);

  	return BLKPREP_OK;

  }

  
  /*
   * Function:    scsi_init_io()
   *
   * Purpose:     SCSI I/O initialize function.
   *
   * Arguments:   cmd   - Command descriptor we wish to initialize
   *
   * Returns:     0 on success
   *		BLKPREP_DEFER if the failure is retryable
   *		BLKPREP_KILL if the failure is fatal
   */
  int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
  {

  	struct request *rq = cmd->request;
  
  	int error = scsi_init_sgtable(rq, &cmd->sdb, gfp_mask);

  	if (error)
  		goto err_exit;

  	if (blk_bidi_rq(rq)) {

  		struct scsi_data_buffer *bidi_sdb = kmem_cache_zalloc(

  			scsi_sdb_cache, GFP_ATOMIC);

  		if (!bidi_sdb) {
  			error = BLKPREP_DEFER;
  			goto err_exit;
  		}

  		rq->next_rq->special = bidi_sdb;
  		error = scsi_init_sgtable(rq->next_rq, bidi_sdb, GFP_ATOMIC);

  		if (error)
  			goto err_exit;
  	}

  	if (blk_integrity_rq(rq)) {

  		struct scsi_data_buffer *prot_sdb = cmd->prot_sdb;
  		int ivecs, count;
  
  		BUG_ON(prot_sdb == NULL);

  		ivecs = blk_rq_count_integrity_sg(rq->q, rq->bio);

  
  		if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask)) {
  			error = BLKPREP_DEFER;
  			goto err_exit;
  		}

  		count = blk_rq_map_integrity_sg(rq->q, rq->bio,

  						prot_sdb->table.sgl);
  		BUG_ON(unlikely(count > ivecs));

  		BUG_ON(unlikely(count > queue_max_integrity_segments(rq->q)));

  
  		cmd->prot_sdb = prot_sdb;
  		cmd->prot_sdb->table.nents = count;
  	}

  	return BLKPREP_OK ;
  
  err_exit:
  	scsi_release_buffers(cmd);

  	cmd->request->special = NULL;

  	scsi_put_command(cmd);

  	return error;
  }

  EXPORT_SYMBOL(scsi_init_io);

  static struct scsi_cmnd *scsi_get_cmd_from_req(struct scsi_device *sdev,
  		struct request *req)
  {
  	struct scsi_cmnd *cmd;
  
  	if (!req->special) {
  		cmd = scsi_get_command(sdev, GFP_ATOMIC);
  		if (unlikely(!cmd))
  			return NULL;
  		req->special = cmd;
  	} else {
  		cmd = req->special;
  	}
  
  	/* pull a tag out of the request if we have one */
  	cmd->tag = req->tag;
  	cmd->request = req;

  	cmd->cmnd = req->cmd;

  	cmd->prot_op = SCSI_PROT_NORMAL;

  	return cmd;
  }

  int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)

  {

  	struct scsi_cmnd *cmd;

  	int ret = scsi_prep_state_check(sdev, req);
  
  	if (ret != BLKPREP_OK)
  		return ret;

  
  	cmd = scsi_get_cmd_from_req(sdev, req);
  	if (unlikely(!cmd))
  		return BLKPREP_DEFER;
  
  	/*
  	 * BLOCK_PC requests may transfer data, in which case they must
  	 * a bio attached to them.  Or they might contain a SCSI command
  	 * that does not transfer data, in which case they may optionally
  	 * submit a request without an attached bio.
  	 */
  	if (req->bio) {
  		int ret;
  
  		BUG_ON(!req->nr_phys_segments);

  		ret = scsi_init_io(cmd, GFP_ATOMIC);

  		if (unlikely(ret))
  			return ret;
  	} else {

  		BUG_ON(blk_rq_bytes(req));

  		memset(&cmd->sdb, 0, sizeof(cmd->sdb));

  		req->buffer = NULL;
  	}

  	cmd->cmd_len = req->cmd_len;

  	if (!blk_rq_bytes(req))

  		cmd->sc_data_direction = DMA_NONE;
  	else if (rq_data_dir(req) == WRITE)
  		cmd->sc_data_direction = DMA_TO_DEVICE;
  	else
  		cmd->sc_data_direction = DMA_FROM_DEVICE;
  	

  	cmd->transfersize = blk_rq_bytes(req);

  	cmd->allowed = req->retries;

  	return BLKPREP_OK;

  }

  EXPORT_SYMBOL(scsi_setup_blk_pc_cmnd);

  /*
   * Setup a REQ_TYPE_FS command.  These are simple read/write request
   * from filesystems that still need to be translated to SCSI CDBs from
   * the ULD.
   */

  int scsi_setup_fs_cmnd(struct scsi_device *sdev, struct request *req)

  {

  	struct scsi_cmnd *cmd;

  	int ret = scsi_prep_state_check(sdev, req);

  	if (ret != BLKPREP_OK)
  		return ret;

  
  	if (unlikely(sdev->scsi_dh_data && sdev->scsi_dh_data->scsi_dh
  			 && sdev->scsi_dh_data->scsi_dh->prep_fn)) {
  		ret = sdev->scsi_dh_data->scsi_dh->prep_fn(sdev, req);
  		if (ret != BLKPREP_OK)
  			return ret;
  	}

  	/*

  	 * Filesystem requests must transfer data.

