// SPDX-License-Identifier: GPL-2.0-only
/*
 *  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 <linux/async.h>
#include <asm/unaligned.h>

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

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

#define CREATE_TRACE_POINTS
#include <trace/events/scsi.h>

/*
 * Definitions and constants.
 */

/*
 * 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

/*
 * Domain for asynchronous system resume operations.  It is marked 'exclusive'
 * to avoid being included in the async_synchronize_full() that is invoked by
 * dpm_resume().
 */
ASYNC_DOMAIN_EXCLUSIVE(scsi_sd_pm_domain);
EXPORT_SYMBOL(scsi_sd_pm_domain);

#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 + cmd address
         *
         * 3: same as 2
         *
         * 4: same as 3
         */
        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: scmd 0x%p\n", cmd);
                        scsi_print_command(cmd);
                }
        }
}

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
         *
         * 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)) {
                        scsi_print_result(cmd, "Done", disposition);
                        scsi_print_command(cmd);
                        if (scsi_status_is_check_condition(cmd->result))
                                scsi_print_sense(cmd);
                        if (level > 3)
                                scmd_printk(KERN_INFO, cmd,
                                            "scsi host busy %d failed %d\n",
                                            scsi_host_busy(cmd->device->host),
                                            cmd->device->host->host_failed);
                }
        }
}
#endif

/**
 * scsi_finish_command - cleanup and pass command back to upper layer
 * @cmd: the command
 *
 * Description: 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_target *starget = scsi_target(sdev);
        struct Scsi_Host *shost = sdev->host;
        struct scsi_driver *drv;
        unsigned int good_bytes;

        scsi_device_unbusy(sdev, cmd);

        /*
         * Clear the flags that say that the device/target/host is no longer
         * capable of accepting new commands.
         */
        if (atomic_read(&shost->host_blocked))
                atomic_set(&shost->host_blocked, 0);
        if (atomic_read(&starget->target_blocked))
                atomic_set(&starget->target_blocked, 0);
        if (atomic_read(&sdev->device_blocked))
                atomic_set(&sdev->device_blocked, 0);

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

        good_bytes = scsi_bufflen(cmd);
        if (!blk_rq_is_passthrough(scsi_cmd_to_rq(cmd))) {
                int old_good_bytes = good_bytes;
                drv = scsi_cmd_to_driver(cmd);
                if (drv->done)
                        good_bytes = drv->done(cmd);
                /*
                 * USB may not give sense identifying bad sector and
                 * simply return a residue instead, so subtract off the
                 * residue if drv->done() error processing indicates no
                 * change to the completion length.
                 */
                if (good_bytes == old_good_bytes)
                        good_bytes -= scsi_get_resid(cmd);
        }
        scsi_io_completion(cmd, good_bytes);
}


/*
 * 1024 is big enough for saturating the fast scsi LUN now
 */
int scsi_device_max_queue_depth(struct scsi_device *sdev)
{
        return max_t(int, sdev->host->can_queue, 1024);
}

/**
 * scsi_change_queue_depth - change a device's queue depth
 * @sdev: SCSI Device in question
 * @depth: number of commands allowed to be queued to the driver
 *
 * Sets the device queue depth and returns the new value.
 */
int scsi_change_queue_depth(struct scsi_device *sdev, int depth)
{
        depth = min_t(int, depth, scsi_device_max_queue_depth(sdev));

        if (depth > 0) {
                sdev->queue_depth = depth;
                wmb();
        }

        if (sdev->request_queue)
                blk_set_queue_depth(sdev->request_queue, depth);

        sbitmap_resize(&sdev->budget_map, sdev->queue_depth);

        return sdev->queue_depth;
}
EXPORT_SYMBOL(scsi_change_queue_depth);

/**
 * scsi_track_queue_full - track QUEUE_FULL events to adjust queue depth
 * @sdev: SCSI Device in question
 * @depth: Current number of outstanding SCSI commands on this device,
 *         not counting the one returned as QUEUE_FULL.
 *
 * Description: 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.
 *
 * 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)
{

        /*
         * Don't let QUEUE_FULLs on the same
         * jiffies count, they could all be from
         * same event.
         */
        if ((jiffies >> 4) == (sdev->last_queue_full_time >> 4))
                return 0;

        sdev->last_queue_full_time = jiffies;
        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;

        return scsi_change_queue_depth(sdev, depth);
}
EXPORT_SYMBOL(scsi_track_queue_full);

/**
 * scsi_vpd_inquiry - Request a device provide us with a VPD page
 * @sdev: The device to ask
 * @buffer: Where to put the result
 * @page: Which Vital Product Data to return
 * @len: The length of the buffer
 *
 * This is an internal helper function.  You probably want to use
 * scsi_get_vpd_page instead.
 *
 * Returns size of the vpd page on success or a negative error number.
 */
static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
                                                        u8 page, unsigned len)
{
        int result;
        unsigned char cmd[16];

        if (len < 4)
                return -EINVAL;

        cmd[0] = INQUIRY;
        cmd[1] = 1;             /* EVPD */
        cmd[2] = page;
        cmd[3] = len >> 8;
        cmd[4] = len & 0xff;
        cmd[5] = 0;             /* Control byte */

