// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Generic SCSI-3 ALUA SCSI Device Handler
 *
 * Copyright (C) 2007-2010 Hannes Reinecke, SUSE Linux Products GmbH.
 * All rights reserved.
 */
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <asm/unaligned.h>
#include <scsi/scsi.h>
#include <scsi/scsi_proto.h>
#include <scsi/scsi_dbg.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_dh.h>

#define ALUA_DH_NAME "alua"
#define ALUA_DH_VER "2.0"

#define TPGS_SUPPORT_NONE               0x00
#define TPGS_SUPPORT_OPTIMIZED          0x01
#define TPGS_SUPPORT_NONOPTIMIZED       0x02
#define TPGS_SUPPORT_STANDBY            0x04
#define TPGS_SUPPORT_UNAVAILABLE        0x08
#define TPGS_SUPPORT_LBA_DEPENDENT      0x10
#define TPGS_SUPPORT_OFFLINE            0x40
#define TPGS_SUPPORT_TRANSITION         0x80
#define TPGS_SUPPORT_ALL                0xdf

#define RTPG_FMT_MASK                   0x70
#define RTPG_FMT_EXT_HDR                0x10

#define TPGS_MODE_UNINITIALIZED          -1
#define TPGS_MODE_NONE                  0x0
#define TPGS_MODE_IMPLICIT              0x1
#define TPGS_MODE_EXPLICIT              0x2

#define ALUA_RTPG_SIZE                  128
#define ALUA_FAILOVER_TIMEOUT           60
#define ALUA_FAILOVER_RETRIES           5
#define ALUA_RTPG_DELAY_MSECS           5
#define ALUA_RTPG_RETRY_DELAY           2

/* device handler flags */
#define ALUA_OPTIMIZE_STPG              0x01
#define ALUA_RTPG_EXT_HDR_UNSUPP        0x02
/* State machine flags */
#define ALUA_PG_RUN_RTPG                0x10
#define ALUA_PG_RUN_STPG                0x20
#define ALUA_PG_RUNNING                 0x40

static uint optimize_stpg;
module_param(optimize_stpg, uint, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(optimize_stpg, "Allow use of a non-optimized path, rather than sending a STPG, when implicit TPGS is supported (0=No,1=Yes). Default is 0.");

static LIST_HEAD(port_group_list);
static DEFINE_SPINLOCK(port_group_lock);
static struct workqueue_struct *kaluad_wq;

struct alua_port_group {
        struct kref             kref;
        struct rcu_head         rcu;
        struct list_head        node;
        struct list_head        dh_list;
        unsigned char           device_id_str[256];
        int                     device_id_len;
        int                     group_id;
        int                     tpgs;
        int                     state;
        int                     pref;
        int                     valid_states;
        unsigned                flags; /* used for optimizing STPG */
        unsigned char           transition_tmo;
        unsigned long           expiry;
        unsigned long           interval;
        struct delayed_work     rtpg_work;
        spinlock_t              lock;
        struct list_head        rtpg_list;
        struct scsi_device      *rtpg_sdev;
};

struct alua_dh_data {
        struct list_head        node;
        struct alua_port_group __rcu *pg;
        int                     group_id;
        spinlock_t              pg_lock;
        struct scsi_device      *sdev;
        int                     init_error;
        struct mutex            init_mutex;
        bool                    disabled;
};

struct alua_queue_data {
        struct list_head        entry;
        activate_complete       callback_fn;
        void                    *callback_data;
};

#define ALUA_POLICY_SWITCH_CURRENT      0
#define ALUA_POLICY_SWITCH_ALL          1

static void alua_rtpg_work(struct work_struct *work);
static bool alua_rtpg_queue(struct alua_port_group *pg,
                            struct scsi_device *sdev,
                            struct alua_queue_data *qdata, bool force);
static void alua_check(struct scsi_device *sdev, bool force);

static void release_port_group(struct kref *kref)
{
        struct alua_port_group *pg;

        pg = container_of(kref, struct alua_port_group, kref);
        if (pg->rtpg_sdev)
                flush_delayed_work(&pg->rtpg_work);
        spin_lock(&port_group_lock);
        list_del(&pg->node);
        spin_unlock(&port_group_lock);
        kfree_rcu(pg, rcu);
}

/*
 * submit_rtpg - Issue a REPORT TARGET GROUP STATES command
 * @sdev: sdev the command should be sent to
 */
static int submit_rtpg(struct scsi_device *sdev, unsigned char *buff,
                       int bufflen, struct scsi_sense_hdr *sshdr, int flags)
{
        u8 cdb[MAX_COMMAND_SIZE];
        int req_flags = REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
                REQ_FAILFAST_DRIVER;

        /* Prepare the command. */
        memset(cdb, 0x0, MAX_COMMAND_SIZE);
        cdb[0] = MAINTENANCE_IN;
        if (!(flags & ALUA_RTPG_EXT_HDR_UNSUPP))
                cdb[1] = MI_REPORT_TARGET_PGS | MI_EXT_HDR_PARAM_FMT;
        else
                cdb[1] = MI_REPORT_TARGET_PGS;
        put_unaligned_be32(bufflen, &cdb[6]);

        return scsi_execute(sdev, cdb, DMA_FROM_DEVICE, buff, bufflen, NULL,
                        sshdr, ALUA_FAILOVER_TIMEOUT * HZ,
                        ALUA_FAILOVER_RETRIES, req_flags, 0, NULL);
}

/*
 * submit_stpg - Issue a SET TARGET PORT GROUP command
 *
 * Currently we're only setting the current target port group state
 * to 'active/optimized' and let the array firmware figure out
 * the states of the remaining groups.
 */
static int submit_stpg(struct scsi_device *sdev, int group_id,
                       struct scsi_sense_hdr *sshdr)
{
        u8 cdb[MAX_COMMAND_SIZE];
        unsigned char stpg_data[8];
        int stpg_len = 8;
        int req_flags = REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
                REQ_FAILFAST_DRIVER;

