scsi_lib.c

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/*
 *  scsi_lib.c Copyright (C) 1999 Eric Youngdale
 *
 *  SCSI queueing library.
 *      Initial versions: Eric Youngdale ([email protected]).
 *                        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;

#ifdef CONFIG_ACPI
#include <acpi/acpi_bus.h>

int scsi_register_acpi_bus_type(struct acpi_bus_type *bus)
{
        bus->bus = &scsi_bus_type;
        return register_acpi_bus_type(bus);
}
EXPORT_SYMBOL_GPL(scsi_register_acpi_bus_type);

void scsi_unregister_acpi_bus_type(struct acpi_bus_type *bus)
{
    unregister_acpi_bus_type(bus);
}
EXPORT_SYMBOL_GPL(scsi_unregister_acpi_bus_type);
#endif

/*
 * 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);
}

static void __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\n", 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. Schedule requeue work under
     * lock such that the kblockd_schedule_work() call happens
     * before blk_cleanup_queue() finishes.
     */
    spin_lock_irqsave(q->queue_lock, flags);
    blk_requeue_request(q, cmd->request);
    kblockd_schedule_work(q, &device->requeue_work);
    spin_unlock_irqrestore(q->queue_lock, flags);
}

/*
 * 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.
 */
void scsi_queue_insert(struct scsi_cmnd *cmd, int reason)
{
    __scsi_queue_insert(cmd, reason, 1);
}
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;

    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 scsi_device *sdev = cmd->device;
    struct request *req = cmd->request;
    unsigned long flags;

    /*
     * We need to hold a reference on the device to avoid the queue being
     * killed after the unlock and before scsi_run_queue is invoked which
     * may happen because scsi_unprep_request() puts the command which
     * releases its reference on the device.
     */
    get_device(&sdev->sdev_gendev);

    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);

    put_device(&sdev->sdev_gendev);
}

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:
        set_host_byte(cmd, DID_OK);
        error = -EREMOTEIO;
        break;
    case DID_NEXUS_FAILURE:
        set_host_byte(cmd, DID_OK);
        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 */
        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);
        }
        /*
         * __scsi_error_from_host_byte may have reset the host_byte
         */
        req->errors = 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.\n",
                      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) {
                switch (cmd->cmnd[0]) {
                case UNMAP:
                    description = "Discard failure";
                    break;
                case WRITE_SAME:
                case WRITE_SAME_16:
                    if (cmd->cmnd[1] & 0x8)
                        description = "Discard failure";
                    else
                        description =
                            "Write same failure";
                    break;
                default:
                    description = "Invalid command failure";
                    break;
                }
                action = ACTION_FAIL;
                error = -EREMOTEIO;
            } 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\n",
                        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:
        case SDEV_TRANSPORT_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\n");
            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\n");
            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\n"));
        } 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\n"));
        } else
            return 0;
    }

    if (scsi_target_is_busy(starget)) {
        list_move_tail(&sdev->starved_entry, &shost->starved_list);
        return 0;
    }

    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\n",
                    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 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;

    if (blk_queue_dead(q))
        return 0;

    shost = sdev->host;

    /*
     * Ignore host/starget busy state.
     * Since block layer does not have a concept of fairness across
     * multiple queues, congestion of host/starget needs to be handled
     * in SCSI layer.
     */
    if (scsi_host_in_recovery(shost) || 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\n");

    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\n",
                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(!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\n");
            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.\n"
                     "please mail a stack trace to "
                     "[email protected]\n",
                     __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->dma_dev;

    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;
}

/*
 * 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\n");
        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\n",
                    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\n",
                    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);
    }
}

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);

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);

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);

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_TRANSPORT_OFFLINE:
        case SDEV_QUIESCE:
        case SDEV_BLOCK:
            break;
        default:
            goto illegal;
        }
        break;

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

    case SDEV_OFFLINE:
    case SDEV_TRANSPORT_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_TRANSPORT_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_TRANSPORT_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\n",
                        scsi_device_state_name(oldstate),
                        scsi_device_state_name(state))
                );
    return -EINVAL;
}
EXPORT_SYMBOL(scsi_device_set_state);

