scsi: document scsi_try_to_abort_cmd

[karo-tx-linux.git] / 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/gfp.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/interrupt.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/jiffies.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_transport.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_ioctl.h>

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

#include <trace/events/scsi.h>

static void scsi_eh_done(struct scsi_cmnd *scmd);

/*
 * 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)

static int scsi_eh_try_stu(struct scsi_cmnd *scmd);
static int scsi_try_to_abort_cmd(struct scsi_host_template *,
                                 struct scsi_cmnd *);

/* called with shost->host_lock held */
void scsi_eh_wakeup(struct Scsi_Host *shost)
{
        if (atomic_read(&shost->host_busy) == shost->host_failed) {
                trace_scsi_eh_wakeup(shost);
                wake_up_process(shost->ehandler);
                SCSI_LOG_ERROR_RECOVERY(5, shost_printk(KERN_INFO, shost,
                        "Waking error handler thread\n"));
        }
}

/**
 * scsi_schedule_eh - schedule EH for SCSI host
 * @shost:      SCSI host to invoke error handling on.
 *
 * Schedule SCSI EH without scmd.
 */
void scsi_schedule_eh(struct Scsi_Host *shost)
{
        unsigned long flags;

        spin_lock_irqsave(shost->host_lock, flags);

        if (scsi_host_set_state(shost, SHOST_RECOVERY) == 0 ||
            scsi_host_set_state(shost, SHOST_CANCEL_RECOVERY) == 0) {
                shost->host_eh_scheduled++;
                scsi_eh_wakeup(shost);
        }

        spin_unlock_irqrestore(shost->host_lock, flags);
}
EXPORT_SYMBOL_GPL(scsi_schedule_eh);

static int scsi_host_eh_past_deadline(struct Scsi_Host *shost)
{
        if (!shost->last_reset || shost->eh_deadline == -1)
                return 0;

        /*
         * 32bit accesses are guaranteed to be atomic
         * (on all supported architectures), so instead
         * of using a spinlock we can as well double check
         * if eh_deadline has been set to 'off' during the
         * time_before call.
         */
        if (time_before(jiffies, shost->last_reset + shost->eh_deadline) &&
            shost->eh_deadline > -1)
                return 0;

        return 1;
}

/**
 * scmd_eh_abort_handler - Handle command aborts
 * @work:       command to be aborted.
 */
void
scmd_eh_abort_handler(struct work_struct *work)
{
        struct scsi_cmnd *scmd =
                container_of(work, struct scsi_cmnd, abort_work.work);
        struct scsi_device *sdev = scmd->device;
        int rtn;

        if (scsi_host_eh_past_deadline(sdev->host)) {
                SCSI_LOG_ERROR_RECOVERY(3,
                        scmd_printk(KERN_INFO, scmd,
                                    "scmd %p eh timeout, not aborting\n",
                                    scmd));
        } else {
                SCSI_LOG_ERROR_RECOVERY(3,
                        scmd_printk(KERN_INFO, scmd,
                                    "aborting command %p\n", scmd));
                rtn = scsi_try_to_abort_cmd(sdev->host->hostt, scmd);
                if (rtn == SUCCESS) {
                        set_host_byte(scmd, DID_TIME_OUT);
                        if (scsi_host_eh_past_deadline(sdev->host)) {
                                SCSI_LOG_ERROR_RECOVERY(3,
                                        scmd_printk(KERN_INFO, scmd,
                                                    "scmd %p eh timeout, "
                                                    "not retrying aborted "
                                                    "command\n", scmd));
                        } else if (!scsi_noretry_cmd(scmd) &&
                            (++scmd->retries <= scmd->allowed)) {
                                SCSI_LOG_ERROR_RECOVERY(3,
                                        scmd_printk(KERN_WARNING, scmd,
                                                    "scmd %p retry "
                                                    "aborted command\n", scmd));
                                scsi_queue_insert(scmd, SCSI_MLQUEUE_EH_RETRY);
                                return;
                        } else {
                                SCSI_LOG_ERROR_RECOVERY(3,
                                        scmd_printk(KERN_WARNING, scmd,
                                                    "scmd %p finish "
                                                    "aborted command\n", scmd));
                                scsi_finish_command(scmd);
                                return;
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                scmd_printk(KERN_INFO, scmd,
                                            "scmd %p abort %s\n", scmd,
                                            (rtn == FAST_IO_FAIL) ?
                                            "not send" : "failed"));
                }
        }

        if (!scsi_eh_scmd_add(scmd, 0)) {
                SCSI_LOG_ERROR_RECOVERY(3,
                        scmd_printk(KERN_WARNING, scmd,
                                    "scmd %p terminate "
                                    "aborted command\n", scmd));
                set_host_byte(scmd, DID_TIME_OUT);
                scsi_finish_command(scmd);
        }
}

/**
 * scsi_abort_command - schedule a command abort
 * @scmd:       scmd to abort.
 *
 * We only need to abort commands after a command timeout
 */
static int
scsi_abort_command(struct scsi_cmnd *scmd)
{
        struct scsi_device *sdev = scmd->device;
        struct Scsi_Host *shost = sdev->host;
        unsigned long flags;

        if (scmd->eh_eflags & SCSI_EH_ABORT_SCHEDULED) {
                /*
                 * Retry after abort failed, escalate to next level.
                 */
                scmd->eh_eflags &= ~SCSI_EH_ABORT_SCHEDULED;
                SCSI_LOG_ERROR_RECOVERY(3,
                        scmd_printk(KERN_INFO, scmd,
                                    "scmd %p previous abort failed\n", scmd));
                BUG_ON(delayed_work_pending(&scmd->abort_work));
                return FAILED;
        }

        /*
         * Do not try a command abort if
         * SCSI EH has already started.
         */
        spin_lock_irqsave(shost->host_lock, flags);
        if (scsi_host_in_recovery(shost)) {
                spin_unlock_irqrestore(shost->host_lock, flags);
                SCSI_LOG_ERROR_RECOVERY(3,
                        scmd_printk(KERN_INFO, scmd,
                                    "scmd %p not aborting, host in recovery\n",
                                    scmd));
                return FAILED;
        }

        if (shost->eh_deadline != -1 && !shost->last_reset)
                shost->last_reset = jiffies;
        spin_unlock_irqrestore(shost->host_lock, flags);

        scmd->eh_eflags |= SCSI_EH_ABORT_SCHEDULED;
        SCSI_LOG_ERROR_RECOVERY(3,
                scmd_printk(KERN_INFO, scmd,
                            "scmd %p abort scheduled\n", scmd));
        queue_delayed_work(shost->tmf_work_q, &scmd->abort_work, HZ / 100);
        return SUCCESS;
}

/**
 * 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;
        int ret = 0;

        if (!shost->ehandler)
                return 0;

        spin_lock_irqsave(shost->host_lock, flags);
        if (scsi_host_set_state(shost, SHOST_RECOVERY))
                if (scsi_host_set_state(shost, SHOST_CANCEL_RECOVERY))
                        goto out_unlock;

        if (shost->eh_deadline != -1 && !shost->last_reset)
                shost->last_reset = jiffies;

        ret = 1;
        if (scmd->eh_eflags & SCSI_EH_ABORT_SCHEDULED)
                eh_flag &= ~SCSI_EH_CANCEL_CMD;
        scmd->eh_eflags |= eh_flag;
        list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q);
        shost->host_failed++;
        scsi_eh_wakeup(shost);
 out_unlock:
        spin_unlock_irqrestore(shost->host_lock, flags);
        return ret;
}