        /*
         * I'm not convinced we need to try quite this hard to get VPD, but
         * all the existing users tried this hard.
         */
        result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer,
                                  len, NULL, 30 * HZ, 3, NULL);
        if (result)
                return -EIO;

        /* Sanity check that we got the page back that we asked for */
        if (buffer[1] != page)
                return -EIO;

        return get_unaligned_be16(&buffer[2]) + 4;
}

/**
 * scsi_get_vpd_page - Get Vital Product Data from a SCSI device
 * @sdev: The device to ask
 * @page: Which Vital Product Data to return
 * @buf: where to store the VPD
 * @buf_len: number of bytes in the VPD buffer area
 *
 * SCSI devices may optionally supply Vital Product Data.  Each 'page'
 * of VPD is defined in the appropriate SCSI document (eg SPC, SBC).
 * If the device supports this VPD page, this routine returns a pointer
 * to a buffer containing the data from that page.  The caller is
 * responsible for calling kfree() on this pointer when it is no longer
 * needed.  If we cannot retrieve the VPD page this routine returns %NULL.
 */
int scsi_get_vpd_page(struct scsi_device *sdev, u8 page, unsigned char *buf,
                      int buf_len)
{
        int i, result;

        if (sdev->skip_vpd_pages)
                goto fail;

        /* Ask for all the pages supported by this device */
        result = scsi_vpd_inquiry(sdev, buf, 0, buf_len);
        if (result < 4)
                goto fail;

        /* If the user actually wanted this page, we can skip the rest */
        if (page == 0)
                return 0;

        for (i = 4; i < min(result, buf_len); i++)
                if (buf[i] == page)
                        goto found;

        if (i < result && i >= buf_len)
                /* ran off the end of the buffer, give us benefit of doubt */
                goto found;
        /* The device claims it doesn't support the requested page */
        goto fail;

 found:
        result = scsi_vpd_inquiry(sdev, buf, page, buf_len);
        if (result < 0)
                goto fail;

        return 0;

 fail:
        return -EINVAL;
}
EXPORT_SYMBOL_GPL(scsi_get_vpd_page);

/**
 * scsi_get_vpd_buf - Get Vital Product Data from a SCSI device
 * @sdev: The device to ask
 * @page: Which Vital Product Data to return
 *
 * Returns %NULL upon failure.
 */
static struct scsi_vpd *scsi_get_vpd_buf(struct scsi_device *sdev, u8 page)
{
        struct scsi_vpd *vpd_buf;
        int vpd_len = SCSI_VPD_PG_LEN, result;

retry_pg:
        vpd_buf = kmalloc(sizeof(*vpd_buf) + vpd_len, GFP_KERNEL);
        if (!vpd_buf)
                return NULL;

        result = scsi_vpd_inquiry(sdev, vpd_buf->data, page, vpd_len);
        if (result < 0) {
                kfree(vpd_buf);
                return NULL;
        }
        if (result > vpd_len) {
                vpd_len = result;
                kfree(vpd_buf);
                goto retry_pg;
        }

        vpd_buf->len = result;

        return vpd_buf;
}

static void scsi_update_vpd_page(struct scsi_device *sdev, u8 page,
                                 struct scsi_vpd __rcu **sdev_vpd_buf)
{
        struct scsi_vpd *vpd_buf;

        vpd_buf = scsi_get_vpd_buf(sdev, page);
        if (!vpd_buf)
                return;

        mutex_lock(&sdev->inquiry_mutex);
        vpd_buf = rcu_replace_pointer(*sdev_vpd_buf, vpd_buf,
                                      lockdep_is_held(&sdev->inquiry_mutex));
        mutex_unlock(&sdev->inquiry_mutex);

        if (vpd_buf)
                kfree_rcu(vpd_buf, rcu);
}

/**
 * scsi_attach_vpd - Attach Vital Product Data to a SCSI device structure
 * @sdev: The device to ask
 *
 * Attach the 'Device Identification' VPD page (0x83) and the
 * 'Unit Serial Number' VPD page (0x80) to a SCSI device
 * structure. This information can be used to identify the device
 * uniquely.
 */
void scsi_attach_vpd(struct scsi_device *sdev)
{
        int i;
        struct scsi_vpd *vpd_buf;

        if (!scsi_device_supports_vpd(sdev))
                return;

        /* Ask for all the pages supported by this device */
        vpd_buf = scsi_get_vpd_buf(sdev, 0);
        if (!vpd_buf)
                return;

        for (i = 4; i < vpd_buf->len; i++) {
                if (vpd_buf->data[i] == 0x0)
                        scsi_update_vpd_page(sdev, 0x0, &sdev->vpd_pg0);
                if (vpd_buf->data[i] == 0x80)
                        scsi_update_vpd_page(sdev, 0x80, &sdev->vpd_pg80);
                if (vpd_buf->data[i] == 0x83)
                        scsi_update_vpd_page(sdev, 0x83, &sdev->vpd_pg83);
                if (vpd_buf->data[i] == 0x89)
                        scsi_update_vpd_page(sdev, 0x89, &sdev->vpd_pg89);
        }
        kfree(vpd_buf);
}