        /* Prepare the data buffer */
        memset(stpg_data, 0, stpg_len);
        stpg_data[4] = SCSI_ACCESS_STATE_OPTIMAL;
        put_unaligned_be16(group_id, &stpg_data[6]);

        /* Prepare the command. */
        memset(cdb, 0x0, MAX_COMMAND_SIZE);
        cdb[0] = MAINTENANCE_OUT;
        cdb[1] = MO_SET_TARGET_PGS;
        put_unaligned_be32(stpg_len, &cdb[6]);

        return scsi_execute(sdev, cdb, DMA_TO_DEVICE, stpg_data, stpg_len, NULL,
                        sshdr, ALUA_FAILOVER_TIMEOUT * HZ,
                        ALUA_FAILOVER_RETRIES, req_flags, 0, NULL);
}

static struct alua_port_group *alua_find_get_pg(char *id_str, size_t id_size,
                                                int group_id)
{
        struct alua_port_group *pg;

        if (!id_str || !id_size || !strlen(id_str))
                return NULL;

        list_for_each_entry(pg, &port_group_list, node) {
                if (pg->group_id != group_id)
                        continue;
                if (!pg->device_id_len || pg->device_id_len != id_size)
                        continue;
                if (strncmp(pg->device_id_str, id_str, id_size))
                        continue;
                if (!kref_get_unless_zero(&pg->kref))
                        continue;
                return pg;
        }

        return NULL;
}

/*
 * alua_alloc_pg - Allocate a new port_group structure
 * @sdev: scsi device
 * @group_id: port group id
 * @tpgs: target port group settings
 *
 * Allocate a new port_group structure for a given
 * device.
 */
static struct alua_port_group *alua_alloc_pg(struct scsi_device *sdev,
                                             int group_id, int tpgs)
{
        struct alua_port_group *pg, *tmp_pg;

        pg = kzalloc(sizeof(struct alua_port_group), GFP_KERNEL);
        if (!pg)
                return ERR_PTR(-ENOMEM);

        pg->device_id_len = scsi_vpd_lun_id(sdev, pg->device_id_str,
                                            sizeof(pg->device_id_str));
        if (pg->device_id_len <= 0) {
                /*
                 * TPGS supported but no device identification found.
                 * Generate private device identification.
                 */
                sdev_printk(KERN_INFO, sdev,
                            "%s: No device descriptors found\n",
                            ALUA_DH_NAME);
                pg->device_id_str[0] = '\0';
                pg->device_id_len = 0;
        }
        pg->group_id = group_id;
        pg->tpgs = tpgs;
        pg->state = SCSI_ACCESS_STATE_OPTIMAL;
        pg->valid_states = TPGS_SUPPORT_ALL;
        if (optimize_stpg)
                pg->flags |= ALUA_OPTIMIZE_STPG;
        kref_init(&pg->kref);
        INIT_DELAYED_WORK(&pg->rtpg_work, alua_rtpg_work);
        INIT_LIST_HEAD(&pg->rtpg_list);
        INIT_LIST_HEAD(&pg->node);
        INIT_LIST_HEAD(&pg->dh_list);
        spin_lock_init(&pg->lock);

        spin_lock(&port_group_lock);
        tmp_pg = alua_find_get_pg(pg->device_id_str, pg->device_id_len,
                                  group_id);
        if (tmp_pg) {
                spin_unlock(&port_group_lock);
                kfree(pg);
                return tmp_pg;
        }

        list_add(&pg->node, &port_group_list);
        spin_unlock(&port_group_lock);

        return pg;
}

/*
 * alua_check_tpgs - Evaluate TPGS setting
 * @sdev: device to be checked
 *
 * Examine the TPGS setting of the sdev to find out if ALUA
 * is supported.
 */
static int alua_check_tpgs(struct scsi_device *sdev)
{
        int tpgs = TPGS_MODE_NONE;

        /*
         * ALUA support for non-disk devices is fraught with
         * difficulties, so disable it for now.
         */
        if (sdev->type != TYPE_DISK) {
                sdev_printk(KERN_INFO, sdev,
                            "%s: disable for non-disk devices\n",
                            ALUA_DH_NAME);
                return tpgs;
        }

        tpgs = scsi_device_tpgs(sdev);
        switch (tpgs) {
        case TPGS_MODE_EXPLICIT|TPGS_MODE_IMPLICIT:
                sdev_printk(KERN_INFO, sdev,
                            "%s: supports implicit and explicit TPGS\n",
                            ALUA_DH_NAME);
                break;
        case TPGS_MODE_EXPLICIT:
                sdev_printk(KERN_INFO, sdev, "%s: supports explicit TPGS\n",
                            ALUA_DH_NAME);
                break;
        case TPGS_MODE_IMPLICIT:
                sdev_printk(KERN_INFO, sdev, "%s: supports implicit TPGS\n",
                            ALUA_DH_NAME);
                break;
        case TPGS_MODE_NONE:
                sdev_printk(KERN_INFO, sdev, "%s: not supported\n",
                            ALUA_DH_NAME);
                break;
        default:
                sdev_printk(KERN_INFO, sdev,
                            "%s: unsupported TPGS setting %d\n",
                            ALUA_DH_NAME, tpgs);
                tpgs = TPGS_MODE_NONE;
                break;
        }

        return tpgs;
}

/*
 * alua_check_vpd - Evaluate INQUIRY vpd page 0x83
 * @sdev: device to be checked
 *
 * Extract the relative target port and the target port group
 * descriptor from the list of identificators.
 */
static int alua_check_vpd(struct scsi_device *sdev, struct alua_dh_data *h,
                          int tpgs)
{
        int rel_port = -1, group_id;
        struct alua_port_group *pg, *old_pg = NULL;
        bool pg_updated = false;
        unsigned long flags;