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);
}

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);
        }
    }
}

void sdev_evt_send(struct scsi_device *sdev, struct scsi_event *evt)
{
    unsigned long flags;

#if 0
    /* FIXME: currently this check eliminates all media change events
     * for polled devices.  Need to update to discriminate between AN
     * and polled events */
    if (!test_bit(evt->evt_type, sdev->supported_events)) {
        kfree(evt);
        return;
    }
#endif

    spin_lock_irqsave(&sdev->list_lock, flags);
    list_add_tail(&evt->node, &sdev->event_list);
    schedule_work(&sdev->event_work);
    spin_unlock_irqrestore(&sdev->list_lock, flags);
}
EXPORT_SYMBOL_GPL(sdev_evt_send);

struct scsi_event *sdev_evt_alloc(enum scsi_device_event evt_type,
                  gfp_t gfpflags)
{
    struct scsi_event *evt = kzalloc(sizeof(struct scsi_event), gfpflags);
    if (!evt)
        return NULL;

    evt->evt_type = evt_type;
    INIT_LIST_HEAD(&evt->node);

    /* evt_type-specific initialization, if any */
    switch (evt_type) {
    case SDEV_EVT_MEDIA_CHANGE:
    default:
        /* do nothing */
        break;
    }

    return evt;
}
EXPORT_SYMBOL_GPL(sdev_evt_alloc);

void sdev_evt_send_simple(struct scsi_device *sdev,
              enum scsi_device_event evt_type, gfp_t gfpflags)
{
    struct scsi_event *evt = sdev_evt_alloc(evt_type, gfpflags);
    if (!evt) {
        sdev_printk(KERN_ERR, sdev, "event %d eaten due to OOM\n",
                evt_type);
        return;
    }

    sdev_evt_send(sdev, evt);
}
EXPORT_SYMBOL_GPL(sdev_evt_send_simple);

int
scsi_device_quiesce(struct scsi_device *sdev)
{
    int err = scsi_device_set_state(sdev, SDEV_QUIESCE);
    if (err)
        return err;

    scsi_run_queue(sdev->request_queue);
    while (sdev->device_busy) {
        msleep_interruptible(200);
        scsi_run_queue(sdev->request_queue);
    }
    return 0;
}
EXPORT_SYMBOL(scsi_device_quiesce);

void scsi_device_resume(struct scsi_device *sdev)
{
    /* check if the device state was mutated prior to resume, and if
     * so assume the state is being managed elsewhere (for example
     * device deleted during suspend)
     */
    if (sdev->sdev_state != SDEV_QUIESCE ||
        scsi_device_set_state(sdev, SDEV_RUNNING))
        return;
    scsi_run_queue(sdev->request_queue);
}
EXPORT_SYMBOL(scsi_device_resume);

static void
device_quiesce_fn(struct scsi_device *sdev, void *data)
{
    scsi_device_quiesce(sdev);
}

void
scsi_target_quiesce(struct scsi_target *starget)
{
    starget_for_each_device(starget, NULL, device_quiesce_fn);
}
EXPORT_SYMBOL(scsi_target_quiesce);

static void
device_resume_fn(struct scsi_device *sdev, void *data)
{
    scsi_device_resume(sdev);
}

void
scsi_target_resume(struct scsi_target *starget)
{
    starget_for_each_device(starget, NULL, device_resume_fn);
}
EXPORT_SYMBOL(scsi_target_resume);

int
scsi_internal_device_block(struct scsi_device *sdev)
{
    struct request_queue *q = sdev->request_queue;
    unsigned long flags;
    int err = 0;

    err = scsi_device_set_state(sdev, SDEV_BLOCK);
    if (err) {
        err = scsi_device_set_state(sdev, SDEV_CREATED_BLOCK);

        if (err)
            return err;
    }

    /* 
     * The device has transitioned to SDEV_BLOCK.  Stop the
     * block layer from calling the midlayer with this device's
     * request queue. 
     */
    spin_lock_irqsave(q->queue_lock, flags);
    blk_stop_queue(q);
    spin_unlock_irqrestore(q->queue_lock, flags);

    return 0;
}
EXPORT_SYMBOL_GPL(scsi_internal_device_block);
 
int
scsi_internal_device_unblock(struct scsi_device *sdev,
                 enum scsi_device_state new_state)
{
    struct request_queue *q = sdev->request_queue; 
    unsigned long flags;

