[safe/jmp/linux-2.6] / drivers / scsi / scsi_error.c

/*
 *  scsi_error.c Copyright (C) 1997 Eric Youngdale
 *
 *  SCSI error/timeout handling
 *      Initial versions: Eric Youngdale.  Based upon conversations with
 *                        Leonard Zubkoff and David Miller at Linux Expo, 
 *                        ideas originating from all over the place.
 *
 *      Restructured scsi_unjam_host and associated functions.
 *      September 04, 2002 Mike Anderson (andmike@us.ibm.com)
 *
 *      Forward port of Russell King's (rmk@arm.linux.org.uk) changes and
 *      minor  cleanups.
 *      September 30, 2002 Mike Anderson (andmike@us.ibm.com)
 */

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/blkdev.h>
#include <linux/delay.h>

#include <scsi/scsi.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_ioctl.h>
#include <scsi/scsi_request.h>

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

#define SENSE_TIMEOUT           (10*HZ)
#define START_UNIT_TIMEOUT      (30*HZ)

/*
 * These should *probably* be handled by the host itself.
 * Since it is allowed to sleep, it probably should.
 */
#define BUS_RESET_SETTLE_TIME   (10)
#define HOST_RESET_SETTLE_TIME  (10)

/* called with shost->host_lock held */
void scsi_eh_wakeup(struct Scsi_Host *shost)
{
        if (shost->host_busy == shost->host_failed) {
                up(shost->eh_wait);
                SCSI_LOG_ERROR_RECOVERY(5,
                                printk("Waking error handler thread\n"));
        }
}

/**
 * scsi_eh_scmd_add - add scsi cmd to error handling.
 * @scmd:       scmd to run eh on.
 * @eh_flag:    optional SCSI_EH flag.
 *
 * Return value:
 *      0 on failure.
 **/
int scsi_eh_scmd_add(struct scsi_cmnd *scmd, int eh_flag)
{
        struct Scsi_Host *shost = scmd->device->host;
        unsigned long flags;

        if (shost->eh_wait == NULL)
                return 0;

        spin_lock_irqsave(shost->host_lock, flags);

        scsi_eh_eflags_set(scmd, eh_flag);
        /*
         * FIXME: Can we stop setting owner and state.
         */
        scmd->owner = SCSI_OWNER_ERROR_HANDLER;
        scmd->state = SCSI_STATE_FAILED;
        list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q);
        set_bit(SHOST_RECOVERY, &shost->shost_state);
        shost->host_failed++;
        scsi_eh_wakeup(shost);
        spin_unlock_irqrestore(shost->host_lock, flags);
        return 1;
}

/**
 * scsi_add_timer - Start timeout timer for a single scsi command.
 * @scmd:       scsi command that is about to start running.
 * @timeout:    amount of time to allow this command to run.
 * @complete:   timeout function to call if timer isn't canceled.
 *
 * Notes:
 *    This should be turned into an inline function.  Each scsi command
 *    has its own timer, and as it is added to the queue, we set up the
 *    timer.  When the command completes, we cancel the timer.
 **/
void scsi_add_timer(struct scsi_cmnd *scmd, int timeout,
                    void (*complete)(struct scsi_cmnd *))
{

        /*
         * If the clock was already running for this command, then
         * first delete the timer.  The timer handling code gets rather
         * confused if we don't do this.
         */
        if (scmd->eh_timeout.function)
                del_timer(&scmd->eh_timeout);

        scmd->eh_timeout.data = (unsigned long)scmd;
        scmd->eh_timeout.expires = jiffies + timeout;
        scmd->eh_timeout.function = (void (*)(unsigned long)) complete;

        SCSI_LOG_ERROR_RECOVERY(5, printk("%s: scmd: %p, time:"
                                          " %d, (%p)\n", __FUNCTION__,
                                          scmd, timeout, complete));

        add_timer(&scmd->eh_timeout);
}
EXPORT_SYMBOL(scsi_add_timer);

/**
 * scsi_delete_timer - Delete/cancel timer for a given function.
 * @scmd:       Cmd that we are canceling timer for
 *
 * Notes:
 *     This should be turned into an inline function.
 *
 * Return value:
 *     1 if we were able to detach the timer.  0 if we blew it, and the
 *     timer function has already started to run.
 **/
int scsi_delete_timer(struct scsi_cmnd *scmd)
{
        int rtn;

        rtn = del_timer(&scmd->eh_timeout);

        SCSI_LOG_ERROR_RECOVERY(5, printk("%s: scmd: %p,"
                                         " rtn: %d\n", __FUNCTION__,
                                         scmd, rtn));

        scmd->eh_timeout.data = (unsigned long)NULL;
        scmd->eh_timeout.function = NULL;

        return rtn;
}
EXPORT_SYMBOL(scsi_delete_timer);

/**
 * scsi_times_out - Timeout function for normal scsi commands.
 * @scmd:       Cmd that is timing out.
 *
 * Notes:
 *     We do not need to lock this.  There is the potential for a race
 *     only in that the normal completion handling might run, but if the
 *     normal completion function determines that the timer has already
 *     fired, then it mustn't do anything.
 **/
void scsi_times_out(struct scsi_cmnd *scmd)
{
        scsi_log_completion(scmd, TIMEOUT_ERROR);

        if (scmd->device->host->hostt->eh_timed_out)
                switch (scmd->device->host->hostt->eh_timed_out(scmd)) {
                case EH_HANDLED:
                        __scsi_done(scmd);
                        return;
                case EH_RESET_TIMER:
                        /* This allows a single retry even of a command
                         * with allowed == 0 */
                        if (scmd->retries++ > scmd->allowed)
                                break;
                        scsi_add_timer(scmd, scmd->timeout_per_command,
                                       scsi_times_out);
                        return;
                case EH_NOT_HANDLED:
                        break;
                }

        if (unlikely(!scsi_eh_scmd_add(scmd, SCSI_EH_CANCEL_CMD))) {
                panic("Error handler thread not present at %p %p %s %d",
                      scmd, scmd->device->host, __FILE__, __LINE__);
        }
}

/**
 * scsi_block_when_processing_errors - Prevent cmds from being queued.
 * @sdev:       Device on which we are performing recovery.
 *
 * Description:
 *     We block until the host is out of error recovery, and then check to
 *     see whether the host or the device is offline.
 *
 * Return value:
 *     0 when dev was taken offline by error recovery. 1 OK to proceed.
 **/
int scsi_block_when_processing_errors(struct scsi_device *sdev)
{
        int online;

        wait_event(sdev->host->host_wait, (!test_bit(SHOST_RECOVERY, &sdev->host->shost_state)));

        online = scsi_device_online(sdev);

        SCSI_LOG_ERROR_RECOVERY(5, printk("%s: rtn: %d\n", __FUNCTION__,
                                          online));

        return online;
}
EXPORT_SYMBOL(scsi_block_when_processing_errors);

#ifdef CONFIG_SCSI_LOGGING
/**
 * scsi_eh_prt_fail_stats - Log info on failures.
 * @shost:      scsi host being recovered.
 * @work_q:     Queue of scsi cmds to process.
 **/
static inline void scsi_eh_prt_fail_stats(struct Scsi_Host *shost,
                                          struct list_head *work_q)
{
        struct scsi_cmnd *scmd;
        struct scsi_device *sdev;
        int total_failures = 0;
        int cmd_failed = 0;
        int cmd_cancel = 0;
        int devices_failed = 0;

        shost_for_each_device(sdev, shost) {
                list_for_each_entry(scmd, work_q, eh_entry) {
                        if (scmd->device == sdev) {
                                ++total_failures;
                                if (scsi_eh_eflags_chk(scmd,
                                                       SCSI_EH_CANCEL_CMD))
                                        ++cmd_cancel;
                                else 
                                        ++cmd_failed;
                        }
                }

                if (cmd_cancel || cmd_failed) {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                printk("%s: %d:%d:%d:%d cmds failed: %d,"
                                       " cancel: %d\n",
                                       __FUNCTION__, shost->host_no,
                                       sdev->channel, sdev->id, sdev->lun,
                                       cmd_failed, cmd_cancel));
                        cmd_cancel = 0;
                        cmd_failed = 0;
                        ++devices_failed;
                }
        }

