// SPDX-License-Identifier: GPL-2.0
/*
 * scsi_scan.c
 *
 * Copyright (C) 2000 Eric Youngdale,
 * Copyright (C) 2002 Patrick Mansfield
 *
 * The general scanning/probing algorithm is as follows, exceptions are
 * made to it depending on device specific flags, compilation options, and
 * global variable (boot or module load time) settings.
 *
 * A specific LUN is scanned via an INQUIRY command; if the LUN has a
 * device attached, a scsi_device is allocated and setup for it.
 *
 * For every id of every channel on the given host:
 *
 *      Scan LUN 0; if the target responds to LUN 0 (even if there is no
 *      device or storage attached to LUN 0):
 *
 *              If LUN 0 has a device attached, allocate and setup a
 *              scsi_device for it.
 *
 *              If target is SCSI-3 or up, issue a REPORT LUN, and scan
 *              all of the LUNs returned by the REPORT LUN; else,
 *              sequentially scan LUNs up until some maximum is reached,
 *              or a LUN is seen that cannot have a device attached to it.
 */

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/spinlock.h>
#include <linux/async.h>
#include <linux/slab.h>
#include <linux/unaligned.h>

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

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

#define ALLOC_FAILURE_MSG       KERN_ERR "%s: Allocation failure during" \
        " SCSI scanning, some SCSI devices might not be configured\n"

/*
 * Default timeout
 */
#define SCSI_TIMEOUT (2*HZ)
#define SCSI_REPORT_LUNS_TIMEOUT (30*HZ)

/*
 * Prefix values for the SCSI id's (stored in sysfs name field)
 */
#define SCSI_UID_SER_NUM 'S'
#define SCSI_UID_UNKNOWN 'Z'

/*
 * Return values of some of the scanning functions.
 *
 * SCSI_SCAN_NO_RESPONSE: no valid response received from the target, this
 * includes allocation or general failures preventing IO from being sent.
 *
 * SCSI_SCAN_TARGET_PRESENT: target responded, but no device is available
 * on the given LUN.
 *
 * SCSI_SCAN_LUN_PRESENT: target responded, and a device is available on a
 * given LUN.
 */
#define SCSI_SCAN_NO_RESPONSE           0
#define SCSI_SCAN_TARGET_PRESENT        1
#define SCSI_SCAN_LUN_PRESENT           2

static const char *scsi_null_device_strs = "nullnullnullnull";

#define MAX_SCSI_LUNS   512

static u64 max_scsi_luns = MAX_SCSI_LUNS;

module_param_named(max_luns, max_scsi_luns, ullong, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(max_luns,
                 "last scsi LUN (should be between 1 and 2^64-1)");

#ifdef CONFIG_SCSI_SCAN_ASYNC
#define SCSI_SCAN_TYPE_DEFAULT "async"
#else
#define SCSI_SCAN_TYPE_DEFAULT "sync"
#endif

static char scsi_scan_type[7] = SCSI_SCAN_TYPE_DEFAULT;

module_param_string(scan, scsi_scan_type, sizeof(scsi_scan_type),
                    S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(scan, "sync, async, manual, or none. "
                 "Setting to 'manual' disables automatic scanning, but allows "
                 "for manual device scan via the 'scan' sysfs attribute.");

static unsigned int scsi_inq_timeout = SCSI_TIMEOUT/HZ + 18;

module_param_named(inq_timeout, scsi_inq_timeout, uint, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(inq_timeout, 
                 "Timeout (in seconds) waiting for devices to answer INQUIRY."
                 " Default is 20. Some devices may need more; most need less.");

/* This lock protects only this list */
static DEFINE_SPINLOCK(async_scan_lock);
static LIST_HEAD(scanning_hosts);

struct async_scan_data {
        struct list_head list;
        struct Scsi_Host *shost;
        struct completion prev_finished;
};

/*
 * scsi_enable_async_suspend - Enable async suspend and resume
 */
void scsi_enable_async_suspend(struct device *dev)
{
        /*
         * If a user has disabled async probing a likely reason is due to a
         * storage enclosure that does not inject staggered spin-ups. For
         * safety, make resume synchronous as well in that case.
         */
        if (strncmp(scsi_scan_type, "async", 5) != 0)
                return;
        /* Enable asynchronous suspend and resume. */
        device_enable_async_suspend(dev);
}

/**
 * scsi_complete_async_scans - Wait for asynchronous scans to complete
 *
 * When this function returns, any host which started scanning before
 * this function was called will have finished its scan.  Hosts which
 * started scanning after this function was called may or may not have
 * finished.
 */
int scsi_complete_async_scans(void)
{
        struct async_scan_data *data;

        do {
                scoped_guard(spinlock, &async_scan_lock)
                        if (list_empty(&scanning_hosts))
                                return 0;
                /* If we can't get memory immediately, that's OK.  Just
                 * sleep a little.  Even if we never get memory, the async
                 * scans will finish eventually.
                 */
                data = kmalloc(sizeof(*data), GFP_KERNEL);
                if (!data)
                        msleep(1);
        } while (!data);

        data->shost = NULL;
        init_completion(&data->prev_finished);

        spin_lock(&async_scan_lock);
        /* Check that there's still somebody else on the list */
        if (list_empty(&scanning_hosts))
                goto done;
        list_add_tail(&data->list, &scanning_hosts);
        spin_unlock(&async_scan_lock);

        printk(KERN_INFO "scsi: waiting for bus probes to complete ...\n");
        wait_for_completion(&data->prev_finished);

        spin_lock(&async_scan_lock);
        list_del(&data->list);
        if (!list_empty(&scanning_hosts)) {
                struct async_scan_data *next = list_entry(scanning_hosts.next,
                                struct async_scan_data, list);
                complete(&next->prev_finished);
        }
 done:
        spin_unlock(&async_scan_lock);

        kfree(data);
        return 0;
}

/**
 * scsi_unlock_floptical - unlock device via a special MODE SENSE command
 * @sdev:       scsi device to send command to
 * @result:     area to store the result of the MODE SENSE
 *
 * Description:
 *     Send a vendor specific MODE SENSE (not a MODE SELECT) command.
 *     Called for BLIST_KEY devices.
 **/
static void scsi_unlock_floptical(struct scsi_device *sdev,
                                  unsigned char *result)
{
        unsigned char scsi_cmd[MAX_COMMAND_SIZE];

        sdev_printk(KERN_NOTICE, sdev, "unlocking floptical drive\n");
        scsi_cmd[0] = MODE_SENSE;
        scsi_cmd[1] = 0;
        scsi_cmd[2] = 0x2e;
        scsi_cmd[3] = 0;
        scsi_cmd[4] = 0x2a;     /* size */
        scsi_cmd[5] = 0;
        scsi_execute_cmd(sdev, scsi_cmd, REQ_OP_DRV_IN, result, 0x2a,
                         SCSI_TIMEOUT, 3, NULL);
}

static int scsi_realloc_sdev_budget_map(struct scsi_device *sdev,
                                        unsigned int depth)
{
        int new_shift = sbitmap_calculate_shift(depth);
        bool need_alloc = !sdev->budget_map.map;
        bool need_free = false;
        unsigned int memflags;
        int ret;
        struct sbitmap sb_backup;

        depth = min_t(unsigned int, depth, scsi_device_max_queue_depth(sdev));

        /*
         * realloc if new shift is calculated, which is caused by setting
         * up one new default queue depth after calling ->sdev_configure
         */
        if (!need_alloc && new_shift != sdev->budget_map.shift)
                need_alloc = need_free = true;

        if (!need_alloc)
                return 0;

        /*
         * Request queue has to be frozen for reallocating budget map,
         * and here disk isn't added yet, so freezing is pretty fast
         */
        if (need_free) {
                memflags = blk_mq_freeze_queue(sdev->request_queue);
                sb_backup = sdev->budget_map;
        }
        ret = sbitmap_init_node(&sdev->budget_map,
                                scsi_device_max_queue_depth(sdev),
                                new_shift, GFP_NOIO,
                                sdev->request_queue->node, false, true);
        if (!ret)
                sbitmap_resize(&sdev->budget_map, depth);

        if (need_free) {
                if (ret)
                        sdev->budget_map = sb_backup;
                else
                        sbitmap_free(&sb_backup);
                ret = 0;
                blk_mq_unfreeze_queue(sdev->request_queue, memflags);
        }
        return ret;
}