/**
 * scsi_report_opcode - Find out if a given command opcode is supported
 * @sdev:       scsi device to query
 * @buffer:     scratch buffer (must be at least 20 bytes long)
 * @len:        length of buffer
 * @opcode:     opcode for command to look up
 *
 * Uses the REPORT SUPPORTED OPERATION CODES to look up the given
 * opcode. Returns -EINVAL if RSOC fails, 0 if the command opcode is
 * unsupported and 1 if the device claims to support the command.
 */
int scsi_report_opcode(struct scsi_device *sdev, unsigned char *buffer,
                       unsigned int len, unsigned char opcode)
{
        unsigned char cmd[16];
        struct scsi_sense_hdr sshdr;
        int result;

        if (sdev->no_report_opcodes || sdev->scsi_level < SCSI_SPC_3)
                return -EINVAL;

        memset(cmd, 0, 16);
        cmd[0] = MAINTENANCE_IN;
        cmd[1] = MI_REPORT_SUPPORTED_OPERATION_CODES;
        cmd[2] = 1;             /* One command format */
        cmd[3] = opcode;
        put_unaligned_be32(len, &cmd[6]);
        memset(buffer, 0, len);

        result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer, len,
                                  &sshdr, 30 * HZ, 3, NULL);

        if (result < 0)
                return result;
        if (result && scsi_sense_valid(&sshdr) &&
            sshdr.sense_key == ILLEGAL_REQUEST &&
            (sshdr.asc == 0x20 || sshdr.asc == 0x24) && sshdr.ascq == 0x00)
                return -EINVAL;

        if ((buffer[1] & 3) == 3) /* Command supported */
                return 1;

        return 0;
}
EXPORT_SYMBOL(scsi_report_opcode);

/**
 * scsi_device_get  -  get an additional reference to a scsi_device
 * @sdev:       device to get a reference to
 *
 * Description: 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.
 *
 * This will fail if a device is deleted or cancelled, or when the LLD module
 * is in the process of being unloaded.
 */
int scsi_device_get(struct scsi_device *sdev)
{
        if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL)
                goto fail;
        if (!get_device(&sdev->sdev_gendev))
                goto fail;
        if (!try_module_get(sdev->host->hostt->module))
                goto fail_put_device;
        return 0;

fail_put_device:
        put_device(&sdev->sdev_gendev);
fail:
        return -ENXIO;
}
EXPORT_SYMBOL(scsi_device_get);

/**
 * scsi_device_put  -  release a reference to a scsi_device
 * @sdev:       device to release a reference on.
 *
 * Description: 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)
{
        struct module *mod = sdev->host->hostt->module;

        put_device(&sdev->sdev_gendev);
        module_put(mod);
}
EXPORT_SYMBOL(scsi_device_put);

/* helper for shost_for_each_device, see that for documentation */
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.
 * @data:       Opaque passed to each function call.
 * @fn:         Function to call on each device
 *
 * This traverses over each device of @starget.  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);

/**
 * __starget_for_each_device - helper to walk all devices of a target (UNLOCKED)
 * @starget:    target whose devices we want to iterate over.
 * @data:       parameter for callback @fn()
 * @fn:         callback function that is invoked for each device
 *
 * This traverses over each device of @starget.  It does _not_
 * take a reference on the scsi_device, so the whole loop must be
 * protected by shost->host_lock.
 *
 * Note:  The only reason why drivers would want to use this is because
 * they need to access the device list in irq context.  Otherwise you
 * really want to use starget_for_each_device instead.
 **/
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
 *
 * Description: Looks up the scsi_device with the specified @lun for a given
 * @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. A scsi_device in state
 * SDEV_DEL is skipped.
 *
 * Note:  The only reason why drivers should use this is because
 * they 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,
                                                   u64 lun)
{
        struct scsi_device *sdev;

        list_for_each_entry(sdev, &starget->devices, same_target_siblings) {
                if (sdev->sdev_state == SDEV_DEL)
                        continue;
                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
 *
 * Description: Looks up the scsi_device with the specified @lun for a given
 * @starget.  The returned scsi_device has an additional reference that
 * needs to be released with scsi_device_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup_by_target(struct scsi_target *starget,
                                                 u64 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)
 * @id:         SCSI target number (physical unit number)
 * @lun:        SCSI Logical Unit Number
 *
 * Description: Looks up the scsi_device with the specified @channel, @id, @lun
 * for a given 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 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, u64 lun)
{
        struct scsi_device *sdev;

        list_for_each_entry(sdev, &shost->__devices, siblings) {
                if (sdev->sdev_state == SDEV_DEL)
                        continue;
                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
 *
 * Description: Looks up the scsi_device with the specified @channel, @id, @lun
 * for a given host.  The returned scsi_device has an additional reference that
 * needs to be released with scsi_device_put once you're done with it.
 **/
struct scsi_device *scsi_device_lookup(struct Scsi_Host *shost,
                uint channel, uint id, u64 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_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);