sched: avoid large irq-latencies in smp-balancing

[linux-2.6] / drivers / scsi / scsi.c

/*
 *  scsi.c Copyright (C) 1992 Drew Eckhardt
 *         Copyright (C) 1993, 1994, 1995, 1999 Eric Youngdale
 *         Copyright (C) 2002, 2003 Christoph Hellwig
 *
 *  generic mid-level SCSI driver
 *      Initial versions: Drew Eckhardt
 *      Subsequent revisions: Eric Youngdale
 *
 *  <drew@colorado.edu>
 *
 *  Bug correction thanks go to :
 *      Rik Faith <faith@cs.unc.edu>
 *      Tommy Thorn <tthorn>
 *      Thomas Wuensche <tw@fgb1.fgb.mw.tu-muenchen.de>
 *
 *  Modified by Eric Youngdale eric@andante.org or ericy@gnu.ai.mit.edu to
 *  add scatter-gather, multiple outstanding request, and other
 *  enhancements.
 *
 *  Native multichannel, wide scsi, /proc/scsi and hot plugging
 *  support added by Michael Neuffer <mike@i-connect.net>
 *
 *  Added request_module("scsi_hostadapter") for kerneld:
 *  (Put an "alias scsi_hostadapter your_hostadapter" in /etc/modprobe.conf)
 *  Bjorn Ekwall  <bj0rn@blox.se>
 *  (changed to kmod)
 *
 *  Major improvements to the timeout, abort, and reset processing,
 *  as well as performance modifications for large queue depths by
 *  Leonard N. Zubkoff <lnz@dandelion.com>
 *
 *  Converted cli() code to spinlocks, Ingo Molnar
 *
 *  Jiffies wrap fixes (host->resetting), 3 Dec 1998 Andrea Arcangeli
 *
 *  out_of_space hacks, D. Gilbert (dpg) 990608
 */

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/unistd.h>
#include <linux/spinlock.h>
#include <linux/kmod.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>

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

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

static void scsi_done(struct scsi_cmnd *cmd);

/*
 * Definitions and constants.
 */

#define MIN_RESET_DELAY (2*HZ)

/* Do not call reset on error if we just did a reset within 15 sec. */
#define MIN_RESET_PERIOD (15*HZ)

/*
 * Macro to determine the size of SCSI command. This macro takes vendor
 * unique commands into account. SCSI commands in groups 6 and 7 are
 * vendor unique and we will depend upon the command length being
 * supplied correctly in cmd_len.
 */
#define CDB_SIZE(cmd)   (((((cmd)->cmnd[0] >> 5) & 7) < 6) ? \
                                COMMAND_SIZE((cmd)->cmnd[0]) : (cmd)->cmd_len)

/*
 * Note - the initial logging level can be set here to log events at boot time.
 * After the system is up, you may enable logging via the /proc interface.
 */
unsigned int scsi_logging_level;
#if defined(CONFIG_SCSI_LOGGING)
EXPORT_SYMBOL(scsi_logging_level);
#endif

/* NB: These are exposed through /proc/scsi/scsi and form part of the ABI.
 * You may not alter any existing entry (although adding new ones is
 * encouraged once assigned by ANSI/INCITS T10
 */
static const char *const scsi_device_types[] = {
        "Direct-Access    ",
        "Sequential-Access",
        "Printer          ",
        "Processor        ",
        "WORM             ",
        "CD-ROM           ",
        "Scanner          ",
        "Optical Device   ",
        "Medium Changer   ",
        "Communications   ",
        "ASC IT8          ",
        "ASC IT8          ",
        "RAID             ",
        "Enclosure        ",
        "Direct-Access-RBC",
        "Optical card     ",
        "Bridge controller",
        "Object storage   ",
        "Automation/Drive ",
};

const char * scsi_device_type(unsigned type)
{
        if (type == 0x1e)
                return "Well-known LUN   ";
        if (type == 0x1f)
                return "No Device        ";
        if (type >= ARRAY_SIZE(scsi_device_types))
                return "Unknown          ";
        return scsi_device_types[type];
}