        SCSI_LOG_ERROR_RECOVERY(2, printk("Total of %d commands on %d"
                                          " devices require eh work\n",
                                  total_failures, devices_failed));
}
#endif

/**
 * scsi_check_sense - Examine scsi cmd sense
 * @scmd:       Cmd to have sense checked.
 *
 * Return value:
 *      SUCCESS or FAILED or NEEDS_RETRY
 *
 * Notes:
 *      When a deferred error is detected the current command has
 *      not been executed and needs retrying.
 **/
static int scsi_check_sense(struct scsi_cmnd *scmd)
{
        struct scsi_sense_hdr sshdr;

        if (! scsi_command_normalize_sense(scmd, &sshdr))
                return FAILED;  /* no valid sense data */

        if (scsi_sense_is_deferred(&sshdr))
                return NEEDS_RETRY;

        /*
         * Previous logic looked for FILEMARK, EOM or ILI which are
         * mainly associated with tapes and returned SUCCESS.
         */
        if (sshdr.response_code == 0x70) {
                /* fixed format */
                if (scmd->sense_buffer[2] & 0xe0)
                        return SUCCESS;
        } else {
                /*
                 * descriptor format: look for "stream commands sense data
                 * descriptor" (see SSC-3). Assume single sense data
                 * descriptor. Ignore ILI from SBC-2 READ LONG and WRITE LONG.
                 */
                if ((sshdr.additional_length > 3) &&
                    (scmd->sense_buffer[8] == 0x4) &&
                    (scmd->sense_buffer[11] & 0xe0))
                        return SUCCESS;
        }

        switch (sshdr.sense_key) {
        case NO_SENSE:
                return SUCCESS;
        case RECOVERED_ERROR:
                return /* soft_error */ SUCCESS;

        case ABORTED_COMMAND:
                return NEEDS_RETRY;
        case NOT_READY:
        case UNIT_ATTENTION:
                /*
                 * if we are expecting a cc/ua because of a bus reset that we
                 * performed, treat this just as a retry.  otherwise this is
                 * information that we should pass up to the upper-level driver
                 * so that we can deal with it there.
                 */
                if (scmd->device->expecting_cc_ua) {
                        scmd->device->expecting_cc_ua = 0;
                        return NEEDS_RETRY;
                }
                /*
                 * if the device is in the process of becoming ready, we 
                 * should retry.
                 */
                if ((sshdr.asc == 0x04) && (sshdr.ascq == 0x01))
                        return NEEDS_RETRY;
                /*
                 * if the device is not started, we need to wake
                 * the error handler to start the motor
                 */
                if (scmd->device->allow_restart &&
                    (sshdr.asc == 0x04) && (sshdr.ascq == 0x02))
                        return FAILED;
                return SUCCESS;

                /* these three are not supported */
        case COPY_ABORTED:
        case VOLUME_OVERFLOW:
        case MISCOMPARE:
                return SUCCESS;

        case MEDIUM_ERROR:
                return NEEDS_RETRY;

        case HARDWARE_ERROR:
                if (scmd->device->retry_hwerror)
                        return NEEDS_RETRY;
                else
                        return SUCCESS;

        case ILLEGAL_REQUEST:
        case BLANK_CHECK:
        case DATA_PROTECT:
        default:
                return SUCCESS;
        }
}

/**
 * scsi_eh_completed_normally - Disposition a eh cmd on return from LLD.
 * @scmd:       SCSI cmd to examine.
 *
 * Notes:
 *    This is *only* called when we are examining the status of commands
 *    queued during error recovery.  the main difference here is that we
 *    don't allow for the possibility of retries here, and we are a lot
 *    more restrictive about what we consider acceptable.
 **/
static int scsi_eh_completed_normally(struct scsi_cmnd *scmd)
{
        /*
         * first check the host byte, to see if there is anything in there
         * that would indicate what we need to do.
         */
        if (host_byte(scmd->result) == DID_RESET) {
                /*
                 * rats.  we are already in the error handler, so we now
                 * get to try and figure out what to do next.  if the sense
                 * is valid, we have a pretty good idea of what to do.
                 * if not, we mark it as FAILED.
                 */
                return scsi_check_sense(scmd);
        }
        if (host_byte(scmd->result) != DID_OK)
                return FAILED;

        /*
         * next, check the message byte.
         */
        if (msg_byte(scmd->result) != COMMAND_COMPLETE)
                return FAILED;

        /*
         * now, check the status byte to see if this indicates
         * anything special.
         */
        switch (status_byte(scmd->result)) {
        case GOOD:
        case COMMAND_TERMINATED:
                return SUCCESS;
        case CHECK_CONDITION:
                return scsi_check_sense(scmd);
        case CONDITION_GOOD:
        case INTERMEDIATE_GOOD:
        case INTERMEDIATE_C_GOOD:
                /*
                 * who knows?  FIXME(eric)
                 */
                return SUCCESS;
        case BUSY:
        case QUEUE_FULL:
        case RESERVATION_CONFLICT:
        default:
                return FAILED;
        }
        return FAILED;
}

/**
 * scsi_eh_times_out - timeout function for error handling.
 * @scmd:       Cmd that is timing out.
 *
 * Notes:
 *    During error handling, the kernel thread will be sleeping waiting
 *    for some action to complete on the device.  our only job is to
 *    record that it timed out, and to wake up the thread.
 **/
static void scsi_eh_times_out(struct scsi_cmnd *scmd)
{
        scsi_eh_eflags_set(scmd, SCSI_EH_REC_TIMEOUT);
        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: scmd:%p\n", __FUNCTION__,
                                          scmd));

        up(scmd->device->host->eh_action);
}

/**
 * scsi_eh_done - Completion function for error handling.
 * @scmd:       Cmd that is done.
 **/
static void scsi_eh_done(struct scsi_cmnd *scmd)
{
        /*
         * if the timeout handler is already running, then just set the
         * flag which says we finished late, and return.  we have no
         * way of stopping the timeout handler from running, so we must
         * always defer to it.
         */
        if (del_timer(&scmd->eh_timeout)) {
                scmd->request->rq_status = RQ_SCSI_DONE;
                scmd->owner = SCSI_OWNER_ERROR_HANDLER;

                SCSI_LOG_ERROR_RECOVERY(3, printk("%s scmd: %p result: %x\n",
                                           __FUNCTION__, scmd, scmd->result));

                up(scmd->device->host->eh_action);
        }
}

/**
 * scsi_send_eh_cmnd  - send a cmd to a device as part of error recovery.
 * @scmd:       SCSI Cmd to send.
 * @timeout:    Timeout for cmd.
 *
 * Notes:
 *    The initialization of the structures is quite a bit different in
 *    this case, and furthermore, there is a different completion handler
 *    vs scsi_dispatch_cmd.
 * Return value:
 *    SUCCESS or FAILED or NEEDS_RETRY
 **/
static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, int timeout)
{
        struct scsi_device *sdev = scmd->device;
        struct Scsi_Host *shost = sdev->host;
        DECLARE_MUTEX_LOCKED(sem);
        unsigned long flags;
        int rtn = SUCCESS;

        /*
         * we will use a queued command if possible, otherwise we will
         * emulate the queuing and calling of completion function ourselves.
         */
        scmd->owner = SCSI_OWNER_LOWLEVEL;

        if (sdev->scsi_level <= SCSI_2)
                scmd->cmnd[1] = (scmd->cmnd[1] & 0x1f) |
                        (sdev->lun << 5 & 0xe0);

        scsi_add_timer(scmd, timeout, scsi_eh_times_out);

        /*
         * set up the semaphore so we wait for the command to complete.
         */
        shost->eh_action = &sem;
        scmd->request->rq_status = RQ_SCSI_BUSY;

        spin_lock_irqsave(shost->host_lock, flags);
        scsi_log_send(scmd);
        shost->hostt->queuecommand(scmd, scsi_eh_done);
        spin_unlock_irqrestore(shost->host_lock, flags);

        down(&sem);
        scsi_log_completion(scmd, SUCCESS);

        shost->eh_action = NULL;

        /*
         * see if timeout.  if so, tell the host to forget about it.
         * in other words, we don't want a callback any more.
         */
        if (scsi_eh_eflags_chk(scmd, SCSI_EH_REC_TIMEOUT)) {
                scsi_eh_eflags_clr(scmd,  SCSI_EH_REC_TIMEOUT);
                scmd->owner = SCSI_OWNER_LOWLEVEL;

