/*
 * Xen SCSI frontend driver
 *
 * Copyright (c) 2008, FUJITSU Limited
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/wait.h>
#include <linux/interrupt.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
#include <linux/blkdev.h>
#include <linux/pfn.h>
#include <linux/slab.h>
#include <linux/bitops.h>

#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi.h>
#include <scsi/scsi_host.h>

#include <xen/xen.h>
#include <xen/xenbus.h>
#include <xen/grant_table.h>
#include <xen/events.h>
#include <xen/page.h>

#include <xen/interface/grant_table.h>
#include <xen/interface/io/vscsiif.h>
#include <xen/interface/io/protocols.h>

#include <asm/xen/hypervisor.h>


#define GRANT_INVALID_REF       0

#define VSCSIFRONT_OP_ADD_LUN   1
#define VSCSIFRONT_OP_DEL_LUN   2

/* Tuning point. */
#define VSCSIIF_DEFAULT_CMD_PER_LUN 10
#define VSCSIIF_MAX_TARGET          64
#define VSCSIIF_MAX_LUN             255

#define VSCSIIF_RING_SIZE       __CONST_RING_SIZE(vscsiif, PAGE_SIZE)
#define VSCSIIF_MAX_REQS        VSCSIIF_RING_SIZE

#define vscsiif_grants_sg(_sg)  (PFN_UP((_sg) *         \
                                sizeof(struct scsiif_request_segment)))

struct vscsifrnt_shadow {
        /* command between backend and frontend */
        unsigned char act;
        uint16_t rqid;

        unsigned int nr_grants;         /* number of grants in gref[] */
        struct scsiif_request_segment *sg;      /* scatter/gather elements */

        /* Do reset or abort function. */
        wait_queue_head_t wq_reset;     /* reset work queue           */
        int wait_reset;                 /* reset work queue condition */
        int32_t rslt_reset;             /* reset response status:     */
                                        /* SUCCESS or FAILED or:      */
#define RSLT_RESET_WAITING      0
#define RSLT_RESET_ERR          -1

        /* Requested struct scsi_cmnd is stored from kernel. */
        struct scsi_cmnd *sc;
        int gref[vscsiif_grants_sg(SG_ALL) + SG_ALL];
};

struct vscsifrnt_info {
        struct xenbus_device *dev;

        struct Scsi_Host *host;
        int host_active;

        unsigned int evtchn;
        unsigned int irq;

        grant_ref_t ring_ref;
        struct vscsiif_front_ring ring;
        struct vscsiif_response ring_rsp;

        spinlock_t shadow_lock;
        DECLARE_BITMAP(shadow_free_bitmap, VSCSIIF_MAX_REQS);
        struct vscsifrnt_shadow *shadow[VSCSIIF_MAX_REQS];

        wait_queue_head_t wq_sync;
        unsigned int wait_ring_available:1;

        char dev_state_path[64];
        struct task_struct *curr;
};

static DEFINE_MUTEX(scsifront_mutex);

static void scsifront_wake_up(struct vscsifrnt_info *info)
{
        info->wait_ring_available = 0;
        wake_up(&info->wq_sync);
}

static int scsifront_get_rqid(struct vscsifrnt_info *info)
{
        unsigned long flags;
        int free;

        spin_lock_irqsave(&info->shadow_lock, flags);

        free = find_first_bit(info->shadow_free_bitmap, VSCSIIF_MAX_REQS);
        __clear_bit(free, info->shadow_free_bitmap);

        spin_unlock_irqrestore(&info->shadow_lock, flags);

        return free;
}

static int _scsifront_put_rqid(struct vscsifrnt_info *info, uint32_t id)
{
        int empty = bitmap_empty(info->shadow_free_bitmap, VSCSIIF_MAX_REQS);