EXPORT_SYMBOL(scsi_device_type);

struct scsi_host_cmd_pool {
        struct kmem_cache       *slab;
        unsigned int    users;
        char            *name;
        unsigned int    slab_flags;
        gfp_t           gfp_mask;
};

static struct scsi_host_cmd_pool scsi_cmd_pool = {
        .name           = "scsi_cmd_cache",
        .slab_flags     = SLAB_HWCACHE_ALIGN,
};

static struct scsi_host_cmd_pool scsi_cmd_dma_pool = {
        .name           = "scsi_cmd_cache(DMA)",
        .slab_flags     = SLAB_HWCACHE_ALIGN|SLAB_CACHE_DMA,
        .gfp_mask       = __GFP_DMA,
};

static DEFINE_MUTEX(host_cmd_pool_mutex);

struct scsi_cmnd *__scsi_get_command(struct Scsi_Host *shost, gfp_t gfp_mask)
{
        struct scsi_cmnd *cmd;

        cmd = kmem_cache_alloc(shost->cmd_pool->slab,
                        gfp_mask | shost->cmd_pool->gfp_mask);

        if (unlikely(!cmd)) {
                unsigned long flags;

                spin_lock_irqsave(&shost->free_list_lock, flags);
                if (likely(!list_empty(&shost->free_list))) {
                        cmd = list_entry(shost->free_list.next,
                                         struct scsi_cmnd, list);
                        list_del_init(&cmd->list);
                }
                spin_unlock_irqrestore(&shost->free_list_lock, flags);
        }

        return cmd;
}
EXPORT_SYMBOL_GPL(__scsi_get_command);

/*
 * Function:    scsi_get_command()
 *
 * Purpose:     Allocate and setup a scsi command block
 *
 * Arguments:   dev     - parent scsi device
 *              gfp_mask- allocator flags
 *
 * Returns:     The allocated scsi command structure.
 */
struct scsi_cmnd *scsi_get_command(struct scsi_device *dev, gfp_t gfp_mask)
{
        struct scsi_cmnd *cmd;

        /* Bail if we can't get a reference to the device */
        if (!get_device(&dev->sdev_gendev))
                return NULL;

        cmd = __scsi_get_command(dev->host, gfp_mask);

        if (likely(cmd != NULL)) {
                unsigned long flags;

                memset(cmd, 0, sizeof(*cmd));
                cmd->device = dev;
                init_timer(&cmd->eh_timeout);
                INIT_LIST_HEAD(&cmd->list);
                spin_lock_irqsave(&dev->list_lock, flags);
                list_add_tail(&cmd->list, &dev->cmd_list);
                spin_unlock_irqrestore(&dev->list_lock, flags);
                cmd->jiffies_at_alloc = jiffies;
        } else
                put_device(&dev->sdev_gendev);

        return cmd;
}
EXPORT_SYMBOL(scsi_get_command);

void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd,
                        struct device *dev)
{
        unsigned long flags;

        /* changing locks here, don't need to restore the irq state */
        spin_lock_irqsave(&shost->free_list_lock, flags);
        if (unlikely(list_empty(&shost->free_list))) {
                list_add(&cmd->list, &shost->free_list);
                cmd = NULL;
        }
        spin_unlock_irqrestore(&shost->free_list_lock, flags);

        if (likely(cmd != NULL))
                kmem_cache_free(shost->cmd_pool->slab, cmd);

        put_device(dev);
}
EXPORT_SYMBOL(__scsi_put_command);

/*
 * Function:    scsi_put_command()
 *
 * Purpose:     Free a scsi command block
 *
 * Arguments:   cmd     - command block to free
 *
 * Returns:     Nothing.
 *
 * Notes:       The command must not belong to any lists.
 */
void scsi_put_command(struct scsi_cmnd *cmd)
{
        struct scsi_device *sdev = cmd->device;
        unsigned long flags;

        /* serious error if the command hasn't come from a device list */
        spin_lock_irqsave(&cmd->device->list_lock, flags);
        BUG_ON(list_empty(&cmd->list));
        list_del_init(&cmd->list);
        spin_unlock_irqrestore(&cmd->device->list_lock, flags);

        __scsi_put_command(cmd->device->host, cmd, &sdev->sdev_gendev);
}
EXPORT_SYMBOL(scsi_put_command);

/*
 * Function:    scsi_setup_command_freelist()
 *
 * Purpose:     Setup the command freelist for a scsi host.
 *
 * Arguments:   shost   - host to allocate the freelist for.
 *
 * Returns:     Nothing.
 */
int scsi_setup_command_freelist(struct Scsi_Host *shost)
{
        struct scsi_host_cmd_pool *pool;
        struct scsi_cmnd *cmd;

        spin_lock_init(&shost->free_list_lock);
        INIT_LIST_HEAD(&shost->free_list);