    /*
     * Try to transition the scsi device to SDEV_RUNNING or one of the
     * offlined states and goose the device queue if successful.
     */
    if ((sdev->sdev_state == SDEV_BLOCK) ||
        (sdev->sdev_state == SDEV_TRANSPORT_OFFLINE))
        sdev->sdev_state = new_state;
    else if (sdev->sdev_state == SDEV_CREATED_BLOCK) {
        if (new_state == SDEV_TRANSPORT_OFFLINE ||
            new_state == SDEV_OFFLINE)
            sdev->sdev_state = new_state;
        else
            sdev->sdev_state = SDEV_CREATED;
    } else if (sdev->sdev_state != SDEV_CANCEL &&
         sdev->sdev_state != SDEV_OFFLINE)
        return -EINVAL;

    spin_lock_irqsave(q->queue_lock, flags);
    blk_start_queue(q);
    spin_unlock_irqrestore(q->queue_lock, flags);

    return 0;
}
EXPORT_SYMBOL_GPL(scsi_internal_device_unblock);

static void
device_block(struct scsi_device *sdev, void *data)
{
    scsi_internal_device_block(sdev);
}

static int
target_block(struct device *dev, void *data)
{
    if (scsi_is_target_device(dev))
        starget_for_each_device(to_scsi_target(dev), NULL,
                    device_block);
    return 0;
}

void
scsi_target_block(struct device *dev)
{
    if (scsi_is_target_device(dev))
        starget_for_each_device(to_scsi_target(dev), NULL,
                    device_block);
    else
        device_for_each_child(dev, NULL, target_block);
}
EXPORT_SYMBOL_GPL(scsi_target_block);

static void
device_unblock(struct scsi_device *sdev, void *data)
{
    scsi_internal_device_unblock(sdev, *(enum scsi_device_state *)data);
}

static int
target_unblock(struct device *dev, void *data)
{
    if (scsi_is_target_device(dev))
        starget_for_each_device(to_scsi_target(dev), data,
                    device_unblock);
    return 0;
}

void
scsi_target_unblock(struct device *dev, enum scsi_device_state new_state)
{
    if (scsi_is_target_device(dev))
        starget_for_each_device(to_scsi_target(dev), &new_state,
                    device_unblock);
    else
        device_for_each_child(dev, &new_state, target_unblock);
}
EXPORT_SYMBOL_GPL(scsi_target_unblock);

void *scsi_kmap_atomic_sg(struct scatterlist *sgl, int sg_count,
              size_t *offset, size_t *len)
{
    int i;
    size_t sg_len = 0, len_complete = 0;
    struct scatterlist *sg;
    struct page *page;

    WARN_ON(!irqs_disabled());

    for_each_sg(sgl, sg, sg_count, i) {
        len_complete = sg_len; /* Complete sg-entries */
        sg_len += sg->length;
        if (sg_len > *offset)
            break;
    }

    if (unlikely(i == sg_count)) {
        printk(KERN_ERR "%s: Bytes in sg: %zu, requested offset %zu, "
            "elements %d\n",
               __func__, sg_len, *offset, sg_count);
        WARN_ON(1);
        return NULL;
    }

    /* Offset starting from the beginning of first page in this sg-entry */
    *offset = *offset - len_complete + sg->offset;

    /* Assumption: contiguous pages can be accessed as "page + i" */
    page = nth_page(sg_page(sg), (*offset >> PAGE_SHIFT));
    *offset &= ~PAGE_MASK;

    /* Bytes in this sg-entry from *offset to the end of the page */
    sg_len = PAGE_SIZE - *offset;
    if (*len > sg_len)
        *len = sg_len;

    return kmap_atomic(page);
}
EXPORT_SYMBOL(scsi_kmap_atomic_sg);

void scsi_kunmap_atomic_sg(void *virt)
{
    kunmap_atomic(virt);
}
EXPORT_SYMBOL(scsi_kunmap_atomic_sg);