                /*
                 * as far as the low level driver is
                 * concerned, this command is still active, so
                 * we must give the low level driver a chance
                 * to abort it. (db) 
                 *
                 * FIXME(eric) - we are not tracking whether we could
                 * abort a timed out command or not.  not sure how
                 * we should treat them differently anyways.
                 */
                if (shost->hostt->eh_abort_handler)
                        shost->hostt->eh_abort_handler(scmd);
                        
                scmd->request->rq_status = RQ_SCSI_DONE;
                scmd->owner = SCSI_OWNER_ERROR_HANDLER;
                        
                rtn = FAILED;
        }

        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: scmd: %p, rtn:%x\n",
                                          __FUNCTION__, scmd, rtn));

        /*
         * now examine the actual status codes to see whether the command
         * actually did complete normally.
         */
        if (rtn == SUCCESS) {
                rtn = scsi_eh_completed_normally(scmd);
                SCSI_LOG_ERROR_RECOVERY(3,
                        printk("%s: scsi_eh_completed_normally %x\n",
                               __FUNCTION__, rtn));
                switch (rtn) {
                case SUCCESS:
                case NEEDS_RETRY:
                case FAILED:
                        break;
                default:
                        rtn = FAILED;
                        break;
                }
        }

        return rtn;
}

/**
 * scsi_request_sense - Request sense data from a particular target.
 * @scmd:       SCSI cmd for request sense.
 *
 * Notes:
 *    Some hosts automatically obtain this information, others require
 *    that we obtain it on our own. This function will *not* return until
 *    the command either times out, or it completes.
 **/
static int scsi_request_sense(struct scsi_cmnd *scmd)
{
        static unsigned char generic_sense[6] =
        {REQUEST_SENSE, 0, 0, 0, 252, 0};
        unsigned char *scsi_result;
        int saved_result;
        int rtn;

        memcpy(scmd->cmnd, generic_sense, sizeof(generic_sense));

        scsi_result = kmalloc(252, GFP_ATOMIC | ((scmd->device->host->hostt->unchecked_isa_dma) ? __GFP_DMA : 0));


        if (unlikely(!scsi_result)) {
                printk(KERN_ERR "%s: cannot allocate scsi_result.\n",
                       __FUNCTION__);
                return FAILED;
        }

        /*
         * zero the sense buffer.  some host adapters automatically always
         * request sense, so it is not a good idea that
         * scmd->request_buffer and scmd->sense_buffer point to the same
         * address (db).  0 is not a valid sense code. 
         */
        memset(scmd->sense_buffer, 0, sizeof(scmd->sense_buffer));
        memset(scsi_result, 0, 252);

        saved_result = scmd->result;
        scmd->request_buffer = scsi_result;
        scmd->request_bufflen = 252;
        scmd->use_sg = 0;
        scmd->cmd_len = COMMAND_SIZE(scmd->cmnd[0]);
        scmd->sc_data_direction = DMA_FROM_DEVICE;
        scmd->underflow = 0;

        rtn = scsi_send_eh_cmnd(scmd, SENSE_TIMEOUT);

        /* last chance to have valid sense data */
        if(!SCSI_SENSE_VALID(scmd)) {
                memcpy(scmd->sense_buffer, scmd->request_buffer,
                       sizeof(scmd->sense_buffer));
        }

        kfree(scsi_result);

        /*
         * when we eventually call scsi_finish, we really wish to complete
         * the original request, so let's restore the original data. (db)
         */
        scsi_setup_cmd_retry(scmd);
        scmd->result = saved_result;
        return rtn;
}

/**
 * scsi_eh_finish_cmd - Handle a cmd that eh is finished with.
 * @scmd:       Original SCSI cmd that eh has finished.
 * @done_q:     Queue for processed commands.
 *
 * Notes:
 *    We don't want to use the normal command completion while we are are
 *    still handling errors - it may cause other commands to be queued,
 *    and that would disturb what we are doing.  thus we really want to
 *    keep a list of pending commands for final completion, and once we
 *    are ready to leave error handling we handle completion for real.
 **/
static void scsi_eh_finish_cmd(struct scsi_cmnd *scmd,
                               struct list_head *done_q)
{
        scmd->device->host->host_failed--;
        scmd->state = SCSI_STATE_BHQUEUE;

        scsi_eh_eflags_clr_all(scmd);

        /*
         * set this back so that the upper level can correctly free up
         * things.
         */
        scsi_setup_cmd_retry(scmd);
        list_move_tail(&scmd->eh_entry, done_q);
}

/**
 * scsi_eh_get_sense - Get device sense data.
 * @work_q:     Queue of commands to process.
 * @done_q:     Queue of proccessed commands..
 *
 * Description:
 *    See if we need to request sense information.  if so, then get it
 *    now, so we have a better idea of what to do.  
 *
 * Notes:
 *    This has the unfortunate side effect that if a shost adapter does
 *    not automatically request sense information, that we end up shutting
 *    it down before we request it.
 *
 *    All drivers should request sense information internally these days,
 *    so for now all I have to say is tough noogies if you end up in here.
 *
 *    XXX: Long term this code should go away, but that needs an audit of
 *         all LLDDs first.
 **/
static int scsi_eh_get_sense(struct list_head *work_q,
                             struct list_head *done_q)
{
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd;
        int rtn;

        list_for_each_safe(lh, lh_sf, work_q) {
                scmd = list_entry(lh, struct scsi_cmnd, eh_entry);
                if (scsi_eh_eflags_chk(scmd, SCSI_EH_CANCEL_CMD) ||
                    SCSI_SENSE_VALID(scmd))
                        continue;

                SCSI_LOG_ERROR_RECOVERY(2, printk("%s: requesting sense"
                                                  " for id: %d\n",
                                                  current->comm,
                                                  scmd->device->id));
                rtn = scsi_request_sense(scmd);
                if (rtn != SUCCESS)
                        continue;

                SCSI_LOG_ERROR_RECOVERY(3, printk("sense requested for %p"
                                                  " result %x\n", scmd,
                                                  scmd->result));
                SCSI_LOG_ERROR_RECOVERY(3, scsi_print_sense("bh", scmd));

                rtn = scsi_decide_disposition(scmd);

                /*
                 * if the result was normal, then just pass it along to the
                 * upper level.
                 */
                if (rtn == SUCCESS)
                        /* we don't want this command reissued, just
                         * finished with the sense data, so set
                         * retries to the max allowed to ensure it
                         * won't get reissued */
                        scmd->retries = scmd->allowed;
                else if (rtn != NEEDS_RETRY)
                        continue;

                scsi_eh_finish_cmd(scmd, done_q);
        }

        return list_empty(work_q);
}

/**
 * scsi_try_to_abort_cmd - Ask host to abort a running command.
 * @scmd:       SCSI cmd to abort from Lower Level.
 *
 * Notes:
 *    This function will not return until the user's completion function
 *    has been called.  there is no timeout on this operation.  if the
 *    author of the low-level driver wishes this operation to be timed,
 *    they can provide this facility themselves.  helper functions in
 *    scsi_error.c can be supplied to make this easier to do.
 **/
static int scsi_try_to_abort_cmd(struct scsi_cmnd *scmd)
{
        if (!scmd->device->host->hostt->eh_abort_handler)
                return FAILED;

        /*
         * scsi_done was called just after the command timed out and before
         * we had a chance to process it. (db)
         */
        if (scmd->serial_number == 0)
                return SUCCESS;

        scmd->owner = SCSI_OWNER_LOWLEVEL;

        return scmd->device->host->hostt->eh_abort_handler(scmd);
}

/**
 * scsi_eh_tur - Send TUR to device.
 * @scmd:       Scsi cmd to send TUR
 *
 * Return value:
 *    0 - Device is ready. 1 - Device NOT ready.
 **/
static int scsi_eh_tur(struct scsi_cmnd *scmd)
{
        static unsigned char tur_command[6] = {TEST_UNIT_READY, 0, 0, 0, 0, 0};
        int retry_cnt = 1, rtn;
        int saved_result;

retry_tur:
        memcpy(scmd->cmnd, tur_command, sizeof(tur_command));