        /*
         * Select a command slab for this host and create it if not
         * yet existant.
         */
        mutex_lock(&host_cmd_pool_mutex);
        pool = (shost->unchecked_isa_dma ? &scsi_cmd_dma_pool : &scsi_cmd_pool);
        if (!pool->users) {
                pool->slab = kmem_cache_create(pool->name,
                                sizeof(struct scsi_cmnd), 0,
                                pool->slab_flags, NULL);
                if (!pool->slab)
                        goto fail;
        }

        pool->users++;
        shost->cmd_pool = pool;
        mutex_unlock(&host_cmd_pool_mutex);

        /*
         * Get one backup command for this host.
         */
        cmd = kmem_cache_alloc(shost->cmd_pool->slab,
                        GFP_KERNEL | shost->cmd_pool->gfp_mask);
        if (!cmd)
                goto fail2;
        list_add(&cmd->list, &shost->free_list);                
        return 0;

 fail2:
        if (!--pool->users)
                kmem_cache_destroy(pool->slab);
        return -ENOMEM;
 fail:
        mutex_unlock(&host_cmd_pool_mutex);
        return -ENOMEM;

}

/*
 * Function:    scsi_destroy_command_freelist()
 *
 * Purpose:     Release the command freelist for a scsi host.
 *
 * Arguments:   shost   - host that's freelist is going to be destroyed
 */
void scsi_destroy_command_freelist(struct Scsi_Host *shost)
{
        while (!list_empty(&shost->free_list)) {
                struct scsi_cmnd *cmd;

                cmd = list_entry(shost->free_list.next, struct scsi_cmnd, list);
                list_del_init(&cmd->list);
                kmem_cache_free(shost->cmd_pool->slab, cmd);
        }

        mutex_lock(&host_cmd_pool_mutex);
        if (!--shost->cmd_pool->users)
                kmem_cache_destroy(shost->cmd_pool->slab);
        mutex_unlock(&host_cmd_pool_mutex);
}

#ifdef CONFIG_SCSI_LOGGING
void scsi_log_send(struct scsi_cmnd *cmd)
{
        unsigned int level;

        /*
         * If ML QUEUE log level is greater than or equal to:
         *
         * 1: nothing (match completion)
         *
         * 2: log opcode + command of all commands
         *
         * 3: same as 2 plus dump cmd address
         *
         * 4: same as 3 plus dump extra junk
         */
        if (unlikely(scsi_logging_level)) {
                level = SCSI_LOG_LEVEL(SCSI_LOG_MLQUEUE_SHIFT,
                                       SCSI_LOG_MLQUEUE_BITS);
                if (level > 1) {
                        scmd_printk(KERN_INFO, cmd, "Send: ");
                        if (level > 2)
                                printk("0x%p ", cmd);
                        printk("\n");
                        scsi_print_command(cmd);
                        if (level > 3) {
                                printk(KERN_INFO "buffer = 0x%p, bufflen = %d,"
                                       " queuecommand 0x%p\n",
                                        scsi_sglist(cmd), scsi_bufflen(cmd),
                                        cmd->device->host->hostt->queuecommand);

                        }
                }
        }
}

void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
{
        unsigned int level;

        /*
         * If ML COMPLETE log level is greater than or equal to:
         *
         * 1: log disposition, result, opcode + command, and conditionally
         * sense data for failures or non SUCCESS dispositions.
         *
         * 2: same as 1 but for all command completions.
         *
         * 3: same as 2 plus dump cmd address
         *
         * 4: same as 3 plus dump extra junk
         */
        if (unlikely(scsi_logging_level)) {
                level = SCSI_LOG_LEVEL(SCSI_LOG_MLCOMPLETE_SHIFT,
                                       SCSI_LOG_MLCOMPLETE_BITS);
                if (((level > 0) && (cmd->result || disposition != SUCCESS)) ||
                    (level > 1)) {
                        scmd_printk(KERN_INFO, cmd, "Done: ");
                        if (level > 2)
                                printk("0x%p ", cmd);
                        /*
                         * Dump truncated values, so we usually fit within
                         * 80 chars.
                         */
                        switch (disposition) {
                        case SUCCESS:
                                printk("SUCCESS\n");
                                break;
                        case NEEDS_RETRY:
                                printk("RETRY\n");
                                break;
                        case ADD_TO_MLQUEUE:
                                printk("MLQUEUE\n");
                                break;
                        case FAILED:
                                printk("FAILED\n");
                                break;
                        case TIMEOUT_ERROR:
                                /* 
                                 * If called via scsi_times_out.
                                 */
                                printk("TIMEOUT\n");
                                break;
                        default:
                                printk("UNKNOWN\n");
                        }
                        scsi_print_result(cmd);
                        scsi_print_command(cmd);
                        if (status_byte(cmd->result) & CHECK_CONDITION)
                                scsi_print_sense("", cmd);
                        if (level > 3)
                                scmd_printk(KERN_INFO, cmd,
                                            "scsi host busy %d failed %d\n",
                                            cmd->device->host->host_busy,
                                            cmd->device->host->host_failed);
                }
        }
}
#endif

