Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 2023 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
new file mode 100644
index 00000000000..7cbc4127fb5
--- /dev/null
+++ b/drivers/scsi/scsi_lib.c
@@ -0,0 +1,2023 @@
+/*
+ *  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/blkdev.h>
+#include <linux/completion.h>
+#include <linux/kernel.h>
+#include <linux/mempool.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/pci.h>
+#include <linux/delay.h>
+
+#include <scsi/scsi.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_request.h>
+
+#include "scsi_priv.h"
+#include "scsi_logging.h"
+
+
+#define SG_MEMPOOL_NR		(sizeof(scsi_sg_pools)/sizeof(struct scsi_host_sg_pool))
+#define SG_MEMPOOL_SIZE		32
+
+struct scsi_host_sg_pool {
+	size_t		size;
+	char		*name; 
+	kmem_cache_t	*slab;
+	mempool_t	*pool;
+};
+
+#if (SCSI_MAX_PHYS_SEGMENTS < 32)
+#error SCSI_MAX_PHYS_SEGMENTS is too small
+#endif
+
+#define SP(x) { x, "sgpool-" #x } 
+struct scsi_host_sg_pool scsi_sg_pools[] = { 
+	SP(8),
+	SP(16),
+	SP(32),
+#if (SCSI_MAX_PHYS_SEGMENTS > 32)
+	SP(64),
+#if (SCSI_MAX_PHYS_SEGMENTS > 64)
+	SP(128),
+#if (SCSI_MAX_PHYS_SEGMENTS > 128)
+	SP(256),
+#if (SCSI_MAX_PHYS_SEGMENTS > 256)
+#error SCSI_MAX_PHYS_SEGMENTS is too large
+#endif
+#endif
+#endif
+#endif
+}; 	
+#undef SP
+
+
+/*
+ * Function:    scsi_insert_special_req()
+ *
+ * Purpose:     Insert pre-formed request into request queue.
+ *
+ * Arguments:   sreq	- request that is ready to be queued.
+ *              at_head	- boolean.  True if we should insert at head
+ *                        of queue, false if we should insert at tail.
+ *
+ * Lock status: Assumed that lock is not held upon entry.
+ *
+ * Returns:     Nothing
+ *
+ * Notes:       This function is called from character device and from
+ *              ioctl types of functions where the caller knows exactly
+ *              what SCSI command needs to be issued.   The idea is that
+ *              we merely inject the command into the queue (at the head
+ *              for now), and then call the queue request function to actually
+ *              process it.
+ */
+int scsi_insert_special_req(struct scsi_request *sreq, int at_head)
+{
+	/*
+	 * Because users of this function are apt to reuse requests with no
+	 * modification, we have to sanitise the request flags here
+	 */
+	sreq->sr_request->flags &= ~REQ_DONTPREP;
+	blk_insert_request(sreq->sr_device->request_queue, sreq->sr_request,
+		       	   at_head, sreq, 0);
+	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)
+{
+	struct Scsi_Host *host = cmd->device->host;
+	struct scsi_device *device = cmd->device;
+
+	SCSI_LOG_MLQUEUE(1,
+		 printk("Inserting command %p into mlqueue\n", cmd));
+
+	/*
+	 * We are inserting the command into the ml queue.  First, we
+	 * cancel the timer, so it doesn't time out.
+	 */
+	scsi_delete_timer(cmd);
+
+	/*
+	 * Next, 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.
+	 */
+	if (reason == SCSI_MLQUEUE_HOST_BUSY)
+		host->host_blocked = host->max_host_blocked;
+	else if (reason == SCSI_MLQUEUE_DEVICE_BUSY)
+		device->device_blocked = device->max_device_blocked;
+
+	/*
+	 * Register the fact that we own the thing for now.
+	 */
+	cmd->state = SCSI_STATE_MLQUEUE;
+	cmd->owner = SCSI_OWNER_MIDLEVEL;
+
+	/*
+	 * Decrement the counters, since these commands are no longer
+	 * active on the host/device.