  	 */

  	BUG_ON(!req->nr_phys_segments);
  
  	cmd = scsi_get_cmd_from_req(sdev, req);
  	if (unlikely(!cmd))
  		return BLKPREP_DEFER;

  	memset(cmd->cmnd, 0, BLK_MAX_CDB);

  	return scsi_init_io(cmd, GFP_ATOMIC);

  }

  EXPORT_SYMBOL(scsi_setup_fs_cmnd);

  int scsi_prep_state_check(struct scsi_device *sdev, struct request *req)

  {

  	int ret = BLKPREP_OK;

  	/*

  	 * If the device is not in running state we will reject some
  	 * or all commands.

  	 */

  	if (unlikely(sdev->sdev_state != SDEV_RUNNING)) {
  		switch (sdev->sdev_state) {
  		case SDEV_OFFLINE:
  			/*
  			 * If the device is offline we refuse to process any
  			 * commands.  The device must be brought online
  			 * before trying any recovery commands.
  			 */
  			sdev_printk(KERN_ERR, sdev,
  				    "rejecting I/O to offline device
  ");
  			ret = BLKPREP_KILL;
  			break;
  		case SDEV_DEL:
  			/*
  			 * If the device is fully deleted, we refuse to
  			 * process any commands as well.
  			 */

  			sdev_printk(KERN_ERR, sdev,

  				    "rejecting I/O to dead device
  ");
  			ret = BLKPREP_KILL;
  			break;
  		case SDEV_QUIESCE:
  		case SDEV_BLOCK:

  		case SDEV_CREATED_BLOCK:

  			/*
  			 * If the devices is blocked we defer normal commands.
  			 */
  			if (!(req->cmd_flags & REQ_PREEMPT))
  				ret = BLKPREP_DEFER;
  			break;
  		default:
  			/*
  			 * For any other not fully online state we only allow
  			 * special commands.  In particular any user initiated
  			 * command is not allowed.
  			 */
  			if (!(req->cmd_flags & REQ_PREEMPT))
  				ret = BLKPREP_KILL;
  			break;

  		}

  	}

  	return ret;
  }
  EXPORT_SYMBOL(scsi_prep_state_check);

  int scsi_prep_return(struct request_queue *q, struct request *req, int ret)
  {
  	struct scsi_device *sdev = q->queuedata;

  	switch (ret) {
  	case BLKPREP_KILL:
  		req->errors = DID_NO_CONNECT << 16;

  		/* release the command and kill it */
  		if (req->special) {
  			struct scsi_cmnd *cmd = req->special;
  			scsi_release_buffers(cmd);
  			scsi_put_command(cmd);
  			req->special = NULL;
  		}

  		break;
  	case BLKPREP_DEFER:

  		/*

  		 * If we defer, the blk_peek_request() returns NULL, but the

  		 * queue must be restarted, so we schedule a callback to happen
  		 * shortly.

  		 */

  		if (sdev->device_busy == 0)

  			blk_delay_queue(q, SCSI_QUEUE_DELAY);

  		break;
  	default:
  		req->cmd_flags |= REQ_DONTPREP;

  	}

  	return ret;

  }

  EXPORT_SYMBOL(scsi_prep_return);

  int scsi_prep_fn(struct request_queue *q, struct request *req)

  {
  	struct scsi_device *sdev = q->queuedata;
  	int ret = BLKPREP_KILL;
  
  	if (req->cmd_type == REQ_TYPE_BLOCK_PC)
  		ret = scsi_setup_blk_pc_cmnd(sdev, req);
  	return scsi_prep_return(q, req, ret);
  }

  EXPORT_SYMBOL(scsi_prep_fn);

  
  /*
   * scsi_dev_queue_ready: if we can send requests to sdev, return 1 else
   * return 0.
   *
   * Called with the queue_lock held.
   */
  static inline int scsi_dev_queue_ready(struct request_queue *q,
  				  struct scsi_device *sdev)
  {

  	if (sdev->device_busy == 0 && sdev->device_blocked) {
  		/*
  		 * unblock after device_blocked iterates to zero
  		 */
  		if (--sdev->device_blocked == 0) {
  			SCSI_LOG_MLQUEUE(3,

  				   sdev_printk(KERN_INFO, sdev,
  				   "unblocking device at zero depth
  "));

  		} else {

  			blk_delay_queue(q, SCSI_QUEUE_DELAY);

  			return 0;
  		}
  	}

  	if (scsi_device_is_busy(sdev))

  		return 0;
  
  	return 1;
  }

  
  /*
   * scsi_target_queue_ready: checks if there we can send commands to target
   * @sdev: scsi device on starget to check.
   *
   * Called with the host lock held.
   */
  static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
  					   struct scsi_device *sdev)
  {
  	struct scsi_target *starget = scsi_target(sdev);
  
  	if (starget->single_lun) {
  		if (starget->starget_sdev_user &&
  		    starget->starget_sdev_user != sdev)
  			return 0;
  		starget->starget_sdev_user = sdev;
  	}
  
  	if (starget->target_busy == 0 && starget->target_blocked) {
  		/*
  		 * unblock after target_blocked iterates to zero
  		 */
  		if (--starget->target_blocked == 0) {
  			SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
  					 "unblocking target at zero depth
  "));