        /*
         * zero the sense buffer.  the scsi spec mandates that any
         * untransferred sense data should be interpreted as being zero.
         */
        memset(scmd->sense_buffer, 0, sizeof(scmd->sense_buffer));

        saved_result = scmd->result;
        scmd->request_buffer = NULL;
        scmd->request_bufflen = 0;
        scmd->use_sg = 0;
        scmd->cmd_len = COMMAND_SIZE(scmd->cmnd[0]);
        scmd->underflow = 0;
        scmd->sc_data_direction = DMA_NONE;

        rtn = scsi_send_eh_cmnd(scmd, SENSE_TIMEOUT);

        /*
         * when we eventually call scsi_finish, we really wish to complete
         * the original request, so let's restore the original data. (db)
         */
        scsi_setup_cmd_retry(scmd);
        scmd->result = saved_result;

        /*
         * hey, we are done.  let's look to see what happened.
         */
        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: scmd %p rtn %x\n",
                __FUNCTION__, scmd, rtn));
        if (rtn == SUCCESS)
                return 0;
        else if (rtn == NEEDS_RETRY)
                if (retry_cnt--)
                        goto retry_tur;
        return 1;
}

/**
 * scsi_eh_abort_cmds - abort canceled commands.
 * @shost:      scsi host being recovered.
 * @eh_done_q:  list_head for processed commands.
 *
 * Decription:
 *    Try and see whether or not it makes sense to try and abort the
 *    running command.  this only works out to be the case if we have one
 *    command that has timed out.  if the command simply failed, it makes
 *    no sense to try and abort the command, since as far as the shost
 *    adapter is concerned, it isn't running.
 **/
static int scsi_eh_abort_cmds(struct list_head *work_q,
                              struct list_head *done_q)
{
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd;
        int rtn;

        list_for_each_safe(lh, lh_sf, work_q) {
                scmd = list_entry(lh, struct scsi_cmnd, eh_entry);
                if (!scsi_eh_eflags_chk(scmd, SCSI_EH_CANCEL_CMD))
                        continue;
                SCSI_LOG_ERROR_RECOVERY(3, printk("%s: aborting cmd:"
                                                  "0x%p\n", current->comm,
                                                  scmd));
                rtn = scsi_try_to_abort_cmd(scmd);
                if (rtn == SUCCESS) {
                        scsi_eh_eflags_clr(scmd,  SCSI_EH_CANCEL_CMD);
                        if (!scsi_device_online(scmd->device) ||
                            !scsi_eh_tur(scmd)) {
                                scsi_eh_finish_cmd(scmd, done_q);
                        }
                                
                } else
                        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: aborting"
                                                          " cmd failed:"
                                                          "0x%p\n",
                                                          current->comm,
                                                          scmd));
        }

        return list_empty(work_q);
}

/**
 * scsi_try_bus_device_reset - Ask host to perform a BDR on a dev
 * @scmd:       SCSI cmd used to send BDR       
 *
 * Notes:
 *    There is no timeout for this operation.  if this operation is
 *    unreliable for a given host, then the host itself needs to put a
 *    timer on it, and set the host back to a consistent state prior to
 *    returning.
 **/
static int scsi_try_bus_device_reset(struct scsi_cmnd *scmd)
{
        int rtn;

        if (!scmd->device->host->hostt->eh_device_reset_handler)
                return FAILED;

        scmd->owner = SCSI_OWNER_LOWLEVEL;

        rtn = scmd->device->host->hostt->eh_device_reset_handler(scmd);

        if (rtn == SUCCESS) {
                scmd->device->was_reset = 1;
                scmd->device->expecting_cc_ua = 1;
        }

        return rtn;
}

/**
 * scsi_eh_try_stu - Send START_UNIT to device.
 * @scmd:       Scsi cmd to send START_UNIT
 *
 * Return value:
 *    0 - Device is ready. 1 - Device NOT ready.
 **/
static int scsi_eh_try_stu(struct scsi_cmnd *scmd)
{
        static unsigned char stu_command[6] = {START_STOP, 0, 0, 0, 1, 0};
        int rtn;
        int saved_result;

        if (!scmd->device->allow_restart)
                return 1;

        memcpy(scmd->cmnd, stu_command, sizeof(stu_command));

        /*
         * zero the sense buffer.  the scsi spec mandates that any
         * untransferred sense data should be interpreted as being zero.
         */
        memset(scmd->sense_buffer, 0, sizeof(scmd->sense_buffer));

        saved_result = scmd->result;
        scmd->request_buffer = NULL;
        scmd->request_bufflen = 0;
        scmd->use_sg = 0;
        scmd->cmd_len = COMMAND_SIZE(scmd->cmnd[0]);
        scmd->underflow = 0;
        scmd->sc_data_direction = DMA_NONE;

        rtn = scsi_send_eh_cmnd(scmd, START_UNIT_TIMEOUT);

        /*
         * when we eventually call scsi_finish, we really wish to complete
         * the original request, so let's restore the original data. (db)
         */
        scsi_setup_cmd_retry(scmd);
        scmd->result = saved_result;

        /*
         * hey, we are done.  let's look to see what happened.
         */
        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: scmd %p rtn %x\n",
                __FUNCTION__, scmd, rtn));
        if (rtn == SUCCESS)
                return 0;
        return 1;
}

 /**
 * scsi_eh_stu - send START_UNIT if needed
 * @shost:      scsi host being recovered.
 * @eh_done_q:  list_head for processed commands.
 *
 * Notes:
 *    If commands are failing due to not ready, initializing command required,
 *      try revalidating the device, which will end up sending a start unit. 
 **/
static int scsi_eh_stu(struct Scsi_Host *shost,
                              struct list_head *work_q,
                              struct list_head *done_q)
{
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd, *stu_scmd;
        struct scsi_device *sdev;

        shost_for_each_device(sdev, shost) {
                stu_scmd = NULL;
                list_for_each_entry(scmd, work_q, eh_entry)
                        if (scmd->device == sdev && SCSI_SENSE_VALID(scmd) &&
                            scsi_check_sense(scmd) == FAILED ) {
                                stu_scmd = scmd;
                                break;
                        }

                if (!stu_scmd)
                        continue;

                SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Sending START_UNIT to sdev:"
                                                  " 0x%p\n", current->comm, sdev));

                if (!scsi_eh_try_stu(stu_scmd)) {
                        if (!scsi_device_online(sdev) ||
                            !scsi_eh_tur(stu_scmd)) {
                                list_for_each_safe(lh, lh_sf, work_q) {
                                        scmd = list_entry(lh, struct scsi_cmnd, eh_entry);
                                        if (scmd->device == sdev)
                                                scsi_eh_finish_cmd(scmd, done_q);
                                }
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                                printk("%s: START_UNIT failed to sdev:"
                                                       " 0x%p\n", current->comm, sdev));
                }
        }

        return list_empty(work_q);
}


/**
 * scsi_eh_bus_device_reset - send bdr if needed
 * @shost:      scsi host being recovered.
 * @eh_done_q:  list_head for processed commands.
 *
 * Notes:
 *    Try a bus device reset.  still, look to see whether we have multiple
 *    devices that are jammed or not - if we have multiple devices, it
 *    makes no sense to try bus_device_reset - we really would need to try
 *    a bus_reset instead. 
 **/
static int scsi_eh_bus_device_reset(struct Scsi_Host *shost,
                                    struct list_head *work_q,
                                    struct list_head *done_q)
{
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd, *bdr_scmd;
        struct scsi_device *sdev;
        int rtn;

        shost_for_each_device(sdev, shost) {
                bdr_scmd = NULL;
                list_for_each_entry(scmd, work_q, eh_entry)
                        if (scmd->device == sdev) {
                                bdr_scmd = scmd;
                                break;
                        }

                if (!bdr_scmd)
                        continue;

                SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Sending BDR sdev:"
                                                  " 0x%p\n", current->comm,
                                                  sdev));
                rtn = scsi_try_bus_device_reset(bdr_scmd);
                if (rtn == SUCCESS) {
                        if (!scsi_device_online(sdev) ||
                            !scsi_eh_tur(bdr_scmd)) {
                                list_for_each_safe(lh, lh_sf,
                                                   work_q) {
                                        scmd = list_entry(lh, struct
                                                          scsi_cmnd,
                                                          eh_entry);
                                        if (scmd->device == sdev)
                                                scsi_eh_finish_cmd(scmd,
                                                                   done_q);
                                }
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: BDR"
                                                          " failed sdev:"
                                                          "0x%p\n",
                                                          current->comm,
                                                           sdev));
                }
        }

        return list_empty(work_q);
}

/**
 * scsi_try_bus_reset - ask host to perform a bus reset
 * @scmd:       SCSI cmd to send bus reset.
 **/
static int scsi_try_bus_reset(struct scsi_cmnd *scmd)
{
        unsigned long flags;
        int rtn;

        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Snd Bus RST\n",
                                          __FUNCTION__));
        scmd->owner = SCSI_OWNER_LOWLEVEL;

        if (!scmd->device->host->hostt->eh_bus_reset_handler)
                return FAILED;

        spin_lock_irqsave(scmd->device->host->host_lock, flags);
        rtn = scmd->device->host->hostt->eh_bus_reset_handler(scmd);
        spin_unlock_irqrestore(scmd->device->host->host_lock, flags);

        if (rtn == SUCCESS) {
                if (!scmd->device->host->hostt->skip_settle_delay)
                        ssleep(BUS_RESET_SETTLE_TIME);
                spin_lock_irqsave(scmd->device->host->host_lock, flags);
                scsi_report_bus_reset(scmd->device->host, scmd->device->channel);
                spin_unlock_irqrestore(scmd->device->host->host_lock, flags);
        }

        return rtn;
}

/**
 * scsi_try_host_reset - ask host adapter to reset itself
 * @scmd:       SCSI cmd to send hsot reset.
 **/
static int scsi_try_host_reset(struct scsi_cmnd *scmd)
{
        unsigned long flags;
        int rtn;

        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Snd Host RST\n",
                                          __FUNCTION__));
        scmd->owner = SCSI_OWNER_LOWLEVEL;

        if (!scmd->device->host->hostt->eh_host_reset_handler)
                return FAILED;

        spin_lock_irqsave(scmd->device->host->host_lock, flags);
        rtn = scmd->device->host->hostt->eh_host_reset_handler(scmd);
        spin_unlock_irqrestore(scmd->device->host->host_lock, flags);

        if (rtn == SUCCESS) {
                if (!scmd->device->host->hostt->skip_settle_delay)
                        ssleep(HOST_RESET_SETTLE_TIME);
                spin_lock_irqsave(scmd->device->host->host_lock, flags);
                scsi_report_bus_reset(scmd->device->host, scmd->device->channel);
                spin_unlock_irqrestore(scmd->device->host->host_lock, flags);
        }

        return rtn;
}

/**
 * scsi_eh_bus_reset - send a bus reset 
 * @shost:      scsi host being recovered.
 * @eh_done_q:  list_head for processed commands.
 **/
static int scsi_eh_bus_reset(struct Scsi_Host *shost,
                             struct list_head *work_q,
                             struct list_head *done_q)
{
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd;
        struct scsi_cmnd *chan_scmd;
        unsigned int channel;
        int rtn;

        /*
         * we really want to loop over the various channels, and do this on
         * a channel by channel basis.  we should also check to see if any
         * of the failed commands are on soft_reset devices, and if so, skip
         * the reset.  
         */

        for (channel = 0; channel <= shost->max_channel; channel++) {
                chan_scmd = NULL;
                list_for_each_entry(scmd, work_q, eh_entry) {
                        if (channel == scmd->device->channel) {
                                chan_scmd = scmd;
                                break;
                                /*
                                 * FIXME add back in some support for
                                 * soft_reset devices.
                                 */
                        }
                }

                if (!chan_scmd)
                        continue;
                SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Sending BRST chan:"
                                                  " %d\n", current->comm,
                                                  channel));
                rtn = scsi_try_bus_reset(chan_scmd);
                if (rtn == SUCCESS) {
                        list_for_each_safe(lh, lh_sf, work_q) {
                                scmd = list_entry(lh, struct scsi_cmnd,
                                                  eh_entry);
                                if (channel == scmd->device->channel)
                                        if (!scsi_device_online(scmd->device) ||
                                            !scsi_eh_tur(scmd))
                                                scsi_eh_finish_cmd(scmd,
                                                                   done_q);
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: BRST"
                                                          " failed chan: %d\n",
                                                          current->comm,
                                                          channel));
                }
        }
        return list_empty(work_q);
}

/**
 * scsi_eh_host_reset - send a host reset 
 * @work_q:     list_head for processed commands.
 * @done_q:     list_head for processed commands.
 **/
static int scsi_eh_host_reset(struct list_head *work_q,
                              struct list_head *done_q)
{
        int rtn;
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd;

        if (!list_empty(work_q)) {
                scmd = list_entry(work_q->next,
                                  struct scsi_cmnd, eh_entry);

                SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Sending HRST\n"
                                                  , current->comm));

                rtn = scsi_try_host_reset(scmd);
                if (rtn == SUCCESS) {
                        list_for_each_safe(lh, lh_sf, work_q) {
                                scmd = list_entry(lh, struct scsi_cmnd, eh_entry);
                                if (!scsi_device_online(scmd->device) ||
                                    (!scsi_eh_try_stu(scmd) && !scsi_eh_tur(scmd)) ||
                                    !scsi_eh_tur(scmd))
                                        scsi_eh_finish_cmd(scmd, done_q);
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: HRST"
                                                          " failed\n",
                                                          current->comm));
                }
        }
        return list_empty(work_q);
}

/**
 * scsi_eh_offline_sdevs - offline scsi devices that fail to recover
 * @work_q:     list_head for processed commands.
 * @done_q:     list_head for processed commands.
 *
 **/
static void scsi_eh_offline_sdevs(struct list_head *work_q,
                                  struct list_head *done_q)
{
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd;

        list_for_each_safe(lh, lh_sf, work_q) {
                scmd = list_entry(lh, struct scsi_cmnd, eh_entry);
                printk(KERN_INFO "scsi: Device offlined - not"
                                " ready after error recovery: host"
                                " %d channel %d id %d lun %d\n",
                                scmd->device->host->host_no,
                                scmd->device->channel,
                                scmd->device->id,
                                scmd->device->lun);
                scsi_device_set_state(scmd->device, SDEV_OFFLINE);
                if (scsi_eh_eflags_chk(scmd, SCSI_EH_CANCEL_CMD)) {
                        /*
                         * FIXME: Handle lost cmds.
                         */
                }
                scsi_eh_finish_cmd(scmd, done_q);
        }
        return;
}

/**
 * scsi_decide_disposition - Disposition a cmd on return from LLD.
 * @scmd:       SCSI cmd to examine.
 *
 * Notes:
 *    This is *only* called when we are examining the status after sending
 *    out the actual data command.  any commands that are queued for error
 *    recovery (e.g. test_unit_ready) do *not* come through here.
 *
 *    When this routine returns failed, it means the error handler thread
 *    is woken.  In cases where the error code indicates an error that
 *    doesn't require the error handler read (i.e. we don't need to
 *    abort/reset), this function should return SUCCESS.
 **/
int scsi_decide_disposition(struct scsi_cmnd *scmd)
{
        int rtn;

        /*
         * if the device is offline, then we clearly just pass the result back
         * up to the top level.
         */
        if (!scsi_device_online(scmd->device)) {
                SCSI_LOG_ERROR_RECOVERY(5, printk("%s: device offline - report"
                                                  " as SUCCESS\n",
                                                  __FUNCTION__));
                return SUCCESS;
        }