/**
 * scsi_alloc_sdev - allocate and setup a scsi_Device
 * @starget: which target to allocate a &scsi_device for
 * @lun: which lun
 * @hostdata: usually NULL and set by ->sdev_init instead
 *
 * Description:
 *     Allocate, initialize for io, and return a pointer to a scsi_Device.
 *     Stores the @shost, @channel, @id, and @lun in the scsi_Device, and
 *     adds scsi_Device to the appropriate list.
 *
 * Return value:
 *     scsi_Device pointer, or NULL on failure.
 **/
static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
                                           u64 lun, void *hostdata)
{
        unsigned int depth;
        struct scsi_device *sdev;
        struct request_queue *q;
        int display_failure_msg = 1, ret;
        struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
        struct queue_limits lim;

        sdev = kzalloc(sizeof(*sdev) + shost->transportt->device_size,
                       GFP_KERNEL);
        if (!sdev)
                goto out;

        sdev->vendor = scsi_null_device_strs;
        sdev->model = scsi_null_device_strs;
        sdev->rev = scsi_null_device_strs;
        sdev->host = shost;
        sdev->queue_ramp_up_period = SCSI_DEFAULT_RAMP_UP_PERIOD;
        sdev->id = starget->id;
        sdev->lun = lun;
        sdev->channel = starget->channel;
        mutex_init(&sdev->state_mutex);
        sdev->sdev_state = SDEV_CREATED;
        INIT_LIST_HEAD(&sdev->siblings);
        INIT_LIST_HEAD(&sdev->same_target_siblings);
        INIT_LIST_HEAD(&sdev->starved_entry);
        INIT_LIST_HEAD(&sdev->event_list);
        spin_lock_init(&sdev->list_lock);
        mutex_init(&sdev->inquiry_mutex);
        INIT_WORK(&sdev->event_work, scsi_evt_thread);
        INIT_WORK(&sdev->requeue_work, scsi_requeue_run_queue);

        sdev->sdev_gendev.parent = get_device(&starget->dev);
        sdev->sdev_target = starget;

        /* usually NULL and set by ->sdev_init instead */
        sdev->hostdata = hostdata;

        /* if the device needs this changing, it may do so in the
         * sdev_configure function */
        sdev->max_device_blocked = SCSI_DEFAULT_DEVICE_BLOCKED;

        /*
         * Some low level driver could use device->type
         */
        sdev->type = -1;

        /*
         * Assume that the device will have handshaking problems,
         * and then fix this field later if it turns out it
         * doesn't
         */
        sdev->borken = 1;

        sdev->sg_reserved_size = INT_MAX;

        scsi_init_limits(shost, &lim);
        q = blk_mq_alloc_queue(&sdev->host->tag_set, &lim, sdev);
        if (IS_ERR(q)) {
                /* release fn is set up in scsi_sysfs_device_initialise, so
                 * have to free and put manually here */
                put_device(&starget->dev);
                kfree(sdev);
                goto out;
        }
        kref_get(&sdev->host->tagset_refcnt);
        sdev->request_queue = q;

        scsi_sysfs_device_initialize(sdev);

        if (scsi_device_is_pseudo_dev(sdev))
                return sdev;

        depth = sdev->host->cmd_per_lun ?: 1;

        /*
         * Use .can_queue as budget map's depth because we have to
         * support adjusting queue depth from sysfs. Meantime use
         * default device queue depth to figure out sbitmap shift
         * since we use this queue depth most of times.
         */
        if (scsi_realloc_sdev_budget_map(sdev, depth))
                goto out_device_destroy;

        scsi_change_queue_depth(sdev, depth);

        if (shost->hostt->sdev_init) {
                ret = shost->hostt->sdev_init(sdev);
                if (ret) {
                        /*
                         * if LLDD reports slave not present, don't clutter
                         * console with alloc failure messages
                         */
                        if (ret == -ENXIO)
                                display_failure_msg = 0;
                        goto out_device_destroy;
                }
        }

        return sdev;

out_device_destroy:
        __scsi_remove_device(sdev);
out:
        if (display_failure_msg)
                printk(ALLOC_FAILURE_MSG, __func__);
        return NULL;
}

static void scsi_target_destroy(struct scsi_target *starget)
{
        struct device *dev = &starget->dev;
        struct Scsi_Host *shost = dev_to_shost(dev->parent);
        unsigned long flags;

        BUG_ON(starget->state == STARGET_DEL);
        starget->state = STARGET_DEL;
        transport_destroy_device(dev);
        spin_lock_irqsave(shost->host_lock, flags);
        if (shost->hostt->target_destroy)
                shost->hostt->target_destroy(starget);
        list_del_init(&starget->siblings);
        spin_unlock_irqrestore(shost->host_lock, flags);
        put_device(dev);
}

static void scsi_target_dev_release(struct device *dev)
{
        struct device *parent = dev->parent;
        struct scsi_target *starget = to_scsi_target(dev);

        kfree(starget);
        put_device(parent);
}

static const struct device_type scsi_target_type = {
        .name =         "scsi_target",
        .release =      scsi_target_dev_release,
};

int scsi_is_target_device(const struct device *dev)
{
        return dev->type == &scsi_target_type;
}
EXPORT_SYMBOL(scsi_is_target_device);

static struct scsi_target *__scsi_find_target(struct device *parent,
                                              int channel, uint id)
{
        struct scsi_target *starget, *found_starget = NULL;
        struct Scsi_Host *shost = dev_to_shost(parent);
        /*
         * Search for an existing target for this sdev.
         */
        list_for_each_entry(starget, &shost->__targets, siblings) {
                if (starget->id == id &&
                    starget->channel == channel) {
                        found_starget = starget;
                        break;
                }
        }
        if (found_starget)
                get_device(&found_starget->dev);

        return found_starget;
}

/**
 * scsi_target_reap_ref_release - remove target from visibility
 * @kref: the reap_ref in the target being released
 *
 * Called on last put of reap_ref, which is the indication that no device
 * under this target is visible anymore, so render the target invisible in
 * sysfs.  Note: we have to be in user context here because the target reaps
 * should be done in places where the scsi device visibility is being removed.
 */
static void scsi_target_reap_ref_release(struct kref *kref)
{
        struct scsi_target *starget
                = container_of(kref, struct scsi_target, reap_ref);

        /*
         * if we get here and the target is still in a CREATED state that
         * means it was allocated but never made visible (because a scan
         * turned up no LUNs), so don't call device_del() on it.
         */
        if ((starget->state != STARGET_CREATED) &&
            (starget->state != STARGET_CREATED_REMOVE)) {
                transport_remove_device(&starget->dev);
                device_del(&starget->dev);
        }
        scsi_target_destroy(starget);
}

static void scsi_target_reap_ref_put(struct scsi_target *starget)
{
        kref_put(&starget->reap_ref, scsi_target_reap_ref_release);
}

/**
 * scsi_alloc_target - allocate a new or find an existing target
 * @parent:     parent of the target (need not be a scsi host)
 * @channel:    target channel number (zero if no channels)
 * @id:         target id number
 *
 * Return an existing target if one exists, provided it hasn't already
 * gone into STARGET_DEL state, otherwise allocate a new target.
 *
 * The target is returned with an incremented reference, so the caller
 * is responsible for both reaping and doing a last put
 */
static struct scsi_target *scsi_alloc_target(struct device *parent,
                                             int channel, uint id)
{
        struct Scsi_Host *shost = dev_to_shost(parent);
        struct device *dev = NULL;
        unsigned long flags;
        const int size = sizeof(struct scsi_target)
                + shost->transportt->target_size;
        struct scsi_target *starget;
        struct scsi_target *found_target;
        int error, ref_got;

        starget = kzalloc(size, GFP_KERNEL);
        if (!starget) {
                printk(KERN_ERR "%s: allocation failure\n", __func__);
                return NULL;
        }
        dev = &starget->dev;
        device_initialize(dev);
        kref_init(&starget->reap_ref);
        dev->parent = get_device(parent);
        dev_set_name(dev, "target%d:%d:%d", shost->host_no, channel, id);
        dev->bus = &scsi_bus_type;
        dev->type = &scsi_target_type;
        scsi_enable_async_suspend(dev);
        starget->id = id;
        starget->channel = channel;
        starget->can_queue = 0;
        INIT_LIST_HEAD(&starget->siblings);
        INIT_LIST_HEAD(&starget->devices);
        starget->state = STARGET_CREATED;
        starget->scsi_level = SCSI_2;
        starget->max_target_blocked = SCSI_DEFAULT_TARGET_BLOCKED;
 retry:
        spin_lock_irqsave(shost->host_lock, flags);

        found_target = __scsi_find_target(parent, channel, id);
        if (found_target)
                goto found;

        list_add_tail(&starget->siblings, &shost->__targets);
        spin_unlock_irqrestore(shost->host_lock, flags);
        /* allocate and add */
        transport_setup_device(dev);
        if (shost->hostt->target_alloc) {
                error = shost->hostt->target_alloc(starget);

                if(error) {
                        if (error != -ENXIO)
                                dev_err(dev, "target allocation failed, error %d\n", error);
                        /* don't want scsi_target_reap to do the final
                         * put because it will be under the host lock */
                        scsi_target_destroy(starget);
                        return NULL;
                }
        }
        get_device(dev);

        return starget;

 found:
        /*
         * release routine already fired if kref is zero, so if we can still
         * take the reference, the target must be alive.  If we can't, it must
         * be dying and we need to wait for a new target
         */
        ref_got = kref_get_unless_zero(&found_target->reap_ref);

        spin_unlock_irqrestore(shost->host_lock, flags);
        if (ref_got) {
                put_device(dev);
                return found_target;
        }
        /*
         * Unfortunately, we found a dying target; need to wait until it's
         * dead before we can get a new one.  There is an anomaly here.  We
         * *should* call scsi_target_reap() to balance the kref_get() of the
         * reap_ref above.  However, since the target being released, it's
         * already invisible and the reap_ref is irrelevant.  If we call
         * scsi_target_reap() we might spuriously do another device_del() on
         * an already invisible target.
         */
        put_device(&found_target->dev);
        /*
         * length of time is irrelevant here, we just want to yield the CPU
         * for a tick to avoid busy waiting for the target to die.
         */
        msleep(1);
        goto retry;
}