  		} else

  			return 0;

  	}
  
  	if (scsi_target_is_busy(starget)) {

  		if (list_empty(&sdev->starved_entry))

  			list_add_tail(&sdev->starved_entry,
  				      &shost->starved_list);

  		return 0;

  	}
  
  	/* We're OK to process the command, so we can't be starved */
  	if (!list_empty(&sdev->starved_entry))
  		list_del_init(&sdev->starved_entry);
  	return 1;
  }

  /*
   * scsi_host_queue_ready: if we can send requests to shost, return 1 else
   * return 0. We must end up running the queue again whenever 0 is
   * returned, else IO can hang.
   *
   * Called with host_lock held.
   */
  static inline int scsi_host_queue_ready(struct request_queue *q,
  				   struct Scsi_Host *shost,
  				   struct scsi_device *sdev)
  {

  	if (scsi_host_in_recovery(shost))

  		return 0;
  	if (shost->host_busy == 0 && shost->host_blocked) {
  		/*
  		 * unblock after host_blocked iterates to zero
  		 */
  		if (--shost->host_blocked == 0) {
  			SCSI_LOG_MLQUEUE(3,
  				printk("scsi%d unblocking host at zero depth
  ",
  					shost->host_no));
  		} else {

  			return 0;
  		}
  	}

  	if (scsi_host_is_busy(shost)) {

  		if (list_empty(&sdev->starved_entry))
  			list_add_tail(&sdev->starved_entry, &shost->starved_list);
  		return 0;
  	}
  
  	/* We're OK to process the command, so we can't be starved */
  	if (!list_empty(&sdev->starved_entry))
  		list_del_init(&sdev->starved_entry);
  
  	return 1;
  }
  
  /*

   * Busy state exporting function for request stacking drivers.
   *
   * For efficiency, no lock is taken to check the busy state of
   * shost/starget/sdev, since the returned value is not guaranteed and
   * may be changed after request stacking drivers call the function,
   * regardless of taking lock or not.
   *
   * When scsi can't dispatch I/Os anymore and needs to kill I/Os
   * (e.g. !sdev), scsi needs to return 'not busy'.
   * Otherwise, request stacking drivers may hold requests forever.
   */
  static int scsi_lld_busy(struct request_queue *q)
  {
  	struct scsi_device *sdev = q->queuedata;
  	struct Scsi_Host *shost;
  	struct scsi_target *starget;
  
  	if (!sdev)
  		return 0;
  
  	shost = sdev->host;
  	starget = scsi_target(sdev);
  
  	if (scsi_host_in_recovery(shost) || scsi_host_is_busy(shost) ||
  	    scsi_target_is_busy(starget) || scsi_device_is_busy(sdev))
  		return 1;
  
  	return 0;
  }
  
  /*

   * Kill a request for a dead device

   */

  static void scsi_kill_request(struct request *req, struct request_queue *q)

  {

  	struct scsi_cmnd *cmd = req->special;

  	struct scsi_device *sdev;
  	struct scsi_target *starget;
  	struct Scsi_Host *shost;

  	blk_start_request(req);

  	scmd_printk(KERN_INFO, cmd, "killing request
  ");

  	sdev = cmd->device;
  	starget = scsi_target(sdev);
  	shost = sdev->host;

  	scsi_init_cmd_errh(cmd);
  	cmd->result = DID_NO_CONNECT << 16;
  	atomic_inc(&cmd->device->iorequest_cnt);

  
  	/*
  	 * SCSI request completion path will do scsi_device_unbusy(),
  	 * bump busy counts.  To bump the counters, we need to dance
  	 * with the locks as normal issue path does.
  	 */
  	sdev->device_busy++;
  	spin_unlock(sdev->request_queue->queue_lock);
  	spin_lock(shost->host_lock);
  	shost->host_busy++;

  	starget->target_busy++;

  	spin_unlock(shost->host_lock);
  	spin_lock(sdev->request_queue->queue_lock);

  	blk_complete_request(req);

  }

  static void scsi_softirq_done(struct request *rq)
  {

  	struct scsi_cmnd *cmd = rq->special;
  	unsigned long wait_for = (cmd->allowed + 1) * rq->timeout;

  	int disposition;
  
  	INIT_LIST_HEAD(&cmd->eh_entry);

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

  	disposition = scsi_decide_disposition(cmd);
  	if (disposition != SUCCESS &&
  	    time_before(cmd->jiffies_at_alloc + wait_for, jiffies)) {
  		sdev_printk(KERN_ERR, cmd->device,
  			    "timing out command, waited %lus
  ",
  			    wait_for/HZ);
  		disposition = SUCCESS;
  	}
  			
  	scsi_log_completion(cmd, disposition);
  
  	switch (disposition) {
  		case SUCCESS:
  			scsi_finish_command(cmd);
  			break;
  		case NEEDS_RETRY:

  			scsi_queue_insert(cmd, SCSI_MLQUEUE_EH_RETRY);

  			break;
  		case ADD_TO_MLQUEUE:
  			scsi_queue_insert(cmd, SCSI_MLQUEUE_DEVICE_BUSY);
  			break;
  		default:
  			if (!scsi_eh_scmd_add(cmd, 0))
  				scsi_finish_command(cmd);
  	}
  }

