/*
 * Generic SCSI-3 ALUA SCSI Device Handler
 *
 * Copyright (C) 2007, 2008 Hannes Reinecke, SUSE Linux Products GmbH.
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 */
#include <scsi/scsi.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_dh.h>

#define ALUA_DH_NAME "alua"
#define ALUA_DH_VER "1.2"

#define TPGS_STATE_OPTIMIZED            0x0
#define TPGS_STATE_NONOPTIMIZED         0x1
#define TPGS_STATE_STANDBY              0x2
#define TPGS_STATE_UNAVAILABLE          0x3
#define TPGS_STATE_OFFLINE              0xe
#define TPGS_STATE_TRANSITIONING        0xf

#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_OFFLINE            0x40
#define TPGS_SUPPORT_TRANSITION         0x80

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

#define ALUA_INQUIRY_SIZE               36
#define ALUA_FAILOVER_TIMEOUT           (60 * HZ)
#define ALUA_FAILOVER_RETRIES           5

struct alua_dh_data {
        int                     group_id;
        int                     rel_port;
        int                     tpgs;
        int                     state;
        unsigned char           inq[ALUA_INQUIRY_SIZE];
        unsigned char           *buff;
        int                     bufflen;
        unsigned char           sense[SCSI_SENSE_BUFFERSIZE];
        int                     senselen;
};

#define ALUA_POLICY_SWITCH_CURRENT      0
#define ALUA_POLICY_SWITCH_ALL          1

static inline struct alua_dh_data *get_alua_data(struct scsi_device *sdev)
{
        struct scsi_dh_data *scsi_dh_data = sdev->scsi_dh_data;
        BUG_ON(scsi_dh_data == NULL);
        return ((struct alua_dh_data *) scsi_dh_data->buf);
}

static int realloc_buffer(struct alua_dh_data *h, unsigned len)
{
        if (h->buff && h->buff != h->inq)
                kfree(h->buff);

        h->buff = kmalloc(len, GFP_NOIO);
        if (!h->buff) {
                h->buff = h->inq;
                h->bufflen = ALUA_INQUIRY_SIZE;
                return 1;
        }
        h->bufflen = len;
        return 0;
}

static struct request *get_alua_req(struct scsi_device *sdev,
                                    void *buffer, unsigned buflen, int rw)
{
        struct request *rq;
        struct request_queue *q = sdev->request_queue;

        rq = blk_get_request(q, rw, GFP_NOIO);

        if (!rq) {
                sdev_printk(KERN_INFO, sdev,
                            "%s: blk_get_request failed\n", __func__);
                return NULL;
        }

        if (buflen && blk_rq_map_kern(q, rq, buffer, buflen, GFP_NOIO)) {
                blk_put_request(rq);
                sdev_printk(KERN_INFO, sdev,
                            "%s: blk_rq_map_kern failed\n", __func__);
                return NULL;
        }

        rq->cmd_type = REQ_TYPE_BLOCK_PC;
        rq->cmd_flags |= REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
                         REQ_FAILFAST_DRIVER;
        rq->retries = ALUA_FAILOVER_RETRIES;
        rq->timeout = ALUA_FAILOVER_TIMEOUT;

        return rq;
}

/*
 * submit_std_inquiry - Issue a standard INQUIRY command
 * @sdev: sdev the command should be send to
 */
static int submit_std_inquiry(struct scsi_device *sdev, struct alua_dh_data *h)
{
        struct request *rq;
        int err = SCSI_DH_RES_TEMP_UNAVAIL;

        rq = get_alua_req(sdev, h->inq, ALUA_INQUIRY_SIZE, READ);
        if (!rq)
                goto done;

        /* Prepare the command. */
        rq->cmd[0] = INQUIRY;
        rq->cmd[1] = 0;
        rq->cmd[2] = 0;
        rq->cmd[4] = ALUA_INQUIRY_SIZE;
        rq->cmd_len = COMMAND_SIZE(INQUIRY);

        rq->sense = h->sense;
        memset(rq->sense, 0, SCSI_SENSE_BUFFERSIZE);
        rq->sense_len = h->senselen = 0;

        err = blk_execute_rq(rq->q, NULL, rq, 1);
        if (err == -EIO) {
                sdev_printk(KERN_INFO, sdev,
                            "%s: std inquiry failed with %x\n",
                            ALUA_DH_NAME, rq->errors);
                h->senselen = rq->sense_len;
                err = SCSI_DH_IO;
        }
        blk_put_request(rq);
done:
        return err;
}