/* 
 * Assign a serial number to the request for error recovery
 * and debugging purposes.  Protected by the Host_Lock of host.
 */
static inline void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd *cmd)
{
        cmd->serial_number = host->cmd_serial_number++;
        if (cmd->serial_number == 0) 
                cmd->serial_number = host->cmd_serial_number++;
}

/*
 * Function:    scsi_dispatch_command
 *
 * Purpose:     Dispatch a command to the low-level driver.
 *
 * Arguments:   cmd - command block we are dispatching.
 *
 * Notes:
 */
int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
{
        struct Scsi_Host *host = cmd->device->host;
        unsigned long flags = 0;
        unsigned long timeout;
        int rtn = 0;

        /* check if the device is still usable */
        if (unlikely(cmd->device->sdev_state == SDEV_DEL)) {
                /* in SDEV_DEL we error all commands. DID_NO_CONNECT
                 * returns an immediate error upwards, and signals
                 * that the device is no longer present */
                cmd->result = DID_NO_CONNECT << 16;
                atomic_inc(&cmd->device->iorequest_cnt);
                __scsi_done(cmd);
                /* return 0 (because the command has been processed) */
                goto out;
        }

        /* Check to see if the scsi lld put this device into state SDEV_BLOCK. */
        if (unlikely(cmd->device->sdev_state == SDEV_BLOCK)) {
                /* 
                 * in SDEV_BLOCK, the command is just put back on the device
                 * queue.  The suspend state has already blocked the queue so
                 * future requests should not occur until the device 
                 * transitions out of the suspend state.
                 */
                scsi_queue_insert(cmd, SCSI_MLQUEUE_DEVICE_BUSY);

                SCSI_LOG_MLQUEUE(3, printk("queuecommand : device blocked \n"));

                /*
                 * NOTE: rtn is still zero here because we don't need the
                 * queue to be plugged on return (it's already stopped)
                 */
                goto out;
        }

        /* 
         * If SCSI-2 or lower, store the LUN value in cmnd.
         */
        if (cmd->device->scsi_level <= SCSI_2 &&
            cmd->device->scsi_level != SCSI_UNKNOWN) {
                cmd->cmnd[1] = (cmd->cmnd[1] & 0x1f) |
                               (cmd->device->lun << 5 & 0xe0);
        }

        /*
         * We will wait MIN_RESET_DELAY clock ticks after the last reset so
         * we can avoid the drive not being ready.
         */
        timeout = host->last_reset + MIN_RESET_DELAY;

        if (host->resetting && time_before(jiffies, timeout)) {
                int ticks_remaining = timeout - jiffies;
                /*
                 * NOTE: This may be executed from within an interrupt
                 * handler!  This is bad, but for now, it'll do.  The irq
                 * level of the interrupt handler has been masked out by the
                 * platform dependent interrupt handling code already, so the
                 * sti() here will not cause another call to the SCSI host's
                 * interrupt handler (assuming there is one irq-level per
                 * host).
                 */
                while (--ticks_remaining >= 0)
                        mdelay(1 + 999 / HZ);
                host->resetting = 0;
        }

        /* 
         * AK: unlikely race here: for some reason the timer could
         * expire before the serial number is set up below.
         */
        scsi_add_timer(cmd, cmd->timeout_per_command, scsi_times_out);

        scsi_log_send(cmd);

