x86/mm: Add TLB purge to free pmd/pte page interfaces

[linux/fpc-iii.git] / drivers / scsi / scsi_lib.c

/*
 * Copyright (C) 1999 Eric Youngdale
 * Copyright (C) 2014 Christoph Hellwig
 *
 *  SCSI queueing library.
 *      Initial versions: Eric Youngdale (eric@andante.org).
 *                        Based upon conversations with large numbers
 *                        of people at Linux Expo.
 */

#include <linux/bio.h>
#include <linux/bitops.h>
#include <linux/blkdev.h>
#include <linux/completion.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/init.h>
#include <linux/pci.h>
#include <linux/delay.h>
#include <linux/hardirq.h>
#include <linux/scatterlist.h>
#include <linux/blk-mq.h>
#include <linux/ratelimit.h>
#include <asm/unaligned.h>

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

#include <trace/events/scsi.h>

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


struct kmem_cache *scsi_sdb_cache;

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

static void
scsi_set_blocked(struct scsi_cmnd *cmd, int reason)
{
        struct Scsi_Host *host = cmd->device->host;
        struct scsi_device *device = cmd->device;
        struct scsi_target *starget = scsi_target(device);

        /*
         * 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:
                atomic_set(&host->host_blocked, host->max_host_blocked);
                break;
        case SCSI_MLQUEUE_DEVICE_BUSY:
        case SCSI_MLQUEUE_EH_RETRY:
                atomic_set(&device->device_blocked,
                           device->max_device_blocked);
                break;
        case SCSI_MLQUEUE_TARGET_BUSY:
                atomic_set(&starget->target_blocked,
                           starget->max_target_blocked);
                break;
        }
}

static void scsi_mq_requeue_cmd(struct scsi_cmnd *cmd)
{
        struct scsi_device *sdev = cmd->device;
        struct request_queue *q = cmd->request->q;

        blk_mq_requeue_request(cmd->request);
        blk_mq_kick_requeue_list(q);
        put_device(&sdev->sdev_gendev);
}

/**
 * __scsi_queue_insert - private queue insertion
 * @cmd: The SCSI command being requeued
 * @reason:  The reason for the requeue
 * @unbusy: Whether the queue should be unbusied
 *
 * This is a private queue insertion.  The public interface
 * scsi_queue_insert() always assumes the queue should be unbusied
 * because it's always called before the completion.  This function is
 * for a requeue after completion, which should only occur in this
 * file.
 */
static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
{
        struct scsi_device *device = cmd->device;
        struct request_queue *q = device->request_queue;
        unsigned long flags;

        SCSI_LOG_MLQUEUE(1, scmd_printk(KERN_INFO, cmd,
                "Inserting command %p into mlqueue\n", cmd));

        scsi_set_blocked(cmd, reason);

        /*
         * 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.
         */
        cmd->result = 0;
        if (q->mq_ops) {
                scsi_mq_requeue_cmd(cmd);
                return;
        }
        spin_lock_irqsave(q->queue_lock, flags);
        blk_requeue_request(q, cmd->request);
        kblockd_schedule_work(&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);
}
/**
 * scsi_execute - insert request and wait for the result
 * @sdev:       scsi device
 * @cmd:        scsi command
 * @data_direction: data direction
 * @buffer:     data buffer
 * @bufflen:    len of buffer
 * @sense:      optional sense buffer
 * @timeout:    request timeout in seconds
 * @retries:    number of times to retry request
 * @flags:      or into request flags;
 * @resid:      optional residual length
 *
 * returns the req->errors value which is the scsi_cmnd result
 * field.
 */
int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
                 int data_direction, void *buffer, unsigned bufflen,
                 unsigned char *sense, int timeout, int retries, u64 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_RECLAIM);
        if (IS_ERR(req))
                return ret;
        blk_rq_set_block_pc(req);

        if (bufflen &&  blk_rq_map_kern(sdev->request_queue, req,
                                        buffer, bufflen, __GFP_RECLAIM))
                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_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_flags(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, u64 flags)
{
        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, flags, resid);
        if (sshdr)
                scsi_normalize_sense(sense, SCSI_SENSE_BUFFERSIZE, sshdr);

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

/*
 * 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;

        atomic_dec(&shost->host_busy);
        if (starget->can_queue > 0)
                atomic_dec(&starget->target_busy);

        if (unlikely(scsi_host_in_recovery(shost) &&
                     (shost->host_failed || shost->host_eh_scheduled))) {
                spin_lock_irqsave(shost->host_lock, flags);
                scsi_eh_wakeup(shost);
                spin_unlock_irqrestore(shost->host_lock, flags);
        }

        atomic_dec(&sdev->device_busy);
}

static void scsi_kick_queue(struct request_queue *q)
{
        if (q->mq_ops)
                blk_mq_start_hw_queues(q);
        else
                blk_run_queue(q);
}

/*
 * 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.
         */
        scsi_kick_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);
                scsi_kick_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 bool scsi_device_is_busy(struct scsi_device *sdev)
{
        if (atomic_read(&sdev->device_busy) >= sdev->queue_depth)
                return true;
        if (atomic_read(&sdev->device_blocked) > 0)
                return true;
        return false;
}

static inline bool scsi_target_is_busy(struct scsi_target *starget)
{
        if (starget->can_queue > 0) {
                if (atomic_read(&starget->target_busy) >= starget->can_queue)
                        return true;
                if (atomic_read(&starget->target_blocked) > 0)
                        return true;
        }
        return false;
}

static inline bool scsi_host_is_busy(struct Scsi_Host *shost)
{
        if (shost->can_queue > 0 &&
            atomic_read(&shost->host_busy) >= shost->can_queue)
                return true;
        if (atomic_read(&shost->host_blocked) > 0)
                return true;
        if (shost->host_self_blocked)
                return true;
        return false;
}

static void scsi_starved_list_run(struct Scsi_Host *shost)
{
        LIST_HEAD(starved_list);
        struct scsi_device *sdev;
        unsigned long flags;

        spin_lock_irqsave(shost->host_lock, flags);
        list_splice_init(&shost->starved_list, &starved_list);

        while (!list_empty(&starved_list)) {
                struct request_queue *slq;

                /*
                 * 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;
                }

                /*
                 * Once we drop the host lock, a racing scsi_remove_device()
                 * call may remove the sdev from the starved list and destroy
                 * it and the queue.  Mitigate by taking a reference to the
                 * queue and never touching the sdev again after we drop the
                 * host lock.  Note: if __scsi_remove_device() invokes
                 * blk_cleanup_queue() before the queue is run from this
                 * function then blk_run_queue() will return immediately since
                 * blk_cleanup_queue() marks the queue with QUEUE_FLAG_DYING.
                 */
                slq = sdev->request_queue;
                if (!blk_get_queue(slq))
                        continue;
                spin_unlock_irqrestore(shost->host_lock, flags);

                scsi_kick_queue(slq);
                blk_put_queue(slq);

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

        if (scsi_target(sdev)->single_lun)
                scsi_single_lun_run(sdev);
        if (!list_empty(&sdev->host->starved_list))
                scsi_starved_list_run(sdev->host);

        if (q->mq_ops)
                blk_mq_start_stopped_hw_queues(q, false);
        else
                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;

        spin_lock_irqsave(q->queue_lock, flags);
        blk_unprep_request(req);
        req->special = NULL;
        scsi_put_command(cmd);
        blk_requeue_request(q, req);
        spin_unlock_irqrestore(q->queue_lock, flags);

        scsi_run_queue(q);