+	 */
+	scsi_device_unbusy(device);
+
+	/*
+	 * Insert this command at the head of the queue for it's device.
+	 * It will go before all other commands that are already in the queue.
+	 *
+	 * NOTE: there is magic here about the way the queue is plugged if
+	 * we have no outstanding commands.
+	 * 
+	 * Although this *doesn't* plug the queue, it does call the request
+	 * function.  The SCSI request function detects the blocked condition
+	 * and plugs the queue appropriately.
+	 */
+	blk_insert_request(device->request_queue, cmd->request, 1, cmd, 1);
+	return 0;
+}
+
+/*
+ * Function:    scsi_do_req
+ *
+ * Purpose:     Queue a SCSI request
+ *
+ * Arguments:   sreq	  - command descriptor.
+ *              cmnd      - actual SCSI command to be performed.
+ *              buffer    - data buffer.
+ *              bufflen   - size of data buffer.
+ *              done      - completion function to be run.
+ *              timeout   - how long to let it run before timeout.
+ *              retries   - number of retries we allow.
+ *
+ * Lock status: No locks held upon entry.
+ *
+ * Returns:     Nothing.
+ *
+ * Notes:	This function is only used for queueing requests for things
+ *		like ioctls and character device requests - this is because
+ *		we essentially just inject a request into the queue for the
+ *		device.
+ *
+ *		In order to support the scsi_device_quiesce function, we
+ *		now inject requests on the *head* of the device queue
+ *		rather than the tail.
+ */
+void scsi_do_req(struct scsi_request *sreq, const void *cmnd,
+		 void *buffer, unsigned bufflen,
+		 void (*done)(struct scsi_cmnd *),
+		 int timeout, int retries)
+{
+	/*
+	 * If the upper level driver is reusing these things, then
+	 * we should release the low-level block now.  Another one will
+	 * be allocated later when this request is getting queued.
+	 */
+	__scsi_release_request(sreq);
+
+	/*
+	 * Our own function scsi_done (which marks the host as not busy,
+	 * disables the timeout counter, etc) will be called by us or by the
+	 * scsi_hosts[host].queuecommand() function needs to also call
+	 * the completion function for the high level driver.
+	 */
+	memcpy(sreq->sr_cmnd, cmnd, sizeof(sreq->sr_cmnd));
+	sreq->sr_bufflen = bufflen;
+	sreq->sr_buffer = buffer;
+	sreq->sr_allowed = retries;
+	sreq->sr_done = done;
+	sreq->sr_timeout_per_command = timeout;
+
+	if (sreq->sr_cmd_len == 0)
+		sreq->sr_cmd_len = COMMAND_SIZE(sreq->sr_cmnd[0]);
+
+	/*
+	 * head injection *required* here otherwise quiesce won't work
+	 */
+	scsi_insert_special_req(sreq, 1);
+}
+EXPORT_SYMBOL(scsi_do_req);
+
+static void scsi_wait_done(struct scsi_cmnd *cmd)
+{
+	struct request *req = cmd->request;
+	struct request_queue *q = cmd->device->request_queue;
+	unsigned long flags;
+
+	req->rq_status = RQ_SCSI_DONE;	/* Busy, but indicate request done */
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	if (blk_rq_tagged(req))
+		blk_queue_end_tag(q, req);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	if (req->waiting)
+		complete(req->waiting);
+}
+
+/* This is the end routine we get to if a command was never attached
+ * to the request.  Simply complete the request without changing
+ * rq_status; this will cause a DRIVER_ERROR. */
+static void scsi_wait_req_end_io(struct request *req)
+{
+	BUG_ON(!req->waiting);
+
+	complete(req->waiting);
+}
+
+void scsi_wait_req(struct scsi_request *sreq, const void *cmnd, void *buffer,
+		   unsigned bufflen, int timeout, int retries)
+{
+	DECLARE_COMPLETION(wait);
+	
+	sreq->sr_request->waiting = &wait;
+	sreq->sr_request->rq_status = RQ_SCSI_BUSY;
+	sreq->sr_request->end_io = scsi_wait_req_end_io;
+	scsi_do_req(sreq, cmnd, buffer, bufflen, scsi_wait_done,
+			timeout, retries);
+	wait_for_completion(&wait);
+	sreq->sr_request->waiting = NULL;
+	if (sreq->sr_request->rq_status != RQ_SCSI_DONE)
+		sreq->sr_result |= (DRIVER_ERROR << 24);
+
+	__scsi_release_request(sreq);
+}
+EXPORT_SYMBOL(scsi_wait_req);
+
+/*
+ * Function:    scsi_init_cmd_errh()
+ *
+ * Purpose:     Initialize cmd fields related to error handling.