        __set_bit(id, info->shadow_free_bitmap);
        info->shadow[id] = NULL;

        return empty || info->wait_ring_available;
}

static void scsifront_put_rqid(struct vscsifrnt_info *info, uint32_t id)
{
        unsigned long flags;
        int kick;

        spin_lock_irqsave(&info->shadow_lock, flags);
        kick = _scsifront_put_rqid(info, id);
        spin_unlock_irqrestore(&info->shadow_lock, flags);

        if (kick)
                scsifront_wake_up(info);
}

static struct vscsiif_request *scsifront_pre_req(struct vscsifrnt_info *info)
{
        struct vscsiif_front_ring *ring = &(info->ring);
        struct vscsiif_request *ring_req;
        uint32_t id;

        id = scsifront_get_rqid(info);  /* use id in response */
        if (id >= VSCSIIF_MAX_REQS)
                return NULL;

        ring_req = RING_GET_REQUEST(&(info->ring), ring->req_prod_pvt);

        ring->req_prod_pvt++;

        ring_req->rqid = (uint16_t)id;

        return ring_req;
}

static void scsifront_do_request(struct vscsifrnt_info *info)
{
        struct vscsiif_front_ring *ring = &(info->ring);
        int notify;

        RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(ring, notify);
        if (notify)
                notify_remote_via_irq(info->irq);
}

static void scsifront_gnttab_done(struct vscsifrnt_info *info, uint32_t id)
{
        struct vscsifrnt_shadow *s = info->shadow[id];
        int i;

        if (s->sc->sc_data_direction == DMA_NONE)
                return;

        for (i = 0; i < s->nr_grants; i++) {
                if (unlikely(gnttab_query_foreign_access(s->gref[i]) != 0)) {
                        shost_printk(KERN_ALERT, info->host, KBUILD_MODNAME
                                     "grant still in use by backend\n");
                        BUG();
                }
                gnttab_end_foreign_access(s->gref[i], 0, 0UL);
        }

        kfree(s->sg);
}

static void scsifront_cdb_cmd_done(struct vscsifrnt_info *info,
                                   struct vscsiif_response *ring_rsp)
{
        struct scsi_cmnd *sc;
        uint32_t id;
        uint8_t sense_len;

        id = ring_rsp->rqid;
        sc = info->shadow[id]->sc;

        BUG_ON(sc == NULL);

        scsifront_gnttab_done(info, id);
        scsifront_put_rqid(info, id);

        sc->result = ring_rsp->rslt;
        scsi_set_resid(sc, ring_rsp->residual_len);

        sense_len = min_t(uint8_t, VSCSIIF_SENSE_BUFFERSIZE,
                          ring_rsp->sense_len);

        if (sense_len)
                memcpy(sc->sense_buffer, ring_rsp->sense_buffer, sense_len);

        sc->scsi_done(sc);
}

static void scsifront_sync_cmd_done(struct vscsifrnt_info *info,
                                    struct vscsiif_response *ring_rsp)
{
        uint16_t id = ring_rsp->rqid;
        unsigned long flags;
        struct vscsifrnt_shadow *shadow = info->shadow[id];
        int kick;

        spin_lock_irqsave(&info->shadow_lock, flags);
        shadow->wait_reset = 1;
        switch (shadow->rslt_reset) {
        case RSLT_RESET_WAITING:
                shadow->rslt_reset = ring_rsp->rslt;
                break;
        case RSLT_RESET_ERR:
                kick = _scsifront_put_rqid(info, id);
                spin_unlock_irqrestore(&info->shadow_lock, flags);
                kfree(shadow);
                if (kick)
                        scsifront_wake_up(info);
                return;
        default:
                shost_printk(KERN_ERR, info->host, KBUILD_MODNAME
                             "bad reset state %d, possibly leaking %u\n",
                             shadow->rslt_reset, id);
                break;
        }
        spin_unlock_irqrestore(&info->shadow_lock, flags);

        wake_up(&shadow->wq_reset);
}

static int scsifront_cmd_done(struct vscsifrnt_info *info)
{
        struct vscsiif_response *ring_rsp;
        RING_IDX i, rp;
        int more_to_do = 0;
        unsigned long flags;

        spin_lock_irqsave(info->host->host_lock, flags);

        rp = info->ring.sring->rsp_prod;
        rmb();  /* ordering required respective to dom0 */
        for (i = info->ring.rsp_cons; i != rp; i++) {

                ring_rsp = RING_GET_RESPONSE(&info->ring, i);

                if (WARN(ring_rsp->rqid >= VSCSIIF_MAX_REQS ||
                         test_bit(ring_rsp->rqid, info->shadow_free_bitmap),
                         "illegal rqid %u returned by backend!\n",
                         ring_rsp->rqid))
                        continue;

                if (info->shadow[ring_rsp->rqid]->act == VSCSIIF_ACT_SCSI_CDB)
                        scsifront_cdb_cmd_done(info, ring_rsp);
                else
                        scsifront_sync_cmd_done(info, ring_rsp);
        }