        /*
         * first check the host byte, to see if there is anything in there
         * that would indicate what we need to do.
         */
        switch (host_byte(scmd->result)) {
        case DID_PASSTHROUGH:
                /*
                 * no matter what, pass this through to the upper layer.
                 * nuke this special code so that it looks like we are saying
                 * did_ok.
                 */
                scmd->result &= 0xff00ffff;
                return SUCCESS;
        case DID_OK:
                /*
                 * looks good.  drop through, and check the next byte.
                 */
                break;
        case DID_NO_CONNECT:
        case DID_BAD_TARGET:
        case DID_ABORT:
                /*
                 * note - this means that we just report the status back
                 * to the top level driver, not that we actually think
                 * that it indicates SUCCESS.
                 */
                return SUCCESS;
                /*
                 * when the low level driver returns did_soft_error,
                 * it is responsible for keeping an internal retry counter 
                 * in order to avoid endless loops (db)
                 *
                 * actually this is a bug in this function here.  we should
                 * be mindful of the maximum number of retries specified
                 * and not get stuck in a loop.
                 */
        case DID_SOFT_ERROR:
                goto maybe_retry;
        case DID_IMM_RETRY:
                return NEEDS_RETRY;

        case DID_REQUEUE:
                return ADD_TO_MLQUEUE;

        case DID_ERROR:
                if (msg_byte(scmd->result) == COMMAND_COMPLETE &&
                    status_byte(scmd->result) == RESERVATION_CONFLICT)
                        /*
                         * execute reservation conflict processing code
                         * lower down
                         */
                        break;
                /* fallthrough */

        case DID_BUS_BUSY:
        case DID_PARITY:
                goto maybe_retry;
        case DID_TIME_OUT:
                /*
                 * when we scan the bus, we get timeout messages for
                 * these commands if there is no device available.
                 * other hosts report did_no_connect for the same thing.
                 */
                if ((scmd->cmnd[0] == TEST_UNIT_READY ||
                     scmd->cmnd[0] == INQUIRY)) {
                        return SUCCESS;
                } else {
                        return FAILED;
                }
        case DID_RESET:
                return SUCCESS;
        default:
                return FAILED;
        }

        /*
         * next, check the message byte.
         */
        if (msg_byte(scmd->result) != COMMAND_COMPLETE)
                return FAILED;

        /*
         * check the status byte to see if this indicates anything special.
         */
        switch (status_byte(scmd->result)) {
        case QUEUE_FULL:
                /*
                 * the case of trying to send too many commands to a
                 * tagged queueing device.
                 */
        case BUSY:
                /*
                 * device can't talk to us at the moment.  Should only
                 * occur (SAM-3) when the task queue is empty, so will cause
                 * the empty queue handling to trigger a stall in the
                 * device.
                 */
                return ADD_TO_MLQUEUE;
        case GOOD:
        case COMMAND_TERMINATED:
        case TASK_ABORTED:
                return SUCCESS;
        case CHECK_CONDITION:
                rtn = scsi_check_sense(scmd);
                if (rtn == NEEDS_RETRY)
                        goto maybe_retry;
                /* if rtn == FAILED, we have no sense information;
                 * returning FAILED will wake the error handler thread
                 * to collect the sense and redo the decide
                 * disposition */
                return rtn;
        case CONDITION_GOOD:
        case INTERMEDIATE_GOOD:
        case INTERMEDIATE_C_GOOD:
        case ACA_ACTIVE:
                /*
                 * who knows?  FIXME(eric)
                 */
                return SUCCESS;

        case RESERVATION_CONFLICT:
                printk(KERN_INFO "scsi: reservation conflict: host"
                                " %d channel %d id %d lun %d\n",
                       scmd->device->host->host_no, scmd->device->channel,
                       scmd->device->id, scmd->device->lun);
                return SUCCESS; /* causes immediate i/o error */
        default:
                return FAILED;
        }
        return FAILED;

      maybe_retry:

        /* we requeue for retry because the error was retryable, and
         * the request was not marked fast fail.  Note that above,
         * even if the request is marked fast fail, we still requeue
         * for queue congestion conditions (QUEUE_FULL or BUSY) */
        if ((++scmd->retries) < scmd->allowed 
            && !blk_noretry_request(scmd->request)) {
                return NEEDS_RETRY;
        } else {
                /*
                 * no more retries - report this one back to upper level.
                 */
                return SUCCESS;
        }
}

/**
 * scsi_eh_lock_done - done function for eh door lock request
 * @scmd:       SCSI command block for the door lock request
 *
 * Notes:
 *      We completed the asynchronous door lock request, and it has either
 *      locked the door or failed.  We must free the command structures
 *      associated with this request.
 **/
static void scsi_eh_lock_done(struct scsi_cmnd *scmd)
{
        struct scsi_request *sreq = scmd->sc_request;

        scsi_release_request(sreq);
}


/**
 * scsi_eh_lock_door - Prevent medium removal for the specified device
 * @sdev:       SCSI device to prevent medium removal
 *
 * Locking:
 *      We must be called from process context; scsi_allocate_request()
 *      may sleep.
 *
 * Notes:
 *      We queue up an asynchronous "ALLOW MEDIUM REMOVAL" request on the
 *      head of the devices request queue, and continue.
 *
 * Bugs:
 *      scsi_allocate_request() may sleep waiting for existing requests to
 *      be processed.  However, since we haven't kicked off any request
 *      processing for this host, this may deadlock.
 *
 *      If scsi_allocate_request() fails for what ever reason, we
 *      completely forget to lock the door.
 **/
static void scsi_eh_lock_door(struct scsi_device *sdev)
{
        struct scsi_request *sreq = scsi_allocate_request(sdev, GFP_KERNEL);

        if (unlikely(!sreq)) {
                printk(KERN_ERR "%s: request allocate failed,"
                       "prevent media removal cmd not sent\n", __FUNCTION__);
                return;
        }

        sreq->sr_cmnd[0] = ALLOW_MEDIUM_REMOVAL;
        sreq->sr_cmnd[1] = 0;
        sreq->sr_cmnd[2] = 0;
        sreq->sr_cmnd[3] = 0;
        sreq->sr_cmnd[4] = SCSI_REMOVAL_PREVENT;
        sreq->sr_cmnd[5] = 0;
        sreq->sr_data_direction = DMA_NONE;
        sreq->sr_bufflen = 0;
        sreq->sr_buffer = NULL;
        sreq->sr_allowed = 5;
        sreq->sr_done = scsi_eh_lock_done;
        sreq->sr_timeout_per_command = 10 * HZ;
        sreq->sr_cmd_len = COMMAND_SIZE(sreq->sr_cmnd[0]);

        scsi_insert_special_req(sreq, 1);
}


/**
 * scsi_restart_operations - restart io operations to the specified host.
 * @shost:      Host we are restarting.
 *
 * Notes:
 *    When we entered the error handler, we blocked all further i/o to
 *    this device.  we need to 'reverse' this process.
 **/
static void scsi_restart_operations(struct Scsi_Host *shost)
{
        struct scsi_device *sdev;

        /*
         * If the door was locked, we need to insert a door lock request
         * onto the head of the SCSI request queue for the device.  There
         * is no point trying to lock the door of an off-line device.
         */
        shost_for_each_device(sdev, shost) {
                if (scsi_device_online(sdev) && sdev->locked)
                        scsi_eh_lock_door(sdev);
        }

        /*
         * next free up anything directly waiting upon the host.  this
         * will be requests for character device operations, and also for
         * ioctls to queued block devices.
         */
        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: waking up host to restart\n",
                                          __FUNCTION__));

        clear_bit(SHOST_RECOVERY, &shost->shost_state);

        wake_up(&shost->host_wait);

        /*
         * finally we need to re-initiate requests that may be pending.  we will
         * have had everything blocked while error handling is taking place, and
         * now that error recovery is done, we will need to ensure that these
         * requests are started.
         */
        scsi_run_host_queues(shost);
}

/**
 * scsi_eh_ready_devs - check device ready state and recover if not.
 * @shost:      host to be recovered.
 * @eh_done_q:  list_head for processed commands.
 *
 **/
static void scsi_eh_ready_devs(struct Scsi_Host *shost,
                               struct list_head *work_q,
                               struct list_head *done_q)
{
        if (!scsi_eh_stu(shost, work_q, done_q))
                if (!scsi_eh_bus_device_reset(shost, work_q, done_q))
                        if (!scsi_eh_bus_reset(shost, work_q, done_q))
                                if (!scsi_eh_host_reset(work_q, done_q))
                                        scsi_eh_offline_sdevs(work_q, done_q);
}