+ *
+ * Arguments:   cmd	- command that is ready to be queued.
+ *
+ * Returns:     Nothing
+ *
+ * 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 int scsi_init_cmd_errh(struct scsi_cmnd *cmd)
+{
+	cmd->owner = SCSI_OWNER_MIDLEVEL;
+	cmd->serial_number = 0;
+	cmd->serial_number_at_timeout = 0;
+	cmd->abort_reason = 0;
+
+	memset(cmd->sense_buffer, 0, sizeof cmd->sense_buffer);
+
+	if (cmd->cmd_len == 0)
+		cmd->cmd_len = COMMAND_SIZE(cmd->cmnd[0]);
+
+	/*
+	 * We need saved copies of a number of fields - this is because
+	 * error handling may need to overwrite these with different values
+	 * to run different commands, and once error handling is complete,
+	 * we will need to restore these values prior to running the actual
+	 * command.
+	 */
+	cmd->old_use_sg = cmd->use_sg;
+	cmd->old_cmd_len = cmd->cmd_len;
+	cmd->sc_old_data_direction = cmd->sc_data_direction;
+	cmd->old_underflow = cmd->underflow;
+	memcpy(cmd->data_cmnd, cmd->cmnd, sizeof(cmd->cmnd));
+	cmd->buffer = cmd->request_buffer;
+	cmd->bufflen = cmd->request_bufflen;
+	cmd->internal_timeout = NORMAL_TIMEOUT;
+	cmd->abort_reason = 0;
+
+	return 1;
+}
+
+/*
+ * Function:   scsi_setup_cmd_retry()
+ *
+ * Purpose:    Restore the command state for a retry
+ *
+ * Arguments:  cmd	- command to be restored
+ *
+ * Returns:    Nothing
+ *
+ * Notes:      Immediately prior to retrying a command, we need
+ *             to restore certain fields that we saved above.
+ */
+void scsi_setup_cmd_retry(struct scsi_cmnd *cmd)
+{
+	memcpy(cmd->cmnd, cmd->data_cmnd, sizeof(cmd->data_cmnd));
+	cmd->request_buffer = cmd->buffer;
+	cmd->request_bufflen = cmd->bufflen;
+	cmd->use_sg = cmd->old_use_sg;
+	cmd->cmd_len = cmd->old_cmd_len;
+	cmd->sc_data_direction = cmd->sc_old_data_direction;
+	cmd->underflow = cmd->old_underflow;
+}
+
+void scsi_device_unbusy(struct scsi_device *sdev)
+{
+	struct Scsi_Host *shost = sdev->host;
+	unsigned long flags;
+
+	spin_lock_irqsave(shost->host_lock, flags);
+	shost->host_busy--;
+	if (unlikely(test_bit(SHOST_RECOVERY, &shost->shost_state) &&
+		     shost->host_failed))
+		scsi_eh_wakeup(shost);
+	spin_unlock(shost->host_lock);
+	spin_lock(&sdev->sdev_lock);
+	sdev->device_busy--;
+	spin_unlock_irqrestore(&sdev->sdev_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);
+}
+
+/*
+ * 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 = sdev->host;
+	unsigned long flags;
+
+	if (sdev->single_lun)
+		scsi_single_lun_run(sdev);
+
+	spin_lock_irqsave(shost->host_lock, flags);
+	while (!list_empty(&shost->starved_list) &&
+	       !shost->host_blocked && !shost->host_self_blocked &&
+		!((shost->can_queue > 0) &&
+		  (shost->host_busy >= shost->can_queue))) {
+		/*
+		 * 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.