        /*
         * We will use a queued command if possible, otherwise we will
         * emulate the queuing and calling of completion function ourselves.
         */
        atomic_inc(&cmd->device->iorequest_cnt);

        /*
         * Before we queue this command, check if the command
         * length exceeds what the host adapter can handle.
         */
        if (CDB_SIZE(cmd) > cmd->device->host->max_cmd_len) {
                SCSI_LOG_MLQUEUE(3,
                                printk("queuecommand : command too long.\n"));
                cmd->result = (DID_ABORT << 16);

                scsi_done(cmd);
                goto out;
        }

        spin_lock_irqsave(host->host_lock, flags);
        scsi_cmd_get_serial(host, cmd); 

        if (unlikely(host->shost_state == SHOST_DEL)) {
                cmd->result = (DID_NO_CONNECT << 16);
                scsi_done(cmd);
        } else {
                rtn = host->hostt->queuecommand(cmd, scsi_done);
        }
        spin_unlock_irqrestore(host->host_lock, flags);
        if (rtn) {
                if (scsi_delete_timer(cmd)) {
                        atomic_inc(&cmd->device->iodone_cnt);
                        scsi_queue_insert(cmd,
                                          (rtn == SCSI_MLQUEUE_DEVICE_BUSY) ?
                                          rtn : SCSI_MLQUEUE_HOST_BUSY);
                }
                SCSI_LOG_MLQUEUE(3,
                    printk("queuecommand : request rejected\n"));
        }

 out:
        SCSI_LOG_MLQUEUE(3, printk("leaving scsi_dispatch_cmnd()\n"));
        return rtn;
}

/**
 * scsi_req_abort_cmd -- Request command recovery for the specified command
 * cmd: pointer to the SCSI command of interest
 *
 * This function requests that SCSI Core start recovery for the
 * command by deleting the timer and adding the command to the eh
 * queue.  It can be called by either LLDDs or SCSI Core.  LLDDs who
 * implement their own error recovery MAY ignore the timeout event if
 * they generated scsi_req_abort_cmd.
 */
void scsi_req_abort_cmd(struct scsi_cmnd *cmd)
{
        if (!scsi_delete_timer(cmd))
                return;
        scsi_times_out(cmd);
}
EXPORT_SYMBOL(scsi_req_abort_cmd);

/**
 * scsi_done - Enqueue the finished SCSI command into the done queue.
 * @cmd: The SCSI Command for which a low-level device driver (LLDD) gives
 * ownership back to SCSI Core -- i.e. the LLDD has finished with it.
 *
 * This function is the mid-level's (SCSI Core) interrupt routine, which
 * regains ownership of the SCSI command (de facto) from a LLDD, and enqueues
 * the command to the done queue for further processing.
 *
 * This is the producer of the done queue who enqueues at the tail.
 *
 * This function is interrupt context safe.
 */
static void scsi_done(struct scsi_cmnd *cmd)
{
        /*
         * We don't have to worry about this one timing out any more.
         * If we are unable to remove the timer, then the command
         * has already timed out.  In which case, we have no choice but to
         * let the timeout function run, as we have no idea where in fact
         * that function could really be.  It might be on another processor,
         * etc, etc.
         */
        if (!scsi_delete_timer(cmd))
                return;
        __scsi_done(cmd);
}

/* Private entry to scsi_done() to complete a command when the timer
 * isn't running --- used by scsi_times_out */
void __scsi_done(struct scsi_cmnd *cmd)
{
        struct request *rq = cmd->request;

        /*
         * Set the serial numbers back to zero
         */
        cmd->serial_number = 0;

        atomic_inc(&cmd->device->iodone_cnt);
        if (cmd->result)
                atomic_inc(&cmd->device->ioerr_cnt);

        BUG_ON(!rq);

        /*
         * The uptodate/nbytes values don't matter, as we allow partial
         * completes and thus will check this in the softirq callback
         */
        rq->completion_data = cmd;
        blk_complete_request(rq);
}

/* Move this to a header if it becomes more generally useful */
static struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
{
        return *(struct scsi_driver **)cmd->request->rq_disk->private_data;
}

/*
 * Function:    scsi_finish_command
 *
 * Purpose:     Pass command off to upper layer for finishing of I/O
 *              request, waking processes that are waiting on results,
 *              etc.
 */
void scsi_finish_command(struct scsi_cmnd *cmd)
{
        struct scsi_device *sdev = cmd->device;
        struct Scsi_Host *shost = sdev->host;
        struct scsi_driver *drv;
        unsigned int good_bytes;

        scsi_device_unbusy(sdev);