/**
 * scsi_eh_flush_done_q - finish processed commands or retry them.
 * @done_q:     list_head of processed commands.
 *
 **/
static void scsi_eh_flush_done_q(struct list_head *done_q)
{
        struct list_head *lh, *lh_sf;
        struct scsi_cmnd *scmd;

        list_for_each_safe(lh, lh_sf, done_q) {
                scmd = list_entry(lh, struct scsi_cmnd, eh_entry);
                list_del_init(lh);
                if (scsi_device_online(scmd->device) &&
                    !blk_noretry_request(scmd->request) &&
                    (++scmd->retries < scmd->allowed)) {
                        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: flush"
                                                          " retry cmd: %p\n",
                                                          current->comm,
                                                          scmd));
                                scsi_queue_insert(scmd, SCSI_MLQUEUE_EH_RETRY);
                } else {
                        /*
                         * If just we got sense for the device (called
                         * scsi_eh_get_sense), scmd->result is already
                         * set, do not set DRIVER_TIMEOUT.
                         */
                        if (!scmd->result)
                                scmd->result |= (DRIVER_TIMEOUT << 24);
                        SCSI_LOG_ERROR_RECOVERY(3, printk("%s: flush finish"
                                                        " cmd: %p\n",
                                                        current->comm, scmd));
                        scsi_finish_command(scmd);
                }
        }
}

/**
 * scsi_unjam_host - Attempt to fix a host which has a cmd that failed.
 * @shost:      Host to unjam.
 *
 * Notes:
 *    When we come in here, we *know* that all commands on the bus have
 *    either completed, failed or timed out.  we also know that no further
 *    commands are being sent to the host, so things are relatively quiet
 *    and we have freedom to fiddle with things as we wish.
 *
 *    This is only the *default* implementation.  it is possible for
 *    individual drivers to supply their own version of this function, and
 *    if the maintainer wishes to do this, it is strongly suggested that
 *    this function be taken as a template and modified.  this function
 *    was designed to correctly handle problems for about 95% of the
 *    different cases out there, and it should always provide at least a
 *    reasonable amount of error recovery.
 *
 *    Any command marked 'failed' or 'timeout' must eventually have
 *    scsi_finish_cmd() called for it.  we do all of the retry stuff
 *    here, so when we restart the host after we return it should have an
 *    empty queue.
 **/
static void scsi_unjam_host(struct Scsi_Host *shost)
{
        unsigned long flags;
        LIST_HEAD(eh_work_q);
        LIST_HEAD(eh_done_q);

        spin_lock_irqsave(shost->host_lock, flags);
        list_splice_init(&shost->eh_cmd_q, &eh_work_q);
        spin_unlock_irqrestore(shost->host_lock, flags);

        SCSI_LOG_ERROR_RECOVERY(1, scsi_eh_prt_fail_stats(shost, &eh_work_q));

        if (!scsi_eh_get_sense(&eh_work_q, &eh_done_q))
                if (!scsi_eh_abort_cmds(&eh_work_q, &eh_done_q))
                        scsi_eh_ready_devs(shost, &eh_work_q, &eh_done_q);

        scsi_eh_flush_done_q(&eh_done_q);
}

/**
 * scsi_error_handler - Handle errors/timeouts of SCSI cmds.
 * @data:       Host for which we are running.
 *
 * Notes:
 *    This is always run in the context of a kernel thread.  The idea is
 *    that we start this thing up when the kernel starts up (one per host
 *    that we detect), and it immediately goes to sleep and waits for some
 *    event (i.e. failure).  When this takes place, we have the job of
 *    trying to unjam the bus and restarting things.
 **/
int scsi_error_handler(void *data)
{
        struct Scsi_Host *shost = (struct Scsi_Host *) data;
        int rtn;
        DECLARE_MUTEX_LOCKED(sem);

        /*
         *    Flush resources
         */

        daemonize("scsi_eh_%d", shost->host_no);

        current->flags |= PF_NOFREEZE;

        shost->eh_wait = &sem;
        shost->ehandler = current;

        /*
         * Wake up the thread that created us.
         */
        SCSI_LOG_ERROR_RECOVERY(3, printk("Wake up parent of"
                                          " scsi_eh_%d\n",shost->host_no));

        complete(shost->eh_notify);

        while (1) {
                /*
                 * If we get a signal, it means we are supposed to go
                 * away and die.  This typically happens if the user is
                 * trying to unload a module.
                 */
                SCSI_LOG_ERROR_RECOVERY(1, printk("Error handler"
                                                  " scsi_eh_%d"
                                                  " sleeping\n",shost->host_no));

                /*
                 * Note - we always use down_interruptible with the semaphore
                 * even if the module was loaded as part of the kernel.  The
                 * reason is that down() will cause this thread to be counted
                 * in the load average as a running process, and down
                 * interruptible doesn't.  Given that we need to allow this
                 * thread to die if the driver was loaded as a module, using
                 * semaphores isn't unreasonable.
                 */
                down_interruptible(&sem);
                if (shost->eh_kill)
                        break;

                SCSI_LOG_ERROR_RECOVERY(1, printk("Error handler"
                                                  " scsi_eh_%d waking"
                                                  " up\n",shost->host_no));

                shost->eh_active = 1;

                /*
                 * We have a host that is failing for some reason.  Figure out
                 * what we need to do to get it up and online again (if we can).
                 * If we fail, we end up taking the thing offline.
                 */
                if (shost->hostt->eh_strategy_handler) 
                        rtn = shost->hostt->eh_strategy_handler(shost);
                else
                        scsi_unjam_host(shost);

                shost->eh_active = 0;

                /*
                 * Note - if the above fails completely, the action is to take
                 * individual devices offline and flush the queue of any
                 * outstanding requests that may have been pending.  When we
                 * restart, we restart any I/O to any other devices on the bus
                 * which are still online.
                 */
                scsi_restart_operations(shost);

        }

        SCSI_LOG_ERROR_RECOVERY(1, printk("Error handler scsi_eh_%d"
                                          " exiting\n",shost->host_no));

        /*
         * Make sure that nobody tries to wake us up again.
         */
        shost->eh_wait = NULL;

        /*
         * Knock this down too.  From this point on, the host is flying
         * without a pilot.  If this is because the module is being unloaded,
         * that's fine.  If the user sent a signal to this thing, we are
         * potentially in real danger.
         */
        shost->eh_active = 0;
        shost->ehandler = NULL;

        /*
         * If anyone is waiting for us to exit (i.e. someone trying to unload
         * a driver), then wake up that process to let them know we are on
         * the way out the door.
         */
        complete_and_exit(shost->eh_notify, 0);
        return 0;
}

/*
 * Function:    scsi_report_bus_reset()
 *
 * Purpose:     Utility function used by low-level drivers to report that
 *              they have observed a bus reset on the bus being handled.
 *
 * Arguments:   shost       - Host in question
 *              channel     - channel on which reset was observed.
 *
 * Returns:     Nothing
 *
 * Lock status: Host lock must be held.
 *
 * Notes:       This only needs to be called if the reset is one which
 *              originates from an unknown location.  Resets originated
 *              by the mid-level itself don't need to call this, but there
 *              should be no harm.
 *
 *              The main purpose of this is to make sure that a CHECK_CONDITION
 *              is properly treated.
 */
void scsi_report_bus_reset(struct Scsi_Host *shost, int channel)
{
        struct scsi_device *sdev;

        __shost_for_each_device(sdev, shost) {
                if (channel == sdev->channel) {
                        sdev->was_reset = 1;
                        sdev->expecting_cc_ua = 1;
                }
        }
}
EXPORT_SYMBOL(scsi_report_bus_reset);

/*
 * Function:    scsi_report_device_reset()
 *
 * Purpose:     Utility function used by low-level drivers to report that
 *              they have observed a device reset on the device being handled.
 *
 * Arguments:   shost       - Host in question
 *              channel     - channel on which reset was observed
 *              target      - target on which reset was observed
 *
 * Returns:     Nothing
 *
 * Lock status: Host lock must be held
 *
 * Notes:       This only needs to be called if the reset is one which
 *              originates from an unknown location.  Resets originated
 *              by the mid-level itself don't need to call this, but there
 *              should be no harm.
 *
 *              The main purpose of this is to make sure that a CHECK_CONDITION
 *              is properly treated.
 */
void scsi_report_device_reset(struct Scsi_Host *shost, int channel, int target)
{
        struct scsi_device *sdev;