/**
 * scsi_times_out - Timeout function for normal scsi commands.
 * @req:        request 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.
 */
enum blk_eh_timer_return scsi_times_out(struct request *req)
{
        struct scsi_cmnd *scmd = req->special;
        enum blk_eh_timer_return rtn = BLK_EH_NOT_HANDLED;
        struct Scsi_Host *host = scmd->device->host;

        trace_scsi_dispatch_cmd_timeout(scmd);
        scsi_log_completion(scmd, TIMEOUT_ERROR);

        if (host->eh_deadline != -1 && !host->last_reset)
                host->last_reset = jiffies;

        if (host->transportt->eh_timed_out)
                rtn = host->transportt->eh_timed_out(scmd);
        else if (host->hostt->eh_timed_out)
                rtn = host->hostt->eh_timed_out(scmd);

        if (rtn == BLK_EH_NOT_HANDLED) {
                if (!host->hostt->no_async_abort &&
                    scsi_abort_command(scmd) == SUCCESS)
                        return BLK_EH_NOT_HANDLED;

                set_host_byte(scmd, DID_TIME_OUT);
                if (!scsi_eh_scmd_add(scmd, SCSI_EH_CANCEL_CMD))
                        rtn = BLK_EH_HANDLED;
        }

        return rtn;
}

/**
 * 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, !scsi_host_in_recovery(sdev->host));

        online = scsi_device_online(sdev);

        SCSI_LOG_ERROR_RECOVERY(5, sdev_printk(KERN_INFO, sdev,
                "%s: rtn: %d\n", __func__, 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 (scmd->eh_eflags & SCSI_EH_CANCEL_CMD)
                                        ++cmd_cancel;
                                else
                                        ++cmd_failed;
                        }
                }

                if (cmd_cancel || cmd_failed) {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                shost_printk(KERN_INFO, shost,
                                            "%s: cmds failed: %d, cancel: %d\n",
                                            __func__, cmd_failed,
                                            cmd_cancel));
                        cmd_cancel = 0;
                        cmd_failed = 0;
                        ++devices_failed;
                }
        }

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

 /**
 * scsi_report_lun_change - Set flag on all *other* devices on the same target
 *                          to indicate that a UNIT ATTENTION is expected.
 * @sdev:       Device reporting the UNIT ATTENTION
 */
static void scsi_report_lun_change(struct scsi_device *sdev)
{
        sdev->sdev_target->expecting_lun_change = 1;
}

/**
 * scsi_report_sense - Examine scsi sense information and log messages for
 *                     certain conditions, also issue uevents for some of them.
 * @sdev:       Device reporting the sense code
 * @sshdr:      sshdr to be examined
 */
static void scsi_report_sense(struct scsi_device *sdev,
                              struct scsi_sense_hdr *sshdr)
{
        enum scsi_device_event evt_type = SDEV_EVT_MAXBITS;     /* i.e. none */

        if (sshdr->sense_key == UNIT_ATTENTION) {
                if (sshdr->asc == 0x3f && sshdr->ascq == 0x03) {
                        evt_type = SDEV_EVT_INQUIRY_CHANGE_REPORTED;
                        sdev_printk(KERN_WARNING, sdev,
                                    "Inquiry data has changed");
                } else if (sshdr->asc == 0x3f && sshdr->ascq == 0x0e) {
                        evt_type = SDEV_EVT_LUN_CHANGE_REPORTED;
                        scsi_report_lun_change(sdev);
                        sdev_printk(KERN_WARNING, sdev,
                                    "Warning! Received an indication that the "
                                    "LUN assignments on this target have "
                                    "changed. The Linux SCSI layer does not "
                                    "automatically remap LUN assignments.\n");
                } else if (sshdr->asc == 0x3f)
                        sdev_printk(KERN_WARNING, sdev,
                                    "Warning! Received an indication that the "
                                    "operating parameters on this target have "
                                    "changed. The Linux SCSI layer does not "
                                    "automatically adjust these parameters.\n");

                if (sshdr->asc == 0x38 && sshdr->ascq == 0x07) {
                        evt_type = SDEV_EVT_SOFT_THRESHOLD_REACHED_REPORTED;
                        sdev_printk(KERN_WARNING, sdev,
                                    "Warning! Received an indication that the "
                                    "LUN reached a thin provisioning soft "
                                    "threshold.\n");
                }

                if (sshdr->asc == 0x2a && sshdr->ascq == 0x01) {
                        evt_type = SDEV_EVT_MODE_PARAMETER_CHANGE_REPORTED;
                        sdev_printk(KERN_WARNING, sdev,
                                    "Mode parameters changed");
                } else if (sshdr->asc == 0x2a && sshdr->ascq == 0x09) {
                        evt_type = SDEV_EVT_CAPACITY_CHANGE_REPORTED;
                        sdev_printk(KERN_WARNING, sdev,
                                    "Capacity data has changed");
                } else if (sshdr->asc == 0x2a)
                        sdev_printk(KERN_WARNING, sdev,
                                    "Parameters changed");
        }

        if (evt_type != SDEV_EVT_MAXBITS) {
                set_bit(evt_type, sdev->pending_events);
                schedule_work(&sdev->event_work);
        }
}

/**
 * scsi_check_sense - Examine scsi cmd sense
 * @scmd:       Cmd to have sense checked.
 *
 * Return value:
 *      SUCCESS or FAILED or NEEDS_RETRY or ADD_TO_MLQUEUE
 *
 * 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_device *sdev = scmd->device;
        struct scsi_sense_hdr sshdr;

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

        scsi_report_sense(sdev, &sshdr);

        if (scsi_sense_is_deferred(&sshdr))
                return NEEDS_RETRY;

        if (sdev->scsi_dh_data && sdev->scsi_dh_data->scsi_dh &&
                        sdev->scsi_dh_data->scsi_dh->check_sense) {
                int rc;

                rc = sdev->scsi_dh_data->scsi_dh->check_sense(sdev, &sshdr);
                if (rc != SCSI_RETURN_NOT_HANDLED)
                        return rc;
                /* handler does not care. Drop down to default handling */
        }

        if (scmd->cmnd[0] == TEST_UNIT_READY && scmd->scsi_done != scsi_eh_done)
                /*
                 * nasty: for mid-layer issued TURs, we need to return the
                 * actual sense data without any recovery attempt.  For eh
                 * issued ones, we need to try to recover and interpret
                 */
                return SUCCESS;

        /*
         * 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:
                if (sshdr.asc == 0x10) /* DIF */
                        return SUCCESS;

                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) {
                        /*
                         * Because some device does not queue unit
                         * attentions correctly, we carefully check
                         * additional sense code and qualifier so as
                         * not to squash media change unit attention.
                         */
                        if (sshdr.asc != 0x28 || sshdr.ascq != 0x00) {
                                scmd->device->expecting_cc_ua = 0;
                                return NEEDS_RETRY;
                        }
                }
                /*
                 * we might also expect a cc/ua if another LUN on the target
                 * reported a UA with an ASC/ASCQ of 3F 0E -
                 * REPORTED LUNS DATA HAS CHANGED.
                 */
                if (scmd->device->sdev_target->expecting_lun_change &&
                    sshdr.asc == 0x3f && sshdr.ascq == 0x0e)
                        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;
                /*
                 * Pass the UA upwards for a determination in the completion
                 * functions.
                 */
                return SUCCESS;