        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_uninit_cmd(struct scsi_cmnd *cmd)
{
        if (cmd->request->cmd_type == REQ_TYPE_FS) {
                struct scsi_driver *drv = scsi_cmd_to_driver(cmd);

                if (drv->uninit_command)
                        drv->uninit_command(cmd);
        }
}

static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd)
{
        struct scsi_data_buffer *sdb;

        if (cmd->sdb.table.nents)
                sg_free_table_chained(&cmd->sdb.table, true);
        if (cmd->request->next_rq) {
                sdb = cmd->request->next_rq->special;
                if (sdb)
                        sg_free_table_chained(&sdb->table, true);
        }
        if (scsi_prot_sg_count(cmd))
                sg_free_table_chained(&cmd->prot_sdb->table, true);
}

static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd)
{
        struct scsi_device *sdev = cmd->device;
        struct Scsi_Host *shost = sdev->host;
        unsigned long flags;

        scsi_mq_free_sgtables(cmd);
        scsi_uninit_cmd(cmd);

        if (shost->use_cmd_list) {
                BUG_ON(list_empty(&cmd->list));
                spin_lock_irqsave(&sdev->list_lock, flags);
                list_del_init(&cmd->list);
                spin_unlock_irqrestore(&sdev->list_lock, flags);
        }
}

/*
 * Function:    scsi_release_buffers()
 *
 * Purpose:     Free resources allocate for a scsi_command.
 *
 * 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.
 */
static void scsi_release_buffers(struct scsi_cmnd *cmd)
{
        if (cmd->sdb.table.nents)
                sg_free_table_chained(&cmd->sdb.table, false);

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

        if (scsi_prot_sg_count(cmd))
                sg_free_table_chained(&cmd->prot_sdb->table, false);
}

static void scsi_release_bidi_buffers(struct scsi_cmnd *cmd)
{
        struct scsi_data_buffer *bidi_sdb = cmd->request->next_rq->special;

        sg_free_table_chained(&bidi_sdb->table, false);
        kmem_cache_free(scsi_sdb_cache, bidi_sdb);
        cmd->request->next_rq->special = NULL;
}

static bool scsi_end_request(struct request *req, int error,
                unsigned int bytes, unsigned int bidi_bytes)
{
        struct scsi_cmnd *cmd = req->special;
        struct scsi_device *sdev = cmd->device;
        struct request_queue *q = sdev->request_queue;

        if (blk_update_request(req, error, bytes))
                return true;

        /* Bidi request must be completed as a whole */
        if (unlikely(bidi_bytes) &&
            blk_update_request(req->next_rq, error, bidi_bytes))
                return true;

        if (blk_queue_add_random(q))
                add_disk_randomness(req->rq_disk);

        if (req->mq_ctx) {
                /*
                 * In the MQ case the command gets freed by __blk_mq_end_request,
                 * so we have to do all cleanup that depends on it earlier.
                 *
                 * We also can't kick the queues from irq context, so we
                 * will have to defer it to a workqueue.
                 */
                scsi_mq_uninit_cmd(cmd);

                __blk_mq_end_request(req, error);

                if (scsi_target(sdev)->single_lun ||
                    !list_empty(&sdev->host->starved_list))
                        kblockd_schedule_work(&sdev->requeue_work);
                else
                        blk_mq_start_stopped_hw_queues(q, true);
        } else {
                unsigned long flags;

                if (bidi_bytes)
                        scsi_release_bidi_buffers(cmd);

                spin_lock_irqsave(q->queue_lock, flags);
                blk_finish_request(req, error);
                spin_unlock_irqrestore(q->queue_lock, flags);

                scsi_release_buffers(cmd);

                scsi_put_command(cmd);
                scsi_run_queue(q);
        }

        put_device(&sdev->sdev_gendev);
        return false;
}

/**
 * __scsi_error_from_host_byte - translate SCSI error code into errno
 * @cmd:        SCSI command (unused)
 * @result:     scsi error code
 *
 * Translate SCSI error code into standard UNIX errno.
 * Return values:
 * -ENOLINK     temporary transport failure
 * -EREMOTEIO   permanent target failure, do not retry
 * -EBADE       permanent nexus failure, retry on other path
 * -ENOSPC      No write space available
 * -ENODATA     Medium error
 * -EIO         unspecified I/O error
 */
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;
        case DID_ALLOC_FAILURE:
                set_host_byte(cmd, DID_OK);
                error = -ENOSPC;
                break;
        case DID_MEDIUM_ERROR:
                set_host_byte(cmd, DID_OK);
                error = -ENODATA;
                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:       We 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 scsi_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;
        bool sense_valid = false;
        int sense_deferred = 0, level = 0;
        enum {ACTION_FAIL, ACTION_REPREP, ACTION_RETRY,
              ACTION_DELAYED_RETRY} action;
        unsigned long wait_for = (cmd->allowed + 1) * req->timeout;

        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;
                        if (scsi_end_request(req, 0, blk_rq_bytes(req),
                                        blk_rq_bytes(req->next_rq)))
                                BUG();
                        return;
                }
        } else if (blk_rq_bytes(req) == 0 && result && !sense_deferred) {
                /*
                 * Certain non BLOCK_PC requests are commands that don't
                 * actually transfer anything (FLUSH), so cannot use
                 * good_bytes != blk_rq_bytes(req) as the signal for an error.
                 * This sets the error explicitly for the problem case.
                 */
                error = __scsi_error_from_host_byte(cmd, result);
        }

        /* 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, scmd_printk(KERN_INFO, cmd,
                "%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;
        }

        /*
         * special case: failed zero length commands always need to
         * drop down into the retry code. Otherwise, if we finished
         * all bytes in the request we are done now.
         */
        if (!(blk_rq_bytes(req) == 0 && error) &&
            !scsi_end_request(req, error, good_bytes, 0))
                return;

        /*
         * Kill remainder if no retrys.
         */
        if (error && scsi_noretry_cmd(cmd)) {
                if (scsi_end_request(req, error, blk_rq_bytes(req), 0))
                        BUG();
                return;
        }

        /*
         * If there had been no error, but we have leftover bytes in the
         * requeues just queue the command up again.
         */
        if (result == 0)
                goto requeue;

        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;
                                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 */ {
                                action = ACTION_FAIL;
                                error = -EILSEQ;
                        /* INVALID COMMAND OPCODE or INVALID FIELD IN CDB */
                        } else if (sshdr.asc == 0x20 || sshdr.asc == 0x24) {
                                action = ACTION_FAIL;
                                error = -EREMOTEIO;
                        } else
                                action = ACTION_FAIL;
                        break;
                case ABORTED_COMMAND:
                        action = ACTION_FAIL;
                        if (sshdr.asc == 0x10) /* DIF */
                                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:
                                        action = ACTION_FAIL;
                                        break;
                                }
                        } else
                                action = ACTION_FAIL;
                        break;
                case VOLUME_OVERFLOW:
                        /* See SSC3rXX or current. */
                        action = ACTION_FAIL;
                        break;
                default:
                        action = ACTION_FAIL;
                        break;
                }
        } else
                action = ACTION_FAIL;

        if (action != ACTION_FAIL &&
            time_before(cmd->jiffies_at_alloc + wait_for, jiffies))
                action = ACTION_FAIL;

        switch (action) {
        case ACTION_FAIL:
                /* Give up and fail the remainder of the request */
                if (!(req->cmd_flags & REQ_QUIET)) {
                        static DEFINE_RATELIMIT_STATE(_rs,
                                        DEFAULT_RATELIMIT_INTERVAL,
                                        DEFAULT_RATELIMIT_BURST);

                        if (unlikely(scsi_logging_level))
                                level = SCSI_LOG_LEVEL(SCSI_LOG_MLCOMPLETE_SHIFT,
                                                       SCSI_LOG_MLCOMPLETE_BITS);