        info->ring.rsp_cons = i;

        if (i != info->ring.req_prod_pvt)
                RING_FINAL_CHECK_FOR_RESPONSES(&info->ring, more_to_do);
        else
                info->ring.sring->rsp_event = i + 1;

        info->wait_ring_available = 0;

        spin_unlock_irqrestore(info->host->host_lock, flags);

        wake_up(&info->wq_sync);

        return more_to_do;
}

static irqreturn_t scsifront_irq_fn(int irq, void *dev_id)
{
        struct vscsifrnt_info *info = dev_id;

        while (scsifront_cmd_done(info))
                /* Yield point for this unbounded loop. */
                cond_resched();

        return IRQ_HANDLED;
}

static int map_data_for_request(struct vscsifrnt_info *info,
                                struct scsi_cmnd *sc,
                                struct vscsiif_request *ring_req,
                                struct vscsifrnt_shadow *shadow)
{
        grant_ref_t gref_head;
        struct page *page;
        int err, ref, ref_cnt = 0;
        int grant_ro = (sc->sc_data_direction == DMA_TO_DEVICE);
        unsigned int i, off, len, bytes;
        unsigned int data_len = scsi_bufflen(sc);
        unsigned int data_grants = 0, seg_grants = 0;
        struct scatterlist *sg;
        unsigned long mfn;
        struct scsiif_request_segment *seg;

        ring_req->nr_segments = 0;
        if (sc->sc_data_direction == DMA_NONE || !data_len)
                return 0;

        scsi_for_each_sg(sc, sg, scsi_sg_count(sc), i)
                data_grants += PFN_UP(sg->offset + sg->length);

        if (data_grants > VSCSIIF_SG_TABLESIZE) {
                if (data_grants > info->host->sg_tablesize) {
                        shost_printk(KERN_ERR, info->host, KBUILD_MODNAME
                             "Unable to map request_buffer for command!\n");
                        return -E2BIG;
                }
                seg_grants = vscsiif_grants_sg(data_grants);
                shadow->sg = kcalloc(data_grants,
                        sizeof(struct scsiif_request_segment), GFP_ATOMIC);
                if (!shadow->sg)
                        return -ENOMEM;
        }
        seg = shadow->sg ? : ring_req->seg;

        err = gnttab_alloc_grant_references(seg_grants + data_grants,
                                            &gref_head);
        if (err) {
                kfree(shadow->sg);
                shost_printk(KERN_ERR, info->host, KBUILD_MODNAME
                             "gnttab_alloc_grant_references() error\n");
                return -ENOMEM;
        }

        if (seg_grants) {
                page = virt_to_page(seg);
                off = (unsigned long)seg & ~PAGE_MASK;
                len = sizeof(struct scsiif_request_segment) * data_grants;
                while (len > 0) {
                        bytes = min_t(unsigned int, len, PAGE_SIZE - off);

                        ref = gnttab_claim_grant_reference(&gref_head);
                        BUG_ON(ref == -ENOSPC);

                        mfn = pfn_to_mfn(page_to_pfn(page));
                        gnttab_grant_foreign_access_ref(ref,
                                info->dev->otherend_id, mfn, 1);
                        shadow->gref[ref_cnt] = ref;
                        ring_req->seg[ref_cnt].gref   = ref;
                        ring_req->seg[ref_cnt].offset = (uint16_t)off;
                        ring_req->seg[ref_cnt].length = (uint16_t)bytes;

                        page++;
                        len -= bytes;
                        off = 0;
                        ref_cnt++;
                }
                BUG_ON(seg_grants < ref_cnt);
                seg_grants = ref_cnt;
        }

        scsi_for_each_sg(sc, sg, scsi_sg_count(sc), i) {
                page = sg_page(sg);
                off = sg->offset;
                len = sg->length;

                while (len > 0 && data_len > 0) {
                        /*
                         * sg sends a scatterlist that is larger than
                         * the data_len it wants transferred for certain
                         * IO sizes.
                         */
                        bytes = min_t(unsigned int, len, PAGE_SIZE - off);
                        bytes = min(bytes, data_len);

                        ref = gnttab_claim_grant_reference(&gref_head);
                        BUG_ON(ref == -ENOSPC);