                /* these are not supported */
        case DATA_PROTECT:
                if (sshdr.asc == 0x27 && sshdr.ascq == 0x07) {
                        /* Thin provisioning hard threshold reached */
                        set_host_byte(scmd, DID_ALLOC_FAILURE);
                        return SUCCESS;
                }
        case COPY_ABORTED:
        case VOLUME_OVERFLOW:
        case MISCOMPARE:
        case BLANK_CHECK:
                set_host_byte(scmd, DID_TARGET_FAILURE);
                return SUCCESS;

        case MEDIUM_ERROR:
                if (sshdr.asc == 0x11 || /* UNRECOVERED READ ERR */
                    sshdr.asc == 0x13 || /* AMNF DATA FIELD */
                    sshdr.asc == 0x14) { /* RECORD NOT FOUND */
                        set_host_byte(scmd, DID_MEDIUM_ERROR);
                        return SUCCESS;
                }
                return NEEDS_RETRY;

        case HARDWARE_ERROR:
                if (scmd->device->retry_hwerror)
                        return ADD_TO_MLQUEUE;
                else
                        set_host_byte(scmd, DID_TARGET_FAILURE);

        case ILLEGAL_REQUEST:
                if (sshdr.asc == 0x20 || /* Invalid command operation code */
                    sshdr.asc == 0x21 || /* Logical block address out of range */
                    sshdr.asc == 0x24 || /* Invalid field in cdb */
                    sshdr.asc == 0x26) { /* Parameter value invalid */
                        set_host_byte(scmd, DID_TARGET_FAILURE);
                }
                return SUCCESS;

        default:
                return SUCCESS;
        }
}

static void scsi_handle_queue_ramp_up(struct scsi_device *sdev)
{
        struct scsi_host_template *sht = sdev->host->hostt;
        struct scsi_device *tmp_sdev;

        if (!sht->change_queue_depth ||
            sdev->queue_depth >= sdev->max_queue_depth)
                return;

        if (time_before(jiffies,
            sdev->last_queue_ramp_up + sdev->queue_ramp_up_period))
                return;

        if (time_before(jiffies,
            sdev->last_queue_full_time + sdev->queue_ramp_up_period))
                return;

        /*
         * Walk all devices of a target and do
         * ramp up on them.
         */
        shost_for_each_device(tmp_sdev, sdev->host) {
                if (tmp_sdev->channel != sdev->channel ||
                    tmp_sdev->id != sdev->id ||
                    tmp_sdev->queue_depth == sdev->max_queue_depth)
                        continue;
                /*
                 * call back into LLD to increase queue_depth by one
                 * with ramp up reason code.
                 */
                sht->change_queue_depth(tmp_sdev, tmp_sdev->queue_depth + 1,
                                        SCSI_QDEPTH_RAMP_UP);
                sdev->last_queue_ramp_up = jiffies;
        }
}

static void scsi_handle_queue_full(struct scsi_device *sdev)
{
        struct scsi_host_template *sht = sdev->host->hostt;
        struct scsi_device *tmp_sdev;

        if (!sht->change_queue_depth)
                return;

        shost_for_each_device(tmp_sdev, sdev->host) {
                if (tmp_sdev->channel != sdev->channel ||
                    tmp_sdev->id != sdev->id)
                        continue;
                /*
                 * We do not know the number of commands that were at
                 * the device when we got the queue full so we start
                 * from the highest possible value and work our way down.
                 */
                sht->change_queue_depth(tmp_sdev, tmp_sdev->queue_depth - 1,
                                        SCSI_QDEPTH_QFULL);
        }
}

/**
 * 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:
                scsi_handle_queue_ramp_up(scmd->device);
        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 RESERVATION_CONFLICT:
                if (scmd->cmnd[0] == TEST_UNIT_READY)
                        /* it is a success, we probed the device and
                         * found it */
                        return SUCCESS;
                /* otherwise, we failed to send the command */
                return FAILED;
        case QUEUE_FULL:
                scsi_handle_queue_full(scmd->device);
                /* fall through */
        case BUSY:
                return NEEDS_RETRY;
        default:
                return FAILED;
        }
        return FAILED;
}

/**
 * scsi_eh_done - Completion function for error handling.
 * @scmd:       Cmd that is done.
 */
static void scsi_eh_done(struct scsi_cmnd *scmd)
{
        struct completion *eh_action;

        SCSI_LOG_ERROR_RECOVERY(3, scmd_printk(KERN_INFO, scmd,
                        "%s scmd: %p result: %x\n",
                        __func__, scmd, scmd->result));

        eh_action = scmd->device->host->eh_action;
        if (eh_action)
                complete(eh_action);
}

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

        SCSI_LOG_ERROR_RECOVERY(3,
                shost_printk(KERN_INFO, host, "Snd Host RST\n"));

        if (!hostt->eh_host_reset_handler)
                return FAILED;

        rtn = hostt->eh_host_reset_handler(scmd);

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

        return rtn;
}

/**
 * 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;
        struct Scsi_Host *host = scmd->device->host;
        struct scsi_host_template *hostt = host->hostt;

        SCSI_LOG_ERROR_RECOVERY(3, scmd_printk(KERN_INFO, scmd,
                "%s: Snd Bus RST\n", __func__));

        if (!hostt->eh_bus_reset_handler)
                return FAILED;

        rtn = hostt->eh_bus_reset_handler(scmd);

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

        return rtn;
}

static void __scsi_report_device_reset(struct scsi_device *sdev, void *data)
{
        sdev->was_reset = 1;
        sdev->expecting_cc_ua = 1;
}

/**
 * scsi_try_target_reset - Ask host to perform a target reset
 * @scmd:       SCSI cmd used to send a target reset
 *
 * 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_target_reset(struct scsi_cmnd *scmd)
{
        unsigned long flags;
        int rtn;
        struct Scsi_Host *host = scmd->device->host;
        struct scsi_host_template *hostt = host->hostt;

        if (!hostt->eh_target_reset_handler)
                return FAILED;

        rtn = hostt->eh_target_reset_handler(scmd);
        if (rtn == SUCCESS) {
                spin_lock_irqsave(host->host_lock, flags);
                __starget_for_each_device(scsi_target(scmd->device), NULL,
                                          __scsi_report_device_reset);
                spin_unlock_irqrestore(host->host_lock, flags);
        }

        return rtn;
}

/**
 * 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;
        struct scsi_host_template *hostt = scmd->device->host->hostt;

        if (!hostt->eh_device_reset_handler)
                return FAILED;

        rtn = hostt->eh_device_reset_handler(scmd);
        if (rtn == SUCCESS)
                __scsi_report_device_reset(scmd->device, NULL);
        return rtn;
}