                        /*
                         * if logging is enabled the failure will be printed
                         * in scsi_log_completion(), so avoid duplicate messages
                         */
                        if (!level && __ratelimit(&_rs)) {
                                scsi_print_result(cmd, NULL, FAILED);
                                if (driver_byte(result) & DRIVER_SENSE)
                                        scsi_print_sense(cmd);
                                scsi_print_command(cmd);
                        }
                }
                if (!scsi_end_request(req, error, blk_rq_err_bytes(req), 0))
                        return;
                /*FALLTHRU*/
        case ACTION_REPREP:
        requeue:
                /* Unprep the request and put it back at the head of the queue.
                 * A new command will be prepared and issued.
                 */
                if (q->mq_ops) {
                        cmd->request->cmd_flags &= ~REQ_DONTPREP;
                        scsi_mq_uninit_cmd(cmd);
                        scsi_mq_requeue_cmd(cmd);
                } else {
                        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)
{
        int count;

        /*
         * If sg table allocation fails, requeue request later.
         */
        if (unlikely(sg_alloc_table_chained(&sdb->table, req->nr_phys_segments,
                                        sdb->table.sgl)))
                return BLKPREP_DEFER;

        /* 
         * 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)
{
        struct scsi_device *sdev = cmd->device;
        struct request *rq = cmd->request;
        bool is_mq = (rq->mq_ctx != NULL);
        int error;

        if (WARN_ON_ONCE(!rq->nr_phys_segments))
                return -EINVAL;

        error = scsi_init_sgtable(rq, &cmd->sdb);
        if (error)
                goto err_exit;

        if (blk_bidi_rq(rq)) {
                if (!rq->q->mq_ops) {
                        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, rq->next_rq->special);
                if (error)
                        goto err_exit;
        }

        if (blk_integrity_rq(rq)) {
                struct scsi_data_buffer *prot_sdb = cmd->prot_sdb;
                int ivecs, count;

                if (prot_sdb == NULL) {
                        /*
                         * This can happen if someone (e.g. multipath)
                         * queues a command to a device on an adapter
                         * that does not support DIX.
                         */
                        WARN_ON_ONCE(1);
                        error = BLKPREP_KILL;
                        goto err_exit;
                }

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

                if (sg_alloc_table_chained(&prot_sdb->table, ivecs,
                                prot_sdb->table.sgl)) {
                        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:
        if (is_mq) {
                scsi_mq_free_sgtables(cmd);
        } else {
                scsi_release_buffers(cmd);
                cmd->request->special = NULL;
                scsi_put_command(cmd);
                put_device(&sdev->sdev_gendev);
        }
        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) {
                /* Bail if we can't get a reference to the device */
                if (!get_device(&sdev->sdev_gendev))
                        return NULL;

                cmd = scsi_get_command(sdev, GFP_ATOMIC);
                if (unlikely(!cmd)) {
                        put_device(&sdev->sdev_gendev);
                        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;
}

static int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
{
        struct scsi_cmnd *cmd = req->special;

        /*
         * 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 = scsi_init_io(cmd);
                if (unlikely(ret))
                        return ret;
        } else {
                BUG_ON(blk_rq_bytes(req));

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

        cmd->cmd_len = req->cmd_len;
        cmd->transfersize = blk_rq_bytes(req);
        cmd->allowed = req->retries;
        return BLKPREP_OK;
}

/*
 * Setup a REQ_TYPE_FS command.  These are simple request from filesystems
 * that still need to be translated to SCSI CDBs from the ULD.
 */
static int scsi_setup_fs_cmnd(struct scsi_device *sdev, struct request *req)
{
        struct scsi_cmnd *cmd = req->special;

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

        memset(cmd->cmnd, 0, BLK_MAX_CDB);
        return scsi_cmd_to_driver(cmd)->init_command(cmd);
}

static int scsi_setup_cmnd(struct scsi_device *sdev, struct request *req)
{
        struct scsi_cmnd *cmd = req->special;

        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;

        switch (req->cmd_type) {
        case REQ_TYPE_FS:
                return scsi_setup_fs_cmnd(sdev, req);
        case REQ_TYPE_BLOCK_PC:
                return scsi_setup_blk_pc_cmnd(sdev, req);
        default:
                return BLKPREP_KILL;
        }
}

static 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_BLOCK:
                case SDEV_CREATED_BLOCK:
                        ret = BLKPREP_DEFER;
                        break;
                case SDEV_QUIESCE:
                        /*
                         * 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;
}

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

        switch (ret) {
        case BLKPREP_KILL:
        case BLKPREP_INVALID:
                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);
                        put_device(&sdev->sdev_gendev);
                        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 (atomic_read(&sdev->device_busy) == 0)
                        blk_delay_queue(q, SCSI_QUEUE_DELAY);
                break;
        default:
                req->cmd_flags |= REQ_DONTPREP;
        }

        return ret;
}

static int scsi_prep_fn(struct request_queue *q, struct request *req)
{
        struct scsi_device *sdev = q->queuedata;
        struct scsi_cmnd *cmd;
        int ret;

        ret = scsi_prep_state_check(sdev, req);
        if (ret != BLKPREP_OK)
                goto out;

        cmd = scsi_get_cmd_from_req(sdev, req);
        if (unlikely(!cmd)) {
                ret = BLKPREP_DEFER;
                goto out;
        }

        ret = scsi_setup_cmnd(sdev, req);
out:
        return scsi_prep_return(q, req, ret);
}

static void scsi_unprep_fn(struct request_queue *q, struct request *req)
{
        scsi_uninit_cmd(req->special);
}

/*
 * 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)
{
        unsigned int busy;

        busy = atomic_inc_return(&sdev->device_busy) - 1;
        if (atomic_read(&sdev->device_blocked)) {
                if (busy)
                        goto out_dec;

                /*
                 * unblock after device_blocked iterates to zero
                 */
                if (atomic_dec_return(&sdev->device_blocked) > 0) {
                        /*
                         * For the MQ case we take care of this in the caller.
                         */
                        if (!q->mq_ops)
                                blk_delay_queue(q, SCSI_QUEUE_DELAY);
                        goto out_dec;
                }
                SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
                                   "unblocking device at zero depth\n"));
        }

        if (busy >= sdev->queue_depth)
                goto out_dec;

        return 1;
out_dec:
        atomic_dec(&sdev->device_busy);
        return 0;
}

/*
 * scsi_target_queue_ready: checks if there we can send commands to target
 * @sdev: scsi device on starget to check.
 */
static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
                                           struct scsi_device *sdev)
{
        struct scsi_target *starget = scsi_target(sdev);
        unsigned int busy;

        if (starget->single_lun) {
                spin_lock_irq(shost->host_lock);
                if (starget->starget_sdev_user &&
                    starget->starget_sdev_user != sdev) {
                        spin_unlock_irq(shost->host_lock);
                        return 0;
                }
                starget->starget_sdev_user = sdev;
                spin_unlock_irq(shost->host_lock);
        }

        if (starget->can_queue <= 0)
                return 1;

        busy = atomic_inc_return(&starget->target_busy) - 1;
        if (atomic_read(&starget->target_blocked) > 0) {
                if (busy)
                        goto starved;

                /*
                 * unblock after target_blocked iterates to zero
                 */
                if (atomic_dec_return(&starget->target_blocked) > 0)
                        goto out_dec;

                SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
                                 "unblocking target at zero depth\n"));
        }

        if (busy >= starget->can_queue)
                goto starved;

        return 1;

starved:
        spin_lock_irq(shost->host_lock);
        list_move_tail(&sdev->starved_entry, &shost->starved_list);
        spin_unlock_irq(shost->host_lock);
out_dec:
        if (starget->can_queue > 0)
                atomic_dec(&starget->target_busy);
        return 0;
}