        group_id = scsi_vpd_tpg_id(sdev, &rel_port);
        if (group_id < 0) {
                /*
                 * Internal error; TPGS supported but required
                 * VPD identification descriptors not present.
                 * Disable ALUA support
                 */
                sdev_printk(KERN_INFO, sdev,
                            "%s: No target port descriptors found\n",
                            ALUA_DH_NAME);
                return SCSI_DH_DEV_UNSUPP;
        }

        pg = alua_alloc_pg(sdev, group_id, tpgs);
        if (IS_ERR(pg)) {
                if (PTR_ERR(pg) == -ENOMEM)
                        return SCSI_DH_NOMEM;
                return SCSI_DH_DEV_UNSUPP;
        }
        if (pg->device_id_len)
                sdev_printk(KERN_INFO, sdev,
                            "%s: device %s port group %x rel port %x\n",
                            ALUA_DH_NAME, pg->device_id_str,
                            group_id, rel_port);
        else
                sdev_printk(KERN_INFO, sdev,
                            "%s: port group %x rel port %x\n",
                            ALUA_DH_NAME, group_id, rel_port);

        /* Check for existing port group references */
        spin_lock(&h->pg_lock);
        old_pg = rcu_dereference_protected(h->pg, lockdep_is_held(&h->pg_lock));
        if (old_pg != pg) {
                /* port group has changed. Update to new port group */
                if (h->pg) {
                        spin_lock_irqsave(&old_pg->lock, flags);
                        list_del_rcu(&h->node);
                        spin_unlock_irqrestore(&old_pg->lock, flags);
                }
                rcu_assign_pointer(h->pg, pg);
                pg_updated = true;
        }

        spin_lock_irqsave(&pg->lock, flags);
        if (pg_updated)
                list_add_rcu(&h->node, &pg->dh_list);
        spin_unlock_irqrestore(&pg->lock, flags);

        alua_rtpg_queue(rcu_dereference_protected(h->pg,
                                                  lockdep_is_held(&h->pg_lock)),
                        sdev, NULL, true);
        spin_unlock(&h->pg_lock);

        if (old_pg)
                kref_put(&old_pg->kref, release_port_group);

        return SCSI_DH_OK;
}

static char print_alua_state(unsigned char state)
{
        switch (state) {
        case SCSI_ACCESS_STATE_OPTIMAL:
                return 'A';
        case SCSI_ACCESS_STATE_ACTIVE:
                return 'N';
        case SCSI_ACCESS_STATE_STANDBY:
                return 'S';
        case SCSI_ACCESS_STATE_UNAVAILABLE:
                return 'U';
        case SCSI_ACCESS_STATE_LBA:
                return 'L';
        case SCSI_ACCESS_STATE_OFFLINE:
                return 'O';
        case SCSI_ACCESS_STATE_TRANSITIONING:
                return 'T';
        default:
                return 'X';
        }
}

static enum scsi_disposition alua_check_sense(struct scsi_device *sdev,
                                              struct scsi_sense_hdr *sense_hdr)
{
        struct alua_dh_data *h = sdev->handler_data;
        struct alua_port_group *pg;

        switch (sense_hdr->sense_key) {
        case NOT_READY:
                if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0a) {
                        /*
                         * LUN Not Accessible - ALUA state transition
                         */
                        rcu_read_lock();
                        pg = rcu_dereference(h->pg);
                        if (pg)
                                pg->state = SCSI_ACCESS_STATE_TRANSITIONING;
                        rcu_read_unlock();
                        alua_check(sdev, false);
                        return NEEDS_RETRY;
                }
                break;
        case UNIT_ATTENTION:
                if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x00) {
                        /*
                         * Power On, Reset, or Bus Device Reset.
                         * Might have obscured a state transition,
                         * so schedule a recheck.
                         */
                        alua_check(sdev, true);
                        return ADD_TO_MLQUEUE;
                }
                if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x04)
                        /*
                         * Device internal reset
                         */
                        return ADD_TO_MLQUEUE;
                if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x01)
                        /*
                         * Mode Parameters Changed
                         */
                        return ADD_TO_MLQUEUE;
                if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x06) {
                        /*
                         * ALUA state changed
                         */
                        alua_check(sdev, true);
                        return ADD_TO_MLQUEUE;
                }
                if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x07) {
                        /*
                         * Implicit ALUA state transition failed
                         */
                        alua_check(sdev, true);
                        return ADD_TO_MLQUEUE;
                }
                if (sense_hdr->asc == 0x3f && sense_hdr->ascq == 0x03)
                        /*
                         * Inquiry data has changed
                         */
                        return ADD_TO_MLQUEUE;
                if (sense_hdr->asc == 0x3f && sense_hdr->ascq == 0x0e)
                        /*
                         * REPORTED_LUNS_DATA_HAS_CHANGED is reported
                         * when switching controllers on targets like
                         * Intel Multi-Flex. We can just retry.
                         */
                        return ADD_TO_MLQUEUE;
                break;
        }

        return SCSI_RETURN_NOT_HANDLED;
}

/*
 * alua_tur - Send a TEST UNIT READY
 * @sdev: device to which the TEST UNIT READY command should be send
 *
 * Send a TEST UNIT READY to @sdev to figure out the device state
 * Returns SCSI_DH_RETRY if the sense code is NOT READY/ALUA TRANSITIONING,
 * SCSI_DH_OK if no error occurred, and SCSI_DH_IO otherwise.
 */
static int alua_tur(struct scsi_device *sdev)
{
        struct scsi_sense_hdr sense_hdr;
        int retval;

        retval = scsi_test_unit_ready(sdev, ALUA_FAILOVER_TIMEOUT * HZ,
                                      ALUA_FAILOVER_RETRIES, &sense_hdr);
        if (sense_hdr.sense_key == NOT_READY &&
            sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a)
                return SCSI_DH_RETRY;
        else if (retval)
                return SCSI_DH_IO;
        else
                return SCSI_DH_OK;
}