/**
 * scsi_try_to_abort_cmd - Ask host to abort a SCSI command
 * @scmd:       SCSI cmd used to send a target reset
 *
 * Return value:
 *      SUCCESS, FAILED, or FAST_IO_FAIL
 *
 * Notes:
 *    SUCCESS does not necessarily indicate that the command
 *    has been aborted; it only indicates that the LLDDs
 *    has cleared all references to that command.
 *    LLDDs should return FAILED only if an abort was required
 *    but could not be executed. LLDDs should return FAST_IO_FAIL
 *    if the device is temporarily unavailable (eg due to a
 *    link down on FibreChannel)
 */
static int scsi_try_to_abort_cmd(struct scsi_host_template *hostt,
                                 struct scsi_cmnd *scmd)
{
        if (!hostt->eh_abort_handler)
                return FAILED;

        return hostt->eh_abort_handler(scmd);
}

static void scsi_abort_eh_cmnd(struct scsi_cmnd *scmd)
{
        if (scsi_try_to_abort_cmd(scmd->device->host->hostt, scmd) != SUCCESS)
                if (scsi_try_bus_device_reset(scmd) != SUCCESS)
                        if (scsi_try_target_reset(scmd) != SUCCESS)
                                if (scsi_try_bus_reset(scmd) != SUCCESS)
                                        scsi_try_host_reset(scmd);
}

/**
 * scsi_eh_prep_cmnd  - Save a scsi command info as part of error recovery
 * @scmd:       SCSI command structure to hijack
 * @ses:        structure to save restore information
 * @cmnd:       CDB to send. Can be NULL if no new cmnd is needed
 * @cmnd_size:  size in bytes of @cmnd (must be <= BLK_MAX_CDB)
 * @sense_bytes: size of sense data to copy. or 0 (if != 0 @cmnd is ignored)
 *
 * This function is used to save a scsi command information before re-execution
 * as part of the error recovery process.  If @sense_bytes is 0 the command
 * sent must be one that does not transfer any data.  If @sense_bytes != 0
 * @cmnd is ignored and this functions sets up a REQUEST_SENSE command
 * and cmnd buffers to read @sense_bytes into @scmd->sense_buffer.
 */
void scsi_eh_prep_cmnd(struct scsi_cmnd *scmd, struct scsi_eh_save *ses,
                        unsigned char *cmnd, int cmnd_size, unsigned sense_bytes)
{
        struct scsi_device *sdev = scmd->device;

        /*
         * We need saved copies of a number of fields - this is because
         * error handling may need to overwrite these with different values
         * to run different commands, and once error handling is complete,
         * we will need to restore these values prior to running the actual
         * command.
         */
        ses->cmd_len = scmd->cmd_len;
        ses->cmnd = scmd->cmnd;
        ses->data_direction = scmd->sc_data_direction;
        ses->sdb = scmd->sdb;
        ses->next_rq = scmd->request->next_rq;
        ses->result = scmd->result;
        ses->underflow = scmd->underflow;
        ses->prot_op = scmd->prot_op;

        scmd->prot_op = SCSI_PROT_NORMAL;
        scmd->eh_eflags = 0;
        scmd->cmnd = ses->eh_cmnd;
        memset(scmd->cmnd, 0, BLK_MAX_CDB);
        memset(&scmd->sdb, 0, sizeof(scmd->sdb));
        scmd->request->next_rq = NULL;
        scmd->result = 0;

        if (sense_bytes) {
                scmd->sdb.length = min_t(unsigned, SCSI_SENSE_BUFFERSIZE,
                                         sense_bytes);
                sg_init_one(&ses->sense_sgl, scmd->sense_buffer,
                            scmd->sdb.length);
                scmd->sdb.table.sgl = &ses->sense_sgl;
                scmd->sc_data_direction = DMA_FROM_DEVICE;
                scmd->sdb.table.nents = 1;
                scmd->cmnd[0] = REQUEST_SENSE;
                scmd->cmnd[4] = scmd->sdb.length;
                scmd->cmd_len = COMMAND_SIZE(scmd->cmnd[0]);
        } else {
                scmd->sc_data_direction = DMA_NONE;
                if (cmnd) {
                        BUG_ON(cmnd_size > BLK_MAX_CDB);
                        memcpy(scmd->cmnd, cmnd, cmnd_size);
                        scmd->cmd_len = COMMAND_SIZE(scmd->cmnd[0]);
                }
        }

        scmd->underflow = 0;

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

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

/**
 * scsi_eh_restore_cmnd  - Restore a scsi command info as part of error recovery
 * @scmd:       SCSI command structure to restore
 * @ses:        saved information from a coresponding call to scsi_eh_prep_cmnd
 *
 * Undo any damage done by above scsi_eh_prep_cmnd().
 */
void scsi_eh_restore_cmnd(struct scsi_cmnd* scmd, struct scsi_eh_save *ses)
{
        /*
         * Restore original data
         */
        scmd->cmd_len = ses->cmd_len;
        scmd->cmnd = ses->cmnd;
        scmd->sc_data_direction = ses->data_direction;
        scmd->sdb = ses->sdb;
        scmd->request->next_rq = ses->next_rq;
        scmd->result = ses->result;
        scmd->underflow = ses->underflow;
        scmd->prot_op = ses->prot_op;
}
EXPORT_SYMBOL(scsi_eh_restore_cmnd);

/**
 * scsi_send_eh_cmnd  - submit a scsi command as part of error recovery
 * @scmd:       SCSI command structure to hijack
 * @cmnd:       CDB to send
 * @cmnd_size:  size in bytes of @cmnd
 * @timeout:    timeout for this request
 * @sense_bytes: size of sense data to copy or 0
 *
 * This function is used to send a scsi command down to a target device
 * as part of the error recovery process. See also scsi_eh_prep_cmnd() above.
 *
 * Return value:
 *    SUCCESS or FAILED or NEEDS_RETRY
 */
static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,
                             int cmnd_size, int timeout, unsigned sense_bytes)
{
        struct scsi_device *sdev = scmd->device;
        struct Scsi_Host *shost = sdev->host;
        DECLARE_COMPLETION_ONSTACK(done);
        unsigned long timeleft = timeout;
        struct scsi_eh_save ses;
        const unsigned long stall_for = msecs_to_jiffies(100);
        int rtn;

retry:
        scsi_eh_prep_cmnd(scmd, &ses, cmnd, cmnd_size, sense_bytes);
        shost->eh_action = &done;

        scsi_log_send(scmd);
        scmd->scsi_done = scsi_eh_done;
        rtn = shost->hostt->queuecommand(shost, scmd);
        if (rtn) {
                if (timeleft > stall_for) {
                        scsi_eh_restore_cmnd(scmd, &ses);
                        timeleft -= stall_for;
                        msleep(jiffies_to_msecs(stall_for));
                        goto retry;
                }
                /* signal not to enter either branch of the if () below */
                timeleft = 0;
                rtn = NEEDS_RETRY;
        } else {
                timeleft = wait_for_completion_timeout(&done, timeout);
                rtn = SUCCESS;
        }

        shost->eh_action = NULL;

        scsi_log_completion(scmd, rtn);

        SCSI_LOG_ERROR_RECOVERY(3, scmd_printk(KERN_INFO, scmd,
                        "%s: scmd: %p, timeleft: %ld\n",
                        __func__, scmd, timeleft));

        /*
         * If there is time left scsi_eh_done got called, and we will examine
         * the actual status codes to see whether the command actually did
         * complete normally, else if we have a zero return and no time left,
         * the command must still be pending, so abort it and return FAILED.
         * If we never actually managed to issue the command, because
         * ->queuecommand() kept returning non zero, use the rtn = FAILED
         * value above (so don't execute either branch of the if)
         */
        if (timeleft) {
                rtn = scsi_eh_completed_normally(scmd);
                SCSI_LOG_ERROR_RECOVERY(3, scmd_printk(KERN_INFO, scmd,
                        "%s: scsi_eh_completed_normally %x\n", __func__, rtn));

                switch (rtn) {
                case SUCCESS:
                case NEEDS_RETRY:
                case FAILED:
                        break;
                case ADD_TO_MLQUEUE:
                        rtn = NEEDS_RETRY;
                        break;
                default:
                        rtn = FAILED;
                        break;
                }
        } else if (!rtn) {
                scsi_abort_eh_cmnd(scmd);
                rtn = FAILED;
        }

        scsi_eh_restore_cmnd(scmd, &ses);