/**
 * scsi_target_reap - check to see if target is in use and destroy if not
 * @starget: target to be checked
 *
 * This is used after removing a LUN or doing a last put of the target
 * it checks atomically that nothing is using the target and removes
 * it if so.
 */
void scsi_target_reap(struct scsi_target *starget)
{
        /*
         * serious problem if this triggers: STARGET_DEL is only set in the if
         * the reap_ref drops to zero, so we're trying to do another final put
         * on an already released kref
         */
        BUG_ON(starget->state == STARGET_DEL);
        scsi_target_reap_ref_put(starget);
}

/**
 * scsi_sanitize_inquiry_string - remove non-graphical chars from an
 *                                INQUIRY result string
 * @s: INQUIRY result string to sanitize
 * @len: length of the string
 *
 * Description:
 *      The SCSI spec says that INQUIRY vendor, product, and revision
 *      strings must consist entirely of graphic ASCII characters,
 *      padded on the right with spaces.  Since not all devices obey
 *      this rule, we will replace non-graphic or non-ASCII characters
 *      with spaces.  Exception: a NUL character is interpreted as a
 *      string terminator, so all the following characters are set to
 *      spaces.
 **/
void scsi_sanitize_inquiry_string(unsigned char *s, int len)
{
        int terminated = 0;

        for (; len > 0; (--len, ++s)) {
                if (*s == 0)
                        terminated = 1;
                if (terminated || *s < 0x20 || *s > 0x7e)
                        *s = ' ';
        }
}
EXPORT_SYMBOL(scsi_sanitize_inquiry_string);


/**
 * scsi_probe_lun - probe a single LUN using a SCSI INQUIRY
 * @sdev:       scsi_device to probe
 * @inq_result: area to store the INQUIRY result
 * @result_len: len of inq_result
 * @bflags:     store any bflags found here
 *
 * Description:
 *     Probe the lun associated with @req using a standard SCSI INQUIRY;
 *
 *     If the INQUIRY is successful, zero is returned and the
 *     INQUIRY data is in @inq_result; the scsi_level and INQUIRY length
 *     are copied to the scsi_device any flags value is stored in *@bflags.
 **/
static int scsi_probe_lun(struct scsi_device *sdev, unsigned char *inq_result,
                          int result_len, blist_flags_t *bflags)
{
        unsigned char scsi_cmd[MAX_COMMAND_SIZE];
        int first_inquiry_len, try_inquiry_len, next_inquiry_len;
        int response_len = 0;
        int pass, count, result, resid;
        struct scsi_failure failure_defs[] = {
                /*
                 * not-ready to ready transition [asc/ascq=0x28/0x0] or
                 * power-on, reset [asc/ascq=0x29/0x0], continue. INQUIRY
                 * should not yield UNIT_ATTENTION but many buggy devices do
                 * so anyway.
                 */
                {
                        .sense = UNIT_ATTENTION,
                        .asc = 0x28,
                        .result = SAM_STAT_CHECK_CONDITION,
                },
                {
                        .sense = UNIT_ATTENTION,
                        .asc = 0x29,
                        .result = SAM_STAT_CHECK_CONDITION,
                },
                {
                        .allowed = 1,
                        .result = DID_TIME_OUT << 16,
                },
                {}
        };
        struct scsi_failures failures = {
                .total_allowed = 3,
                .failure_definitions = failure_defs,
        };
        const struct scsi_exec_args exec_args = {
                .resid = &resid,
                .failures = &failures,
        };

        *bflags = 0;

        /* Perform up to 3 passes.  The first pass uses a conservative
         * transfer length of 36 unless sdev->inquiry_len specifies a
         * different value. */
        first_inquiry_len = sdev->inquiry_len ? sdev->inquiry_len : 36;
        try_inquiry_len = first_inquiry_len;
        pass = 1;

 next_pass:
        SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
                                "scsi scan: INQUIRY pass %d length %d\n",
                                pass, try_inquiry_len));

        /* Each pass gets up to three chances to ignore Unit Attention */
        scsi_failures_reset_retries(&failures);

        for (count = 0; count < 3; ++count) {
                memset(scsi_cmd, 0, 6);
                scsi_cmd[0] = INQUIRY;
                scsi_cmd[4] = (unsigned char) try_inquiry_len;

                memset(inq_result, 0, try_inquiry_len);

                result = scsi_execute_cmd(sdev,  scsi_cmd, REQ_OP_DRV_IN,
                                          inq_result, try_inquiry_len,
                                          HZ / 2 + HZ * scsi_inq_timeout, 3,
                                          &exec_args);

                SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
                                "scsi scan: INQUIRY %s with code 0x%x\n",
                                result ? "failed" : "successful", result));

                if (result == 0) {
                        /*
                         * if nothing was transferred, we try
                         * again. It's a workaround for some USB
                         * devices.
                         */
                        if (resid == try_inquiry_len)
                                continue;
                }
                break;
        }

        if (result == 0) {
                scsi_sanitize_inquiry_string(&inq_result[8], 8);
                scsi_sanitize_inquiry_string(&inq_result[16], 16);
                scsi_sanitize_inquiry_string(&inq_result[32], 4);

                response_len = inq_result[4] + 5;
                if (response_len > 255)
                        response_len = first_inquiry_len;       /* sanity */

                /*
                 * Get any flags for this device.
                 *
                 * XXX add a bflags to scsi_device, and replace the
                 * corresponding bit fields in scsi_device, so bflags
                 * need not be passed as an argument.
                 */
                *bflags = scsi_get_device_flags(sdev, &inq_result[8],
                                &inq_result[16]);

                /* When the first pass succeeds we gain information about
                 * what larger transfer lengths might work. */
                if (pass == 1) {
                        if (BLIST_INQUIRY_36 & *bflags)
                                next_inquiry_len = 36;
                        /*
                         * LLD specified a maximum sdev->inquiry_len
                         * but device claims it has more data. Capping
                         * the length only makes sense for legacy
                         * devices. If a device supports SPC-4 (2014)
                         * or newer, assume that it is safe to ask for
                         * as much as the device says it supports.
                         */
                        else if (sdev->inquiry_len &&
                                 response_len > sdev->inquiry_len &&
                                 (inq_result[2] & 0x7) < 6) /* SPC-4 */
                                next_inquiry_len = sdev->inquiry_len;
                        else
                                next_inquiry_len = response_len;

                        /* If more data is available perform the second pass */
                        if (next_inquiry_len > try_inquiry_len) {
                                try_inquiry_len = next_inquiry_len;
                                pass = 2;
                                goto next_pass;
                        }
                }

        } else if (pass == 2) {
                sdev_printk(KERN_INFO, sdev,
                            "scsi scan: %d byte inquiry failed.  "
                            "Consider BLIST_INQUIRY_36 for this device\n",
                            try_inquiry_len);

                /* If this pass failed, the third pass goes back and transfers
                 * the same amount as we successfully got in the first pass. */
                try_inquiry_len = first_inquiry_len;
                pass = 3;
                goto next_pass;
        }

        /* If the last transfer attempt got an error, assume the
         * peripheral doesn't exist or is dead. */
        if (result)
                return -EIO;

        /* Don't report any more data than the device says is valid */
        sdev->inquiry_len = min(try_inquiry_len, response_len);

        /*
         * XXX Abort if the response length is less than 36? If less than
         * 32, the lookup of the device flags (above) could be invalid,
         * and it would be possible to take an incorrect action - we do
         * not want to hang because of a short INQUIRY. On the flip side,
         * if the device is spun down or becoming ready (and so it gives a
         * short INQUIRY), an abort here prevents any further use of the
         * device, including spin up.
         *
         * On the whole, the best approach seems to be to assume the first
         * 36 bytes are valid no matter what the device says.  That's
         * better than copying < 36 bytes to the inquiry-result buffer
         * and displaying garbage for the Vendor, Product, or Revision
         * strings.
         */
        if (sdev->inquiry_len < 36) {
                if (!sdev->host->short_inquiry) {
                        shost_printk(KERN_INFO, sdev->host,
                                    "scsi scan: INQUIRY result too short (%d),"
                                    " using 36\n", sdev->inquiry_len);
                        sdev->host->short_inquiry = 1;
                }
                sdev->inquiry_len = 36;
        }

        /*
         * Related to the above issue:
         *
         * XXX Devices (disk or all?) should be sent a TEST UNIT READY,
         * and if not ready, sent a START_STOP to start (maybe spin up) and
         * then send the INQUIRY again, since the INQUIRY can change after
         * a device is initialized.
         *
         * Ideally, start a device if explicitly asked to do so.  This
         * assumes that a device is spun up on power on, spun down on
         * request, and then spun up on request.
         */