+		 */
+		sdev = list_entry(shost->starved_list.next,
+					  struct scsi_device, starved_entry);
+		list_del_init(&sdev->starved_entry);
+		spin_unlock_irqrestore(shost->host_lock, flags);
+
+		blk_run_queue(sdev->request_queue);
+
+		spin_lock_irqsave(shost->host_lock, flags);
+		if (unlikely(!list_empty(&sdev->starved_entry)))
+			/*
+			 * sdev lost a race, and was put back on the
+			 * starved list. This is unlikely but without this
+			 * in theory we could loop forever.
+			 */
+			break;
+	}
+	spin_unlock_irqrestore(shost->host_lock, flags);
+
+	blk_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.
+ */
+static void scsi_requeue_command(struct request_queue *q, struct scsi_cmnd *cmd)
+{
+	cmd->request->flags &= ~REQ_DONTPREP;
+	blk_insert_request(q, cmd->request, 1, cmd, 1);
+
+	scsi_run_queue(q);
+}
+
+void scsi_next_command(struct scsi_cmnd *cmd)
+{
+	struct request_queue *q = cmd->device->request_queue;
+
+	scsi_put_command(cmd);
+	scsi_run_queue(q);
+}
+
+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);
+}
+
+/*
+ * 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.
+ *              uptodate - 1 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 done or 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.
+ */
+static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int uptodate,
+					  int bytes, int requeue)
+{
+	request_queue_t *q = cmd->device->request_queue;
+	struct request *req = cmd->request;
+	unsigned long flags;
+
+	/*
+	 * If there are blocks left over at the end, set up the command
+	 * to queue the remainder of them.
+	 */
+	if (end_that_request_chunk(req, uptodate, bytes)) {
+		int leftover = (req->hard_nr_sectors << 9);
+
+		if (blk_pc_request(req))
+			leftover = req->data_len;
+
+		/* kill remainder if no retrys */
+		if (!uptodate && blk_noretry_request(req))
+			end_that_request_chunk(req, 0, leftover);
+		else {
+			if (requeue)
+				/*
+				 * Bleah.  Leftovers again.  Stick the
+				 * leftovers in the front of the
+				 * queue, and goose the queue again.
+				 */
+				scsi_requeue_command(q, cmd);
+
+			return cmd;
+		}
+	}
+
+	add_disk_randomness(req->rq_disk);
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	if (blk_rq_tagged(req))
+		blk_queue_end_tag(q, req);
+	end_that_request_last(req);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	/*
+	 * This will goose the queue request function at the end, so we don't
+	 * need to worry about launching another command.