        __shost_for_each_device(sdev, shost) {
                if (channel == sdev->channel &&
                    target == sdev->id) {
                        sdev->was_reset = 1;
                        sdev->expecting_cc_ua = 1;
                }
        }
}
EXPORT_SYMBOL(scsi_report_device_reset);

static void
scsi_reset_provider_done_command(struct scsi_cmnd *scmd)
{
}

/*
 * Function:    scsi_reset_provider
 *
 * Purpose:     Send requested reset to a bus or device at any phase.
 *
 * Arguments:   device  - device to send reset to
 *              flag - reset type (see scsi.h)
 *
 * Returns:     SUCCESS/FAILURE.
 *
 * Notes:       This is used by the SCSI Generic driver to provide
 *              Bus/Device reset capability.
 */
int
scsi_reset_provider(struct scsi_device *dev, int flag)
{
        struct scsi_cmnd *scmd = scsi_get_command(dev, GFP_KERNEL);
        struct request req;
        int rtn;

        scmd->request = &req;
        memset(&scmd->eh_timeout, 0, sizeof(scmd->eh_timeout));
        scmd->request->rq_status        = RQ_SCSI_BUSY;
        scmd->state                     = SCSI_STATE_INITIALIZING;
        scmd->owner                     = SCSI_OWNER_MIDLEVEL;
    
        memset(&scmd->cmnd, '\0', sizeof(scmd->cmnd));
    
        scmd->scsi_done         = scsi_reset_provider_done_command;
        scmd->done                      = NULL;
        scmd->buffer                    = NULL;
        scmd->bufflen                   = 0;
        scmd->request_buffer            = NULL;
        scmd->request_bufflen           = 0;
        scmd->abort_reason              = DID_ABORT;

        scmd->cmd_len                   = 0;

        scmd->sc_data_direction         = DMA_BIDIRECTIONAL;
        scmd->sc_request                = NULL;
        scmd->sc_magic                  = SCSI_CMND_MAGIC;

        init_timer(&scmd->eh_timeout);

        /*
         * Sometimes the command can get back into the timer chain,
         * so use the pid as an identifier.
         */
        scmd->pid                       = 0;

        switch (flag) {
        case SCSI_TRY_RESET_DEVICE:
                rtn = scsi_try_bus_device_reset(scmd);
                if (rtn == SUCCESS)
                        break;
                /* FALLTHROUGH */
        case SCSI_TRY_RESET_BUS:
                rtn = scsi_try_bus_reset(scmd);
                if (rtn == SUCCESS)
                        break;
                /* FALLTHROUGH */
        case SCSI_TRY_RESET_HOST:
                rtn = scsi_try_host_reset(scmd);
                break;
        default:
                rtn = FAILED;
        }

        scsi_next_command(scmd);
        return rtn;
}
EXPORT_SYMBOL(scsi_reset_provider);

/**
 * scsi_normalize_sense - normalize main elements from either fixed or
 *                      descriptor sense data format into a common format.
 *
 * @sense_buffer:       byte array containing sense data returned by device
 * @sb_len:             number of valid bytes in sense_buffer
 * @sshdr:              pointer to instance of structure that common
 *                      elements are written to.
 *
 * Notes:
 *      The "main elements" from sense data are: response_code, sense_key,
 *      asc, ascq and additional_length (only for descriptor format).
 *
 *      Typically this function can be called after a device has
 *      responded to a SCSI command with the CHECK_CONDITION status.
 *
 * Return value:
 *      1 if valid sense data information found, else 0;
 **/
int scsi_normalize_sense(const u8 *sense_buffer, int sb_len,
                         struct scsi_sense_hdr *sshdr)
{
        if (!sense_buffer || !sb_len || (sense_buffer[0] & 0x70) != 0x70)
                return 0;

        memset(sshdr, 0, sizeof(struct scsi_sense_hdr));

        sshdr->response_code = (sense_buffer[0] & 0x7f);
        if (sshdr->response_code >= 0x72) {
                /*
                 * descriptor format
                 */
                if (sb_len > 1)
                        sshdr->sense_key = (sense_buffer[1] & 0xf);
                if (sb_len > 2)
                        sshdr->asc = sense_buffer[2];
                if (sb_len > 3)
                        sshdr->ascq = sense_buffer[3];
                if (sb_len > 7)
                        sshdr->additional_length = sense_buffer[7];
        } else {
                /* 
                 * fixed format
                 */
                if (sb_len > 2)
                        sshdr->sense_key = (sense_buffer[2] & 0xf);
                if (sb_len > 7) {
                        sb_len = (sb_len < (sense_buffer[7] + 8)) ?
                                         sb_len : (sense_buffer[7] + 8);
                        if (sb_len > 12)
                                sshdr->asc = sense_buffer[12];
                        if (sb_len > 13)
                                sshdr->ascq = sense_buffer[13];
                }
        }

        return 1;
}
EXPORT_SYMBOL(scsi_normalize_sense);

int scsi_request_normalize_sense(struct scsi_request *sreq,
                                 struct scsi_sense_hdr *sshdr)
{
        return scsi_normalize_sense(sreq->sr_sense_buffer,
                        sizeof(sreq->sr_sense_buffer), sshdr);
}
EXPORT_SYMBOL(scsi_request_normalize_sense);

int scsi_command_normalize_sense(struct scsi_cmnd *cmd,
                                 struct scsi_sense_hdr *sshdr)
{
        return scsi_normalize_sense(cmd->sense_buffer,
                        sizeof(cmd->sense_buffer), sshdr);
}
EXPORT_SYMBOL(scsi_command_normalize_sense);

/**
 * scsi_sense_desc_find - search for a given descriptor type in
 *                      descriptor sense data format.
 *
 * @sense_buffer:       byte array of descriptor format sense data
 * @sb_len:             number of valid bytes in sense_buffer
 * @desc_type:          value of descriptor type to find
 *                      (e.g. 0 -> information)
 *
 * Notes:
 *      only valid when sense data is in descriptor format
 *
 * Return value:
 *      pointer to start of (first) descriptor if found else NULL
 **/
const u8 * scsi_sense_desc_find(const u8 * sense_buffer, int sb_len,
                                int desc_type)
{
        int add_sen_len, add_len, desc_len, k;
        const u8 * descp;

        if ((sb_len < 8) || (0 == (add_sen_len = sense_buffer[7])))
                return NULL;
        if ((sense_buffer[0] < 0x72) || (sense_buffer[0] > 0x73))
                return NULL;
        add_sen_len = (add_sen_len < (sb_len - 8)) ?
                        add_sen_len : (sb_len - 8);
        descp = &sense_buffer[8];
        for (desc_len = 0, k = 0; k < add_sen_len; k += desc_len) {
                descp += desc_len;
                add_len = (k < (add_sen_len - 1)) ? descp[1]: -1;
                desc_len = add_len + 2;
                if (descp[0] == desc_type)
                        return descp;
                if (add_len < 0) // short descriptor ??
                        break;
        }
        return NULL;
}
EXPORT_SYMBOL(scsi_sense_desc_find);

/**
 * scsi_get_sense_info_fld - attempts to get information field from
 *                      sense data (either fixed or descriptor format)
 *
 * @sense_buffer:       byte array of sense data
 * @sb_len:             number of valid bytes in sense_buffer
 * @info_out:           pointer to 64 integer where 8 or 4 byte information
 *                      field will be placed if found.
 *
 * Return value:
 *      1 if information field found, 0 if not found.
 **/
int scsi_get_sense_info_fld(const u8 * sense_buffer, int sb_len,
                            u64 * info_out)
{
        int j;
        const u8 * ucp;
        u64 ull;

        if (sb_len < 7)
                return 0;
        switch (sense_buffer[0] & 0x7f) {
        case 0x70:
        case 0x71:
                if (sense_buffer[0] & 0x80) {
                        *info_out = (sense_buffer[3] << 24) +
                                    (sense_buffer[4] << 16) +
                                    (sense_buffer[5] << 8) + sense_buffer[6];
                        return 1;
                } else
                        return 0;
        case 0x72:
        case 0x73:
                ucp = scsi_sense_desc_find(sense_buffer, sb_len,
                                           0 /* info desc */);
                if (ucp && (0xa == ucp[1])) {
                        ull = 0;
                        for (j = 0; j < 8; ++j) {
                                if (j > 0)
                                        ull <<= 8;
                                ull |= ucp[4 + j];
                        }
                        *info_out = ull;
                        return 1;
                } else
                        return 0;
        default:
                return 0;
        }
}
EXPORT_SYMBOL(scsi_get_sense_info_fld);