        /*
         * Clear the flags which say that the device/host is no longer
         * capable of accepting new commands.  These are set in scsi_queue.c
         * for both the queue full condition on a device, and for a
         * host full condition on the host.
         *
         * XXX(hch): What about locking?
         */
        shost->host_blocked = 0;
        sdev->device_blocked = 0;

        /*
         * If we have valid sense information, then some kind of recovery
         * must have taken place.  Make a note of this.
         */
        if (SCSI_SENSE_VALID(cmd))
                cmd->result |= (DRIVER_SENSE << 24);

        SCSI_LOG_MLCOMPLETE(4, sdev_printk(KERN_INFO, sdev,
                                "Notifying upper driver of completion "
                                "(result %x)\n", cmd->result));

        good_bytes = cmd->request_bufflen;
        if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {
                drv = scsi_cmd_to_driver(cmd);
                if (drv->done)
                        good_bytes = drv->done(cmd);
        }
        scsi_io_completion(cmd, good_bytes);
}
EXPORT_SYMBOL(scsi_finish_command);

/*
 * Function:    scsi_adjust_queue_depth()
 *
 * Purpose:     Allow low level drivers to tell us to change the queue depth
 *              on a specific SCSI device
 *
 * Arguments:   sdev    - SCSI Device in question
 *              tagged  - Do we use tagged queueing (non-0) or do we treat
 *                        this device as an untagged device (0)
 *              tags    - Number of tags allowed if tagged queueing enabled,
 *                        or number of commands the low level driver can
 *                        queue up in non-tagged mode (as per cmd_per_lun).
 *
 * Returns:     Nothing
 *
 * Lock Status: None held on entry
 *
 * Notes:       Low level drivers may call this at any time and we will do
 *              the right thing depending on whether or not the device is
 *              currently active and whether or not it even has the
 *              command blocks built yet.
 */
void scsi_adjust_queue_depth(struct scsi_device *sdev, int tagged, int tags)
{
        unsigned long flags;

        /*
         * refuse to set tagged depth to an unworkable size
         */
        if (tags <= 0)
                return;

        spin_lock_irqsave(sdev->request_queue->queue_lock, flags);

        /* Check to see if the queue is managed by the block layer
         * if it is, and we fail to adjust the depth, exit */
        if (blk_queue_tagged(sdev->request_queue) &&
            blk_queue_resize_tags(sdev->request_queue, tags) != 0)
                goto out;

        sdev->queue_depth = tags;
        switch (tagged) {
                case MSG_ORDERED_TAG:
                        sdev->ordered_tags = 1;
                        sdev->simple_tags = 1;
                        break;
                case MSG_SIMPLE_TAG:
                        sdev->ordered_tags = 0;
                        sdev->simple_tags = 1;
                        break;
                default:
                        sdev_printk(KERN_WARNING, sdev,
                                    "scsi_adjust_queue_depth, bad queue type, "
                                    "disabled\n");
                case 0:
                        sdev->ordered_tags = sdev->simple_tags = 0;
                        sdev->queue_depth = tags;
                        break;
        }
 out:
        spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
}
EXPORT_SYMBOL(scsi_adjust_queue_depth);

/*
 * Function:    scsi_track_queue_full()
 *
 * Purpose:     This function will track successive QUEUE_FULL events on a
 *              specific SCSI device to determine if and when there is a
 *              need to adjust the queue depth on the device.
 *
 * Arguments:   sdev    - SCSI Device in question
 *              depth   - Current number of outstanding SCSI commands on
 *                        this device, not counting the one returned as
 *                        QUEUE_FULL.
 *
 * Returns:     0 - No change needed
 *              >0 - Adjust queue depth to this new depth
 *              -1 - Drop back to untagged operation using host->cmd_per_lun
 *                      as the untagged command depth
 *
 * Lock Status: None held on entry
 *
 * Notes:       Low level drivers may call this at any time and we will do
 *              "The Right Thing."  We are interrupt context safe.
 */
int scsi_track_queue_full(struct scsi_device *sdev, int depth)
{
        if ((jiffies >> 4) == sdev->last_queue_full_time)
                return 0;