        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)
{
        return scsi_send_eh_cmnd(scmd, NULL, 0, scmd->device->eh_timeout, ~0);
}

static int scsi_eh_action(struct scsi_cmnd *scmd, int rtn)
{
        if (scmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {
                struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
                if (sdrv->eh_action)
                        rtn = sdrv->eh_action(scmd, rtn);
        }
        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.
 */
void scsi_eh_finish_cmd(struct scsi_cmnd *scmd, struct list_head *done_q)
{
        scmd->device->host->host_failed--;
        scmd->eh_eflags = 0;
        list_move_tail(&scmd->eh_entry, done_q);
}
EXPORT_SYMBOL(scsi_eh_finish_cmd);

/**
 * scsi_eh_get_sense - Get device sense data.
 * @work_q:     Queue of commands to process.
 * @done_q:     Queue of processed 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, 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.
 */
int scsi_eh_get_sense(struct list_head *work_q,
                      struct list_head *done_q)
{
        struct scsi_cmnd *scmd, *next;
        struct Scsi_Host *shost;
        int rtn;

        list_for_each_entry_safe(scmd, next, work_q, eh_entry) {
                if ((scmd->eh_eflags & SCSI_EH_CANCEL_CMD) ||
                    SCSI_SENSE_VALID(scmd))
                        continue;

                shost = scmd->device->host;
                if (scsi_host_eh_past_deadline(shost)) {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                scmd_printk(KERN_INFO, scmd,
                                            "%s: skip request sense, past eh deadline\n",
                                             current->comm));
                        break;
                }
                if (status_byte(scmd->result) != CHECK_CONDITION)
                        /*
                         * don't request sense if there's no check condition
                         * status because the error we're processing isn't one
                         * that has a sense code (and some devices get
                         * confused by sense requests out of the blue)
                         */
                        continue;

                SCSI_LOG_ERROR_RECOVERY(2, scmd_printk(KERN_INFO, scmd,
                                                  "%s: requesting sense\n",
                                                  current->comm));
                rtn = scsi_request_sense(scmd);
                if (rtn != SUCCESS)
                        continue;

                SCSI_LOG_ERROR_RECOVERY(3, scmd_printk(KERN_INFO, scmd,
                        "sense requested for %p result %x\n",
                        scmd, scmd->result));
                SCSI_LOG_ERROR_RECOVERY(3, scsi_print_sense(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);
}
EXPORT_SYMBOL_GPL(scsi_eh_get_sense);

/**
 * scsi_eh_tur - Send TUR to device.
 * @scmd:       &scsi_cmnd 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;

retry_tur:
        rtn = scsi_send_eh_cmnd(scmd, tur_command, 6,
                                scmd->device->eh_timeout, 0);

        SCSI_LOG_ERROR_RECOVERY(3, scmd_printk(KERN_INFO, scmd,
                "%s: scmd %p rtn %x\n", __func__, scmd, rtn));

        switch (rtn) {
        case NEEDS_RETRY:
                if (retry_cnt--)
                        goto retry_tur;
                /*FALLTHRU*/
        case SUCCESS:
                return 0;
        default:
                return 1;
        }
}

/**
 * scsi_eh_test_devices - check if devices are responding from error recovery.
 * @cmd_list:   scsi commands in error recovery.
 * @work_q:     queue for commands which still need more error recovery
 * @done_q:     queue for commands which are finished
 * @try_stu:    boolean on if a STU command should be tried in addition to TUR.
 *
 * Decription:
 *    Tests if devices are in a working state.  Commands to devices now in
 *    a working state are sent to the done_q while commands to devices which
 *    are still failing to respond are returned to the work_q for more
 *    processing.
 **/
static int scsi_eh_test_devices(struct list_head *cmd_list,
                                struct list_head *work_q,
                                struct list_head *done_q, int try_stu)
{
        struct scsi_cmnd *scmd, *next;
        struct scsi_device *sdev;
        int finish_cmds;

        while (!list_empty(cmd_list)) {
                scmd = list_entry(cmd_list->next, struct scsi_cmnd, eh_entry);
                sdev = scmd->device;

                if (!try_stu) {
                        if (scsi_host_eh_past_deadline(sdev->host)) {
                                /* Push items back onto work_q */
                                list_splice_init(cmd_list, work_q);
                                SCSI_LOG_ERROR_RECOVERY(3,
                                        sdev_printk(KERN_INFO, sdev,
                                                    "%s: skip test device, past eh deadline",
                                                    current->comm));
                                break;
                        }
                }

                finish_cmds = !scsi_device_online(scmd->device) ||
                        (try_stu && !scsi_eh_try_stu(scmd) &&
                         !scsi_eh_tur(scmd)) ||
                        !scsi_eh_tur(scmd);

                list_for_each_entry_safe(scmd, next, cmd_list, eh_entry)
                        if (scmd->device == sdev) {
                                if (finish_cmds &&
                                    (try_stu ||
                                     scsi_eh_action(scmd, SUCCESS) == SUCCESS))
                                        scsi_eh_finish_cmd(scmd, done_q);
                                else
                                        list_move_tail(&scmd->eh_entry, work_q);
                        }
        }
        return list_empty(work_q);
}


/**
 * scsi_eh_abort_cmds - abort pending commands.
 * @work_q:     &list_head for pending commands.
 * @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 scsi_cmnd *scmd, *next;
        LIST_HEAD(check_list);
        int rtn;
        struct Scsi_Host *shost;

        list_for_each_entry_safe(scmd, next, work_q, eh_entry) {
                if (!(scmd->eh_eflags & SCSI_EH_CANCEL_CMD))
                        continue;
                shost = scmd->device->host;
                if (scsi_host_eh_past_deadline(shost)) {
                        list_splice_init(&check_list, work_q);
                        SCSI_LOG_ERROR_RECOVERY(3,
                                scmd_printk(KERN_INFO, scmd,
                                            "%s: skip aborting cmd, past eh deadline\n",
                                            current->comm));
                        return list_empty(work_q);
                }
                SCSI_LOG_ERROR_RECOVERY(3,
                        scmd_printk(KERN_INFO, scmd,
                                     "%s: aborting cmd\n", current->comm));
                rtn = scsi_try_to_abort_cmd(shost->hostt, scmd);
                if (rtn == FAILED) {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                scmd_printk(KERN_INFO, scmd,
                                            "%s: aborting cmd failed\n",
                                             current->comm));
                        list_splice_init(&check_list, work_q);
                        return list_empty(work_q);
                }
                scmd->eh_eflags &= ~SCSI_EH_CANCEL_CMD;
                if (rtn == FAST_IO_FAIL)
                        scsi_eh_finish_cmd(scmd, done_q);
                else
                        list_move_tail(&scmd->eh_entry, &check_list);
        }