+	 */
+	scsi_next_command(cmd);
+	return NULL;
+}
+
+static struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, int gfp_mask)
+{
+	struct scsi_host_sg_pool *sgp;
+	struct scatterlist *sgl;
+
+	BUG_ON(!cmd->use_sg);
+
+	switch (cmd->use_sg) {
+	case 1 ... 8:
+		cmd->sglist_len = 0;
+		break;
+	case 9 ... 16:
+		cmd->sglist_len = 1;
+		break;
+	case 17 ... 32:
+		cmd->sglist_len = 2;
+		break;
+#if (SCSI_MAX_PHYS_SEGMENTS > 32)
+	case 33 ... 64:
+		cmd->sglist_len = 3;
+		break;
+#if (SCSI_MAX_PHYS_SEGMENTS > 64)
+	case 65 ... 128:
+		cmd->sglist_len = 4;
+		break;
+#if (SCSI_MAX_PHYS_SEGMENTS  > 128)
+	case 129 ... 256:
+		cmd->sglist_len = 5;
+		break;
+#endif
+#endif
+#endif
+	default:
+		return NULL;
+	}
+
+	sgp = scsi_sg_pools + cmd->sglist_len;
+	sgl = mempool_alloc(sgp->pool, gfp_mask);
+	if (sgl)
+		memset(sgl, 0, sgp->size);
+	return sgl;
+}
+
+static void scsi_free_sgtable(struct scatterlist *sgl, int index)
+{
+	struct scsi_host_sg_pool *sgp;
+
+	BUG_ON(index > SG_MEMPOOL_NR);
+
+	sgp = scsi_sg_pools + index;
+	mempool_free(sgl, sgp->pool);
+}
+
+/*
+ * 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.
+ */
+static void scsi_release_buffers(struct scsi_cmnd *cmd)
+{
+	struct request *req = cmd->request;
+
+	/*
+	 * Free up any indirection buffers we allocated for DMA purposes. 
+	 */
+	if (cmd->use_sg)
+		scsi_free_sgtable(cmd->request_buffer, cmd->sglist_len);
+	else if (cmd->request_buffer != req->buffer)
+		kfree(cmd->request_buffer);
+
+	/*
+	 * Zero these out.  They now point to freed memory, and it is
+	 * dangerous to hang onto the pointers.
+	 */
+	cmd->buffer  = NULL;
+	cmd->bufflen = 0;
+	cmd->request_buffer = NULL;
+	cmd->request_bufflen = 0;
+}
+
+/*
+ * 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 do one of several things here:
+ *
+ *		a) 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
+ *		   scsi_end_request will directly goose the queue.
+ *
+ *		b) We can just use scsi_requeue_command() here.  This would
+ *		   be used if we just wanted to retry, for example.
+ */
+void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes,
+			unsigned int block_bytes)
+{
+	int result = cmd->result;
+	int this_count = cmd->bufflen;
+	request_queue_t *q = cmd->device->request_queue;
+	struct request *req = cmd->request;
+	int clear_errors = 1;
+	struct scsi_sense_hdr sshdr;
+	int sense_valid = 0;
+	int sense_deferred = 0;
+
+	if (blk_complete_barrier_rq(q, req, good_bytes >> 9))
+		return;
+
+	/*
+	 * Free up any indirection buffers we allocated for DMA purposes. 
+	 * For the case of a READ, we need to copy the data out of the
+	 * bounce buffer and into the real buffer.
+	 */
+	if (cmd->use_sg)
+		scsi_free_sgtable(cmd->buffer, cmd->sglist_len);
+	else if (cmd->buffer != req->buffer) {
+		if (rq_data_dir(req) == READ) {
+			unsigned long flags;
+			char *to = bio_kmap_irq(req->bio, &flags);
+			memcpy(to, cmd->buffer, cmd->bufflen);
+			bio_kunmap_irq(to, &flags);
+		}
+		kfree(cmd->buffer);
+	}
+
+	if (result) {
+		sense_valid = scsi_command_normalize_sense(cmd, &sshdr);
+		if (sense_valid)
+			sense_deferred = scsi_sense_is_deferred(&sshdr);
+	}
+	if (blk_pc_request(req)) { /* SG_IO ioctl from block level */
+		req->errors = result;
+		if (result) {
+			clear_errors = 0;
+			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;
+			}
+		} else
+			req->data_len = cmd->resid;
+	}
+
+	/*
+	 * Zero these out.  They now point to freed memory, and it is
+	 * dangerous to hang onto the pointers.