/*
 * alua_rtpg - Evaluate REPORT TARGET GROUP STATES
 * @sdev: the device to be evaluated.
 *
 * Evaluate the Target Port Group State.
 * Returns SCSI_DH_DEV_OFFLINED if the path is
 * found to be unusable.
 */
static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
{
        struct scsi_sense_hdr sense_hdr;
        struct alua_port_group *tmp_pg;
        int len, k, off, bufflen = ALUA_RTPG_SIZE;
        int group_id_old, state_old, pref_old, valid_states_old;
        unsigned char *desc, *buff;
        unsigned err;
        int retval;
        unsigned int tpg_desc_tbl_off;
        unsigned char orig_transition_tmo;
        unsigned long flags;
        bool transitioning_sense = false;

        group_id_old = pg->group_id;
        state_old = pg->state;
        pref_old = pg->pref;
        valid_states_old = pg->valid_states;

        if (!pg->expiry) {
                unsigned long transition_tmo = ALUA_FAILOVER_TIMEOUT * HZ;

                if (pg->transition_tmo)
                        transition_tmo = pg->transition_tmo * HZ;

                pg->expiry = round_jiffies_up(jiffies + transition_tmo);
        }

        buff = kzalloc(bufflen, GFP_KERNEL);
        if (!buff)
                return SCSI_DH_DEV_TEMP_BUSY;

 retry:
        err = 0;
        retval = submit_rtpg(sdev, buff, bufflen, &sense_hdr, pg->flags);

        if (retval) {
                /*
                 * Some (broken) implementations have a habit of returning
                 * an error during things like firmware update etc.
                 * But if the target only supports active/optimized there's
                 * not much we can do; it's not that we can switch paths
                 * or anything.
                 * So ignore any errors to avoid spurious failures during
                 * path failover.
                 */
                if ((pg->valid_states & ~TPGS_SUPPORT_OPTIMIZED) == 0) {
                        sdev_printk(KERN_INFO, sdev,
                                    "%s: ignoring rtpg result %d\n",
                                    ALUA_DH_NAME, retval);
                        kfree(buff);
                        return SCSI_DH_OK;
                }
                if (retval < 0 || !scsi_sense_valid(&sense_hdr)) {
                        sdev_printk(KERN_INFO, sdev,
                                    "%s: rtpg failed, result %d\n",
                                    ALUA_DH_NAME, retval);
                        kfree(buff);
                        if (retval < 0)
                                return SCSI_DH_DEV_TEMP_BUSY;
                        if (host_byte(retval) == DID_NO_CONNECT)
                                return SCSI_DH_RES_TEMP_UNAVAIL;
                        return SCSI_DH_IO;
                }

                /*
                 * submit_rtpg() has failed on existing arrays
                 * when requesting extended header info, and
                 * the array doesn't support extended headers,
                 * even though it shouldn't according to T10.
                 * The retry without rtpg_ext_hdr_req set
                 * handles this.
                 * Note:  some arrays return a sense key of ILLEGAL_REQUEST
                 * with ASC 00h if they don't support the extended header.
                 */
                if (!(pg->flags & ALUA_RTPG_EXT_HDR_UNSUPP) &&
                    sense_hdr.sense_key == ILLEGAL_REQUEST) {
                        pg->flags |= ALUA_RTPG_EXT_HDR_UNSUPP;
                        goto retry;
                }
                /*
                 * If the array returns with 'ALUA state transition'
                 * sense code here it cannot return RTPG data during
                 * transition. So set the state to 'transitioning' directly.
                 */
                if (sense_hdr.sense_key == NOT_READY &&
                    sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a) {
                        transitioning_sense = true;
                        goto skip_rtpg;
                }
                /*
                 * Retry on any other UNIT ATTENTION occurred.
                 */
                if (sense_hdr.sense_key == UNIT_ATTENTION)
                        err = SCSI_DH_RETRY;
                if (err == SCSI_DH_RETRY &&
                    pg->expiry != 0 && time_before(jiffies, pg->expiry)) {
                        sdev_printk(KERN_ERR, sdev, "%s: rtpg retry\n",
                                    ALUA_DH_NAME);
                        scsi_print_sense_hdr(sdev, ALUA_DH_NAME, &sense_hdr);
                        kfree(buff);
                        return err;
                }
                sdev_printk(KERN_ERR, sdev, "%s: rtpg failed\n",
                            ALUA_DH_NAME);
                scsi_print_sense_hdr(sdev, ALUA_DH_NAME, &sense_hdr);
                kfree(buff);
                pg->expiry = 0;
                return SCSI_DH_IO;
        }

        len = get_unaligned_be32(&buff[0]) + 4;

        if (len > bufflen) {
                /* Resubmit with the correct length */
                kfree(buff);
                bufflen = len;
                buff = kmalloc(bufflen, GFP_KERNEL);
                if (!buff) {
                        sdev_printk(KERN_WARNING, sdev,
                                    "%s: kmalloc buffer failed\n",__func__);
                        /* Temporary failure, bypass */
                        pg->expiry = 0;
                        return SCSI_DH_DEV_TEMP_BUSY;
                }
                goto retry;
        }

        orig_transition_tmo = pg->transition_tmo;
        if ((buff[4] & RTPG_FMT_MASK) == RTPG_FMT_EXT_HDR && buff[5] != 0)
                pg->transition_tmo = buff[5];
        else
                pg->transition_tmo = ALUA_FAILOVER_TIMEOUT;