        return scsi_eh_test_devices(&check_list, work_q, done_q, 0);
}

/**
 * scsi_eh_try_stu - Send START_UNIT to device.
 * @scmd:       &scsi_cmnd 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};

        if (scmd->device->allow_restart) {
                int i, rtn = NEEDS_RETRY;

                for (i = 0; rtn == NEEDS_RETRY && i < 2; i++)
                        rtn = scsi_send_eh_cmnd(scmd, stu_command, 6, scmd->device->request_queue->rq_timeout, 0);

                if (rtn == SUCCESS)
                        return 0;
        }

        return 1;
}

 /**
 * scsi_eh_stu - send START_UNIT if needed
 * @shost:      &scsi host being recovered.
 * @work_q:     &list_head for pending commands.
 * @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 scsi_cmnd *scmd, *stu_scmd, *next;
        struct scsi_device *sdev;

        shost_for_each_device(sdev, shost) {
                if (scsi_host_eh_past_deadline(shost)) {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                sdev_printk(KERN_INFO, sdev,
                                            "%s: skip START_UNIT, past eh deadline\n",
                                            current->comm));
                        break;
                }
                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,
                        sdev_printk(KERN_INFO, sdev,
                                     "%s: Sending START_UNIT\n",
                                    current->comm));

                if (!scsi_eh_try_stu(stu_scmd)) {
                        if (!scsi_device_online(sdev) ||
                            !scsi_eh_tur(stu_scmd)) {
                                list_for_each_entry_safe(scmd, next,
                                                          work_q, eh_entry) {
                                        if (scmd->device == sdev &&
                                            scsi_eh_action(scmd, SUCCESS) == SUCCESS)
                                                scsi_eh_finish_cmd(scmd, done_q);
                                }
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                sdev_printk(KERN_INFO, sdev,
                                            "%s: START_UNIT failed\n",
                                            current->comm));
                }
        }

        return list_empty(work_q);
}


/**
 * scsi_eh_bus_device_reset - send bdr if needed
 * @shost:      scsi host being recovered.
 * @work_q:     &list_head for pending commands.
 * @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 scsi_cmnd *scmd, *bdr_scmd, *next;
        struct scsi_device *sdev;
        int rtn;

        shost_for_each_device(sdev, shost) {
                if (scsi_host_eh_past_deadline(shost)) {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                sdev_printk(KERN_INFO, sdev,
                                            "%s: skip BDR, past eh deadline\n",
                                             current->comm));
                        break;
                }
                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,
                        sdev_printk(KERN_INFO, sdev,
                                     "%s: Sending BDR\n", current->comm));
                rtn = scsi_try_bus_device_reset(bdr_scmd);
                if (rtn == SUCCESS || rtn == FAST_IO_FAIL) {
                        if (!scsi_device_online(sdev) ||
                            rtn == FAST_IO_FAIL ||
                            !scsi_eh_tur(bdr_scmd)) {
                                list_for_each_entry_safe(scmd, next,
                                                         work_q, eh_entry) {
                                        if (scmd->device == sdev &&
                                            scsi_eh_action(scmd, rtn) != FAILED)
                                                scsi_eh_finish_cmd(scmd,
                                                                   done_q);
                                }
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                sdev_printk(KERN_INFO, sdev,
                                            "%s: BDR failed\n", current->comm));
                }
        }

        return list_empty(work_q);
}

/**
 * scsi_eh_target_reset - send target reset if needed
 * @shost:      scsi host being recovered.
 * @work_q:     &list_head for pending commands.
 * @done_q:     &list_head for processed commands.
 *
 * Notes:
 *    Try a target reset.
 */
static int scsi_eh_target_reset(struct Scsi_Host *shost,
                                struct list_head *work_q,
                                struct list_head *done_q)
{
        LIST_HEAD(tmp_list);
        LIST_HEAD(check_list);

        list_splice_init(work_q, &tmp_list);

        while (!list_empty(&tmp_list)) {
                struct scsi_cmnd *next, *scmd;
                int rtn;
                unsigned int id;

                if (scsi_host_eh_past_deadline(shost)) {
                        /* push back on work queue for further processing */
                        list_splice_init(&check_list, work_q);
                        list_splice_init(&tmp_list, work_q);
                        SCSI_LOG_ERROR_RECOVERY(3,
                                shost_printk(KERN_INFO, shost,
                                            "%s: Skip target reset, past eh deadline\n",
                                             current->comm));
                        return list_empty(work_q);
                }

                scmd = list_entry(tmp_list.next, struct scsi_cmnd, eh_entry);
                id = scmd_id(scmd);

                SCSI_LOG_ERROR_RECOVERY(3,
                        shost_printk(KERN_INFO, shost,
                                     "%s: Sending target reset to target %d\n",
                                     current->comm, id));
                rtn = scsi_try_target_reset(scmd);
                if (rtn != SUCCESS && rtn != FAST_IO_FAIL)
                        SCSI_LOG_ERROR_RECOVERY(3,
                                shost_printk(KERN_INFO, shost,
                                             "%s: Target reset failed"
                                             " target: %d\n",
                                             current->comm, id));
                list_for_each_entry_safe(scmd, next, &tmp_list, eh_entry) {
                        if (scmd_id(scmd) != id)
                                continue;

                        if (rtn == SUCCESS)
                                list_move_tail(&scmd->eh_entry, &check_list);
                        else if (rtn == FAST_IO_FAIL)
                                scsi_eh_finish_cmd(scmd, done_q);
                        else
                                /* push back on work queue for further processing */
                                list_move(&scmd->eh_entry, work_q);
                }
        }

        return scsi_eh_test_devices(&check_list, work_q, done_q, 0);
}

/**
 * scsi_eh_bus_reset - send a bus reset
 * @shost:      &scsi host being recovered.
 * @work_q:     &list_head for pending commands.
 * @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 scsi_cmnd *scmd, *chan_scmd, *next;
        LIST_HEAD(check_list);
        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++) {
                if (scsi_host_eh_past_deadline(shost)) {
                        list_splice_init(&check_list, work_q);
                        SCSI_LOG_ERROR_RECOVERY(3,
                                shost_printk(KERN_INFO, shost,
                                            "%s: skip BRST, past eh deadline\n",
                                             current->comm));
                        return list_empty(work_q);
                }

                chan_scmd = NULL;
                list_for_each_entry(scmd, work_q, eh_entry) {
                        if (channel == scmd_channel(scmd)) {
                                chan_scmd = scmd;
                                break;
                                /*
                                 * FIXME add back in some support for
                                 * soft_reset devices.
                                 */
                        }
                }

                if (!chan_scmd)
                        continue;
                SCSI_LOG_ERROR_RECOVERY(3,
                        shost_printk(KERN_INFO, shost,
                                     "%s: Sending BRST chan: %d\n",
                                     current->comm, channel));
                rtn = scsi_try_bus_reset(chan_scmd);
                if (rtn == SUCCESS || rtn == FAST_IO_FAIL) {
                        list_for_each_entry_safe(scmd, next, work_q, eh_entry) {
                                if (channel == scmd_channel(scmd)) {
                                        if (rtn == FAST_IO_FAIL)
                                                scsi_eh_finish_cmd(scmd,
                                                                   done_q);
                                        else
                                                list_move_tail(&scmd->eh_entry,
                                                               &check_list);
                                }
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                shost_printk(KERN_INFO, shost,
                                             "%s: BRST failed chan: %d\n",
                                             current->comm, channel));
                }
        }
        return scsi_eh_test_devices(&check_list, work_q, done_q, 0);
}