+	 */
+	cmd->buffer  = NULL;
+	cmd->bufflen = 0;
+	cmd->request_buffer = NULL;
+	cmd->request_bufflen = 0;
+
+	/*
+	 * Next deal with any sectors which we were able to correctly
+	 * handle.
+	 */
+	if (good_bytes >= 0) {
+		SCSI_LOG_HLCOMPLETE(1, printk("%ld sectors total, %d bytes done.\n",
+					      req->nr_sectors, good_bytes));
+		SCSI_LOG_HLCOMPLETE(1, printk("use_sg is %d\n", cmd->use_sg));
+
+		if (clear_errors)
+			req->errors = 0;
+		/*
+		 * If multiple sectors are requested in one buffer, then
+		 * they will have been finished off by the first command.
+		 * If not, then we have a multi-buffer command.
+		 *
+		 * If block_bytes != 0, it means we had a medium error
+		 * of some sort, and that we want to mark some number of
+		 * sectors as not uptodate.  Thus we want to inhibit
+		 * requeueing right here - we will requeue down below
+		 * when we handle the bad sectors.
+		 */
+		cmd = scsi_end_request(cmd, 1, good_bytes, result == 0);
+
+		/*
+		 * If the command completed without error, then either finish off the
+		 * rest of the command, or start a new one.
+		 */
+		if (result == 0 || cmd == NULL ) {
+			return;
+		}
+	}
+	/*
+	 * Now, if we were good little boys and girls, Santa left us a request
+	 * sense buffer.  We can extract information from this, so we
+	 * can choose a block to remap, etc.
+	 */
+	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;
+				cmd = scsi_end_request(cmd, 0,
+						this_count, 1);
+				return;
+			} else {
+				/*
+				* Must have been a power glitch, or a
+				* bus reset.  Could not have been a
+				* media change, so we just retry the
+				* request and see what happens.  
+				*/
+				scsi_requeue_command(q, cmd);
+				return;
+			}
+			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 &&
+			    (cmd->cmnd[0] == READ_10 ||
+			     cmd->cmnd[0] == WRITE_10)) {
+				cmd->device->use_10_for_rw = 0;
+				/*
+				 * This will cause a retry with a 6-byte
+				 * command.
+				 */
+				scsi_requeue_command(q, cmd);
+				result = 0;
+			} else {
+				cmd = scsi_end_request(cmd, 0, this_count, 1);
+				return;
+			}
+			break;
+		case NOT_READY:
+			/*
+			 * If the device is in the process of becoming ready,
+			 * retry.
+			 */
+			if (sshdr.asc == 0x04 && sshdr.ascq == 0x01) {
+				scsi_requeue_command(q, cmd);
+				return;
+			}
+			printk(KERN_INFO "Device %s not ready.\n",
+			       req->rq_disk ? req->rq_disk->disk_name : "");
+			cmd = scsi_end_request(cmd, 0, this_count, 1);
+			return;
+		case VOLUME_OVERFLOW:
+			printk(KERN_INFO "Volume overflow <%d %d %d %d> CDB: ",
+			       cmd->device->host->host_no,
+			       (int)cmd->device->channel,
+			       (int)cmd->device->id, (int)cmd->device->lun);
+			__scsi_print_command(cmd->data_cmnd);
+			scsi_print_sense("", cmd);
+			cmd = scsi_end_request(cmd, 0, block_bytes, 1);
+			return;
+		default:
+			break;
+		}
+	}			/* driver byte != 0 */
+	if (host_byte(result) == DID_RESET) {
+		/*
+		 * Third party bus reset or reset for error
+		 * recovery reasons.  Just retry the request
+		 * and see what happens.  
+		 */
+		scsi_requeue_command(q, cmd);
+		return;
+	}
+	if (result) {
+		printk(KERN_INFO "SCSI error : <%d %d %d %d> return code "
+		       "= 0x%x\n", cmd->device->host->host_no,
+		       cmd->device->channel,
+		       cmd->device->id,
+		       cmd->device->lun, result);
+
+		if (driver_byte(result) & DRIVER_SENSE)
+			scsi_print_sense("", cmd);
+		/*
+		 * Mark a single buffer as not uptodate.  Queue the remainder.