        /*
         * The scanning code needs to know the scsi_level, even if no
         * device is attached at LUN 0 (SCSI_SCAN_TARGET_PRESENT) so
         * non-zero LUNs can be scanned.
         */
        sdev->scsi_level = inq_result[2] & 0x0f;
        if (sdev->scsi_level >= 2 ||
            (sdev->scsi_level == 1 && (inq_result[3] & 0x0f) == 1))
                sdev->scsi_level++;
        sdev->sdev_target->scsi_level = sdev->scsi_level;

        /*
         * If SCSI-2 or lower, and if the transport requires it,
         * store the LUN value in CDB[1].
         */
        sdev->lun_in_cdb = 0;
        if (sdev->scsi_level <= SCSI_2 &&
            sdev->scsi_level != SCSI_UNKNOWN &&
            !sdev->host->no_scsi2_lun_in_cdb)
                sdev->lun_in_cdb = 1;

        return 0;
}

/**
 * scsi_add_lun - allocate and fully initialze a scsi_device
 * @sdev:       holds information to be stored in the new scsi_device
 * @inq_result: holds the result of a previous INQUIRY to the LUN
 * @bflags:     black/white list flag
 * @async:      1 if this device is being scanned asynchronously
 *
 * Description:
 *     Initialize the scsi_device @sdev.  Optionally set fields based
 *     on values in *@bflags.
 *
 * Return:
 *     SCSI_SCAN_NO_RESPONSE: could not allocate or setup a scsi_device
 *     SCSI_SCAN_LUN_PRESENT: a new scsi_device was allocated and initialized
 **/
static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
                blist_flags_t *bflags, int async)
{
        const struct scsi_host_template *hostt = sdev->host->hostt;
        struct queue_limits lim;
        int ret;

        /*
         * XXX do not save the inquiry, since it can change underneath us,
         * save just vendor/model/rev.
         *
         * Rather than save it and have an ioctl that retrieves the saved
         * value, have an ioctl that executes the same INQUIRY code used
         * in scsi_probe_lun, let user level programs doing INQUIRY
         * scanning run at their own risk, or supply a user level program
         * that can correctly scan.
         */

        /*
         * Copy at least 36 bytes of INQUIRY data, so that we don't
         * dereference unallocated memory when accessing the Vendor,
         * Product, and Revision strings.  Badly behaved devices may set
         * the INQUIRY Additional Length byte to a small value, indicating
         * these strings are invalid, but often they contain plausible data
         * nonetheless.  It doesn't matter if the device sent < 36 bytes
         * total, since scsi_probe_lun() initializes inq_result with 0s.
         */
        sdev->inquiry = kmemdup(inq_result,
                                max_t(size_t, sdev->inquiry_len, 36),
                                GFP_KERNEL);
        if (sdev->inquiry == NULL)
                return SCSI_SCAN_NO_RESPONSE;

        sdev->vendor = (char *) (sdev->inquiry + 8);
        sdev->model = (char *) (sdev->inquiry + 16);
        sdev->rev = (char *) (sdev->inquiry + 32);

        sdev->is_ata = strncmp(sdev->vendor, "ATA     ", 8) == 0;
        if (sdev->is_ata) {
                /*
                 * sata emulation layer device.  This is a hack to work around
                 * the SATL power management specifications which state that
                 * when the SATL detects the device has gone into standby
                 * mode, it shall respond with NOT READY.
                 */
                sdev->allow_restart = 1;
        }

        if (*bflags & BLIST_ISROM) {
                sdev->type = TYPE_ROM;
                sdev->removable = 1;
        } else {
                sdev->type = (inq_result[0] & 0x1f);
                sdev->removable = (inq_result[1] & 0x80) >> 7;

                /*
                 * some devices may respond with wrong type for
                 * well-known logical units. Force well-known type
                 * to enumerate them correctly.
                 */
                if (scsi_is_wlun(sdev->lun) && sdev->type != TYPE_WLUN) {
                        sdev_printk(KERN_WARNING, sdev,
                                "%s: correcting incorrect peripheral device type 0x%x for W-LUN 0x%16xhN\n",
                                __func__, sdev->type, (unsigned int)sdev->lun);
                        sdev->type = TYPE_WLUN;
                }

        }

        if (sdev->type == TYPE_RBC || sdev->type == TYPE_ROM) {
                /* RBC and MMC devices can return SCSI-3 compliance and yet
                 * still not support REPORT LUNS, so make them act as
                 * BLIST_NOREPORTLUN unless BLIST_REPORTLUN2 is
                 * specifically set */
                if ((*bflags & BLIST_REPORTLUN2) == 0)
                        *bflags |= BLIST_NOREPORTLUN;
        }

        /*
         * For a peripheral qualifier (PQ) value of 1 (001b), the SCSI
         * spec says: The device server is capable of supporting the
         * specified peripheral device type on this logical unit. However,
         * the physical device is not currently connected to this logical
         * unit.
         *
         * The above is vague, as it implies that we could treat 001 and
         * 011 the same. Stay compatible with previous code, and create a
         * scsi_device for a PQ of 1
         *
         * Don't set the device offline here; rather let the upper
         * level drivers eval the PQ to decide whether they should
         * attach. So remove ((inq_result[0] >> 5) & 7) == 1 check.
         */ 

        sdev->inq_periph_qual = (inq_result[0] >> 5) & 7;
        sdev->lockable = sdev->removable;
        sdev->soft_reset = (inq_result[7] & 1) && ((inq_result[3] & 7) == 2);

        if (sdev->scsi_level >= SCSI_3 ||
                        (sdev->inquiry_len > 56 && inq_result[56] & 0x04))
                sdev->ppr = 1;
        if (inq_result[7] & 0x60)
                sdev->wdtr = 1;
        if (inq_result[7] & 0x10)
                sdev->sdtr = 1;

        sdev_printk(KERN_NOTICE, sdev, "%s %.8s %.16s %.4s PQ: %d "
                        "ANSI: %d%s\n", scsi_device_type(sdev->type),
                        sdev->vendor, sdev->model, sdev->rev,
                        sdev->inq_periph_qual, inq_result[2] & 0x07,
                        (inq_result[3] & 0x0f) == 1 ? " CCS" : "");

        if ((sdev->scsi_level >= SCSI_2) && (inq_result[7] & 2) &&
            !(*bflags & BLIST_NOTQ)) {
                sdev->tagged_supported = 1;
                sdev->simple_tags = 1;
        }

        /*
         * Some devices (Texel CD ROM drives) have handshaking problems
         * when used with the Seagate controllers. borken is initialized
         * to 1, and then set it to 0 here.
         */
        if ((*bflags & BLIST_BORKEN) == 0)
                sdev->borken = 0;

        if (*bflags & BLIST_NO_ULD_ATTACH)
                sdev->no_uld_attach = 1;

        /*
         * Apparently some really broken devices (contrary to the SCSI
         * standards) need to be selected without asserting ATN
         */
        if (*bflags & BLIST_SELECT_NO_ATN)
                sdev->select_no_atn = 1;

        /*
         * Some devices may not want to have a start command automatically
         * issued when a device is added.
         */
        if (*bflags & BLIST_NOSTARTONADD)
                sdev->no_start_on_add = 1;

        if (*bflags & BLIST_SINGLELUN)
                scsi_target(sdev)->single_lun = 1;

        sdev->use_10_for_rw = 1;

        /* some devices don't like REPORT SUPPORTED OPERATION CODES
         * and will simply timeout causing sd_mod init to take a very
         * very long time */
        if (*bflags & BLIST_NO_RSOC)
                sdev->no_report_opcodes = 1;

        /* set the device running here so that slave configure
         * may do I/O */
        mutex_lock(&sdev->state_mutex);
        ret = scsi_device_set_state(sdev, SDEV_RUNNING);
        if (ret)
                ret = scsi_device_set_state(sdev, SDEV_BLOCK);
        mutex_unlock(&sdev->state_mutex);

        if (ret) {
                sdev_printk(KERN_ERR, sdev,
                            "in wrong state %s to complete scan\n",
                            scsi_device_state_name(sdev->sdev_state));
                return SCSI_SCAN_NO_RESPONSE;
        }

        if (*bflags & BLIST_NOT_LOCKABLE)
                sdev->lockable = 0;

        if (*bflags & BLIST_RETRY_HWERROR)
                sdev->retry_hwerror = 1;

        if (*bflags & BLIST_NO_DIF)
                sdev->no_dif = 1;

        if (*bflags & BLIST_UNMAP_LIMIT_WS)
                sdev->unmap_limit_for_ws = 1;

        if (*bflags & BLIST_IGN_MEDIA_CHANGE)
                sdev->ignore_media_change = 1;

        sdev->eh_timeout = SCSI_DEFAULT_EH_TIMEOUT;

        if (*bflags & BLIST_TRY_VPD_PAGES)
                sdev->try_vpd_pages = 1;
        else if (*bflags & BLIST_SKIP_VPD_PAGES)
                sdev->skip_vpd_pages = 1;

        if (*bflags & BLIST_NO_VPD_SIZE)
                sdev->no_vpd_size = 1;

        transport_configure_device(&sdev->sdev_gendev);

        sdev->sdev_bflags = *bflags;

        if (scsi_device_is_pseudo_dev(sdev))
                return SCSI_SCAN_LUN_PRESENT;