  /*
   * Function:    scsi_request_fn()
   *
   * Purpose:     Main strategy routine for SCSI.
   *
   * Arguments:   q       - Pointer to actual queue.
   *
   * Returns:     Nothing
   *
   * Lock status: IO request lock assumed to be held when called.
   */
  static void scsi_request_fn(struct request_queue *q)
  {
  	struct scsi_device *sdev = q->queuedata;
  	struct Scsi_Host *shost;
  	struct scsi_cmnd *cmd;
  	struct request *req;
  
  	if (!sdev) {

  		while ((req = blk_peek_request(q)) != NULL)

  			scsi_kill_request(req, q);

  		return;
  	}
  
  	if(!get_device(&sdev->sdev_gendev))
  		/* We must be tearing the block queue down already */
  		return;
  
  	/*
  	 * To start with, we keep looping until the queue is empty, or until
  	 * the host is no longer able to accept any more requests.
  	 */
  	shost = sdev->host;

  	for (;;) {

  		int rtn;
  		/*
  		 * get next queueable request.  We do this early to make sure
  		 * that the request is fully prepared even if we cannot 
  		 * accept it.
  		 */

  		req = blk_peek_request(q);

  		if (!req || !scsi_dev_queue_ready(q, sdev))
  			break;
  
  		if (unlikely(!scsi_device_online(sdev))) {

  			sdev_printk(KERN_ERR, sdev,
  				    "rejecting I/O to offline device
  ");

  			scsi_kill_request(req, q);

  			continue;
  		}
  
  
  		/*
  		 * Remove the request from the request list.
  		 */
  		if (!(blk_queue_tagged(q) && !blk_queue_start_tag(q, req)))

  			blk_start_request(req);

  		sdev->device_busy++;
  
  		spin_unlock(q->queue_lock);

  		cmd = req->special;
  		if (unlikely(cmd == NULL)) {
  			printk(KERN_CRIT "impossible request in %s.
  "
  					 "please mail a stack trace to "

  					 "linux-scsi@vger.kernel.org
  ",

  					 __func__);

  			blk_dump_rq_flags(req, "foo");

  			BUG();
  		}

  		spin_lock(shost->host_lock);

  		/*
  		 * We hit this when the driver is using a host wide
  		 * tag map. For device level tag maps the queue_depth check
  		 * in the device ready fn would prevent us from trying
  		 * to allocate a tag. Since the map is a shared host resource
  		 * we add the dev to the starved list so it eventually gets
  		 * a run when a tag is freed.
  		 */

  		if (blk_queue_tagged(q) && !blk_rq_tagged(req)) {

  			if (list_empty(&sdev->starved_entry))
  				list_add_tail(&sdev->starved_entry,
  					      &shost->starved_list);
  			goto not_ready;
  		}

  		if (!scsi_target_queue_ready(shost, sdev))
  			goto not_ready;

  		if (!scsi_host_queue_ready(q, shost, sdev))
  			goto not_ready;

  
  		scsi_target(sdev)->target_busy++;

  		shost->host_busy++;
  
  		/*
  		 * XXX(hch): This is rather suboptimal, scsi_dispatch_cmd will
  		 *		take the lock again.
  		 */
  		spin_unlock_irq(shost->host_lock);

  		/*
  		 * Finally, initialize any error handling parameters, and set up
  		 * the timers for timeouts.
  		 */
  		scsi_init_cmd_errh(cmd);
  
  		/*
  		 * Dispatch the command to the low-level driver.
  		 */
  		rtn = scsi_dispatch_cmd(cmd);
  		spin_lock_irq(q->queue_lock);

  		if (rtn)
  			goto out_delay;

  	}
  
  	goto out;
  
   not_ready:
  	spin_unlock_irq(shost->host_lock);
  
  	/*
  	 * lock q, handle tag, requeue req, and decrement device_busy. We
  	 * must return with queue_lock held.
  	 *
  	 * Decrementing device_busy without checking it is OK, as all such
  	 * cases (host limits or settings) should run the queue at some
  	 * later time.
  	 */
  	spin_lock_irq(q->queue_lock);
  	blk_requeue_request(q, req);
  	sdev->device_busy--;

  out_delay:
  	if (sdev->device_busy == 0)
  		blk_delay_queue(q, SCSI_QUEUE_DELAY);
  out:

  	/* must be careful here...if we trigger the ->remove() function
  	 * we cannot be holding the q lock */
  	spin_unlock_irq(q->queue_lock);
  	put_device(&sdev->sdev_gendev);
  	spin_lock_irq(q->queue_lock);
  }
  
  u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
  {
  	struct device *host_dev;
  	u64 bounce_limit = 0xffffffff;
  
  	if (shost->unchecked_isa_dma)
  		return BLK_BOUNCE_ISA;
  	/*
  	 * Platforms with virtual-DMA translation
  	 * hardware have no practical limit.
  	 */
  	if (!PCI_DMA_BUS_IS_PHYS)
  		return BLK_BOUNCE_ANY;
  
  	host_dev = scsi_get_device(shost);
  	if (host_dev && host_dev->dma_mask)
  		bounce_limit = *host_dev->dma_mask;
  
  	return bounce_limit;
  }
  EXPORT_SYMBOL(scsi_calculate_bounce_limit);

  struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
  					 request_fn_proc *request_fn)

  {

  	struct request_queue *q;

  	struct device *dev = shost->shost_gendev.parent;

  	q = blk_init_queue(request_fn, NULL);

  	if (!q)
  		return NULL;

  	/*
  	 * this limit is imposed by hardware restrictions
  	 */

  	blk_queue_max_segments(q, min_t(unsigned short, shost->sg_tablesize,
  					SCSI_MAX_SG_CHAIN_SEGMENTS));

  	if (scsi_host_prot_dma(shost)) {
  		shost->sg_prot_tablesize =
  			min_not_zero(shost->sg_prot_tablesize,
  				     (unsigned short)SCSI_MAX_PROT_SG_SEGMENTS);
  		BUG_ON(shost->sg_prot_tablesize < shost->sg_tablesize);
  		blk_queue_max_integrity_segments(q, shost->sg_prot_tablesize);
  	}

  	blk_queue_max_hw_sectors(q, shost->max_sectors);

  	blk_queue_bounce_limit(q, scsi_calculate_bounce_limit(shost));
  	blk_queue_segment_boundary(q, shost->dma_boundary);

  	dma_set_seg_boundary(dev, shost->dma_boundary);

  	blk_queue_max_segment_size(q, dma_get_max_seg_size(dev));

  	if (!shost->use_clustering)

  		q->limits.cluster = 0;

  
  	/*
  	 * set a reasonable default alignment on word boundaries: the
  	 * host and device may alter it using
  	 * blk_queue_update_dma_alignment() later.
  	 */
  	blk_queue_dma_alignment(q, 0x03);

  	return q;
  }

  EXPORT_SYMBOL(__scsi_alloc_queue);
  
  struct request_queue *scsi_alloc_queue(struct scsi_device *sdev)
  {
  	struct request_queue *q;
  
  	q = __scsi_alloc_queue(sdev->host, scsi_request_fn);
  	if (!q)
  		return NULL;
  
  	blk_queue_prep_rq(q, scsi_prep_fn);

  	blk_queue_softirq_done(q, scsi_softirq_done);

  	blk_queue_rq_timed_out(q, scsi_times_out);

  	blk_queue_lld_busy(q, scsi_lld_busy);

  	return q;
  }

  
  void scsi_free_queue(struct request_queue *q)
  {

  	unsigned long flags;
  
  	WARN_ON(q->queuedata);
  
  	/* cause scsi_request_fn() to kill all non-finished requests */
  	spin_lock_irqsave(q->queue_lock, flags);
  	q->request_fn(q);
  	spin_unlock_irqrestore(q->queue_lock, flags);

  	blk_cleanup_queue(q);
  }
  
  /*
   * Function:    scsi_block_requests()
   *
   * Purpose:     Utility function used by low-level drivers to prevent further
   *		commands from being queued to the device.
   *
   * Arguments:   shost       - Host in question
   *
   * Returns:     Nothing
   *
   * Lock status: No locks are assumed held.
   *
   * Notes:       There is no timer nor any other means by which the requests
   *		get unblocked other than the low-level driver calling
   *		scsi_unblock_requests().
   */
  void scsi_block_requests(struct Scsi_Host *shost)
  {
  	shost->host_self_blocked = 1;
  }
  EXPORT_SYMBOL(scsi_block_requests);
  
  /*
   * Function:    scsi_unblock_requests()
   *
   * Purpose:     Utility function used by low-level drivers to allow further
   *		commands from being queued to the device.
   *
   * Arguments:   shost       - Host in question
   *
   * Returns:     Nothing
   *
   * Lock status: No locks are assumed held.
   *
   * Notes:       There is no timer nor any other means by which the requests
   *		get unblocked other than the low-level driver calling
   *		scsi_unblock_requests().
   *
   *		This is done as an API function so that changes to the
   *		internals of the scsi mid-layer won't require wholesale
   *		changes to drivers that use this feature.
   */
  void scsi_unblock_requests(struct Scsi_Host *shost)
  {
  	shost->host_self_blocked = 0;
  	scsi_run_host_queues(shost);
  }
  EXPORT_SYMBOL(scsi_unblock_requests);
  
  int __init scsi_init_queue(void)
  {
  	int i;

  	scsi_sdb_cache = kmem_cache_create("scsi_data_buffer",
  					   sizeof(struct scsi_data_buffer),
  					   0, 0, NULL);
  	if (!scsi_sdb_cache) {
  		printk(KERN_ERR "SCSI: can't init scsi sdb cache
  ");

  		return -ENOMEM;