+		 * We sometimes get this cruft in the event that a medium error
+		 * isn't properly reported.
+		 */
+		block_bytes = req->hard_cur_sectors << 9;
+		if (!block_bytes)
+			block_bytes = req->data_len;
+		cmd = scsi_end_request(cmd, 0, block_bytes, 1);
+	}
+}
+EXPORT_SYMBOL(scsi_io_completion);
+
+/*
+ * 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
+ */
+static int scsi_init_io(struct scsi_cmnd *cmd)
+{
+	struct request     *req = cmd->request;
+	struct scatterlist *sgpnt;
+	int		   count;
+
+	/*
+	 * if this is a rq->data based REQ_BLOCK_PC, setup for a non-sg xfer
+	 */
+	if ((req->flags & REQ_BLOCK_PC) && !req->bio) {
+		cmd->request_bufflen = req->data_len;
+		cmd->request_buffer = req->data;
+		req->buffer = req->data;
+		cmd->use_sg = 0;
+		return 0;
+	}
+
+	/*
+	 * we used to not use scatter-gather for single segment request,
+	 * but now we do (it makes highmem I/O easier to support without
+	 * kmapping pages)
+	 */
+	cmd->use_sg = req->nr_phys_segments;
+
+	/*
+	 * if sg table allocation fails, requeue request later.
+	 */
+	sgpnt = scsi_alloc_sgtable(cmd, GFP_ATOMIC);
+	if (unlikely(!sgpnt)) {
+		req->flags |= REQ_SPECIAL;
+		return BLKPREP_DEFER;
+	}
+
+	cmd->request_buffer = (char *) sgpnt;
+	cmd->request_bufflen = req->nr_sectors << 9;
+	if (blk_pc_request(req))
+		cmd->request_bufflen = req->data_len;
+	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, cmd->request_buffer);
+
+	/*
+	 * mapped well, send it off
+	 */
+	if (likely(count <= cmd->use_sg)) {
+		cmd->use_sg = count;
+		return 0;
+	}
+
+	printk(KERN_ERR "Incorrect number of segments after building list\n");
+	printk(KERN_ERR "counted %d, received %d\n", count, cmd->use_sg);
+	printk(KERN_ERR "req nr_sec %lu, cur_nr_sec %u\n", req->nr_sectors,
+			req->current_nr_sectors);
+
+	/* release the command and kill it */
+	scsi_release_buffers(cmd);
+	scsi_put_command(cmd);
+	return BLKPREP_KILL;
+}
+
+static int scsi_prepare_flush_fn(request_queue_t *q, struct request *rq)
+{
+	struct scsi_device *sdev = q->queuedata;
+	struct scsi_driver *drv;
+
+	if (sdev->sdev_state == SDEV_RUNNING) {
+		drv = *(struct scsi_driver **) rq->rq_disk->private_data;
+
+		if (drv->prepare_flush)
+			return drv->prepare_flush(q, rq);
+	}
+
+	return 0;
+}
+
+static void scsi_end_flush_fn(request_queue_t *q, struct request *rq)
+{
+	struct scsi_device *sdev = q->queuedata;
+	struct request *flush_rq = rq->end_io_data;
+	struct scsi_driver *drv;
+
+	if (flush_rq->errors) {
+		printk("scsi: barrier error, disabling flush support\n");
+		blk_queue_ordered(q, QUEUE_ORDERED_NONE);
+	}
+
+	if (sdev->sdev_state == SDEV_RUNNING) {
+		drv = *(struct scsi_driver **) rq->rq_disk->private_data;
+		drv->end_flush(q, rq);
+	}
+}
+
+static int scsi_issue_flush_fn(request_queue_t *q, struct gendisk *disk,
+			       sector_t *error_sector)
+{
+	struct scsi_device *sdev = q->queuedata;
+	struct scsi_driver *drv;
+
+	if (sdev->sdev_state != SDEV_RUNNING)
+		return -ENXIO;