                        mfn = pfn_to_mfn(page_to_pfn(page));
                        gnttab_grant_foreign_access_ref(ref,
                                info->dev->otherend_id, mfn, grant_ro);

                        shadow->gref[ref_cnt] = ref;
                        seg->gref   = ref;
                        seg->offset = (uint16_t)off;
                        seg->length = (uint16_t)bytes;

                        page++;
                        seg++;
                        len -= bytes;
                        data_len -= bytes;
                        off = 0;
                        ref_cnt++;
                }
        }

        if (seg_grants)
                ring_req->nr_segments = VSCSIIF_SG_GRANT | seg_grants;
        else
                ring_req->nr_segments = (uint8_t)ref_cnt;
        shadow->nr_grants = ref_cnt;

        return 0;
}

static struct vscsiif_request *scsifront_command2ring(
                struct vscsifrnt_info *info, struct scsi_cmnd *sc,
                struct vscsifrnt_shadow *shadow)
{
        struct vscsiif_request *ring_req;

        memset(shadow, 0, sizeof(*shadow));

        ring_req = scsifront_pre_req(info);
        if (!ring_req)
                return NULL;

        info->shadow[ring_req->rqid] = shadow;
        shadow->rqid = ring_req->rqid;

        ring_req->id      = sc->device->id;
        ring_req->lun     = sc->device->lun;
        ring_req->channel = sc->device->channel;
        ring_req->cmd_len = sc->cmd_len;

        BUG_ON(sc->cmd_len > VSCSIIF_MAX_COMMAND_SIZE);

        memcpy(ring_req->cmnd, sc->cmnd, sc->cmd_len);

        ring_req->sc_data_direction   = (uint8_t)sc->sc_data_direction;
        ring_req->timeout_per_command = sc->request->timeout / HZ;

        return ring_req;
}

static int scsifront_queuecommand(struct Scsi_Host *shost,
                                  struct scsi_cmnd *sc)
{
        struct vscsifrnt_info *info = shost_priv(shost);
        struct vscsiif_request *ring_req;
        struct vscsifrnt_shadow *shadow = scsi_cmd_priv(sc);
        unsigned long flags;
        int err;
        uint16_t rqid;

        spin_lock_irqsave(shost->host_lock, flags);
        if (RING_FULL(&info->ring))
                goto busy;

        ring_req = scsifront_command2ring(info, sc, shadow);
        if (!ring_req)
                goto busy;

        sc->result = 0;

        rqid = ring_req->rqid;
        ring_req->act = VSCSIIF_ACT_SCSI_CDB;

        shadow->sc  = sc;
        shadow->act = VSCSIIF_ACT_SCSI_CDB;

        err = map_data_for_request(info, sc, ring_req, shadow);
        if (err < 0) {
                pr_debug("%s: err %d\n", __func__, err);
                scsifront_put_rqid(info, rqid);
                spin_unlock_irqrestore(shost->host_lock, flags);
                if (err == -ENOMEM)
                        return SCSI_MLQUEUE_HOST_BUSY;
                sc->result = DID_ERROR << 16;
                sc->scsi_done(sc);
                return 0;
        }

        scsifront_do_request(info);
        spin_unlock_irqrestore(shost->host_lock, flags);

        return 0;

busy:
        spin_unlock_irqrestore(shost->host_lock, flags);
        pr_debug("%s: busy\n", __func__);
        return SCSI_MLQUEUE_HOST_BUSY;
}

/*
 * Any exception handling (reset or abort) must be forwarded to the backend.
 * We have to wait until an answer is returned. This answer contains the
 * result to be returned to the requestor.
 */
static int scsifront_action_handler(struct scsi_cmnd *sc, uint8_t act)
{
        struct Scsi_Host *host = sc->device->host;
        struct vscsifrnt_info *info = shost_priv(host);
        struct vscsifrnt_shadow *shadow, *s = scsi_cmd_priv(sc);
        struct vscsiif_request *ring_req;
        int err = 0;

        shadow = kmalloc(sizeof(*shadow), GFP_NOIO);
        if (!shadow)
                return FAILED;

        spin_lock_irq(host->host_lock);

        for (;;) {
                if (!RING_FULL(&info->ring)) {
                        ring_req = scsifront_command2ring(info, sc, shadow);
                        if (ring_req)
                                break;
                }
                if (err) {
                        spin_unlock_irq(host->host_lock);
                        kfree(shadow);
                        return FAILED;
                }
                info->wait_ring_available = 1;
                spin_unlock_irq(host->host_lock);
                err = wait_event_interruptible(info->wq_sync,
                                               !info->wait_ring_available);
                spin_lock_irq(host->host_lock);
        }