/*
 * 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.
 */
static inline int scsi_host_queue_ready(struct request_queue *q,
                                   struct Scsi_Host *shost,
                                   struct scsi_device *sdev)
{
        unsigned int busy;

        if (scsi_host_in_recovery(shost))
                return 0;

        busy = atomic_inc_return(&shost->host_busy) - 1;
        if (atomic_read(&shost->host_blocked) > 0) {
                if (busy)
                        goto starved;

                /*
                 * unblock after host_blocked iterates to zero
                 */
                if (atomic_dec_return(&shost->host_blocked) > 0)
                        goto out_dec;

                SCSI_LOG_MLQUEUE(3,
                        shost_printk(KERN_INFO, shost,
                                     "unblocking host at zero depth\n"));
        }

        if (shost->can_queue > 0 && busy >= shost->can_queue)
                goto starved;
        if (shost->host_self_blocked)
                goto starved;

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

        return 1;

starved:
        spin_lock_irq(shost->host_lock);
        if (list_empty(&sdev->starved_entry))
                list_add_tail(&sdev->starved_entry, &shost->starved_list);
        spin_unlock_irq(shost->host_lock);
out_dec:
        atomic_dec(&shost->host_busy);
        return 0;
}

/*
 * 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_dying(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.
         */
        atomic_inc(&sdev->device_busy);
        atomic_inc(&shost->host_busy);
        if (starget->can_queue > 0)
                atomic_inc(&starget->target_busy);

        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);
        }
}

/**
 * scsi_dispatch_command - Dispatch a command to the low-level driver.
 * @cmd: command block we are dispatching.
 *
 * Return: nonzero return request was rejected and device's queue needs to be
 * plugged.
 */
static int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
{
        struct Scsi_Host *host = cmd->device->host;
        int rtn = 0;

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

        /* check if the device is still usable */
        if (unlikely(cmd->device->sdev_state == SDEV_DEL)) {
                /* in SDEV_DEL we error all commands. DID_NO_CONNECT
                 * returns an immediate error upwards, and signals
                 * that the device is no longer present */
                cmd->result = DID_NO_CONNECT << 16;
                goto done;
        }

        /* Check to see if the scsi lld made this device blocked. */
        if (unlikely(scsi_device_blocked(cmd->device))) {
                /*
                 * in blocked state, the command is just put back on
                 * the device queue.  The suspend state has already
                 * blocked the queue so future requests should not
                 * occur until the device transitions out of the
                 * suspend state.
                 */
                SCSI_LOG_MLQUEUE(3, scmd_printk(KERN_INFO, cmd,
                        "queuecommand : device blocked\n"));
                return SCSI_MLQUEUE_DEVICE_BUSY;
        }

        /* Store the LUN value in cmnd, if needed. */
        if (cmd->device->lun_in_cdb)
                cmd->cmnd[1] = (cmd->cmnd[1] & 0x1f) |
                               (cmd->device->lun << 5 & 0xe0);

        scsi_log_send(cmd);

        /*
         * Before we queue this command, check if the command
         * length exceeds what the host adapter can handle.
         */
        if (cmd->cmd_len > cmd->device->host->max_cmd_len) {
                SCSI_LOG_MLQUEUE(3, scmd_printk(KERN_INFO, cmd,
                               "queuecommand : command too long. "
                               "cdb_size=%d host->max_cmd_len=%d\n",
                               cmd->cmd_len, cmd->device->host->max_cmd_len));
                cmd->result = (DID_ABORT << 16);
                goto done;
        }

        if (unlikely(host->shost_state == SHOST_DEL)) {
                cmd->result = (DID_NO_CONNECT << 16);
                goto done;

        }

        trace_scsi_dispatch_cmd_start(cmd);
        rtn = host->hostt->queuecommand(host, cmd);
        if (rtn) {
                trace_scsi_dispatch_cmd_error(cmd, rtn);
                if (rtn != SCSI_MLQUEUE_DEVICE_BUSY &&
                    rtn != SCSI_MLQUEUE_TARGET_BUSY)
                        rtn = SCSI_MLQUEUE_HOST_BUSY;

                SCSI_LOG_MLQUEUE(3, scmd_printk(KERN_INFO, cmd,
                        "queuecommand : request rejected\n"));
        }

        return rtn;
 done:
        cmd->scsi_done(cmd);
        return 0;
}

/**
 * scsi_done - Invoke completion on finished SCSI command.
 * @cmd: The SCSI Command for which a low-level device driver (LLDD) gives
 * ownership back to SCSI Core -- i.e. the LLDD has finished with it.
 *
 * Description: This function is the mid-level's (SCSI Core) interrupt routine,
 * which regains ownership of the SCSI command (de facto) from a LLDD, and
 * calls blk_complete_request() for further processing.
 *
 * This function is interrupt context safe.
 */
static void scsi_done(struct scsi_cmnd *cmd)
{
        trace_scsi_dispatch_cmd_done(cmd);
        blk_complete_request(cmd->request);
}

/*
 * 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)
        __releases(q->queue_lock)
        __acquires(q->queue_lock)
{
        struct scsi_device *sdev = q->queuedata;
        struct Scsi_Host *shost;
        struct scsi_cmnd *cmd;
        struct request *req;

        /*
         * 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)
                        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;
                }

                if (!scsi_dev_queue_ready(q, sdev))
                        break;

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

                spin_unlock_irq(q->queue_lock);
                cmd = req->special;
                if (unlikely(cmd == NULL)) {
                        printk(KERN_CRIT "impossible request in %s.\n"
                                         "please mail a stack trace to "
                                         "linux-scsi@vger.kernel.org\n",
                                         __func__);
                        blk_dump_rq_flags(req, "foo");
                        BUG();
                }

                /*
                 * 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) && !(req->cmd_flags & REQ_QUEUED)) {
                        spin_lock_irq(shost->host_lock);
                        if (list_empty(&sdev->starved_entry))
                                list_add_tail(&sdev->starved_entry,
                                              &shost->starved_list);
                        spin_unlock_irq(shost->host_lock);
                        goto not_ready;
                }

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

                if (!scsi_host_queue_ready(q, shost, sdev))
                        goto host_not_ready;
        
                if (sdev->simple_tags)
                        cmd->flags |= SCMD_TAGGED;
                else
                        cmd->flags &= ~SCMD_TAGGED;

                /*
                 * 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.
                 */
                cmd->scsi_done = scsi_done;
                rtn = scsi_dispatch_cmd(cmd);
                if (rtn) {
                        scsi_queue_insert(cmd, rtn);
                        spin_lock_irq(q->queue_lock);
                        goto out_delay;
                }
                spin_lock_irq(q->queue_lock);
        }

        return;

 host_not_ready:
        if (scsi_target(sdev)->can_queue > 0)
                atomic_dec(&scsi_target(sdev)->target_busy);
 not_ready:
        /*
         * 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);
        atomic_dec(&sdev->device_busy);
out_delay:
        if (!atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev))
                blk_delay_queue(q, SCSI_QUEUE_DELAY);
}

static inline int prep_to_mq(int ret)
{
        switch (ret) {
        case BLKPREP_OK:
                return 0;
        case BLKPREP_DEFER:
                return BLK_MQ_RQ_QUEUE_BUSY;
        default:
                return BLK_MQ_RQ_QUEUE_ERROR;
        }
}

static int scsi_mq_prep_fn(struct request *req)
{
        struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
        struct scsi_device *sdev = req->q->queuedata;
        struct Scsi_Host *shost = sdev->host;
        unsigned char *sense_buf = cmd->sense_buffer;
        struct scatterlist *sg;

        memset(cmd, 0, sizeof(struct scsi_cmnd));

        req->special = cmd;

        cmd->request = req;
        cmd->device = sdev;
        cmd->sense_buffer = sense_buf;

        cmd->tag = req->tag;

        cmd->cmnd = req->cmd;
        cmd->prot_op = SCSI_PROT_NORMAL;