        sdev->last_queue_full_time = (jiffies >> 4);
        if (sdev->last_queue_full_depth != depth) {
                sdev->last_queue_full_count = 1;
                sdev->last_queue_full_depth = depth;
        } else {
                sdev->last_queue_full_count++;
        }

        if (sdev->last_queue_full_count <= 10)
                return 0;
        if (sdev->last_queue_full_depth < 8) {
                /* Drop back to untagged */
                scsi_adjust_queue_depth(sdev, 0, sdev->host->cmd_per_lun);
                return -1;
        }
        
        if (sdev->ordered_tags)
                scsi_adjust_queue_depth(sdev, MSG_ORDERED_TAG, depth);
        else
                scsi_adjust_queue_depth(sdev, MSG_SIMPLE_TAG, depth);
        return depth;
}
EXPORT_SYMBOL(scsi_track_queue_full);

/**
 * scsi_device_get  -  get an addition reference to a scsi_device
 * @sdev:       device to get a reference to
 *
 * Gets a reference to the scsi_device and increments the use count
 * of the underlying LLDD module.  You must hold host_lock of the
 * parent Scsi_Host or already have a reference when calling this.
 */
int scsi_device_get(struct scsi_device *sdev)
{
        if (sdev->sdev_state == SDEV_DEL)
                return -ENXIO;
        if (!get_device(&sdev->sdev_gendev))
                return -ENXIO;
        /* We can fail this if we're doing SCSI operations
         * from module exit (like cache flush) */
        try_module_get(sdev->host->hostt->module);

        return 0;
}
EXPORT_SYMBOL(scsi_device_get);

/**
 * scsi_device_put  -  release a reference to a scsi_device
 * @sdev:       device to release a reference on.
 *
 * Release a reference to the scsi_device and decrements the use count
 * of the underlying LLDD module.  The device is freed once the last
 * user vanishes.
 */
void scsi_device_put(struct scsi_device *sdev)
{
#ifdef CONFIG_MODULE_UNLOAD
        struct module *module = sdev->host->hostt->module;

        /* The module refcount will be zero if scsi_device_get()
         * was called from a module removal routine */
        if (module && module_refcount(module) != 0)
                module_put(module);
#endif
        put_device(&sdev->sdev_gendev);
}
EXPORT_SYMBOL(scsi_device_put);

/* helper for shost_for_each_device, thus not documented */
struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
                                           struct scsi_device *prev)
{
        struct list_head *list = (prev ? &prev->siblings : &shost->__devices);
        struct scsi_device *next = NULL;
        unsigned long flags;

        spin_lock_irqsave(shost->host_lock, flags);
        while (list->next != &shost->__devices) {
                next = list_entry(list->next, struct scsi_device, siblings);
                /* skip devices that we can't get a reference to */
                if (!scsi_device_get(next))
                        break;
                next = NULL;
                list = list->next;
        }
        spin_unlock_irqrestore(shost->host_lock, flags);

        if (prev)
                scsi_device_put(prev);
        return next;
}
EXPORT_SYMBOL(__scsi_iterate_devices);

/**
 * starget_for_each_device  -  helper to walk all devices of a target
 * @starget:    target whose devices we want to iterate over.
 *
 * This traverses over each devices of @shost.  The devices have
 * a reference that must be released by scsi_host_put when breaking
 * out of the loop.
 */
void starget_for_each_device(struct scsi_target *starget, void * data,
                     void (*fn)(struct scsi_device *, void *))
{
        struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
        struct scsi_device *sdev;

        shost_for_each_device(sdev, shost) {
                if ((sdev->channel == starget->channel) &&
                    (sdev->id == starget->id))
                        fn(sdev, data);
        }
}
EXPORT_SYMBOL(starget_for_each_device);

/**
 * __scsi_device_lookup_by_target - find a device given the target (UNLOCKED)
 * @starget:    SCSI target pointer
 * @lun:        SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @lun for a give
 * @starget. The returned scsi_device does not have an additional
 * reference.  You must hold the host's host_lock over this call and
 * any access to the returned scsi_device.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they're need to access the device list in irq context.  Otherwise you
 * really want to use scsi_device_lookup_by_target instead.
 **/
struct scsi_device *__scsi_device_lookup_by_target(struct scsi_target *starget,
                                                   uint lun)
{
        struct scsi_device *sdev;

        list_for_each_entry(sdev, &starget->devices, same_target_siblings) {
                if (sdev->lun ==lun)
                        return sdev;
        }

        return NULL;
}
EXPORT_SYMBOL(__scsi_device_lookup_by_target);