        ring_req->act = act;
        ring_req->ref_rqid = s->rqid;

        shadow->act = act;
        shadow->rslt_reset = RSLT_RESET_WAITING;
        init_waitqueue_head(&shadow->wq_reset);

        ring_req->nr_segments = 0;

        scsifront_do_request(info);

        spin_unlock_irq(host->host_lock);
        err = wait_event_interruptible(shadow->wq_reset, shadow->wait_reset);
        spin_lock_irq(host->host_lock);

        if (!err) {
                err = shadow->rslt_reset;
                scsifront_put_rqid(info, shadow->rqid);
                kfree(shadow);
        } else {
                spin_lock(&info->shadow_lock);
                shadow->rslt_reset = RSLT_RESET_ERR;
                spin_unlock(&info->shadow_lock);
                err = FAILED;
        }

        spin_unlock_irq(host->host_lock);
        return err;
}

static int scsifront_eh_abort_handler(struct scsi_cmnd *sc)
{
        pr_debug("%s\n", __func__);
        return scsifront_action_handler(sc, VSCSIIF_ACT_SCSI_ABORT);
}

static int scsifront_dev_reset_handler(struct scsi_cmnd *sc)
{
        pr_debug("%s\n", __func__);
        return scsifront_action_handler(sc, VSCSIIF_ACT_SCSI_RESET);
}

static int scsifront_sdev_configure(struct scsi_device *sdev)
{
        struct vscsifrnt_info *info = shost_priv(sdev->host);

        if (info && current == info->curr)
                xenbus_printf(XBT_NIL, info->dev->nodename,
                              info->dev_state_path, "%d", XenbusStateConnected);

        return 0;
}

static void scsifront_sdev_destroy(struct scsi_device *sdev)
{
        struct vscsifrnt_info *info = shost_priv(sdev->host);

        if (info && current == info->curr)
                xenbus_printf(XBT_NIL, info->dev->nodename,
                              info->dev_state_path, "%d", XenbusStateClosed);
}

static struct scsi_host_template scsifront_sht = {
        .module                 = THIS_MODULE,
        .name                   = "Xen SCSI frontend driver",
        .queuecommand           = scsifront_queuecommand,
        .eh_abort_handler       = scsifront_eh_abort_handler,
        .eh_device_reset_handler = scsifront_dev_reset_handler,
        .slave_configure        = scsifront_sdev_configure,
        .slave_destroy          = scsifront_sdev_destroy,
        .cmd_per_lun            = VSCSIIF_DEFAULT_CMD_PER_LUN,
        .can_queue              = VSCSIIF_MAX_REQS,
        .this_id                = -1,
        .cmd_size               = sizeof(struct vscsifrnt_shadow),
        .sg_tablesize           = VSCSIIF_SG_TABLESIZE,
        .use_clustering         = DISABLE_CLUSTERING,
        .proc_name              = "scsifront",
};

static int scsifront_alloc_ring(struct vscsifrnt_info *info)
{
        struct xenbus_device *dev = info->dev;
        struct vscsiif_sring *sring;
        int err = -ENOMEM;

        /***** Frontend to Backend ring start *****/
        sring = (struct vscsiif_sring *)__get_free_page(GFP_KERNEL);
        if (!sring) {
                xenbus_dev_fatal(dev, err,
                        "fail to allocate shared ring (Front to Back)");
                return err;
        }
        SHARED_RING_INIT(sring);
        FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);

        err = xenbus_grant_ring(dev, virt_to_mfn(sring));
        if (err < 0) {
                free_page((unsigned long)sring);
                xenbus_dev_fatal(dev, err,
                        "fail to grant shared ring (Front to Back)");
                return err;
        }
        info->ring_ref = err;

        err = xenbus_alloc_evtchn(dev, &info->evtchn);
        if (err) {
                xenbus_dev_fatal(dev, err, "xenbus_alloc_evtchn");
                goto free_gnttab;
        }

        err = bind_evtchn_to_irq(info->evtchn);
        if (err <= 0) {
                xenbus_dev_fatal(dev, err, "bind_evtchn_to_irq");
                goto free_gnttab;
        }

        info->irq = err;

        err = request_threaded_irq(info->irq, NULL, scsifront_irq_fn,
                                   IRQF_ONESHOT, "scsifront", info);
        if (err) {
                xenbus_dev_fatal(dev, err, "request_threaded_irq");
                goto free_irq;
        }

        return 0;