        INIT_LIST_HEAD(&cmd->list);
        INIT_DELAYED_WORK(&cmd->abort_work, scmd_eh_abort_handler);
        cmd->jiffies_at_alloc = jiffies;

        if (shost->use_cmd_list) {
                spin_lock_irq(&sdev->list_lock);
                list_add_tail(&cmd->list, &sdev->cmd_list);
                spin_unlock_irq(&sdev->list_lock);
        }

        sg = (void *)cmd + sizeof(struct scsi_cmnd) + shost->hostt->cmd_size;
        cmd->sdb.table.sgl = sg;

        if (scsi_host_get_prot(shost)) {
                cmd->prot_sdb = (void *)sg +
                        min_t(unsigned int,
                              shost->sg_tablesize, SG_CHUNK_SIZE) *
                        sizeof(struct scatterlist);
                memset(cmd->prot_sdb, 0, sizeof(struct scsi_data_buffer));

                cmd->prot_sdb->table.sgl =
                        (struct scatterlist *)(cmd->prot_sdb + 1);
        }

        if (blk_bidi_rq(req)) {
                struct request *next_rq = req->next_rq;
                struct scsi_data_buffer *bidi_sdb = blk_mq_rq_to_pdu(next_rq);

                memset(bidi_sdb, 0, sizeof(struct scsi_data_buffer));
                bidi_sdb->table.sgl =
                        (struct scatterlist *)(bidi_sdb + 1);

                next_rq->special = bidi_sdb;
        }

        blk_mq_start_request(req);

        return scsi_setup_cmnd(sdev, req);
}

static void scsi_mq_done(struct scsi_cmnd *cmd)
{
        trace_scsi_dispatch_cmd_done(cmd);
        blk_mq_complete_request(cmd->request, cmd->request->errors);
}

static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
                         const struct blk_mq_queue_data *bd)
{
        struct request *req = bd->rq;
        struct request_queue *q = req->q;
        struct scsi_device *sdev = q->queuedata;
        struct Scsi_Host *shost = sdev->host;
        struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
        int ret;
        int reason;

        ret = prep_to_mq(scsi_prep_state_check(sdev, req));
        if (ret)
                goto out;

        ret = BLK_MQ_RQ_QUEUE_BUSY;
        if (!get_device(&sdev->sdev_gendev))
                goto out;

        if (!scsi_dev_queue_ready(q, sdev))
                goto out_put_device;
        if (!scsi_target_queue_ready(shost, sdev))
                goto out_dec_device_busy;
        if (!scsi_host_queue_ready(q, shost, sdev))
                goto out_dec_target_busy;


        if (!(req->cmd_flags & REQ_DONTPREP)) {
                ret = prep_to_mq(scsi_mq_prep_fn(req));
                if (ret)
                        goto out_dec_host_busy;
                req->cmd_flags |= REQ_DONTPREP;
        } else {
                blk_mq_start_request(req);
        }

        if (sdev->simple_tags)
                cmd->flags |= SCMD_TAGGED;
        else
                cmd->flags &= ~SCMD_TAGGED;

        scsi_init_cmd_errh(cmd);
        cmd->scsi_done = scsi_mq_done;

        reason = scsi_dispatch_cmd(cmd);
        if (reason) {
                scsi_set_blocked(cmd, reason);
                ret = BLK_MQ_RQ_QUEUE_BUSY;
                goto out_dec_host_busy;
        }

        return BLK_MQ_RQ_QUEUE_OK;

out_dec_host_busy:
        atomic_dec(&shost->host_busy);
out_dec_target_busy:
        if (scsi_target(sdev)->can_queue > 0)
                atomic_dec(&scsi_target(sdev)->target_busy);
out_dec_device_busy:
        atomic_dec(&sdev->device_busy);
out_put_device:
        put_device(&sdev->sdev_gendev);
out:
        switch (ret) {
        case BLK_MQ_RQ_QUEUE_BUSY:
                blk_mq_stop_hw_queue(hctx);
                if (atomic_read(&sdev->device_busy) == 0 &&
                    !scsi_device_blocked(sdev))
                        blk_mq_delay_queue(hctx, SCSI_QUEUE_DELAY);
                break;
        case BLK_MQ_RQ_QUEUE_ERROR:
                /*
                 * Make sure to release all allocated ressources when
                 * we hit an error, as we will never see this command
                 * again.
                 */
                if (req->cmd_flags & REQ_DONTPREP)
                        scsi_mq_uninit_cmd(cmd);
                break;
        default:
                break;
        }
        return ret;
}

static enum blk_eh_timer_return scsi_timeout(struct request *req,
                bool reserved)
{
        if (reserved)
                return BLK_EH_RESET_TIMER;
        return scsi_times_out(req);
}

static int scsi_init_request(void *data, struct request *rq,
                unsigned int hctx_idx, unsigned int request_idx,
                unsigned int numa_node)
{
        struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);

        cmd->sense_buffer = kzalloc_node(SCSI_SENSE_BUFFERSIZE, GFP_KERNEL,
                        numa_node);
        if (!cmd->sense_buffer)
                return -ENOMEM;
        return 0;
}

static void scsi_exit_request(void *data, struct request *rq,
                unsigned int hctx_idx, unsigned int request_idx)
{
        struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);

        kfree(cmd->sense_buffer);
}

static 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 = (u64)dma_max_pfn(host_dev) << PAGE_SHIFT;

        return bounce_limit;
}

static void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
{
        struct device *dev = shost->dma_dev;

        /*
         * this limit is imposed by hardware restrictions
         */
        blk_queue_max_segments(q, min_t(unsigned short, shost->sg_tablesize,
                                        SG_MAX_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:  The larger of 32-byte (dword),
         * which is a common minimum for HBAs, and the minimum DMA alignment,
         * which is set by the platform.
         *
         * Devices that require a bigger alignment can increase it later.
         */
        blk_queue_dma_alignment(q, max(4, dma_get_cache_alignment()) - 1);
}

struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
                                         request_fn_proc *request_fn)
{
        struct request_queue *q;

        q = blk_init_queue(request_fn, NULL);
        if (!q)
                return NULL;
        __scsi_init_queue(shost, q);
        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_unprep_rq(q, scsi_unprep_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;
}

static struct blk_mq_ops scsi_mq_ops = {
        .queue_rq       = scsi_queue_rq,
        .complete       = scsi_softirq_done,
        .timeout        = scsi_timeout,
        .init_request   = scsi_init_request,
        .exit_request   = scsi_exit_request,
};

struct request_queue *scsi_mq_alloc_queue(struct scsi_device *sdev)
{
        sdev->request_queue = blk_mq_init_queue(&sdev->host->tag_set);
        if (IS_ERR(sdev->request_queue))
                return NULL;

        sdev->request_queue->queuedata = sdev;
        __scsi_init_queue(sdev->host, sdev->request_queue);
        return sdev->request_queue;
}

int scsi_mq_setup_tags(struct Scsi_Host *shost)
{
        unsigned int cmd_size, sgl_size, tbl_size;

        tbl_size = shost->sg_tablesize;
        if (tbl_size > SG_CHUNK_SIZE)
                tbl_size = SG_CHUNK_SIZE;
        sgl_size = tbl_size * sizeof(struct scatterlist);
        cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size;
        if (scsi_host_get_prot(shost))
                cmd_size += sizeof(struct scsi_data_buffer) + sgl_size;

        memset(&shost->tag_set, 0, sizeof(shost->tag_set));
        shost->tag_set.ops = &scsi_mq_ops;
        shost->tag_set.nr_hw_queues = shost->nr_hw_queues ? : 1;
        shost->tag_set.queue_depth = shost->can_queue;
        shost->tag_set.cmd_size = cmd_size;
        shost->tag_set.numa_node = NUMA_NO_NODE;
        shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
        shost->tag_set.flags |=
                BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
        shost->tag_set.driver_data = shost;

        return blk_mq_alloc_tag_set(&shost->tag_set);
}

void scsi_mq_destroy_tags(struct Scsi_Host *shost)
{
        blk_mq_free_tag_set(&shost->tag_set);
}