/*
 * submit_vpd_inquiry - Issue an INQUIRY VPD page 0x83 command
 * @sdev: sdev the command should be sent to
 */
static int submit_vpd_inquiry(struct scsi_device *sdev, struct alua_dh_data *h)
{
        struct request *rq;
        int err = SCSI_DH_RES_TEMP_UNAVAIL;

        rq = get_alua_req(sdev, h->buff, h->bufflen, READ);
        if (!rq)
                goto done;

        /* Prepare the command. */
        rq->cmd[0] = INQUIRY;
        rq->cmd[1] = 1;
        rq->cmd[2] = 0x83;
        rq->cmd[4] = h->bufflen;
        rq->cmd_len = COMMAND_SIZE(INQUIRY);

        rq->sense = h->sense;
        memset(rq->sense, 0, SCSI_SENSE_BUFFERSIZE);
        rq->sense_len = h->senselen = 0;

        err = blk_execute_rq(rq->q, NULL, rq, 1);
        if (err == -EIO) {
                sdev_printk(KERN_INFO, sdev,
                            "%s: evpd inquiry failed with %x\n",
                            ALUA_DH_NAME, rq->errors);
                h->senselen = rq->sense_len;
                err = SCSI_DH_IO;
        }
        blk_put_request(rq);
done:
        return err;
}

/*
 * submit_rtpg - Issue a REPORT TARGET GROUP STATES command
 * @sdev: sdev the command should be sent to
 */
static unsigned submit_rtpg(struct scsi_device *sdev, struct alua_dh_data *h)
{
        struct request *rq;
        int err = SCSI_DH_RES_TEMP_UNAVAIL;

        rq = get_alua_req(sdev, h->buff, h->bufflen, READ);
        if (!rq)
                goto done;

        /* Prepare the command. */
        rq->cmd[0] = MAINTENANCE_IN;
        rq->cmd[1] = MI_REPORT_TARGET_PGS;
        rq->cmd[6] = (h->bufflen >> 24) & 0xff;
        rq->cmd[7] = (h->bufflen >> 16) & 0xff;
        rq->cmd[8] = (h->bufflen >>  8) & 0xff;
        rq->cmd[9] = h->bufflen & 0xff;
        rq->cmd_len = COMMAND_SIZE(MAINTENANCE_IN);

        rq->sense = h->sense;
        memset(rq->sense, 0, SCSI_SENSE_BUFFERSIZE);
        rq->sense_len = h->senselen = 0;

        err = blk_execute_rq(rq->q, NULL, rq, 1);
        if (err == -EIO) {
                sdev_printk(KERN_INFO, sdev,
                            "%s: rtpg failed with %x\n",
                            ALUA_DH_NAME, rq->errors);
                h->senselen = rq->sense_len;
                err = SCSI_DH_IO;
        }
        blk_put_request(rq);
done:
        return err;
}

/*
 * submit_stpg - Issue a SET TARGET GROUP STATES command
 * @sdev: sdev the command should be sent to
 *
 * 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 unsigned submit_stpg(struct scsi_device *sdev, struct alua_dh_data *h)
{
        struct request *rq;
        int err = SCSI_DH_RES_TEMP_UNAVAIL;
        int stpg_len = 8;

        /* Prepare the data buffer */
        memset(h->buff, 0, stpg_len);
        h->buff[4] = TPGS_STATE_OPTIMIZED & 0x0f;
        h->buff[6] = (h->group_id >> 8) & 0xff;
        h->buff[7] = h->group_id & 0xff;

        rq = get_alua_req(sdev, h->buff, stpg_len, WRITE);
        if (!rq)
                goto done;

        /* Prepare the command. */
        rq->cmd[0] = MAINTENANCE_OUT;
        rq->cmd[1] = MO_SET_TARGET_PGS;
        rq->cmd[6] = (stpg_len >> 24) & 0xff;
        rq->cmd[7] = (stpg_len >> 16) & 0xff;
        rq->cmd[8] = (stpg_len >>  8) & 0xff;
        rq->cmd[9] = stpg_len & 0xff;
        rq->cmd_len = COMMAND_SIZE(MAINTENANCE_OUT);

        rq->sense = h->sense;
        memset(rq->sense, 0, SCSI_SENSE_BUFFERSIZE);
        rq->sense_len = h->senselen = 0;

        err = blk_execute_rq(rq->q, NULL, rq, 1);
        if (err == -EIO) {
                sdev_printk(KERN_INFO, sdev,
                            "%s: stpg failed with %x\n",
                            ALUA_DH_NAME, rq->errors);
                h->senselen = rq->sense_len;
                err = SCSI_DH_IO;
        }
        blk_put_request(rq);
done:
        return err;
}