        if (orig_transition_tmo != pg->transition_tmo) {
                sdev_printk(KERN_INFO, sdev,
                            "%s: transition timeout set to %d seconds\n",
                            ALUA_DH_NAME, pg->transition_tmo);
                pg->expiry = jiffies + pg->transition_tmo * HZ;
        }

        if ((buff[4] & RTPG_FMT_MASK) == RTPG_FMT_EXT_HDR)
                tpg_desc_tbl_off = 8;
        else
                tpg_desc_tbl_off = 4;

        for (k = tpg_desc_tbl_off, desc = buff + tpg_desc_tbl_off;
             k < len;
             k += off, desc += off) {
                u16 group_id = get_unaligned_be16(&desc[2]);

                spin_lock_irqsave(&port_group_lock, flags);
                tmp_pg = alua_find_get_pg(pg->device_id_str, pg->device_id_len,
                                          group_id);
                spin_unlock_irqrestore(&port_group_lock, flags);
                if (tmp_pg) {
                        if (spin_trylock_irqsave(&tmp_pg->lock, flags)) {
                                if ((tmp_pg == pg) ||
                                    !(tmp_pg->flags & ALUA_PG_RUNNING)) {
                                        struct alua_dh_data *h;

                                        tmp_pg->state = desc[0] & 0x0f;
                                        tmp_pg->pref = desc[0] >> 7;
                                        rcu_read_lock();
                                        list_for_each_entry_rcu(h,
                                                &tmp_pg->dh_list, node) {
                                                if (!h->sdev)
                                                        continue;
                                                h->sdev->access_state = desc[0];
                                        }
                                        rcu_read_unlock();
                                }
                                if (tmp_pg == pg)
                                        tmp_pg->valid_states = desc[1];
                                spin_unlock_irqrestore(&tmp_pg->lock, flags);
                        }
                        kref_put(&tmp_pg->kref, release_port_group);
                }
                off = 8 + (desc[7] * 4);
        }

 skip_rtpg:
        spin_lock_irqsave(&pg->lock, flags);
        if (transitioning_sense)
                pg->state = SCSI_ACCESS_STATE_TRANSITIONING;

        if (group_id_old != pg->group_id || state_old != pg->state ||
                pref_old != pg->pref || valid_states_old != pg->valid_states)
                sdev_printk(KERN_INFO, sdev,
                        "%s: port group %02x state %c %s supports %c%c%c%c%c%c%c\n",
                        ALUA_DH_NAME, pg->group_id, print_alua_state(pg->state),
                        pg->pref ? "preferred" : "non-preferred",
                        pg->valid_states&TPGS_SUPPORT_TRANSITION?'T':'t',
                        pg->valid_states&TPGS_SUPPORT_OFFLINE?'O':'o',
                        pg->valid_states&TPGS_SUPPORT_LBA_DEPENDENT?'L':'l',
                        pg->valid_states&TPGS_SUPPORT_UNAVAILABLE?'U':'u',
                        pg->valid_states&TPGS_SUPPORT_STANDBY?'S':'s',
                        pg->valid_states&TPGS_SUPPORT_NONOPTIMIZED?'N':'n',
                        pg->valid_states&TPGS_SUPPORT_OPTIMIZED?'A':'a');

        switch (pg->state) {
        case SCSI_ACCESS_STATE_TRANSITIONING:
                if (time_before(jiffies, pg->expiry)) {
                        /* State transition, retry */
                        pg->interval = ALUA_RTPG_RETRY_DELAY;
                        err = SCSI_DH_RETRY;
                } else {
                        struct alua_dh_data *h;

                        /* Transitioning time exceeded, set port to standby */
                        err = SCSI_DH_IO;
                        pg->state = SCSI_ACCESS_STATE_STANDBY;
                        pg->expiry = 0;
                        rcu_read_lock();
                        list_for_each_entry_rcu(h, &pg->dh_list, node) {
                                if (!h->sdev)
                                        continue;
                                h->sdev->access_state =
                                        (pg->state & SCSI_ACCESS_STATE_MASK);
                                if (pg->pref)
                                        h->sdev->access_state |=
                                                SCSI_ACCESS_STATE_PREFERRED;
                        }
                        rcu_read_unlock();
                }
                break;
        case SCSI_ACCESS_STATE_OFFLINE:
                /* Path unusable */
                err = SCSI_DH_DEV_OFFLINED;
                pg->expiry = 0;
                break;
        default:
                /* Useable path if active */
                err = SCSI_DH_OK;
                pg->expiry = 0;
                break;
        }
        spin_unlock_irqrestore(&pg->lock, flags);
        kfree(buff);
        return err;
}

/*
 * alua_stpg - Issue a SET TARGET PORT GROUP command
 *
 * Issue a SET TARGET PORT GROUP command and evaluate the
 * response. Returns SCSI_DH_RETRY per default to trigger
 * a re-evaluation of the target group state or SCSI_DH_OK
 * if no further action needs to be taken.
 */
static unsigned alua_stpg(struct scsi_device *sdev, struct alua_port_group *pg)
{
        int retval;
        struct scsi_sense_hdr sense_hdr;

        if (!(pg->tpgs & TPGS_MODE_EXPLICIT)) {
                /* Only implicit ALUA supported, retry */
                return SCSI_DH_RETRY;
        }
        switch (pg->state) {
        case SCSI_ACCESS_STATE_OPTIMAL:
                return SCSI_DH_OK;
        case SCSI_ACCESS_STATE_ACTIVE:
                if ((pg->flags & ALUA_OPTIMIZE_STPG) &&
                    !pg->pref &&
                    (pg->tpgs & TPGS_MODE_IMPLICIT))
                        return SCSI_DH_OK;
                break;
        case SCSI_ACCESS_STATE_STANDBY:
        case SCSI_ACCESS_STATE_UNAVAILABLE:
                break;
        case SCSI_ACCESS_STATE_OFFLINE:
                return SCSI_DH_IO;
        case SCSI_ACCESS_STATE_TRANSITIONING:
                break;
        default:
                sdev_printk(KERN_INFO, sdev,
                            "%s: stpg failed, unhandled TPGS state %d",
                            ALUA_DH_NAME, pg->state);
                return SCSI_DH_NOSYS;
        }
        retval = submit_stpg(sdev, pg->group_id, &sense_hdr);