/**
 * scsi_device_from_queue - return sdev associated with a request_queue
 * @q: The request queue to return the sdev from
 *
 * Return the sdev associated with a request queue or NULL if the
 * request_queue does not reference a SCSI device.
 */
struct scsi_device *scsi_device_from_queue(struct request_queue *q)
{
        struct scsi_device *sdev = NULL;

        if (q->mq_ops) {
                if (q->mq_ops == &scsi_mq_ops)
                        sdev = q->queuedata;
        } else if (q->request_fn == scsi_request_fn)
                sdev = q->queuedata;
        if (!sdev || !get_device(&sdev->sdev_gendev))
                sdev = NULL;

        return sdev;
}
EXPORT_SYMBOL_GPL(scsi_device_from_queue);

/*
 * 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)
{
        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;
        }

        return 0;
}

void scsi_exit_queue(void)
{
        kmem_cache_destroy(scsi_sdb_cache);
}

/**
 *      scsi_mode_select - issue a mode select
 *      @sdev:  SCSI device to be queried
 *      @pf:    Page format bit (1 == standard, 0 == vendor specific)
 *      @sp:    Save page bit (0 == don't save, 1 == save)
 *      @modepage: mode page being requested
 *      @buffer: request buffer (may not be smaller than eight bytes)
 *      @len:   length of request buffer.
 *      @timeout: command timeout
 *      @retries: number of retries before failing
 *      @data: returns a structure abstracting the mode header data
 *      @sshdr: place to put sense data (or NULL if no sense to be collected).
 *              must be SCSI_SENSE_BUFFERSIZE big.
 *
 *      Returns zero if successful; negative error number or scsi
 *      status on error
 *
 */
int
scsi_mode_select(struct scsi_device *sdev, int pf, int sp, int modepage,
                 unsigned char *buffer, int len, int timeout, int retries,
                 struct scsi_mode_data *data, struct scsi_sense_hdr *sshdr)
{
        unsigned char cmd[10];
        unsigned char *real_buffer;
        int ret;

        memset(cmd, 0, sizeof(cmd));
        cmd[1] = (pf ? 0x10 : 0) | (sp ? 0x01 : 0);

        if (sdev->use_10_for_ms) {
                if (len > 65535)
                        return -EINVAL;
                real_buffer = kmalloc(8 + len, GFP_KERNEL);
                if (!real_buffer)
                        return -ENOMEM;
                memcpy(real_buffer + 8, buffer, len);
                len += 8;
                real_buffer[0] = 0;
                real_buffer[1] = 0;
                real_buffer[2] = data->medium_type;
                real_buffer[3] = data->device_specific;
                real_buffer[4] = data->longlba ? 0x01 : 0;
                real_buffer[5] = 0;
                real_buffer[6] = data->block_descriptor_length >> 8;
                real_buffer[7] = data->block_descriptor_length;

                cmd[0] = MODE_SELECT_10;
                cmd[7] = len >> 8;
                cmd[8] = len;
        } else {
                if (len > 255 || data->block_descriptor_length > 255 ||
                    data->longlba)
                        return -EINVAL;

                real_buffer = kmalloc(4 + len, GFP_KERNEL);
                if (!real_buffer)
                        return -ENOMEM;
                memcpy(real_buffer + 4, buffer, len);
                len += 4;
                real_buffer[0] = 0;
                real_buffer[1] = data->medium_type;
                real_buffer[2] = data->device_specific;
                real_buffer[3] = data->block_descriptor_length;
                

                cmd[0] = MODE_SELECT;
                cmd[4] = len;
        }

        ret = scsi_execute_req(sdev, cmd, DMA_TO_DEVICE, real_buffer, len,
                               sshdr, timeout, retries, NULL);
        kfree(real_buffer);
        return ret;
}
EXPORT_SYMBOL_GPL(scsi_mode_select);

/**
 *      scsi_mode_sense - issue a mode sense, falling back from 10 to six bytes if necessary.
 *      @sdev:  SCSI device to be queried
 *      @dbd:   set if mode sense will allow block descriptors to be returned
 *      @modepage: mode page being requested
 *      @buffer: request buffer (may not be smaller than eight bytes)
 *      @len:   length of request buffer.
 *      @timeout: command timeout
 *      @retries: number of retries before failing
 *      @data: returns a structure abstracting the mode header data
 *      @sshdr: place to put sense data (or NULL if no sense to be collected).
 *              must be SCSI_SENSE_BUFFERSIZE big.
 *
 *      Returns zero if unsuccessful, or the header offset (either 4
 *      or 8 depending on whether a six or ten byte command was
 *      issued) if successful.
 */
int
scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,
                  unsigned char *buffer, int len, int timeout, int retries,
                  struct scsi_mode_data *data, struct scsi_sense_hdr *sshdr)
{
        unsigned char cmd[12];
        int use_10_for_ms;
        int header_length;
        int result, retry_count = retries;
        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;
        } else if ((status_byte(result) == CHECK_CONDITION) &&
                   scsi_sense_valid(sshdr) &&
                   sshdr->sense_key == UNIT_ATTENTION && retry_count) {
                retry_count--;
                goto retry;
        }

        return result;
}
EXPORT_SYMBOL(scsi_mode_sense);

/**
 *      scsi_test_unit_ready - test if unit is ready
 *      @sdev:  scsi device to change the state of.
 *      @timeout: command timeout
 *      @retries: number of retries before failing
 *      @sshdr_external: Optional pointer to struct scsi_sense_hdr for
 *              returning sense. Make sure that this is cleared before passing
 *              in.
 *
 *      Returns zero if unsuccessful or an error if TUR failed.  For
 *      removable media, UNIT_ATTENTION sets ->changed flag.
 **/
int
scsi_test_unit_ready(struct scsi_device *sdev, int timeout, int retries,
                     struct scsi_sense_hdr *sshdr_external)
{
        char cmd[] = {
                TEST_UNIT_READY, 0, 0, 0, 0, 0,
        };
        struct scsi_sense_hdr *sshdr;
        int result;

        if (!sshdr_external)
                sshdr = kzalloc(sizeof(*sshdr), GFP_KERNEL);
        else
                sshdr = sshdr_external;

        /* try to eat the UNIT_ATTENTION if there are enough retries */
        do {
                result = scsi_execute_req(sdev, cmd, DMA_NONE, NULL, 0, sshdr,
                                          timeout, retries, NULL);
                if (sdev->removable && scsi_sense_valid(sshdr) &&
                    sshdr->sense_key == UNIT_ATTENTION)
                        sdev->changed = 1;
        } while (scsi_sense_valid(sshdr) &&
                 sshdr->sense_key == UNIT_ATTENTION && --retries);

        if (!sshdr_external)
                kfree(sshdr);
        return result;
}
EXPORT_SYMBOL(scsi_test_unit_ready);