        /*
         * No need to freeze the queue as it isn't reachable to anyone else yet.
         */
        lim = queue_limits_start_update(sdev->request_queue);
        if (*bflags & BLIST_MAX_512)
                lim.max_hw_sectors = 512;
        else if (*bflags & BLIST_MAX_1024)
                lim.max_hw_sectors = 1024;

        if (hostt->sdev_configure)
                ret = hostt->sdev_configure(sdev, &lim);
        if (ret) {
                queue_limits_cancel_update(sdev->request_queue);
                /*
                 * If the LLDD reports device not present, don't clutter the
                 * console with failure messages.
                 */
                if (ret != -ENXIO)
                        sdev_printk(KERN_ERR, sdev,
                                "failed to configure device\n");
                return SCSI_SCAN_NO_RESPONSE;
        }

        ret = queue_limits_commit_update(sdev->request_queue, &lim);
        if (ret) {
                sdev_printk(KERN_ERR, sdev, "failed to apply queue limits.\n");
                return SCSI_SCAN_NO_RESPONSE;
        }

        /*
         * The queue_depth is often changed in ->sdev_configure.
         *
         * Set up budget map again since memory consumption of the map depends
         * on actual queue depth.
         */
        if (hostt->sdev_configure)
                scsi_realloc_sdev_budget_map(sdev, sdev->queue_depth);

        if (sdev->scsi_level >= SCSI_3)
                scsi_attach_vpd(sdev);

        scsi_cdl_check(sdev);

        sdev->max_queue_depth = sdev->queue_depth;
        WARN_ON_ONCE(sdev->max_queue_depth > sdev->budget_map.depth);

        /*
         * Ok, the device is now all set up, we can
         * register it and tell the rest of the kernel
         * about it.
         */
        if (!async && scsi_sysfs_add_sdev(sdev) != 0)
                return SCSI_SCAN_NO_RESPONSE;

        return SCSI_SCAN_LUN_PRESENT;
}

#ifdef CONFIG_SCSI_LOGGING
/** 
 * scsi_inq_str - print INQUIRY data from min to max index, strip trailing whitespace
 * @buf:   Output buffer with at least end-first+1 bytes of space
 * @inq:   Inquiry buffer (input)
 * @first: Offset of string into inq
 * @end:   Index after last character in inq
 */
static unsigned char *scsi_inq_str(unsigned char *buf, unsigned char *inq,
                                   unsigned first, unsigned end)
{
        unsigned term = 0, idx;

        for (idx = 0; idx + first < end && idx + first < inq[4] + 5; idx++) {
                if (inq[idx+first] > ' ') {
                        buf[idx] = inq[idx+first];
                        term = idx+1;
                } else {
                        buf[idx] = ' ';
                }
        }
        buf[term] = 0;
        return buf;
}
#endif

/**
 * scsi_probe_and_add_lun - probe a LUN, if a LUN is found add it
 * @starget:    pointer to target device structure
 * @lun:        LUN of target device
 * @bflagsp:    store bflags here if not NULL
 * @sdevp:      probe the LUN corresponding to this scsi_device
 * @rescan:     if not equal to SCSI_SCAN_INITIAL skip some code only
 *              needed on first scan
 * @hostdata:   passed to scsi_alloc_sdev()
 *
 * Description:
 *     Call scsi_probe_lun, if a LUN with an attached device is found,
 *     allocate and set it up by calling scsi_add_lun.
 *
 * Return:
 *
 *   - SCSI_SCAN_NO_RESPONSE: could not allocate or setup a scsi_device
 *   - SCSI_SCAN_TARGET_PRESENT: target responded, but no device is
 *         attached at the LUN
 *   - SCSI_SCAN_LUN_PRESENT: a new scsi_device was allocated and initialized
 **/
static int scsi_probe_and_add_lun(struct scsi_target *starget,
                                  u64 lun, blist_flags_t *bflagsp,
                                  struct scsi_device **sdevp,
                                  enum scsi_scan_mode rescan,
                                  void *hostdata)
{
        struct scsi_device *sdev;
        unsigned char *result;
        blist_flags_t bflags;
        int res = SCSI_SCAN_NO_RESPONSE, result_len = 256;
        struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);

        /*
         * The rescan flag is used as an optimization, the first scan of a
         * host adapter calls into here with rescan == 0.
         */
        sdev = scsi_device_lookup_by_target(starget, lun);
        if (sdev) {
                if (rescan != SCSI_SCAN_INITIAL || !scsi_device_created(sdev)) {
                        SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
                                "scsi scan: device exists on %s\n",
                                dev_name(&sdev->sdev_gendev)));
                        if (sdevp)
                                *sdevp = sdev;
                        else
                                scsi_device_put(sdev);

                        if (bflagsp)
                                *bflagsp = scsi_get_device_flags(sdev,
                                                                 sdev->vendor,
                                                                 sdev->model);
                        return SCSI_SCAN_LUN_PRESENT;
                }
                scsi_device_put(sdev);
        } else
                sdev = scsi_alloc_sdev(starget, lun, hostdata);
        if (!sdev)
                goto out;

        if (scsi_device_is_pseudo_dev(sdev)) {
                if (bflagsp)
                        *bflagsp = BLIST_NOLUN;
                return SCSI_SCAN_LUN_PRESENT;
        }

        result = kmalloc(result_len, GFP_KERNEL);
        if (!result)
                goto out_free_sdev;

        if (scsi_probe_lun(sdev, result, result_len, &bflags))
                goto out_free_result;

        if (bflagsp)
                *bflagsp = bflags;
        /*
         * result contains valid SCSI INQUIRY data.
         */
        if ((result[0] >> 5) == 3) {
                /*
                 * For a Peripheral qualifier 3 (011b), the SCSI
                 * spec says: The device server is not capable of
                 * supporting a physical device on this logical
                 * unit.
                 *
                 * For disks, this implies that there is no
                 * logical disk configured at sdev->lun, but there
                 * is a target id responding.
                 */
                SCSI_LOG_SCAN_BUS(2, sdev_printk(KERN_INFO, sdev, "scsi scan:"
                                   " peripheral qualifier of 3, device not"
                                   " added\n"))
                if (lun == 0) {
                        SCSI_LOG_SCAN_BUS(1, {
                                unsigned char vend[9];
                                unsigned char mod[17];

                                sdev_printk(KERN_INFO, sdev,
                                        "scsi scan: consider passing scsi_mod."
                                        "dev_flags=%s:%s:0x240 or 0x1000240\n",
                                        scsi_inq_str(vend, result, 8, 16),
                                        scsi_inq_str(mod, result, 16, 32));
                        });

                }

                res = SCSI_SCAN_TARGET_PRESENT;
                goto out_free_result;
        }

        /*
         * Some targets may set slight variations of PQ and PDT to signal
         * that no LUN is present, so don't add sdev in these cases.
         * Two specific examples are:
         * 1) NetApp targets: return PQ=1, PDT=0x1f
         * 2) USB UFI: returns PDT=0x1f, with the PQ bits being "reserved"
         *    in the UFI 1.0 spec (we cannot rely on reserved bits).
         *
         * References:
         * 1) SCSI SPC-3, pp. 145-146
         * PQ=1: "A peripheral device having the specified peripheral
         * device type is not connected to this logical unit. However, the
         * device server is capable of supporting the specified peripheral
         * device type on this logical unit."
         * PDT=0x1f: "Unknown or no device type"
         * 2) USB UFI 1.0, p. 20
         * PDT=00h Direct-access device (floppy)
         * PDT=1Fh none (no FDD connected to the requested logical unit)
         */
        if (((result[0] >> 5) == 1 || starget->pdt_1f_for_no_lun) &&
            (result[0] & 0x1f) == 0x1f &&
            !scsi_is_wlun(lun)) {
                SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
                                        "scsi scan: peripheral device type"
                                        " of 31, no device added\n"));
                res = SCSI_SCAN_TARGET_PRESENT;
                goto out_free_result;
        }

        res = scsi_add_lun(sdev, result, &bflags, shost->async_scan);
        if (res == SCSI_SCAN_LUN_PRESENT) {
                if (bflags & BLIST_KEY) {
                        sdev->lockable = 0;
                        scsi_unlock_floptical(sdev, result);
                }
        }

 out_free_result:
        kfree(result);
 out_free_sdev:
        if (res == SCSI_SCAN_LUN_PRESENT) {
                if (sdevp) {
                        if (scsi_device_get(sdev) == 0) {
                                *sdevp = sdev;
                        } else {
                                __scsi_remove_device(sdev);
                                res = SCSI_SCAN_NO_RESPONSE;
                        }
                }
        } else
                __scsi_remove_device(sdev);
 out:
        return res;
}

/**
 * scsi_sequential_lun_scan - sequentially scan a SCSI target
 * @starget:    pointer to target structure to scan
 * @bflags:     black/white list flag for LUN 0
 * @scsi_level: Which version of the standard does this device adhere to
 * @rescan:     passed to scsi_probe_add_lun()
 *
 * Description:
 *     Generally, scan from LUN 1 (LUN 0 is assumed to already have been
 *     scanned) to some maximum lun until a LUN is found with no device
 *     attached. Use the bflags to figure out any oddities.
 *
 *     Modifies sdevscan->lun.
 **/
static void scsi_sequential_lun_scan(struct scsi_target *starget,
                                     blist_flags_t bflags, int scsi_level,
                                     enum scsi_scan_mode rescan)
{
        uint max_dev_lun;
        u64 sparse_lun, lun;
        struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);