        if (retval) {
                if (retval < 0 || !scsi_sense_valid(&sense_hdr)) {
                        sdev_printk(KERN_INFO, sdev,
                                    "%s: stpg failed, result %d",
                                    ALUA_DH_NAME, retval);
                        if (retval < 0)
                                return SCSI_DH_DEV_TEMP_BUSY;
                } else {
                        sdev_printk(KERN_INFO, sdev, "%s: stpg failed\n",
                                    ALUA_DH_NAME);
                        scsi_print_sense_hdr(sdev, ALUA_DH_NAME, &sense_hdr);
                }
        }
        /* Retry RTPG */
        return SCSI_DH_RETRY;
}

static bool alua_rtpg_select_sdev(struct alua_port_group *pg)
{
        struct alua_dh_data *h;
        struct scsi_device *sdev = NULL;

        lockdep_assert_held(&pg->lock);
        if (WARN_ON(!pg->rtpg_sdev))
                return false;

        /*
         * RCU protection isn't necessary for dh_list here
         * as we hold pg->lock, but for access to h->pg.
         */
        rcu_read_lock();
        list_for_each_entry_rcu(h, &pg->dh_list, node) {
                if (!h->sdev)
                        continue;
                if (h->sdev == pg->rtpg_sdev) {
                        h->disabled = true;
                        continue;
                }
                if (rcu_dereference(h->pg) == pg &&
                    !h->disabled &&
                    !scsi_device_get(h->sdev)) {
                        sdev = h->sdev;
                        break;
                }
        }
        rcu_read_unlock();

        if (!sdev) {
                pr_warn("%s: no device found for rtpg\n",
                        (pg->device_id_len ?
                         (char *)pg->device_id_str : "(nameless PG)"));
                return false;
        }

        sdev_printk(KERN_INFO, sdev, "rtpg retry on different device\n");

        scsi_device_put(pg->rtpg_sdev);
        pg->rtpg_sdev = sdev;

        return true;
}

static void alua_rtpg_work(struct work_struct *work)
{
        struct alua_port_group *pg =
                container_of(work, struct alua_port_group, rtpg_work.work);
        struct scsi_device *sdev;
        LIST_HEAD(qdata_list);
        int err = SCSI_DH_OK;
        struct alua_queue_data *qdata, *tmp;
        struct alua_dh_data *h;
        unsigned long flags;

        spin_lock_irqsave(&pg->lock, flags);
        sdev = pg->rtpg_sdev;
        if (!sdev) {
                WARN_ON(pg->flags & ALUA_PG_RUN_RTPG);
                WARN_ON(pg->flags & ALUA_PG_RUN_STPG);
                spin_unlock_irqrestore(&pg->lock, flags);
                kref_put(&pg->kref, release_port_group);
                return;
        }
        pg->flags |= ALUA_PG_RUNNING;
        if (pg->flags & ALUA_PG_RUN_RTPG) {
                int state = pg->state;

                pg->flags &= ~ALUA_PG_RUN_RTPG;
                spin_unlock_irqrestore(&pg->lock, flags);
                if (state == SCSI_ACCESS_STATE_TRANSITIONING) {
                        if (alua_tur(sdev) == SCSI_DH_RETRY) {
                                spin_lock_irqsave(&pg->lock, flags);
                                pg->flags &= ~ALUA_PG_RUNNING;
                                pg->flags |= ALUA_PG_RUN_RTPG;
                                if (!pg->interval)
                                        pg->interval = ALUA_RTPG_RETRY_DELAY;
                                spin_unlock_irqrestore(&pg->lock, flags);
                                queue_delayed_work(kaluad_wq, &pg->rtpg_work,
                                                   pg->interval * HZ);
                                return;
                        }
                        /* Send RTPG on failure or if TUR indicates SUCCESS */
                }
                err = alua_rtpg(sdev, pg);
                spin_lock_irqsave(&pg->lock, flags);

                /* If RTPG failed on the current device, try using another */
                if (err == SCSI_DH_RES_TEMP_UNAVAIL &&
                    alua_rtpg_select_sdev(pg))
                        err = SCSI_DH_IMM_RETRY;

                if (err == SCSI_DH_RETRY || err == SCSI_DH_IMM_RETRY ||
                    pg->flags & ALUA_PG_RUN_RTPG) {
                        pg->flags &= ~ALUA_PG_RUNNING;
                        if (err == SCSI_DH_IMM_RETRY)
                                pg->interval = 0;
                        else if (!pg->interval && !(pg->flags & ALUA_PG_RUN_RTPG))
                                pg->interval = ALUA_RTPG_RETRY_DELAY;
                        pg->flags |= ALUA_PG_RUN_RTPG;
                        spin_unlock_irqrestore(&pg->lock, flags);
                        queue_delayed_work(kaluad_wq, &pg->rtpg_work,
                                           pg->interval * HZ);
                        return;
                }
                if (err != SCSI_DH_OK)
                        pg->flags &= ~ALUA_PG_RUN_STPG;
        }
        if (pg->flags & ALUA_PG_RUN_STPG) {
                pg->flags &= ~ALUA_PG_RUN_STPG;
                spin_unlock_irqrestore(&pg->lock, flags);
                err = alua_stpg(sdev, pg);
                spin_lock_irqsave(&pg->lock, flags);
                if (err == SCSI_DH_RETRY || pg->flags & ALUA_PG_RUN_RTPG) {
                        pg->flags |= ALUA_PG_RUN_RTPG;
                        pg->interval = 0;
                        pg->flags &= ~ALUA_PG_RUNNING;
                        spin_unlock_irqrestore(&pg->lock, flags);
                        queue_delayed_work(kaluad_wq, &pg->rtpg_work,
                                           pg->interval * HZ);
                        return;
                }
        }