/**
 *      scsi_device_set_state - Take the given device through the device state model.
 *      @sdev:  scsi device to change the state of.
 *      @state: state to change to.
 *
 *      Returns zero if unsuccessful or an error if the requested 
 *      transition is illegal.
 */
int
scsi_device_set_state(struct scsi_device *sdev, enum scsi_device_state state)
{
        enum scsi_device_state oldstate = sdev->sdev_state;

        if (state == oldstate)
                return 0;

        switch (state) {
        case SDEV_CREATED:
                switch (oldstate) {
                case SDEV_CREATED_BLOCK:
                        break;
                default:
                        goto illegal;
                }
                break;
                        
        case SDEV_RUNNING:
                switch (oldstate) {
                case SDEV_CREATED:
                case SDEV_OFFLINE:
                case SDEV_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:
                case SDEV_CREATED_BLOCK:
                        break;
                default:
                        goto illegal;
                }
                break;

        }
        sdev->sdev_state = state;
        return 0;

 illegal:
        SCSI_LOG_ERROR_RECOVERY(1,
                                sdev_printk(KERN_ERR, sdev,
                                            "Illegal state transition %s->%s",
                                            scsi_device_state_name(oldstate),
                                            scsi_device_state_name(state))
                                );
        return -EINVAL;
}
EXPORT_SYMBOL(scsi_device_set_state);

/**
 *      sdev_evt_emit - emit a single SCSI device uevent
 *      @sdev: associated SCSI device
 *      @evt: event to emit
 *
 *      Send a single uevent (scsi_event) to the associated scsi_device.
 */
static void scsi_evt_emit(struct scsi_device *sdev, struct scsi_event *evt)
{
        int idx = 0;
        char *envp[3];

        switch (evt->evt_type) {
        case SDEV_EVT_MEDIA_CHANGE:
                envp[idx++] = "SDEV_MEDIA_CHANGE=1";
                break;
        case SDEV_EVT_INQUIRY_CHANGE_REPORTED:
                scsi_rescan_device(&sdev->sdev_gendev);
                envp[idx++] = "SDEV_UA=INQUIRY_DATA_HAS_CHANGED";
                break;
        case SDEV_EVT_CAPACITY_CHANGE_REPORTED:
                envp[idx++] = "SDEV_UA=CAPACITY_DATA_HAS_CHANGED";
                break;
        case SDEV_EVT_SOFT_THRESHOLD_REACHED_REPORTED:
               envp[idx++] = "SDEV_UA=THIN_PROVISIONING_SOFT_THRESHOLD_REACHED";
                break;
        case SDEV_EVT_MODE_PARAMETER_CHANGE_REPORTED:
                envp[idx++] = "SDEV_UA=MODE_PARAMETERS_CHANGED";
                break;
        case SDEV_EVT_LUN_CHANGE_REPORTED:
                envp[idx++] = "SDEV_UA=REPORTED_LUNS_DATA_HAS_CHANGED";
                break;
        case SDEV_EVT_ALUA_STATE_CHANGE_REPORTED:
                envp[idx++] = "SDEV_UA=ASYMMETRIC_ACCESS_STATE_CHANGED";
                break;
        default:
                /* do nothing */
                break;
        }

        envp[idx++] = NULL;

        kobject_uevent_env(&sdev->sdev_gendev.kobj, KOBJ_CHANGE, envp);
}

/**
 *      sdev_evt_thread - send a uevent for each scsi event
 *      @work: work struct for scsi_device
 *
 *      Dispatch queued events to their associated scsi_device kobjects
 *      as uevents.
 */
void scsi_evt_thread(struct work_struct *work)
{
        struct scsi_device *sdev;
        enum scsi_device_event evt_type;
        LIST_HEAD(event_list);

        sdev = container_of(work, struct scsi_device, event_work);

        for (evt_type = SDEV_EVT_FIRST; evt_type <= SDEV_EVT_LAST; evt_type++)
                if (test_and_clear_bit(evt_type, sdev->pending_events))
                        sdev_evt_send_simple(sdev, evt_type, GFP_KERNEL);

        while (1) {
                struct scsi_event *evt;
                struct list_head *this, *tmp;
                unsigned long flags;

                spin_lock_irqsave(&sdev->list_lock, flags);
                list_splice_init(&sdev->event_list, &event_list);
                spin_unlock_irqrestore(&sdev->list_lock, flags);

                if (list_empty(&event_list))
                        break;

                list_for_each_safe(this, tmp, &event_list) {
                        evt = list_entry(this, struct scsi_event, node);
                        list_del(&evt->node);
                        scsi_evt_emit(sdev, evt);
                        kfree(evt);
                }
        }
}

/**
 *      sdev_evt_send - send asserted event to uevent thread
 *      @sdev: scsi_device event occurred on
 *      @evt: event to send
 *
 *      Assert scsi device event asynchronously.
 */
void sdev_evt_send(struct scsi_device *sdev, struct scsi_event *evt)
{
        unsigned long flags;

#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);

/**
 *      sdev_evt_alloc - allocate a new scsi event
 *      @evt_type: type of event to allocate
 *      @gfpflags: GFP flags for allocation
 *
 *      Allocates and returns a new scsi_event.
 */
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:
        case SDEV_EVT_INQUIRY_CHANGE_REPORTED:
        case SDEV_EVT_CAPACITY_CHANGE_REPORTED:
        case SDEV_EVT_SOFT_THRESHOLD_REACHED_REPORTED:
        case SDEV_EVT_MODE_PARAMETER_CHANGE_REPORTED:
        case SDEV_EVT_LUN_CHANGE_REPORTED:
        case SDEV_EVT_ALUA_STATE_CHANGE_REPORTED:
        default:
                /* do nothing */
                break;
        }

        return evt;
}
EXPORT_SYMBOL_GPL(sdev_evt_alloc);

/**
 *      sdev_evt_send_simple - send asserted event to uevent thread
 *      @sdev: scsi_device event occurred on
 *      @evt_type: type of event to send
 *      @gfpflags: GFP flags for allocation
 *
 *      Assert scsi device event asynchronously, given an event type.
 */
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);

/**
 *      scsi_device_quiesce - Block user issued commands.
 *      @sdev:  scsi device to quiesce.
 *
 *      This works by trying to transition to the SDEV_QUIESCE state
 *      (which must be a legal transition).  When the device is in this
 *      state, only special requests will be accepted, all others will
 *      be deferred.  Since special requests may also be requeued requests,
 *      a successful return doesn't guarantee the device will be 
 *      totally quiescent.
 *
 *      Must be called with user context, may sleep.
 *
 *      Returns zero if unsuccessful or an error if not.
 */
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 (atomic_read(&sdev->device_busy)) {
                msleep_interruptible(200);
                scsi_run_queue(sdev->request_queue);
        }
        return 0;
}
EXPORT_SYMBOL(scsi_device_quiesce);

/**
 *      scsi_device_resume - Restart user issued commands to a quiesced device.
 *      @sdev:  scsi device to resume.
 *
 *      Moves the device from quiesced back to running and restarts the
 *      queues.
 *
 *      Must be called with user context, may sleep.
 */
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);

/**
 * scsi_internal_device_block - internal function to put a device temporarily into the SDEV_BLOCK state
 * @sdev:       device to block
 *
 * Block request made by scsi lld's to temporarily stop all
 * scsi commands on the specified device.  Called from interrupt
 * or normal process context.
 *
 * Returns zero if successful or error if not
 *
 * Notes:       
 *      This routine transitions the device to the SDEV_BLOCK state
 *      (which must be a legal transition).  When the device is in this
 *      state, all commands are deferred until the scsi lld reenables
 *      the device with scsi_device_unblock or device_block_tmo fires.
 */
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. 
         */
        if (q->mq_ops) {
                blk_mq_stop_hw_queues(q);
        } else {
                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);
 
/**
 * scsi_internal_device_unblock - resume a device after a block request
 * @sdev:       device to resume
 * @new_state:  state to set devices to after unblocking
 *
 * Called by scsi lld's or the midlayer to restart the device queue
 * for the previously suspended scsi device.  Called from interrupt or
 * normal process context.
 *
 * Returns zero if successful or error if not.
 *
 * Notes:       
 *      This routine transitions the device to the SDEV_RUNNING state
 *      or to one of the offline states (which must be a legal transition)
 *      allowing the midlayer to goose the queue for this device.
 */
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;

        if (q->mq_ops) {
                blk_mq_start_stopped_hw_queues(q, false);
        } else {
                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);