        SCSI_LOG_SCAN_BUS(3, starget_printk(KERN_INFO, starget,
                "scsi scan: Sequential scan\n"));

        max_dev_lun = min(max_scsi_luns, shost->max_lun);
        /*
         * If this device is known to support sparse multiple units,
         * override the other settings, and scan all of them. Normally,
         * SCSI-3 devices should be scanned via the REPORT LUNS.
         */
        if (bflags & BLIST_SPARSELUN) {
                max_dev_lun = shost->max_lun;
                sparse_lun = 1;
        } else
                sparse_lun = 0;

        /*
         * If less than SCSI_1_CCS, and no special lun scanning, stop
         * scanning; this matches 2.4 behaviour, but could just be a bug
         * (to continue scanning a SCSI_1_CCS device).
         *
         * This test is broken.  We might not have any device on lun0 for
         * a sparselun device, and if that's the case then how would we
         * know the real scsi_level, eh?  It might make sense to just not
         * scan any SCSI_1 device for non-0 luns, but that check would best
         * go into scsi_alloc_sdev() and just have it return null when asked
         * to alloc an sdev for lun > 0 on an already found SCSI_1 device.
         *
        if ((sdevscan->scsi_level < SCSI_1_CCS) &&
            ((bflags & (BLIST_FORCELUN | BLIST_SPARSELUN | BLIST_MAX5LUN))
             == 0))
                return;
         */
        /*
         * If this device is known to support multiple units, override
         * the other settings, and scan all of them.
         */
        if (bflags & BLIST_FORCELUN)
                max_dev_lun = shost->max_lun;
        /*
         * REGAL CDC-4X: avoid hang after LUN 4
         */
        if (bflags & BLIST_MAX5LUN)
                max_dev_lun = min(5U, max_dev_lun);
        /*
         * Do not scan SCSI-2 or lower device past LUN 7, unless
         * BLIST_LARGELUN.
         */
        if (scsi_level < SCSI_3 && !(bflags & BLIST_LARGELUN))
                max_dev_lun = min(8U, max_dev_lun);
        else
                max_dev_lun = min(256U, max_dev_lun);

        /*
         * We have already scanned LUN 0, so start at LUN 1. Keep scanning
         * until we reach the max, or no LUN is found and we are not
         * sparse_lun.
         */
        for (lun = 1; lun < max_dev_lun; ++lun)
                if ((scsi_probe_and_add_lun(starget, lun, NULL, NULL, rescan,
                                            NULL) != SCSI_SCAN_LUN_PRESENT) &&
                    !sparse_lun)
                        return;
}

/**
 * scsi_report_lun_scan - Scan using SCSI REPORT LUN results
 * @starget: which target
 * @bflags: Zero or a mix of BLIST_NOLUN, BLIST_REPORTLUN2, or BLIST_NOREPORTLUN
 * @rescan: nonzero if we can skip code only needed on first scan
 *
 * Description:
 *   Fast scanning for modern (SCSI-3) devices by sending a REPORT LUN command.
 *   Scan the resulting list of LUNs by calling scsi_probe_and_add_lun.
 *
 *   If BLINK_REPORTLUN2 is set, scan a target that supports more than 8
 *   LUNs even if it's older than SCSI-3.
 *   If BLIST_NOREPORTLUN is set, return 1 always.
 *   If BLIST_NOLUN is set, return 0 always.
 *   If starget->no_report_luns is set, return 1 always.
 *
 * Return:
 *     0: scan completed (or no memory, so further scanning is futile)
 *     1: could not scan with REPORT LUN
 **/
static int scsi_report_lun_scan(struct scsi_target *starget, blist_flags_t bflags,
                                enum scsi_scan_mode rescan)
{
        unsigned char scsi_cmd[MAX_COMMAND_SIZE];
        unsigned int length;
        u64 lun;
        unsigned int num_luns;
        int result;
        struct scsi_lun *lunp, *lun_data;
        struct scsi_device *sdev;
        struct Scsi_Host *shost = dev_to_shost(&starget->dev);
        struct scsi_failure failure_defs[] = {
                {
                        .sense = UNIT_ATTENTION,
                        .asc = SCMD_FAILURE_ASC_ANY,
                        .ascq = SCMD_FAILURE_ASCQ_ANY,
                        .result = SAM_STAT_CHECK_CONDITION,
                },
                /* Fail all CCs except the UA above */
                {
                        .sense = SCMD_FAILURE_SENSE_ANY,
                        .result = SAM_STAT_CHECK_CONDITION,
                },
                /* Retry any other errors not listed above */
                {
                        .result = SCMD_FAILURE_RESULT_ANY,
                },
                {}
        };
        struct scsi_failures failures = {
                .total_allowed = 3,
                .failure_definitions = failure_defs,
        };
        const struct scsi_exec_args exec_args = {
                .failures = &failures,
        };
        int ret = 0;

        /*
         * Only support SCSI-3 and up devices if BLIST_NOREPORTLUN is not set.
         * Also allow SCSI-2 if BLIST_REPORTLUN2 is set and host adapter does
         * support more than 8 LUNs.
         * Don't attempt if the target doesn't support REPORT LUNS.
         */
        if (bflags & BLIST_NOREPORTLUN)
                return 1;
        if (starget->scsi_level < SCSI_2 &&
            starget->scsi_level != SCSI_UNKNOWN)
                return 1;
        if (starget->scsi_level < SCSI_3 &&
            (!(bflags & BLIST_REPORTLUN2) || shost->max_lun <= 8))
                return 1;
        if (bflags & BLIST_NOLUN)
                return 0;
        if (starget->no_report_luns)
                return 1;

        if (!(sdev = scsi_device_lookup_by_target(starget, 0))) {
                sdev = scsi_alloc_sdev(starget, 0, NULL);
                if (!sdev)
                        return 0;
                if (scsi_device_get(sdev)) {
                        __scsi_remove_device(sdev);
                        return 0;
                }
        }

        /*
         * Allocate enough to hold the header (the same size as one scsi_lun)
         * plus the number of luns we are requesting.  511 was the default
         * value of the now removed max_report_luns parameter.
         */
        length = (511 + 1) * sizeof(struct scsi_lun);
retry:
        lun_data = kmalloc(length, GFP_KERNEL);
        if (!lun_data) {
                printk(ALLOC_FAILURE_MSG, __func__);
                goto out;
        }

        scsi_cmd[0] = REPORT_LUNS;

        /*
         * bytes 1 - 5: reserved, set to zero.
         */
        memset(&scsi_cmd[1], 0, 5);

        /*
         * bytes 6 - 9: length of the command.
         */
        put_unaligned_be32(length, &scsi_cmd[6]);

        scsi_cmd[10] = 0;       /* reserved */
        scsi_cmd[11] = 0;       /* control */

        /*
         * We can get a UNIT ATTENTION, for example a power on/reset, so
         * retry a few times (like sd.c does for TEST UNIT READY).
         * Experience shows some combinations of adapter/devices get at
         * least two power on/resets.
         *
         * Illegal requests (for devices that do not support REPORT LUNS)
         * should come through as a check condition, and will not generate
         * a retry.
         */
        scsi_failures_reset_retries(&failures);

        SCSI_LOG_SCAN_BUS(3, sdev_printk (KERN_INFO, sdev,
                          "scsi scan: Sending REPORT LUNS\n"));

        result = scsi_execute_cmd(sdev, scsi_cmd, REQ_OP_DRV_IN, lun_data,
                                  length, SCSI_REPORT_LUNS_TIMEOUT, 3,
                                  &exec_args);

        SCSI_LOG_SCAN_BUS(3, sdev_printk (KERN_INFO, sdev,
                          "scsi scan: REPORT LUNS  %s result 0x%x\n",
                          result ?  "failed" : "successful", result));
        if (result) {
                /*
                 * The device probably does not support a REPORT LUN command
                 */
                ret = 1;
                goto out_err;
        }

        /*
         * Get the length from the first four bytes of lun_data.
         */
        if (get_unaligned_be32(lun_data->scsi_lun) +
            sizeof(struct scsi_lun) > length) {
                length = get_unaligned_be32(lun_data->scsi_lun) +
                         sizeof(struct scsi_lun);
                kfree(lun_data);
                goto retry;
        }
        length = get_unaligned_be32(lun_data->scsi_lun);

        num_luns = (length / sizeof(struct scsi_lun));

        SCSI_LOG_SCAN_BUS(3, sdev_printk (KERN_INFO, sdev,
                "scsi scan: REPORT LUN scan\n"));

        /*
         * Scan the luns in lun_data. The entry at offset 0 is really
         * the header, so start at 1 and go up to and including num_luns.
         */
        for (lunp = &lun_data[1]; lunp <= &lun_data[num_luns]; lunp++) {
                lun = scsilun_to_int(lunp);

                if (lun > sdev->host->max_lun) {
                        sdev_printk(KERN_WARNING, sdev,
                                    "lun%llu has a LUN larger than"
                                    " allowed by the host adapter\n", lun);
                } else {
                        int res;