/*
 * alua_std_inquiry - Evaluate standard INQUIRY command
 * @sdev: device to be checked
 *
 * Just extract the TPGS setting to find out if ALUA
 * is supported.
 */
static int alua_std_inquiry(struct scsi_device *sdev, struct alua_dh_data *h)
{
        int err;

        err = submit_std_inquiry(sdev, h);

        if (err != SCSI_DH_OK)
                return err;

        /* Check TPGS setting */
        h->tpgs = (h->inq[5] >> 4) & 0x3;
        switch (h->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;
        default:
                h->tpgs = TPGS_MODE_NONE;
                sdev_printk(KERN_INFO, sdev, "%s: not supported\n",
                            ALUA_DH_NAME);
                err = SCSI_DH_DEV_UNSUPP;
                break;
        }

        return err;
}

/*
 * alua_vpd_inquiry - 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_vpd_inquiry(struct scsi_device *sdev, struct alua_dh_data *h)
{
        int len;
        unsigned err;
        unsigned char *d;

 retry:
        err = submit_vpd_inquiry(sdev, h);

        if (err != SCSI_DH_OK)
                return err;

        /* Check if vpd page exceeds initial buffer */
        len = (h->buff[2] << 8) + h->buff[3] + 4;
        if (len > h->bufflen) {
                /* Resubmit with the correct length */
                if (realloc_buffer(h, len)) {
                        sdev_printk(KERN_WARNING, sdev,
                                    "%s: kmalloc buffer failed\n",
                                    ALUA_DH_NAME);
                        /* Temporary failure, bypass */
                        return SCSI_DH_DEV_TEMP_BUSY;
                }
                goto retry;
        }

        /*
         * Now look for the correct descriptor.
         */
        d = h->buff + 4;
        while (d < h->buff + len) {
                switch (d[1] & 0xf) {
                case 0x4:
                        /* Relative target port */
                        h->rel_port = (d[6] << 8) + d[7];
                        break;
                case 0x5:
                        /* Target port group */
                        h->group_id = (d[6] << 8) + d[7];
                        break;
                default:
                        break;
                }
                d += d[3] + 4;
        }

        if (h->group_id == -1) {
                /*
                 * 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);
                h->state = TPGS_STATE_OPTIMIZED;
                h->tpgs = TPGS_MODE_NONE;
                err = SCSI_DH_DEV_UNSUPP;
        } else {
                sdev_printk(KERN_INFO, sdev,
                            "%s: port group %02x rel port %02x\n",
                            ALUA_DH_NAME, h->group_id, h->rel_port);
        }

        return err;
}

static char print_alua_state(int state)
{
        switch (state) {
        case TPGS_STATE_OPTIMIZED:
                return 'A';
        case TPGS_STATE_NONOPTIMIZED:
                return 'N';
        case TPGS_STATE_STANDBY:
                return 'S';
        case TPGS_STATE_UNAVAILABLE:
                return 'U';
        case TPGS_STATE_OFFLINE:
                return 'O';
        case TPGS_STATE_TRANSITIONING:
                return 'T';
        default:
                return 'X';
        }
}

static int alua_check_sense(struct scsi_device *sdev,
                            struct scsi_sense_hdr *sense_hdr)
{
        switch (sense_hdr->sense_key) {
        case NOT_READY:
                if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0a)
                        /*
                         * LUN Not Accessible - ALUA state transition
                         */
                        return ADD_TO_MLQUEUE;
                if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0b)
                        /*
                         * LUN Not Accessible -- Target port in standby state
                         */
                        return SUCCESS;
                if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x0c)
                        /*
                         * LUN Not Accessible -- Target port in unavailable state
                         */
                        return SUCCESS;
                if (sense_hdr->asc == 0x04 && sense_hdr->ascq == 0x12)
                        /*
                         * LUN Not Ready -- Offline
                         */
                        return SUCCESS;
                break;
        case UNIT_ATTENTION:
                if (sense_hdr->asc == 0x29 && sense_hdr->ascq == 0x00)
                        /*
                         * Power On, Reset, or Bus Device Reset, just retry.
                         */
                        return ADD_TO_MLQUEUE;
                if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x06) {
                        /*
                         * ALUA state changed
                         */
                        return ADD_TO_MLQUEUE;
                }
                if (sense_hdr->asc == 0x2a && sense_hdr->ascq == 0x07) {
                        /*
                         * Implicit ALUA state transition failed
                         */
                        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_stpg - Evaluate SET TARGET GROUP STATES
 * @sdev: the device to be evaluated
 * @state: the new target group state
 *
 * Send a SET TARGET GROUP STATES command to the device.
 * We only have to test here if we should resubmit the command;
 * any other error is assumed as a failure.
 */
static int alua_stpg(struct scsi_device *sdev, int state,
                     struct alua_dh_data *h)
{
        struct scsi_sense_hdr sense_hdr;
        unsigned err;
        int retry = ALUA_FAILOVER_RETRIES;