  	}

  	for (i = 0; i < SG_MEMPOOL_NR; i++) {
  		struct scsi_host_sg_pool *sgp = scsi_sg_pools + i;
  		int size = sgp->size * sizeof(struct scatterlist);
  
  		sgp->slab = kmem_cache_create(sgp->name, size, 0,

  				SLAB_HWCACHE_ALIGN, NULL);

  		if (!sgp->slab) {
  			printk(KERN_ERR "SCSI: can't init sg slab %s
  ",
  					sgp->name);

  			goto cleanup_sdb;

  		}

  		sgp->pool = mempool_create_slab_pool(SG_MEMPOOL_SIZE,
  						     sgp->slab);

  		if (!sgp->pool) {
  			printk(KERN_ERR "SCSI: can't init sg mempool %s
  ",
  					sgp->name);

  			goto cleanup_sdb;

  		}
  	}
  
  	return 0;

  cleanup_sdb:

  	for (i = 0; i < SG_MEMPOOL_NR; i++) {
  		struct scsi_host_sg_pool *sgp = scsi_sg_pools + i;
  		if (sgp->pool)
  			mempool_destroy(sgp->pool);
  		if (sgp->slab)
  			kmem_cache_destroy(sgp->slab);
  	}

  	kmem_cache_destroy(scsi_sdb_cache);

  
  	return -ENOMEM;

  }
  
  void scsi_exit_queue(void)
  {
  	int i;

  	kmem_cache_destroy(scsi_sdb_cache);

  	for (i = 0; i < SG_MEMPOOL_NR; i++) {
  		struct scsi_host_sg_pool *sgp = scsi_sg_pools + i;
  		mempool_destroy(sgp->pool);
  		kmem_cache_destroy(sgp->slab);
  	}
  }

  
  /**
   *	scsi_mode_select - issue a mode select
   *	@sdev:	SCSI device to be queried
   *	@pf:	Page format bit (1 == standard, 0 == vendor specific)
   *	@sp:	Save page bit (0 == don't save, 1 == save)
   *	@modepage: mode page being requested
   *	@buffer: request buffer (may not be smaller than eight bytes)
   *	@len:	length of request buffer.
   *	@timeout: command timeout
   *	@retries: number of retries before failing
   *	@data: returns a structure abstracting the mode header data

   *	@sshdr: place to put sense data (or NULL if no sense to be collected).

   *		must be SCSI_SENSE_BUFFERSIZE big.
   *
   *	Returns zero if successful; negative error number or scsi
   *	status on error
   *
   */
  int
  scsi_mode_select(struct scsi_device *sdev, int pf, int sp, int modepage,
  		 unsigned char *buffer, int len, int timeout, int retries,
  		 struct scsi_mode_data *data, struct scsi_sense_hdr *sshdr)
  {
  	unsigned char cmd[10];
  	unsigned char *real_buffer;
  	int ret;
  
  	memset(cmd, 0, sizeof(cmd));
  	cmd[1] = (pf ? 0x10 : 0) | (sp ? 0x01 : 0);
  
  	if (sdev->use_10_for_ms) {
  		if (len > 65535)
  			return -EINVAL;
  		real_buffer = kmalloc(8 + len, GFP_KERNEL);
  		if (!real_buffer)
  			return -ENOMEM;
  		memcpy(real_buffer + 8, buffer, len);
  		len += 8;
  		real_buffer[0] = 0;
  		real_buffer[1] = 0;
  		real_buffer[2] = data->medium_type;
  		real_buffer[3] = data->device_specific;
  		real_buffer[4] = data->longlba ? 0x01 : 0;
  		real_buffer[5] = 0;
  		real_buffer[6] = data->block_descriptor_length >> 8;
  		real_buffer[7] = data->block_descriptor_length;
  
  		cmd[0] = MODE_SELECT_10;
  		cmd[7] = len >> 8;
  		cmd[8] = len;
  	} else {
  		if (len > 255 || data->block_descriptor_length > 255 ||
  		    data->longlba)
  			return -EINVAL;
  
  		real_buffer = kmalloc(4 + len, GFP_KERNEL);
  		if (!real_buffer)
  			return -ENOMEM;
  		memcpy(real_buffer + 4, buffer, len);
  		len += 4;
  		real_buffer[0] = 0;
  		real_buffer[1] = data->medium_type;
  		real_buffer[2] = data->device_specific;
  		real_buffer[3] = data->block_descriptor_length;
  		
  
  		cmd[0] = MODE_SELECT;
  		cmd[4] = len;
  	}
  
  	ret = scsi_execute_req(sdev, cmd, DMA_TO_DEVICE, real_buffer, len,

  			       sshdr, timeout, retries, NULL);

  	kfree(real_buffer);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(scsi_mode_select);

  /**

   *	scsi_mode_sense - issue a mode sense, falling back from 10 to six bytes if necessary.

   *	@sdev:	SCSI device to be queried

   *	@dbd:	set if mode sense will allow block descriptors to be returned
   *	@modepage: mode page being requested
   *	@buffer: request buffer (may not be smaller than eight bytes)
   *	@len:	length of request buffer.
   *	@timeout: command timeout
   *	@retries: number of retries before failing
   *	@data: returns a structure abstracting the mode header data

   *	@sshdr: place to put sense data (or NULL if no sense to be collected).