                        res = scsi_probe_and_add_lun(starget,
                                lun, NULL, NULL, rescan, NULL);
                        if (res == SCSI_SCAN_NO_RESPONSE) {
                                /*
                                 * Got some results, but now none, abort.
                                 */
                                sdev_printk(KERN_ERR, sdev,
                                        "Unexpected response"
                                        " from lun %llu while scanning, scan"
                                        " aborted\n", (unsigned long long)lun);
                                break;
                        }
                }
        }

 out_err:
        kfree(lun_data);
 out:
        if (scsi_device_created(sdev))
                /*
                 * the sdev we used didn't appear in the report luns scan
                 */
                __scsi_remove_device(sdev);
        scsi_device_put(sdev);
        return ret;
}

struct scsi_device *__scsi_add_device(struct Scsi_Host *shost, uint channel,
                                      uint id, u64 lun, void *hostdata)
{
        struct scsi_device *sdev = ERR_PTR(-ENODEV);
        struct device *parent = &shost->shost_gendev;
        struct scsi_target *starget;

        if (strncmp(scsi_scan_type, "none", 4) == 0)
                return ERR_PTR(-ENODEV);

        starget = scsi_alloc_target(parent, channel, id);
        if (!starget)
                return ERR_PTR(-ENOMEM);
        scsi_autopm_get_target(starget);

        mutex_lock(&shost->scan_mutex);
        if (!shost->async_scan)
                scsi_complete_async_scans();

        if (scsi_host_scan_allowed(shost) && scsi_autopm_get_host(shost) == 0) {
                scsi_probe_and_add_lun(starget, lun, NULL, &sdev,
                                       SCSI_SCAN_RESCAN, hostdata);
                scsi_autopm_put_host(shost);
        }
        mutex_unlock(&shost->scan_mutex);
        scsi_autopm_put_target(starget);
        /*
         * paired with scsi_alloc_target().  Target will be destroyed unless
         * scsi_probe_and_add_lun made an underlying device visible
         */
        scsi_target_reap(starget);
        put_device(&starget->dev);

        return sdev;
}
EXPORT_SYMBOL(__scsi_add_device);

/**
 * scsi_add_device - creates a new SCSI (LU) instance
 * @host: the &Scsi_Host instance where the device is located
 * @channel: target channel number (rarely other than %0)
 * @target: target id number
 * @lun: LUN of target device
 *
 * Probe for a specific LUN and add it if found.
 *
 * Notes: This call is usually performed internally during a SCSI
 * bus scan when an HBA is added (i.e. scsi_scan_host()). So it
 * should only be called if the HBA becomes aware of a new SCSI
 * device (LU) after scsi_scan_host() has completed. If successful
 * this call can lead to sdev_init() and sdev_configure() callbacks
 * into the LLD.
 *
 * Return: %0 on success or negative error code on failure
 */
int scsi_add_device(struct Scsi_Host *host, uint channel,
                    uint target, u64 lun)
{
        struct scsi_device *sdev = 
                __scsi_add_device(host, channel, target, lun, NULL);
        if (IS_ERR(sdev))
                return PTR_ERR(sdev);

        scsi_device_put(sdev);
        return 0;
}
EXPORT_SYMBOL(scsi_add_device);

int scsi_resume_device(struct scsi_device *sdev)
{
        struct device *dev = &sdev->sdev_gendev;
        int ret = 0;

        device_lock(dev);

        /*
         * Bail out if the device or its queue are not running. Otherwise,
         * the rescan may block waiting for commands to be executed, with us
         * holding the device lock. This can result in a potential deadlock
         * in the power management core code when system resume is on-going.
         */
        if (sdev->sdev_state != SDEV_RUNNING ||
            blk_queue_pm_only(sdev->request_queue)) {
                ret = -EWOULDBLOCK;
                goto unlock;
        }

        if (dev->driver && try_module_get(dev->driver->owner)) {
                struct scsi_driver *drv = to_scsi_driver(dev->driver);

                if (drv->resume)
                        ret = drv->resume(dev);
                module_put(dev->driver->owner);
        }

unlock:
        device_unlock(dev);

        return ret;
}
EXPORT_SYMBOL(scsi_resume_device);

int scsi_rescan_device(struct scsi_device *sdev)
{
        struct device *dev = &sdev->sdev_gendev;
        int ret = 0;

        device_lock(dev);

        /*
         * Bail out if the device or its queue are not running. Otherwise,
         * the rescan may block waiting for commands to be executed, with us
         * holding the device lock. This can result in a potential deadlock
         * in the power management core code when system resume is on-going.
         */
        if (sdev->sdev_state != SDEV_RUNNING ||
            blk_queue_pm_only(sdev->request_queue)) {
                ret = -EWOULDBLOCK;
                goto unlock;
        }

        scsi_attach_vpd(sdev);
        scsi_cdl_check(sdev);

        if (sdev->handler && sdev->handler->rescan)
                sdev->handler->rescan(sdev);

        if (dev->driver && try_module_get(dev->driver->owner)) {
                struct scsi_driver *drv = to_scsi_driver(dev->driver);

                if (drv->rescan)
                        drv->rescan(dev);
                module_put(dev->driver->owner);
        }

unlock:
        device_unlock(dev);

        return ret;
}
EXPORT_SYMBOL(scsi_rescan_device);

static void __scsi_scan_target(struct device *parent, unsigned int channel,
                unsigned int id, u64 lun, enum scsi_scan_mode rescan)
{
        struct Scsi_Host *shost = dev_to_shost(parent);
        blist_flags_t bflags = 0;
        int res;
        struct scsi_target *starget;

        if (shost->this_id == id)
                /*
                 * Don't scan the host adapter
                 */
                return;

        starget = scsi_alloc_target(parent, channel, id);
        if (!starget)
                return;
        scsi_autopm_get_target(starget);

        if (lun != SCAN_WILD_CARD) {
                /*
                 * Scan for a specific host/chan/id/lun.
                 */
                scsi_probe_and_add_lun(starget, lun, NULL, NULL, rescan, NULL);
                goto out_reap;
        }

        /*
         * Scan LUN 0, if there is some response, scan further. Ideally, we
         * would not configure LUN 0 until all LUNs are scanned.
         */
        res = scsi_probe_and_add_lun(starget, 0, &bflags, NULL, rescan, NULL);
        if (res == SCSI_SCAN_LUN_PRESENT || res == SCSI_SCAN_TARGET_PRESENT) {
                if (scsi_report_lun_scan(starget, bflags, rescan) != 0)
                        /*
                         * The REPORT LUN did not scan the target,
                         * do a sequential scan.
                         */
                        scsi_sequential_lun_scan(starget, bflags,
                                                 starget->scsi_level, rescan);
        }

 out_reap:
        scsi_autopm_put_target(starget);
        /*
         * paired with scsi_alloc_target(): determine if the target has
         * any children at all and if not, nuke it
         */
        scsi_target_reap(starget);

        put_device(&starget->dev);
}

/**
 * scsi_scan_target - scan a target id, possibly including all LUNs on the target.
 * @parent:     host to scan
 * @channel:    channel to scan
 * @id:         target id to scan
 * @lun:        Specific LUN to scan or SCAN_WILD_CARD
 * @rescan:     passed to LUN scanning routines; SCSI_SCAN_INITIAL for
 *              no rescan, SCSI_SCAN_RESCAN to rescan existing LUNs,
 *              and SCSI_SCAN_MANUAL to force scanning even if
 *              'scan=manual' is set.
 *
 * Description:
 *     Scan the target id on @parent, @channel, and @id. Scan at least LUN 0,
 *     and possibly all LUNs on the target id.
 *
 *     First try a REPORT LUN scan, if that does not scan the target, do a
 *     sequential scan of LUNs on the target id.
 **/
void scsi_scan_target(struct device *parent, unsigned int channel,
                      unsigned int id, u64 lun, enum scsi_scan_mode rescan)
{
        struct Scsi_Host *shost = dev_to_shost(parent);

        if (strncmp(scsi_scan_type, "none", 4) == 0)
                return;

        if (rescan != SCSI_SCAN_MANUAL &&
            strncmp(scsi_scan_type, "manual", 6) == 0)
                return;

        mutex_lock(&shost->scan_mutex);
        if (!shost->async_scan)
                scsi_complete_async_scans();

        if (scsi_host_scan_allowed(shost) && scsi_autopm_get_host(shost) == 0) {
                __scsi_scan_target(parent, channel, id, lun, rescan);
                scsi_autopm_put_host(shost);
        }
        mutex_unlock(&shost->scan_mutex);
}
EXPORT_SYMBOL(scsi_scan_target);

static void scsi_scan_channel(struct Scsi_Host *shost, unsigned int channel,
                              unsigned int id, u64 lun,
                              enum scsi_scan_mode rescan)
{
        uint order_id;