 retry:
        err = submit_stpg(sdev, h);
        if (err == SCSI_DH_IO && h->senselen > 0) {
                err = scsi_normalize_sense(h->sense, SCSI_SENSE_BUFFERSIZE,
                                           &sense_hdr);
                if (!err)
                        return SCSI_DH_IO;
                err = alua_check_sense(sdev, &sense_hdr);
                if (retry > 0 && err == ADD_TO_MLQUEUE) {
                        retry--;
                        goto retry;
                }
                sdev_printk(KERN_INFO, sdev,
                            "%s: stpg sense code: %02x/%02x/%02x\n",
                            ALUA_DH_NAME, sense_hdr.sense_key,
                            sense_hdr.asc, sense_hdr.ascq);
                err = SCSI_DH_IO;
        }
        if (err == SCSI_DH_OK) {
                h->state = state;
                sdev_printk(KERN_INFO, sdev,
                            "%s: port group %02x switched to state %c\n",
                            ALUA_DH_NAME, h->group_id,
                            print_alua_state(h->state) );
        }
        return err;
}

/*
 * 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 unuseable.
 */
static int alua_rtpg(struct scsi_device *sdev, struct alua_dh_data *h)
{
        struct scsi_sense_hdr sense_hdr;
        int len, k, off, valid_states = 0;
        char *ucp;
        unsigned err;

 retry:
        err = submit_rtpg(sdev, h);

        if (err == SCSI_DH_IO && h->senselen > 0) {
                err = scsi_normalize_sense(h->sense, SCSI_SENSE_BUFFERSIZE,
                                           &sense_hdr);
                if (!err)
                        return SCSI_DH_IO;

                err = alua_check_sense(sdev, &sense_hdr);
                if (err == ADD_TO_MLQUEUE)
                        goto retry;
                sdev_printk(KERN_INFO, sdev,
                            "%s: rtpg sense code %02x/%02x/%02x\n",
                            ALUA_DH_NAME, sense_hdr.sense_key,
                            sense_hdr.asc, sense_hdr.ascq);
                err = SCSI_DH_IO;
        }
        if (err != SCSI_DH_OK)
                return err;

        len = (h->buff[0] << 24) + (h->buff[1] << 16) +
                (h->buff[2] << 8) + h->buff[3] + 4;

        if (len > h->bufflen) {
                /* Resubmit with the correct length */
                if (realloc_buffer(h, len)) {
                        sdev_printk(KERN_WARNING, sdev,
                                    "%s: kmalloc buffer failed\n",__func__);
                        /* Temporary failure, bypass */
                        return SCSI_DH_DEV_TEMP_BUSY;
                }
                goto retry;
        }

        for (k = 4, ucp = h->buff + 4; k < len; k += off, ucp += off) {
                if (h->group_id == (ucp[2] << 8) + ucp[3]) {
                        h->state = ucp[0] & 0x0f;
                        valid_states = ucp[1];
                }
                off = 8 + (ucp[7] * 4);
        }

        sdev_printk(KERN_INFO, sdev,
                    "%s: port group %02x state %c supports %c%c%c%c%c%c\n",
                    ALUA_DH_NAME, h->group_id, print_alua_state(h->state),
                    valid_states&TPGS_SUPPORT_TRANSITION?'T':'t',
                    valid_states&TPGS_SUPPORT_OFFLINE?'O':'o',
                    valid_states&TPGS_SUPPORT_UNAVAILABLE?'U':'u',
                    valid_states&TPGS_SUPPORT_STANDBY?'S':'s',
                    valid_states&TPGS_SUPPORT_NONOPTIMIZED?'N':'n',
                    valid_states&TPGS_SUPPORT_OPTIMIZED?'A':'a');

        if (h->tpgs & TPGS_MODE_EXPLICIT) {
                switch (h->state) {
                case TPGS_STATE_TRANSITIONING:
                        /* State transition, retry */
                        goto retry;
                        break;
                case TPGS_STATE_OFFLINE:
                        /* Path is offline, fail */
                        err = SCSI_DH_DEV_OFFLINED;
                        break;
                default:
                        break;
                }
        } else {
                /* Only Implicit ALUA support */
                if (h->state == TPGS_STATE_OPTIMIZED ||
                    h->state == TPGS_STATE_NONOPTIMIZED ||
                    h->state == TPGS_STATE_STANDBY)
                        /* Useable path if active */
                        err = SCSI_DH_OK;
                else
                        /* Path unuseable for unavailable/offline */
                        err = SCSI_DH_DEV_OFFLINED;
        }
        return err;
}