/**
 * scsi_eh_host_reset - send a host reset
 * @shost:      host to be reset.
 * @work_q:     &list_head for pending commands.
 * @done_q:     &list_head for processed commands.
 */
static int scsi_eh_host_reset(struct Scsi_Host *shost,
                              struct list_head *work_q,
                              struct list_head *done_q)
{
        struct scsi_cmnd *scmd, *next;
        LIST_HEAD(check_list);
        int rtn;

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

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

                rtn = scsi_try_host_reset(scmd);
                if (rtn == SUCCESS) {
                        list_splice_init(work_q, &check_list);
                } else if (rtn == FAST_IO_FAIL) {
                        list_for_each_entry_safe(scmd, next, work_q, eh_entry) {
                                        scsi_eh_finish_cmd(scmd, done_q);
                        }
                } else {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                shost_printk(KERN_INFO, shost,
                                             "%s: HRST failed\n",
                                             current->comm));
                }
        }
        return scsi_eh_test_devices(&check_list, work_q, done_q, 1);
}

/**
 * scsi_eh_offline_sdevs - offline scsi devices that fail to recover
 * @work_q:     &list_head for pending 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 scsi_cmnd *scmd, *next;

        list_for_each_entry_safe(scmd, next, work_q, eh_entry) {
                sdev_printk(KERN_INFO, scmd->device, "Device offlined - "
                            "not ready after error recovery\n");
                scsi_device_set_state(scmd->device, SDEV_OFFLINE);
                if (scmd->eh_eflags & SCSI_EH_CANCEL_CMD) {
                        /*
                         * FIXME: Handle lost cmds.
                         */
                }
                scsi_eh_finish_cmd(scmd, done_q);
        }
        return;
}

/**
 * scsi_noretry_cmd - determine if command should be failed fast
 * @scmd:       SCSI cmd to examine.
 */
int scsi_noretry_cmd(struct scsi_cmnd *scmd)
{
        switch (host_byte(scmd->result)) {
        case DID_OK:
                break;
        case DID_TIME_OUT:
                goto check_type;
        case DID_BUS_BUSY:
                return (scmd->request->cmd_flags & REQ_FAILFAST_TRANSPORT);
        case DID_PARITY:
                return (scmd->request->cmd_flags & REQ_FAILFAST_DEV);
        case DID_ERROR:
                if (msg_byte(scmd->result) == COMMAND_COMPLETE &&
                    status_byte(scmd->result) == RESERVATION_CONFLICT)
                        return 0;
                /* fall through */
        case DID_SOFT_ERROR:
                return (scmd->request->cmd_flags & REQ_FAILFAST_DRIVER);
        }

        if (status_byte(scmd->result) != CHECK_CONDITION)
                return 0;

check_type:
        /*
         * assume caller has checked sense and determined
         * the check condition was retryable.
         */
        if (scmd->request->cmd_flags & REQ_FAILFAST_DEV ||
            scmd->request->cmd_type == REQ_TYPE_BLOCK_PC)
                return 1;
        else
                return 0;
}

/**
 * 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, scmd_printk(KERN_INFO, scmd,
                        "%s: device offline - report as SUCCESS\n", __func__));
                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_ABORT:
                if (scmd->eh_eflags & SCSI_EH_ABORT_SCHEDULED) {
                        set_host_byte(scmd, DID_TIME_OUT);
                        return SUCCESS;
                }
        case DID_NO_CONNECT:
        case DID_BAD_TARGET:
                /*
                 * 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_TRANSPORT_DISRUPTED:
                /*
                 * LLD/transport was disrupted during processing of the IO.
                 * The transport class is now blocked/blocking,
                 * and the transport will decide what to do with the IO
                 * based on its timers and recovery capablilities if
                 * there are enough retries.
                 */
                goto maybe_retry;
        case DID_TRANSPORT_FAILFAST:
                /*
                 * The transport decided to failfast the IO (most likely
                 * the fast io fail tmo fired), so send IO directly upwards.
                 */
                return SUCCESS;
        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:
                scsi_handle_queue_full(scmd->device);
                /*
                 * 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:
                if (scmd->cmnd[0] == REPORT_LUNS)
                        scmd->device->sdev_target->expecting_lun_change = 0;
                scsi_handle_queue_ramp_up(scmd->device);
        case COMMAND_TERMINATED:
                return SUCCESS;
        case TASK_ABORTED:
                goto maybe_retry;
        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:
                sdev_printk(KERN_INFO, scmd->device,
                            "reservation conflict\n");
                set_host_byte(scmd, DID_NEXUS_FAILURE);
                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
            && !scsi_noretry_cmd(scmd)) {
                return NEEDS_RETRY;
        } else {
                /*
                 * no more retries - report this one back to upper level.
                 */
                return SUCCESS;
        }
}

static void eh_lock_door_done(struct request *req, int uptodate)
{
        __blk_put_request(req->q, req);
}

/**
 * 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.
 *
 * Notes:
 *      We queue up an asynchronous "ALLOW MEDIUM REMOVAL" request on the
 *      head of the devices request queue, and continue.
 */
static void scsi_eh_lock_door(struct scsi_device *sdev)
{
        struct request *req;

        /*
         * blk_get_request with GFP_KERNEL (__GFP_WAIT) sleeps until a
         * request becomes available
         */
        req = blk_get_request(sdev->request_queue, READ, GFP_KERNEL);
        if (IS_ERR(req))
                return;

        blk_rq_set_block_pc(req);

        req->cmd[0] = ALLOW_MEDIUM_REMOVAL;
        req->cmd[1] = 0;
        req->cmd[2] = 0;
        req->cmd[3] = 0;
        req->cmd[4] = SCSI_REMOVAL_PREVENT;
        req->cmd[5] = 0;

        req->cmd_len = COMMAND_SIZE(req->cmd[0]);

        req->cmd_flags |= REQ_QUIET;
        req->timeout = 10 * HZ;
        req->retries = 5;

        blk_execute_rq_nowait(req->q, NULL, req, 1, eh_lock_door_done);
}

/**
 * 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;
        unsigned long flags;

        /*
         * 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->was_reset && sdev->locked) {
                        scsi_eh_lock_door(sdev);
                        sdev->was_reset = 0;
                }
        }

        /*
         * 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,
                shost_printk(KERN_INFO, shost, "waking up host to restart\n"));

        spin_lock_irqsave(shost->host_lock, flags);
        if (scsi_host_set_state(shost, SHOST_RUNNING))
                if (scsi_host_set_state(shost, SHOST_CANCEL))
                        BUG_ON(scsi_host_set_state(shost, SHOST_DEL));
        spin_unlock_irqrestore(shost->host_lock, flags);

        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);

        /*
         * if eh is active and host_eh_scheduled is pending we need to re-run
         * recovery.  we do this check after scsi_run_host_queues() to allow
         * everything pent up since the last eh run a chance to make forward
         * progress before we sync again.  Either we'll immediately re-run
         * recovery or scsi_device_unbusy() will wake us again when these
         * pending commands complete.
         */
        spin_lock_irqsave(shost->host_lock, flags);
        if (shost->host_eh_scheduled)
                if (scsi_host_set_state(shost, SHOST_RECOVERY))
                        WARN_ON(scsi_host_set_state(shost, SHOST_CANCEL_RECOVERY));
        spin_unlock_irqrestore(shost->host_lock, flags);
}