        if (id == SCAN_WILD_CARD)
                for (id = 0; id < shost->max_id; ++id) {
                        /*
                         * XXX adapter drivers when possible (FCP, iSCSI)
                         * could modify max_id to match the current max,
                         * not the absolute max.
                         *
                         * XXX add a shost id iterator, so for example,
                         * the FC ID can be the same as a target id
                         * without a huge overhead of sparse id's.
                         */
                        if (shost->reverse_ordering)
                                /*
                                 * Scan from high to low id.
                                 */
                                order_id = shost->max_id - id - 1;
                        else
                                order_id = id;
                        __scsi_scan_target(&shost->shost_gendev, channel,
                                        order_id, lun, rescan);
                }
        else
                __scsi_scan_target(&shost->shost_gendev, channel,
                                id, lun, rescan);
}

int scsi_scan_host_selected(struct Scsi_Host *shost, unsigned int channel,
                            unsigned int id, u64 lun,
                            enum scsi_scan_mode rescan)
{
        SCSI_LOG_SCAN_BUS(3, shost_printk (KERN_INFO, shost,
                "%s: <%u:%u:%llu>\n",
                __func__, channel, id, lun));

        if (((channel != SCAN_WILD_CARD) && (channel > shost->max_channel)) ||
            ((id != SCAN_WILD_CARD) && (id >= shost->max_id)) ||
            ((lun != SCAN_WILD_CARD) && (lun >= shost->max_lun)))
                return -EINVAL;

        mutex_lock(&shost->scan_mutex);
        if (!shost->async_scan)
                scsi_complete_async_scans();

        if (scsi_host_scan_allowed(shost) && scsi_autopm_get_host(shost) == 0) {
                if (channel == SCAN_WILD_CARD)
                        for (channel = 0; channel <= shost->max_channel;
                             channel++)
                                scsi_scan_channel(shost, channel, id, lun,
                                                  rescan);
                else
                        scsi_scan_channel(shost, channel, id, lun, rescan);
                scsi_autopm_put_host(shost);
        }
        mutex_unlock(&shost->scan_mutex);

        return 0;
}
EXPORT_SYMBOL(scsi_scan_host_selected);
static void scsi_sysfs_add_devices(struct Scsi_Host *shost)
{
        struct scsi_device *sdev;
        shost_for_each_device(sdev, shost) {
                /* target removed before the device could be added */
                if (sdev->sdev_state == SDEV_DEL)
                        continue;
                /* If device is already visible, skip adding it to sysfs */
                if (sdev->is_visible)
                        continue;
                if (!scsi_host_scan_allowed(shost) ||
                    scsi_sysfs_add_sdev(sdev) != 0)
                        __scsi_remove_device(sdev);
        }
}

/**
 * scsi_prep_async_scan - prepare for an async scan
 * @shost: the host which will be scanned
 * Returns: a cookie to be passed to scsi_finish_async_scan()
 *
 * Tells the midlayer this host is going to do an asynchronous scan.
 * It reserves the host's position in the scanning list and ensures
 * that other asynchronous scans started after this one won't affect the
 * ordering of the discovered devices.
 */
static struct async_scan_data *scsi_prep_async_scan(struct Scsi_Host *shost)
{
        struct async_scan_data *data = NULL;
        unsigned long flags;

        if (strncmp(scsi_scan_type, "sync", 4) == 0)
                return NULL;

        mutex_lock(&shost->scan_mutex);
        if (shost->async_scan) {
                shost_printk(KERN_DEBUG, shost, "%s called twice\n", __func__);
                goto err;
        }

        data = kmalloc_obj(*data);
        if (!data)
                goto err;
        data->shost = scsi_host_get(shost);
        if (!data->shost)
                goto err;
        init_completion(&data->prev_finished);

        spin_lock_irqsave(shost->host_lock, flags);
        shost->async_scan = 1;
        spin_unlock_irqrestore(shost->host_lock, flags);
        mutex_unlock(&shost->scan_mutex);

        spin_lock(&async_scan_lock);
        if (list_empty(&scanning_hosts))
                complete(&data->prev_finished);
        list_add_tail(&data->list, &scanning_hosts);
        spin_unlock(&async_scan_lock);

        return data;

 err:
        mutex_unlock(&shost->scan_mutex);
        kfree(data);
        return NULL;
}

/**
 * scsi_finish_async_scan - asynchronous scan has finished
 * @data: cookie returned from earlier call to scsi_prep_async_scan()
 *
 * All the devices currently attached to this host have been found.
 * This function announces all the devices it has found to the rest
 * of the system.
 */
static void scsi_finish_async_scan(struct async_scan_data *data)
{
        struct Scsi_Host *shost;
        unsigned long flags;

        if (!data)
                return;

        shost = data->shost;

        mutex_lock(&shost->scan_mutex);

        if (!shost->async_scan) {
                shost_printk(KERN_INFO, shost, "%s called twice\n", __func__);
                dump_stack();
                mutex_unlock(&shost->scan_mutex);
                return;
        }

        wait_for_completion(&data->prev_finished);

        scsi_sysfs_add_devices(shost);

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

        mutex_unlock(&shost->scan_mutex);

        spin_lock(&async_scan_lock);
        list_del(&data->list);
        if (!list_empty(&scanning_hosts)) {
                struct async_scan_data *next = list_entry(scanning_hosts.next,
                                struct async_scan_data, list);
                complete(&next->prev_finished);
        }
        spin_unlock(&async_scan_lock);

        scsi_autopm_put_host(shost);
        scsi_host_put(shost);
        kfree(data);
}

static void do_scsi_scan_host(struct Scsi_Host *shost)
{
        if (shost->hostt->scan_finished) {
                unsigned long start = jiffies;
                if (shost->hostt->scan_start)
                        shost->hostt->scan_start(shost);

                while (!shost->hostt->scan_finished(shost, jiffies - start))
                        msleep(10);
        } else {
                scsi_scan_host_selected(shost, SCAN_WILD_CARD, SCAN_WILD_CARD,
                                SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
        }
}

static void do_scan_async(void *_data, async_cookie_t c)
{
        struct async_scan_data *data = _data;
        struct Scsi_Host *shost = data->shost;

        do_scsi_scan_host(shost);
        scsi_finish_async_scan(data);
}

/**
 * scsi_scan_host - scan the given adapter
 * @shost:      adapter to scan
 *
 * Notes: Should be called after scsi_add_host()
 **/
void scsi_scan_host(struct Scsi_Host *shost)
{
        struct async_scan_data *data;

        if (strncmp(scsi_scan_type, "none", 4) == 0 ||
            strncmp(scsi_scan_type, "manual", 6) == 0)
                return;
        if (scsi_autopm_get_host(shost) < 0)
                return;

        data = scsi_prep_async_scan(shost);
        if (!data) {
                do_scsi_scan_host(shost);
                scsi_autopm_put_host(shost);
                return;
        }

        /* register with the async subsystem so wait_for_device_probe()
         * will flush this work
         */
        async_schedule(do_scan_async, data);

        /* scsi_autopm_put_host(shost) is called in scsi_finish_async_scan() */
}
EXPORT_SYMBOL(scsi_scan_host);

void scsi_forget_host(struct Scsi_Host *shost)
{
        struct scsi_device *sdev;
        unsigned long flags;

 restart:
        spin_lock_irqsave(shost->host_lock, flags);
        list_for_each_entry(sdev, &shost->__devices, siblings) {
                if (scsi_device_is_pseudo_dev(sdev) ||
                    sdev->sdev_state == SDEV_DEL)
                        continue;
                spin_unlock_irqrestore(shost->host_lock, flags);
                __scsi_remove_device(sdev);
                goto restart;
        }
        spin_unlock_irqrestore(shost->host_lock, flags);

        /*
         * Remove the pseudo device last since it may be needed during removal
         * of other SCSI devices.
         */
        if (shost->pseudo_sdev)
                __scsi_remove_device(shost->pseudo_sdev);
}

/**
 * scsi_get_pseudo_sdev() - Attach a pseudo SCSI device to a SCSI host
 * @shost: Host that needs a pseudo SCSI device
 *
 * Lock status: None assumed.
 *
 * Returns:     The scsi_device or NULL
 *
 * Notes:
 *      Attach a single scsi_device to the Scsi_Host. The primary aim for this
 *      device is to serve as a container from which SCSI commands can be
 *      allocated. Each SCSI command will carry a command tag allocated by the
 *      block layer. These SCSI commands can be used by the LLDD to send
 *      internal or passthrough commands without having to manage tag allocation
 *      inside the LLDD.
 */
struct scsi_device *scsi_get_pseudo_sdev(struct Scsi_Host *shost)
{
        struct scsi_device *sdev = NULL;
        struct scsi_target *starget;

        guard(mutex)(&shost->scan_mutex);

        if (!scsi_host_scan_allowed(shost))
                goto out;

        starget = scsi_alloc_target(&shost->shost_gendev, 0, shost->max_id);
        if (!starget)
                goto out;

        sdev = scsi_alloc_sdev(starget, U64_MAX, NULL);
        if (!sdev) {
                scsi_target_reap(starget);
                goto put_target;
        }

        sdev->borken = 0;

put_target:
        /* See also the get_device(dev) call in scsi_alloc_target(). */
        put_device(&starget->dev);

out:
        return sdev;
}