        list_splice_init(&pg->rtpg_list, &qdata_list);
        /*
         * We went through an RTPG, for good or bad.
         * Re-enable all devices for the next attempt.
         */
        list_for_each_entry(h, &pg->dh_list, node)
                h->disabled = false;
        pg->rtpg_sdev = NULL;
        spin_unlock_irqrestore(&pg->lock, flags);

        list_for_each_entry_safe(qdata, tmp, &qdata_list, entry) {
                list_del(&qdata->entry);
                if (qdata->callback_fn)
                        qdata->callback_fn(qdata->callback_data, err);
                kfree(qdata);
        }
        spin_lock_irqsave(&pg->lock, flags);
        pg->flags &= ~ALUA_PG_RUNNING;
        spin_unlock_irqrestore(&pg->lock, flags);
        scsi_device_put(sdev);
        kref_put(&pg->kref, release_port_group);
}

/**
 * alua_rtpg_queue() - cause RTPG to be submitted asynchronously
 * @pg: ALUA port group associated with @sdev.
 * @sdev: SCSI device for which to submit an RTPG.
 * @qdata: Information about the callback to invoke after the RTPG.
 * @force: Whether or not to submit an RTPG if a work item that will submit an
 *         RTPG already has been scheduled.
 *
 * Returns true if and only if alua_rtpg_work() will be called asynchronously.
 * That function is responsible for calling @qdata->fn().
 */
static bool alua_rtpg_queue(struct alua_port_group *pg,
                            struct scsi_device *sdev,
                            struct alua_queue_data *qdata, bool force)
{
        int start_queue = 0;
        unsigned long flags;
        if (WARN_ON_ONCE(!pg) || scsi_device_get(sdev))
                return false;

        spin_lock_irqsave(&pg->lock, flags);
        if (qdata) {
                list_add_tail(&qdata->entry, &pg->rtpg_list);
                pg->flags |= ALUA_PG_RUN_STPG;
                force = true;
        }
        if (pg->rtpg_sdev == NULL) {
                pg->interval = 0;
                pg->flags |= ALUA_PG_RUN_RTPG;
                kref_get(&pg->kref);
                pg->rtpg_sdev = sdev;
                start_queue = 1;
        } else if (!(pg->flags & ALUA_PG_RUN_RTPG) && force) {
                pg->flags |= ALUA_PG_RUN_RTPG;
                /* Do not queue if the worker is already running */
                if (!(pg->flags & ALUA_PG_RUNNING)) {
                        kref_get(&pg->kref);
                        start_queue = 1;
                }

        }

        spin_unlock_irqrestore(&pg->lock, flags);

        if (start_queue) {
                if (queue_delayed_work(kaluad_wq, &pg->rtpg_work,
                                msecs_to_jiffies(ALUA_RTPG_DELAY_MSECS)))
                        sdev = NULL;
                else
                        kref_put(&pg->kref, release_port_group);
        }
        if (sdev)
                scsi_device_put(sdev);

        return true;
}

/*
 * alua_initialize - Initialize ALUA state
 * @sdev: the device to be initialized
 *
 * For the prep_fn to work correctly we have
 * to initialize the ALUA state for the device.
 */
static int alua_initialize(struct scsi_device *sdev, struct alua_dh_data *h)
{
        int err = SCSI_DH_DEV_UNSUPP, tpgs;

        mutex_lock(&h->init_mutex);
        h->disabled = false;
        tpgs = alua_check_tpgs(sdev);
        if (tpgs != TPGS_MODE_NONE)
                err = alua_check_vpd(sdev, h, tpgs);
        h->init_error = err;
        mutex_unlock(&h->init_mutex);
        return err;
}
/*
 * alua_set_params - set/unset the optimize flag
 * @sdev: device on the path to be activated
 * params - parameters in the following format
 *      "no_of_params\0param1\0param2\0param3\0...\0"
 * For example, to set the flag pass the following parameters
 * from multipath.conf
 *     hardware_handler        "2 alua 1"
 */
static int alua_set_params(struct scsi_device *sdev, const char *params)
{
        struct alua_dh_data *h = sdev->handler_data;
        struct alua_port_group *pg = NULL;
        unsigned int optimize = 0, argc;
        const char *p = params;
        int result = SCSI_DH_OK;
        unsigned long flags;

        if ((sscanf(params, "%u", &argc) != 1) || (argc != 1))
                return -EINVAL;

        while (*p++)
                ;
        if ((sscanf(p, "%u", &optimize) != 1) || (optimize > 1))
                return -EINVAL;

        rcu_read_lock();
        pg = rcu_dereference(h->pg);
        if (!pg) {
                rcu_read_unlock();
                return -ENXIO;
        }
        spin_lock_irqsave(&pg->lock, flags);
        if (optimize)
                pg->flags |= ALUA_OPTIMIZE_STPG;
        else
                pg->flags &= ~ALUA_OPTIMIZE_STPG;
        spin_unlock_irqrestore(&pg->lock, flags);
        rcu_read_unlock();

        return result;
}

/*
 * alua_activate - activate a path
 * @sdev: device on the path to be activated
 *
 * We're currently switching the port group to be activated only and
 * let the array figure out the rest.
 * There may be other arrays which require us to switch all port groups
 * based on a certain policy. But until we actually encounter them it
 * should be okay.
 */
static int alua_activate(struct scsi_device *sdev,
                        activate_complete fn, void *data)
{
        struct alua_dh_data *h = sdev->handler_data;
        int err = SCSI_DH_OK;
        struct alua_queue_data *qdata;
        struct alua_port_group *pg;