/**
 * scsi_eh_ready_devs - check device ready state and recover if not.
 * @shost:      host to be recovered.
 * @work_q:     &list_head for pending commands.
 * @done_q:     &list_head for processed commands.
 */
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_target_reset(shost, work_q, done_q))
                                if (!scsi_eh_bus_reset(shost, work_q, done_q))
                                        if (!scsi_eh_host_reset(shost, work_q, done_q))
                                                scsi_eh_offline_sdevs(work_q,
                                                                      done_q);
}
EXPORT_SYMBOL_GPL(scsi_eh_ready_devs);

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

        list_for_each_entry_safe(scmd, next, done_q, eh_entry) {
                list_del_init(&scmd->eh_entry);
                if (scsi_device_online(scmd->device) &&
                    !scsi_noretry_cmd(scmd) &&
                    (++scmd->retries <= scmd->allowed)) {
                        SCSI_LOG_ERROR_RECOVERY(3,
                                scmd_printk(KERN_INFO, scmd,
                                             "%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,
                                scmd_printk(KERN_INFO, scmd,
                                             "%s: flush finish cmd: %p\n",
                                             current->comm, scmd));
                        scsi_finish_command(scmd);
                }
        }
}
EXPORT_SYMBOL(scsi_eh_flush_done_q);

/**
 * 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);

        spin_lock_irqsave(shost->host_lock, flags);
        if (shost->eh_deadline != -1)
                shost->last_reset = 0;
        spin_unlock_irqrestore(shost->host_lock, flags);
        scsi_eh_flush_done_q(&eh_done_q);
}

/**
 * scsi_error_handler - SCSI error handler thread
 * @data:       Host for which we are running.
 *
 * Notes:
 *    This is the main error handling loop.  This is run as a kernel thread
 *    for every SCSI host and handles all error handling activity.
 */
int scsi_error_handler(void *data)
{
        struct Scsi_Host *shost = data;

        /*
         * We use TASK_INTERRUPTIBLE so that the thread is not
         * counted against the load average as a running process.
         * We never actually get interrupted because kthread_run
         * disables signal delivery for the created thread.
         */
        while (!kthread_should_stop()) {
                set_current_state(TASK_INTERRUPTIBLE);
                if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) ||
                    shost->host_failed != atomic_read(&shost->host_busy)) {
                        SCSI_LOG_ERROR_RECOVERY(1,
                                shost_printk(KERN_INFO, shost,
                                             "scsi_eh_%d: sleeping\n",
                                             shost->host_no));
                        schedule();
                        continue;
                }

                __set_current_state(TASK_RUNNING);
                SCSI_LOG_ERROR_RECOVERY(1,
                        shost_printk(KERN_INFO, shost,
                                     "scsi_eh_%d: waking up %d/%d/%d\n",
                                     shost->host_no, shost->host_eh_scheduled,
                                     shost->host_failed,
                                     atomic_read(&shost->host_busy)));

                /*
                 * 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->eh_noresume && scsi_autopm_get_host(shost) != 0) {
                        SCSI_LOG_ERROR_RECOVERY(1,
                                shost_printk(KERN_ERR, shost,
                                             "scsi_eh_%d: unable to autoresume\n",
                                             shost->host_no));
                        continue;
                }

                if (shost->transportt->eh_strategy_handler)
                        shost->transportt->eh_strategy_handler(shost);
                else
                        scsi_unjam_host(shost);

                /*
                 * 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);
                if (!shost->eh_noresume)
                        scsi_autopm_put_host(shost);
        }
        __set_current_state(TASK_RUNNING);

        SCSI_LOG_ERROR_RECOVERY(1,
                shost_printk(KERN_INFO, shost,
                             "Error handler scsi_eh_%d exiting\n",
                             shost->host_no));
        shost->ehandler = NULL;
        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))
                        __scsi_report_device_reset(sdev, NULL);
        }
}
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(sdev) &&
                    target == sdev_id(sdev))
                        __scsi_report_device_reset(sdev, NULL);
        }
}
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;
        struct Scsi_Host *shost = dev->host;
        struct request req;
        unsigned long flags;
        int rtn;

        if (scsi_autopm_get_host(shost) < 0)
                return FAILED;

        if (!get_device(&dev->sdev_gendev)) {
                rtn = FAILED;
                goto out_put_autopm_host;
        }

        scmd = scsi_get_command(dev, GFP_KERNEL);
        if (!scmd) {
                rtn = FAILED;
                put_device(&dev->sdev_gendev);
                goto out_put_autopm_host;
        }

        blk_rq_init(NULL, &req);
        scmd->request = &req;

        scmd->cmnd = req.cmd;

        scmd->scsi_done         = scsi_reset_provider_done_command;
        memset(&scmd->sdb, 0, sizeof(scmd->sdb));

        scmd->cmd_len                   = 0;

        scmd->sc_data_direction         = DMA_BIDIRECTIONAL;

        spin_lock_irqsave(shost->host_lock, flags);
        shost->tmf_in_progress = 1;
        spin_unlock_irqrestore(shost->host_lock, flags);

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

        spin_lock_irqsave(shost->host_lock, flags);
        shost->tmf_in_progress = 0;
        spin_unlock_irqrestore(shost->host_lock, flags);

        /*
         * be sure to wake up anyone who was sleeping or had their queue
         * suspended while we performed the TMF.
         */
        SCSI_LOG_ERROR_RECOVERY(3,
                shost_printk(KERN_INFO, shost,
                             "waking up host to restart after TMF\n"));

        wake_up(&shost->host_wait);

        scsi_run_host_queues(shost);

        scsi_next_command(scmd);
out_put_autopm_host:
        scsi_autopm_put_host(shost);
        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:
 *      true if valid sense data information found, else false;
 */
bool scsi_normalize_sense(const u8 *sense_buffer, int sb_len,
                          struct scsi_sense_hdr *sshdr)
{
        if (!sense_buffer || !sb_len)
                return false;

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

        sshdr->response_code = (sense_buffer[0] & 0x7f);

        if (!scsi_sense_valid(sshdr))
                return false;

        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 true;
}
EXPORT_SYMBOL(scsi_normalize_sense);

bool scsi_command_normalize_sense(const struct scsi_cmnd *cmd,
                                  struct scsi_sense_hdr *sshdr)
{
        return scsi_normalize_sense(cmd->sense_buffer,
                        SCSI_SENSE_BUFFERSIZE, 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 - 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);

/**
 * scsi_build_sense_buffer - build sense data in a buffer
 * @desc:       Sense format (non zero == descriptor format,
 *              0 == fixed format)
 * @buf:        Where to build sense data
 * @key:        Sense key
 * @asc:        Additional sense code
 * @ascq:       Additional sense code qualifier
 *
 **/
void scsi_build_sense_buffer(int desc, u8 *buf, u8 key, u8 asc, u8 ascq)
{
        if (desc) {
                buf[0] = 0x72;  /* descriptor, current */
                buf[1] = key;
                buf[2] = asc;
                buf[3] = ascq;
                buf[7] = 0;
        } else {
                buf[0] = 0x70;  /* fixed, current */
                buf[2] = key;
                buf[7] = 0xa;
                buf[12] = asc;
                buf[13] = ascq;
        }
}
EXPORT_SYMBOL(scsi_build_sense_buffer);