/**
 * scsi_device_lookup_by_target - find a device given the target
 * @starget:    SCSI target pointer
 * @lun:        SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @channel, @id, @lun for a
 * give host.  The returned scsi_device has an additional reference that
 * needs to be release with scsi_host_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup_by_target(struct scsi_target *starget,
                                                 uint lun)
{
        struct scsi_device *sdev;
        struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
        unsigned long flags;

        spin_lock_irqsave(shost->host_lock, flags);
        sdev = __scsi_device_lookup_by_target(starget, lun);
        if (sdev && scsi_device_get(sdev))
                sdev = NULL;
        spin_unlock_irqrestore(shost->host_lock, flags);

        return sdev;
}
EXPORT_SYMBOL(scsi_device_lookup_by_target);

/**
 * scsi_device_lookup - find a device given the host (UNLOCKED)
 * @shost:      SCSI host pointer
 * @channel:    SCSI channel (zero if only one channel)
 * @pun:        SCSI target number (physical unit number)
 * @lun:        SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @channel, @id, @lun for a
 * give host. The returned scsi_device does not have an additional reference.
 * You must hold the host's host_lock over this call and any access to the
 * returned scsi_device.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they're need to access the device list in irq context.  Otherwise you
 * really want to use scsi_device_lookup instead.
 **/
struct scsi_device *__scsi_device_lookup(struct Scsi_Host *shost,
                uint channel, uint id, uint lun)
{
        struct scsi_device *sdev;

        list_for_each_entry(sdev, &shost->__devices, siblings) {
                if (sdev->channel == channel && sdev->id == id &&
                                sdev->lun ==lun)
                        return sdev;
        }

        return NULL;
}
EXPORT_SYMBOL(__scsi_device_lookup);

/**
 * scsi_device_lookup - find a device given the host
 * @shost:      SCSI host pointer
 * @channel:    SCSI channel (zero if only one channel)
 * @id:         SCSI target number (physical unit number)
 * @lun:        SCSI Logical Unit Number
 *
 * Looks up the scsi_device with the specified @channel, @id, @lun for a
 * give host.  The returned scsi_device has an additional reference that
 * needs to be release with scsi_host_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup(struct Scsi_Host *shost,
                uint channel, uint id, uint lun)
{
        struct scsi_device *sdev;
        unsigned long flags;

        spin_lock_irqsave(shost->host_lock, flags);
        sdev = __scsi_device_lookup(shost, channel, id, lun);
        if (sdev && scsi_device_get(sdev))
                sdev = NULL;
        spin_unlock_irqrestore(shost->host_lock, flags);

        return sdev;
}
EXPORT_SYMBOL(scsi_device_lookup);

MODULE_DESCRIPTION("SCSI core");
MODULE_LICENSE("GPL");

module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");

static int __init init_scsi(void)
{
        int error;

        error = scsi_init_queue();
        if (error)
                return error;
        error = scsi_init_procfs();
        if (error)
                goto cleanup_queue;
        error = scsi_init_devinfo();
        if (error)
                goto cleanup_procfs;
        error = scsi_init_hosts();
        if (error)
                goto cleanup_devlist;
        error = scsi_init_sysctl();
        if (error)
                goto cleanup_hosts;
        error = scsi_sysfs_register();
        if (error)
                goto cleanup_sysctl;

        scsi_netlink_init();

        printk(KERN_NOTICE "SCSI subsystem initialized\n");
        return 0;

cleanup_sysctl:
        scsi_exit_sysctl();
cleanup_hosts:
        scsi_exit_hosts();
cleanup_devlist:
        scsi_exit_devinfo();
cleanup_procfs:
        scsi_exit_procfs();
cleanup_queue:
        scsi_exit_queue();
        printk(KERN_ERR "SCSI subsystem failed to initialize, error = %d\n",
               -error);
        return error;
}

static void __exit exit_scsi(void)
{
        scsi_netlink_exit();
        scsi_sysfs_unregister();
        scsi_exit_sysctl();
        scsi_exit_hosts();
        scsi_exit_devinfo();
        scsi_exit_procfs();
        scsi_exit_queue();
}

subsys_initcall(init_scsi);
module_exit(exit_scsi);