/**
 * scsi_kmap_atomic_sg - find and atomically map an sg-elemnt
 * @sgl:        scatter-gather list
 * @sg_count:   number of segments in sg
 * @offset:     offset in bytes into sg, on return offset into the mapped area
 * @len:        bytes to map, on return number of bytes mapped
 *
 * Returns virtual address of the start of the mapped page
 */
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);

/**
 * scsi_kunmap_atomic_sg - atomically unmap a virtual address, previously mapped with scsi_kmap_atomic_sg
 * @virt:       virtual address to be unmapped
 */
void scsi_kunmap_atomic_sg(void *virt)
{
        kunmap_atomic(virt);
}
EXPORT_SYMBOL(scsi_kunmap_atomic_sg);

void sdev_disable_disk_events(struct scsi_device *sdev)
{
        atomic_inc(&sdev->disk_events_disable_depth);
}
EXPORT_SYMBOL(sdev_disable_disk_events);

void sdev_enable_disk_events(struct scsi_device *sdev)
{
        if (WARN_ON_ONCE(atomic_read(&sdev->disk_events_disable_depth) <= 0))
                return;
        atomic_dec(&sdev->disk_events_disable_depth);
}
EXPORT_SYMBOL(sdev_enable_disk_events);

/**
 * scsi_vpd_lun_id - return a unique device identification
 * @sdev: SCSI device
 * @id:   buffer for the identification
 * @id_len:  length of the buffer
 *
 * Copies a unique device identification into @id based
 * on the information in the VPD page 0x83 of the device.
 * The string will be formatted as a SCSI name string.
 *
 * Returns the length of the identification or error on failure.
 * If the identifier is longer than the supplied buffer the actual
 * identifier length is returned and the buffer is not zero-padded.
 */
int scsi_vpd_lun_id(struct scsi_device *sdev, char *id, size_t id_len)
{
        u8 cur_id_type = 0xff;
        u8 cur_id_size = 0;
        unsigned char *d, *cur_id_str;
        unsigned char __rcu *vpd_pg83;
        int id_size = -EINVAL;

        rcu_read_lock();
        vpd_pg83 = rcu_dereference(sdev->vpd_pg83);
        if (!vpd_pg83) {
                rcu_read_unlock();
                return -ENXIO;
        }

        /*
         * Look for the correct descriptor.
         * Order of preference for lun descriptor:
         * - SCSI name string
         * - NAA IEEE Registered Extended
         * - EUI-64 based 16-byte
         * - EUI-64 based 12-byte
         * - NAA IEEE Registered
         * - NAA IEEE Extended
         * - T10 Vendor ID
         * as longer descriptors reduce the likelyhood
         * of identification clashes.
         */

        /* The id string must be at least 20 bytes + terminating NULL byte */
        if (id_len < 21) {
                rcu_read_unlock();
                return -EINVAL;
        }

        memset(id, 0, id_len);
        d = vpd_pg83 + 4;
        while (d < vpd_pg83 + sdev->vpd_pg83_len) {
                /* Skip designators not referring to the LUN */
                if ((d[1] & 0x30) != 0x00)
                        goto next_desig;

                switch (d[1] & 0xf) {
                case 0x1:
                        /* T10 Vendor ID */
                        if (cur_id_size > d[3])
                                break;
                        /* Prefer anything */
                        if (cur_id_type > 0x01 && cur_id_type != 0xff)
                                break;
                        cur_id_size = d[3];
                        if (cur_id_size + 4 > id_len)
                                cur_id_size = id_len - 4;
                        cur_id_str = d + 4;
                        cur_id_type = d[1] & 0xf;
                        id_size = snprintf(id, id_len, "t10.%*pE",
                                           cur_id_size, cur_id_str);
                        break;
                case 0x2:
                        /* EUI-64 */
                        if (cur_id_size > d[3])
                                break;
                        /* Prefer NAA IEEE Registered Extended */
                        if (cur_id_type == 0x3 &&
                            cur_id_size == d[3])
                                break;
                        cur_id_size = d[3];
                        cur_id_str = d + 4;
                        cur_id_type = d[1] & 0xf;
                        switch (cur_id_size) {
                        case 8:
                                id_size = snprintf(id, id_len,
                                                   "eui.%8phN",
                                                   cur_id_str);
                                break;
                        case 12:
                                id_size = snprintf(id, id_len,
                                                   "eui.%12phN",
                                                   cur_id_str);
                                break;
                        case 16:
                                id_size = snprintf(id, id_len,
                                                   "eui.%16phN",
                                                   cur_id_str);
                                break;
                        default:
                                cur_id_size = 0;
                                break;
                        }
                        break;
                case 0x3:
                        /* NAA */
                        if (cur_id_size > d[3])
                                break;
                        cur_id_size = d[3];
                        cur_id_str = d + 4;
                        cur_id_type = d[1] & 0xf;
                        switch (cur_id_size) {
                        case 8:
                                id_size = snprintf(id, id_len,
                                                   "naa.%8phN",
                                                   cur_id_str);
                                break;
                        case 16:
                                id_size = snprintf(id, id_len,
                                                   "naa.%16phN",
                                                   cur_id_str);
                                break;
                        default:
                                cur_id_size = 0;
                                break;
                        }
                        break;
                case 0x8:
                        /* SCSI name string */
                        if (cur_id_size + 4 > d[3])
                                break;
                        /* Prefer others for truncated descriptor */
                        if (cur_id_size && d[3] > id_len)
                                break;
                        cur_id_size = id_size = d[3];
                        cur_id_str = d + 4;
                        cur_id_type = d[1] & 0xf;
                        if (cur_id_size >= id_len)
                                cur_id_size = id_len - 1;
                        memcpy(id, cur_id_str, cur_id_size);
                        /* Decrease priority for truncated descriptor */
                        if (cur_id_size != id_size)
                                cur_id_size = 6;
                        break;
                default:
                        break;
                }
next_desig:
                d += d[3] + 4;
        }
        rcu_read_unlock();

        return id_size;
}
EXPORT_SYMBOL(scsi_vpd_lun_id);

/*
 * scsi_vpd_tpg_id - return a target port group identifier
 * @sdev: SCSI device
 *
 * Returns the Target Port Group identifier from the information
 * froom VPD page 0x83 of the device.
 *
 * Returns the identifier or error on failure.
 */
int scsi_vpd_tpg_id(struct scsi_device *sdev, int *rel_id)
{
        unsigned char *d;
        unsigned char __rcu *vpd_pg83;
        int group_id = -EAGAIN, rel_port = -1;

        rcu_read_lock();
        vpd_pg83 = rcu_dereference(sdev->vpd_pg83);
        if (!vpd_pg83) {
                rcu_read_unlock();
                return -ENXIO;
        }

        d = sdev->vpd_pg83 + 4;
        while (d < sdev->vpd_pg83 + sdev->vpd_pg83_len) {
                switch (d[1] & 0xf) {
                case 0x4:
                        /* Relative target port */
                        rel_port = get_unaligned_be16(&d[6]);
                        break;
                case 0x5:
                        /* Target port group */
                        group_id = get_unaligned_be16(&d[6]);
                        break;
                default:
                        break;
                }
                d += d[3] + 4;
        }
        rcu_read_unlock();

        if (group_id >= 0 && rel_id && rel_port != -1)
                *rel_id = rel_port;

        return group_id;
}
EXPORT_SYMBOL(scsi_vpd_tpg_id);