+
+	drv = *(struct scsi_driver **) disk->private_data;
+	if (drv->issue_flush)
+		return drv->issue_flush(&sdev->sdev_gendev, error_sector);
+
+	return -EOPNOTSUPP;
+}
+
+static int scsi_prep_fn(struct request_queue *q, struct request *req)
+{
+	struct scsi_device *sdev = q->queuedata;
+	struct scsi_cmnd *cmd;
+	int specials_only = 0;
+
+	/*
+	 * Just check to see if the device is online.  If it isn't, we
+	 * refuse to process any commands.  The device must be brought
+	 * online before trying any recovery commands
+	 */
+	if (unlikely(!scsi_device_online(sdev))) {
+		printk(KERN_ERR "scsi%d (%d:%d): rejecting I/O to offline device\n",
+		       sdev->host->host_no, sdev->id, sdev->lun);
+		return BLKPREP_KILL;
+	}
+	if (unlikely(sdev->sdev_state != SDEV_RUNNING)) {
+		/* OK, we're not in a running state don't prep
+		 * user commands */
+		if (sdev->sdev_state == SDEV_DEL) {
+			/* Device is fully deleted, no commands
+			 * at all allowed down */
+			printk(KERN_ERR "scsi%d (%d:%d): rejecting I/O to dead device\n",
+			       sdev->host->host_no, sdev->id, sdev->lun);
+			return BLKPREP_KILL;
+		}
+		/* OK, we only allow special commands (i.e. not
+		 * user initiated ones */
+		specials_only = sdev->sdev_state;
+	}
+
+	/*
+	 * Find the actual device driver associated with this command.
+	 * The SPECIAL requests are things like character device or
+	 * ioctls, which did not originate from ll_rw_blk.  Note that
+	 * the special field is also used to indicate the cmd for
+	 * the remainder of a partially fulfilled request that can 
+	 * come up when there is a medium error.  We have to treat
+	 * these two cases differently.  We differentiate by looking
+	 * at request->cmd, as this tells us the real story.
+	 */
+	if (req->flags & REQ_SPECIAL) {
+		struct scsi_request *sreq = req->special;
+
+		if (sreq->sr_magic == SCSI_REQ_MAGIC) {
+			cmd = scsi_get_command(sreq->sr_device, GFP_ATOMIC);
+			if (unlikely(!cmd))
+				goto defer;
+			scsi_init_cmd_from_req(cmd, sreq);
+		} else
+			cmd = req->special;
+	} else if (req->flags & (REQ_CMD | REQ_BLOCK_PC)) {
+
+		if(unlikely(specials_only)) {
+			if(specials_only == SDEV_QUIESCE ||
+					specials_only == SDEV_BLOCK)
+				return BLKPREP_DEFER;
+			
+			printk(KERN_ERR "scsi%d (%d:%d): rejecting I/O to device being removed\n",
+			       sdev->host->host_no, sdev->id, sdev->lun);
+			return BLKPREP_KILL;
+		}
+			
+			
+		/*
+		 * Now try and find a command block that we can use.
+		 */
+		if (!req->special) {
+			cmd = scsi_get_command(sdev, GFP_ATOMIC);
+			if (unlikely(!cmd))
+				goto defer;
+		} else
+			cmd = req->special;
+		
+		/* pull a tag out of the request if we have one */
+		cmd->tag = req->tag;
+	} else {
+		blk_dump_rq_flags(req, "SCSI bad req");
+		return BLKPREP_KILL;
+	}
+	
+	/* note the overloading of req->special.  When the tag
+	 * is active it always means cmd.  If the tag goes
+	 * back for re-queueing, it may be reset */
+	req->special = cmd;