   *		must be SCSI_SENSE_BUFFERSIZE big.

   *
   *	Returns zero if unsuccessful, or the header offset (either 4
   *	or 8 depending on whether a six or ten byte command was
   *	issued) if successful.

   */

  int

  scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,

  		  unsigned char *buffer, int len, int timeout, int retries,

  		  struct scsi_mode_data *data, struct scsi_sense_hdr *sshdr)
  {

  	unsigned char cmd[12];
  	int use_10_for_ms;
  	int header_length;

  	int result;

  	struct scsi_sense_hdr my_sshdr;

  
  	memset(data, 0, sizeof(*data));
  	memset(&cmd[0], 0, 12);
  	cmd[1] = dbd & 0x18;	/* allows DBD and LLBA bits */
  	cmd[2] = modepage;

  	/* caller might not be interested in sense, but we need it */
  	if (!sshdr)
  		sshdr = &my_sshdr;

   retry:

  	use_10_for_ms = sdev->use_10_for_ms;

  
  	if (use_10_for_ms) {
  		if (len < 8)
  			len = 8;
  
  		cmd[0] = MODE_SENSE_10;
  		cmd[8] = len;
  		header_length = 8;
  	} else {
  		if (len < 4)
  			len = 4;
  
  		cmd[0] = MODE_SENSE;
  		cmd[4] = len;
  		header_length = 4;
  	}

  	memset(buffer, 0, len);

  	result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer, len,

  				  sshdr, timeout, retries, NULL);

  
  	/* This code looks awful: what it's doing is making sure an
  	 * ILLEGAL REQUEST sense return identifies the actual command
  	 * byte as the problem.  MODE_SENSE commands can return
  	 * ILLEGAL REQUEST if the code page isn't supported */

  	if (use_10_for_ms && !scsi_status_is_good(result) &&
  	    (driver_byte(result) & DRIVER_SENSE)) {

  		if (scsi_sense_valid(sshdr)) {
  			if ((sshdr->sense_key == ILLEGAL_REQUEST) &&
  			    (sshdr->asc == 0x20) && (sshdr->ascq == 0)) {

  				/* 
  				 * Invalid command operation code
  				 */

  				sdev->use_10_for_ms = 0;

  				goto retry;
  			}
  		}
  	}

  	if(scsi_status_is_good(result)) {

  		if (unlikely(buffer[0] == 0x86 && buffer[1] == 0x0b &&
  			     (modepage == 6 || modepage == 8))) {
  			/* Initio breakage? */
  			header_length = 0;
  			data->length = 13;
  			data->medium_type = 0;
  			data->device_specific = 0;
  			data->longlba = 0;
  			data->block_descriptor_length = 0;
  		} else if(use_10_for_ms) {

  			data->length = buffer[0]*256 + buffer[1] + 2;
  			data->medium_type = buffer[2];
  			data->device_specific = buffer[3];
  			data->longlba = buffer[4] & 0x01;
  			data->block_descriptor_length = buffer[6]*256
  				+ buffer[7];
  		} else {
  			data->length = buffer[0] + 1;
  			data->medium_type = buffer[1];
  			data->device_specific = buffer[2];
  			data->block_descriptor_length = buffer[3];
  		}

  		data->header_length = header_length;

  	}

  	return result;

  }
  EXPORT_SYMBOL(scsi_mode_sense);

  /**
   *	scsi_test_unit_ready - test if unit is ready
   *	@sdev:	scsi device to change the state of.
   *	@timeout: command timeout
   *	@retries: number of retries before failing
   *	@sshdr_external: Optional pointer to struct scsi_sense_hdr for
   *		returning sense. Make sure that this is cleared before passing
   *		in.
   *
   *	Returns zero if unsuccessful or an error if TUR failed.  For

   *	removable media, UNIT_ATTENTION sets ->changed flag.

   **/

  int

  scsi_test_unit_ready(struct scsi_device *sdev, int timeout, int retries,
  		     struct scsi_sense_hdr *sshdr_external)

  {

  	char cmd[] = {
  		TEST_UNIT_READY, 0, 0, 0, 0, 0,
  	};

  	struct scsi_sense_hdr *sshdr;

  	int result;

  
  	if (!sshdr_external)
  		sshdr = kzalloc(sizeof(*sshdr), GFP_KERNEL);
  	else
  		sshdr = sshdr_external;
  
  	/* try to eat the UNIT_ATTENTION if there are enough retries */
  	do {
  		result = scsi_execute_req(sdev, cmd, DMA_NONE, NULL, 0, sshdr,

  					  timeout, retries, NULL);

  		if (sdev->removable && scsi_sense_valid(sshdr) &&
  		    sshdr->sense_key == UNIT_ATTENTION)
  			sdev->changed = 1;
  	} while (scsi_sense_valid(sshdr) &&
  		 sshdr->sense_key == UNIT_ATTENTION && --retries);

  	if (!sshdr_external)
  		kfree(sshdr);

  	return result;
  }
  EXPORT_SYMBOL(scsi_test_unit_ready);
  
  /**

   *	scsi_device_set_state - Take the given device through the device state model.