/*
 * 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;

        err = alua_std_inquiry(sdev, h);
        if (err != SCSI_DH_OK)
                goto out;

        err = alua_vpd_inquiry(sdev, h);
        if (err != SCSI_DH_OK)
                goto out;

        err = alua_rtpg(sdev, h);
        if (err != SCSI_DH_OK)
                goto out;

out:
        return err;
}

/*
 * 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)
{
        struct alua_dh_data *h = get_alua_data(sdev);
        int err = SCSI_DH_OK;

        if (h->group_id != -1) {
                err = alua_rtpg(sdev, h);
                if (err != SCSI_DH_OK)
                        goto out;
        }

        if (h->tpgs & TPGS_MODE_EXPLICIT && h->state != TPGS_STATE_OPTIMIZED)
                err = alua_stpg(sdev, TPGS_STATE_OPTIMIZED, h);

out:
        return err;
}

/*
 * alua_prep_fn - request callback
 *
 * Fail I/O to all paths not in state
 * active/optimized or active/non-optimized.
 */
static int alua_prep_fn(struct scsi_device *sdev, struct request *req)
{
        struct alua_dh_data *h = get_alua_data(sdev);
        int ret = BLKPREP_OK;

        if (h->state != TPGS_STATE_OPTIMIZED &&
            h->state != TPGS_STATE_NONOPTIMIZED) {
                ret = BLKPREP_KILL;
                req->cmd_flags |= REQ_QUIET;
        }
        return ret;

}

static const struct scsi_dh_devlist alua_dev_list[] = {
        {"HP", "MSA VOLUME" },
        {"HP", "HSV101" },
        {"HP", "HSV111" },
        {"HP", "HSV200" },
        {"HP", "HSV210" },
        {"HP", "HSV300" },
        {"IBM", "2107900" },
        {"IBM", "2145" },
        {"Pillar", "Axiom" },
        {"Intel", "Multi-Flex"},
        {NULL, NULL}
};

static int alua_bus_attach(struct scsi_device *sdev);
static void alua_bus_detach(struct scsi_device *sdev);

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

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

        scsi_dh_data = kzalloc(sizeof(struct scsi_device_handler *)
                               + sizeof(*h) , GFP_KERNEL);
        if (!scsi_dh_data) {
                sdev_printk(KERN_ERR, sdev, "%s: Attach failed\n",
                            ALUA_DH_NAME);
                return -ENOMEM;
        }

        scsi_dh_data->scsi_dh = &alua_dh;
        h = (struct alua_dh_data *) scsi_dh_data->buf;
        h->tpgs = TPGS_MODE_UNINITIALIZED;
        h->state = TPGS_STATE_OPTIMIZED;
        h->group_id = -1;
        h->rel_port = -1;
        h->buff = h->inq;
        h->bufflen = ALUA_INQUIRY_SIZE;

        err = alua_initialize(sdev, h);
        if (err != SCSI_DH_OK)
                goto failed;

        if (!try_module_get(THIS_MODULE))
                goto failed;

        spin_lock_irqsave(sdev->request_queue->queue_lock, flags);
        sdev->scsi_dh_data = scsi_dh_data;
        spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);

        return 0;

failed:
        kfree(scsi_dh_data);
        sdev_printk(KERN_ERR, sdev, "%s: not attached\n", ALUA_DH_NAME);
        return -EINVAL;
}

/*
 * alua_bus_detach - Detach device handler
 * @sdev: device to be detached from
 */
static void alua_bus_detach(struct scsi_device *sdev)
{
        struct scsi_dh_data *scsi_dh_data;
        struct alua_dh_data *h;
        unsigned long flags;

        spin_lock_irqsave(sdev->request_queue->queue_lock, flags);
        scsi_dh_data = sdev->scsi_dh_data;
        sdev->scsi_dh_data = NULL;
        spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);

        h = (struct alua_dh_data *) scsi_dh_data->buf;
        if (h->buff && h->inq != h->buff)
                kfree(h->buff);
        kfree(scsi_dh_data);
        module_put(THIS_MODULE);
        sdev_printk(KERN_NOTICE, sdev, "%s: Detached\n", ALUA_DH_NAME);
}

static int __init alua_init(void)
{
        int r;

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

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

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);