        qdata = kzalloc(sizeof(*qdata), GFP_KERNEL);
        if (!qdata) {
                err = SCSI_DH_RES_TEMP_UNAVAIL;
                goto out;
        }
        qdata->callback_fn = fn;
        qdata->callback_data = data;

        mutex_lock(&h->init_mutex);
        rcu_read_lock();
        pg = rcu_dereference(h->pg);
        if (!pg || !kref_get_unless_zero(&pg->kref)) {
                rcu_read_unlock();
                kfree(qdata);
                err = h->init_error;
                mutex_unlock(&h->init_mutex);
                goto out;
        }
        rcu_read_unlock();
        mutex_unlock(&h->init_mutex);

        if (alua_rtpg_queue(pg, sdev, qdata, true))
                fn = NULL;
        else
                err = SCSI_DH_DEV_OFFLINED;
        kref_put(&pg->kref, release_port_group);
out:
        if (fn)
                fn(data, err);
        return 0;
}

/*
 * alua_check - check path status
 * @sdev: device on the path to be checked
 *
 * Check the device status
 */
static void alua_check(struct scsi_device *sdev, bool force)
{
        struct alua_dh_data *h = sdev->handler_data;
        struct alua_port_group *pg;

        rcu_read_lock();
        pg = rcu_dereference(h->pg);
        if (!pg || !kref_get_unless_zero(&pg->kref)) {
                rcu_read_unlock();
                return;
        }
        rcu_read_unlock();
        alua_rtpg_queue(pg, sdev, NULL, force);
        kref_put(&pg->kref, release_port_group);
}

/*
 * alua_prep_fn - request callback
 *
 * Fail I/O to all paths not in state
 * active/optimized or active/non-optimized.
 */
static blk_status_t alua_prep_fn(struct scsi_device *sdev, struct request *req)
{
        struct alua_dh_data *h = sdev->handler_data;
        struct alua_port_group *pg;
        unsigned char state = SCSI_ACCESS_STATE_OPTIMAL;

        rcu_read_lock();
        pg = rcu_dereference(h->pg);
        if (pg)
                state = pg->state;
        rcu_read_unlock();

        switch (state) {
        case SCSI_ACCESS_STATE_OPTIMAL:
        case SCSI_ACCESS_STATE_ACTIVE:
        case SCSI_ACCESS_STATE_LBA:
                return BLK_STS_OK;
        case SCSI_ACCESS_STATE_TRANSITIONING:
                return BLK_STS_AGAIN;
        default:
                req->rq_flags |= RQF_QUIET;
                return BLK_STS_IOERR;
        }
}

static void alua_rescan(struct scsi_device *sdev)
{
        struct alua_dh_data *h = sdev->handler_data;

        alua_initialize(sdev, h);
}

/*
 * alua_bus_attach - Attach device handler
 * @sdev: device to be attached to
 */
static int alua_bus_attach(struct scsi_device *sdev)
{
        struct alua_dh_data *h;
        int err;

        h = kzalloc(sizeof(*h) , GFP_KERNEL);
        if (!h)
                return SCSI_DH_NOMEM;
        spin_lock_init(&h->pg_lock);
        rcu_assign_pointer(h->pg, NULL);
        h->init_error = SCSI_DH_OK;
        h->sdev = sdev;
        INIT_LIST_HEAD(&h->node);

        mutex_init(&h->init_mutex);
        err = alua_initialize(sdev, h);
        if (err != SCSI_DH_OK && err != SCSI_DH_DEV_OFFLINED)
                goto failed;

        sdev->handler_data = h;
        return SCSI_DH_OK;
failed:
        kfree(h);
        return err;
}

/*
 * alua_bus_detach - Detach device handler
 * @sdev: device to be detached from
 */
static void alua_bus_detach(struct scsi_device *sdev)
{
        struct alua_dh_data *h = sdev->handler_data;
        struct alua_port_group *pg;

        spin_lock(&h->pg_lock);
        pg = rcu_dereference_protected(h->pg, lockdep_is_held(&h->pg_lock));
        rcu_assign_pointer(h->pg, NULL);
        spin_unlock(&h->pg_lock);
        if (pg) {
                spin_lock_irq(&pg->lock);
                list_del_rcu(&h->node);
                spin_unlock_irq(&pg->lock);
                kref_put(&pg->kref, release_port_group);
        }
        sdev->handler_data = NULL;
        synchronize_rcu();
        kfree(h);
}

static struct scsi_device_handler alua_dh = {
        .name = ALUA_DH_NAME,
        .module = THIS_MODULE,
        .attach = alua_bus_attach,
        .detach = alua_bus_detach,
        .prep_fn = alua_prep_fn,
        .check_sense = alua_check_sense,
        .activate = alua_activate,
        .rescan = alua_rescan,
        .set_params = alua_set_params,
};

static int __init alua_init(void)
{
        int r;

        kaluad_wq = alloc_workqueue("kaluad", WQ_MEM_RECLAIM, 0);
        if (!kaluad_wq)
                return -ENOMEM;

        r = scsi_register_device_handler(&alua_dh);
        if (r != 0) {
                printk(KERN_ERR "%s: Failed to register scsi device handler",
                        ALUA_DH_NAME);
                destroy_workqueue(kaluad_wq);
        }
        return r;
}

static void __exit alua_exit(void)
{
        scsi_unregister_device_handler(&alua_dh);
        destroy_workqueue(kaluad_wq);
}

module_init(alua_init);
module_exit(alua_exit);

MODULE_DESCRIPTION("DM Multipath ALUA support");
MODULE_AUTHOR("Hannes Reinecke <hare@suse.de>");
MODULE_LICENSE("GPL");
MODULE_VERSION(ALUA_DH_VER);