   *	@sdev:	scsi device to change the state of.
   *	@state:	state to change to.
   *
   *	Returns zero if unsuccessful or an error if the requested 
   *	transition is illegal.

   */

  int
  scsi_device_set_state(struct scsi_device *sdev, enum scsi_device_state state)
  {
  	enum scsi_device_state oldstate = sdev->sdev_state;
  
  	if (state == oldstate)
  		return 0;
  
  	switch (state) {
  	case SDEV_CREATED:

  		switch (oldstate) {
  		case SDEV_CREATED_BLOCK:
  			break;
  		default:
  			goto illegal;
  		}
  		break;

  			
  	case SDEV_RUNNING:
  		switch (oldstate) {
  		case SDEV_CREATED:
  		case SDEV_OFFLINE:
  		case SDEV_QUIESCE:
  		case SDEV_BLOCK:
  			break;
  		default:
  			goto illegal;
  		}
  		break;
  
  	case SDEV_QUIESCE:
  		switch (oldstate) {
  		case SDEV_RUNNING:
  		case SDEV_OFFLINE:
  			break;
  		default:
  			goto illegal;
  		}
  		break;
  
  	case SDEV_OFFLINE:
  		switch (oldstate) {
  		case SDEV_CREATED:
  		case SDEV_RUNNING:
  		case SDEV_QUIESCE:
  		case SDEV_BLOCK:
  			break;
  		default:
  			goto illegal;
  		}
  		break;
  
  	case SDEV_BLOCK:
  		switch (oldstate) {

  		case SDEV_RUNNING:

  		case SDEV_CREATED_BLOCK:
  			break;
  		default:
  			goto illegal;
  		}
  		break;
  
  	case SDEV_CREATED_BLOCK:
  		switch (oldstate) {
  		case SDEV_CREATED:

  			break;
  		default:
  			goto illegal;
  		}
  		break;
  
  	case SDEV_CANCEL:
  		switch (oldstate) {
  		case SDEV_CREATED:
  		case SDEV_RUNNING:

  		case SDEV_QUIESCE:

  		case SDEV_OFFLINE:
  		case SDEV_BLOCK:
  			break;
  		default:
  			goto illegal;
  		}
  		break;
  
  	case SDEV_DEL:
  		switch (oldstate) {

  		case SDEV_CREATED:
  		case SDEV_RUNNING:
  		case SDEV_OFFLINE:

  		case SDEV_CANCEL:
  			break;
  		default:
  			goto illegal;
  		}
  		break;
  
  	}
  	sdev->sdev_state = state;
  	return 0;
  
   illegal:
  	SCSI_LOG_ERROR_RECOVERY(1, 

  				sdev_printk(KERN_ERR, sdev,
  					    "Illegal state transition %s->%s
  ",
  					    scsi_device_state_name(oldstate),
  					    scsi_device_state_name(state))

  				);
  	return -EINVAL;
  }
  EXPORT_SYMBOL(scsi_device_set_state);
  
  /**

   * 	sdev_evt_emit - emit a single SCSI device uevent
   *	@sdev: associated SCSI device
   *	@evt: event to emit
   *
   *	Send a single uevent (scsi_event) to the associated scsi_device.
   */
  static void scsi_evt_emit(struct scsi_device *sdev, struct scsi_event *evt)
  {
  	int idx = 0;
  	char *envp[3];
  
  	switch (evt->evt_type) {
  	case SDEV_EVT_MEDIA_CHANGE:
  		envp[idx++] = "SDEV_MEDIA_CHANGE=1";
  		break;
  
  	default:
  		/* do nothing */
  		break;
  	}
  
  	envp[idx++] = NULL;
  
  	kobject_uevent_env(&sdev->sdev_gendev.kobj, KOBJ_CHANGE, envp);
  }
  
  /**
   * 	sdev_evt_thread - send a uevent for each scsi event
   *	@work: work struct for scsi_device
   *
   *	Dispatch queued events to their associated scsi_device kobjects
   *	as uevents.
   */
  void scsi_evt_thread(struct work_struct *work)
  {
  	struct scsi_device *sdev;
  	LIST_HEAD(event_list);
  
  	sdev = container_of(work, struct scsi_device, event_work);
  
  	while (1) {
  		struct scsi_event *evt;
  		struct list_head *this, *tmp;
  		unsigned long flags;
  
  		spin_lock_irqsave(&sdev->list_lock, flags);
  		list_splice_init(&sdev->event_list, &event_list);
  		spin_unlock_irqrestore(&sdev->list_lock, flags);
  
  		if (list_empty(&event_list))
  			break;
  
  		list_for_each_safe(this, tmp, &event_list) {
  			evt = list_entry(this, struct scsi_event, node);
  			list_del(&evt->node);
  			scsi_evt_emit(sdev, evt);
  			kfree(evt);
  		}
  	}
  }
  
  /**
   * 	sdev_evt_send - send asserted event to uevent thread
   *	@sdev: scsi_device event occurred on
   *	@evt: event to send
   *
   *	Assert scsi device event asynchronously.
   */
  void sdev_evt_send(struct scsi_device *sdev, struct scsi_event *evt)
  {
  	unsigned long flags;