/* free resource */
free_irq:
        unbind_from_irqhandler(info->irq, info);
free_gnttab:
        gnttab_end_foreign_access(info->ring_ref, 0,
                                  (unsigned long)info->ring.sring);

        return err;
}

static int scsifront_init_ring(struct vscsifrnt_info *info)
{
        struct xenbus_device *dev = info->dev;
        struct xenbus_transaction xbt;
        int err;

        pr_debug("%s\n", __func__);

        err = scsifront_alloc_ring(info);
        if (err)
                return err;
        pr_debug("%s: %u %u\n", __func__, info->ring_ref, info->evtchn);

again:
        err = xenbus_transaction_start(&xbt);
        if (err)
                xenbus_dev_fatal(dev, err, "starting transaction");

        err = xenbus_printf(xbt, dev->nodename, "ring-ref", "%u",
                            info->ring_ref);
        if (err) {
                xenbus_dev_fatal(dev, err, "%s", "writing ring-ref");
                goto fail;
        }

        err = xenbus_printf(xbt, dev->nodename, "event-channel", "%u",
                            info->evtchn);

        if (err) {
                xenbus_dev_fatal(dev, err, "%s", "writing event-channel");
                goto fail;
        }

        err = xenbus_transaction_end(xbt, 0);
        if (err) {
                if (err == -EAGAIN)
                        goto again;
                xenbus_dev_fatal(dev, err, "completing transaction");
                goto free_sring;
        }

        return 0;

fail:
        xenbus_transaction_end(xbt, 1);
free_sring:
        unbind_from_irqhandler(info->irq, info);
        gnttab_end_foreign_access(info->ring_ref, 0,
                                  (unsigned long)info->ring.sring);

        return err;
}


static int scsifront_probe(struct xenbus_device *dev,
                           const struct xenbus_device_id *id)
{
        struct vscsifrnt_info *info;
        struct Scsi_Host *host;
        int err = -ENOMEM;
        char name[TASK_COMM_LEN];

        host = scsi_host_alloc(&scsifront_sht, sizeof(*info));
        if (!host) {
                xenbus_dev_fatal(dev, err, "fail to allocate scsi host");
                return err;
        }
        info = (struct vscsifrnt_info *)host->hostdata;

        dev_set_drvdata(&dev->dev, info);
        info->dev = dev;

        bitmap_fill(info->shadow_free_bitmap, VSCSIIF_MAX_REQS);

        err = scsifront_init_ring(info);
        if (err) {
                scsi_host_put(host);
                return err;
        }

        init_waitqueue_head(&info->wq_sync);
        spin_lock_init(&info->shadow_lock);

        snprintf(name, TASK_COMM_LEN, "vscsiif.%d", host->host_no);

        host->max_id      = VSCSIIF_MAX_TARGET;
        host->max_channel = 0;
        host->max_lun     = VSCSIIF_MAX_LUN;
        host->max_sectors = (host->sg_tablesize - 1) * PAGE_SIZE / 512;
        host->max_cmd_len = VSCSIIF_MAX_COMMAND_SIZE;

        err = scsi_add_host(host, &dev->dev);
        if (err) {
                dev_err(&dev->dev, "fail to add scsi host %d\n", err);
                goto free_sring;
        }
        info->host = host;
        info->host_active = 1;

        xenbus_switch_state(dev, XenbusStateInitialised);

        return 0;

free_sring:
        unbind_from_irqhandler(info->irq, info);
        gnttab_end_foreign_access(info->ring_ref, 0,
                                  (unsigned long)info->ring.sring);
        scsi_host_put(host);
        return err;
}

static int scsifront_remove(struct xenbus_device *dev)
{
        struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);

        pr_debug("%s: %s removed\n", __func__, dev->nodename);

        mutex_lock(&scsifront_mutex);
        if (info->host_active) {
                /* Scsi_host not yet removed */
                scsi_remove_host(info->host);
                info->host_active = 0;
        }
        mutex_unlock(&scsifront_mutex);

        gnttab_end_foreign_access(info->ring_ref, 0,
                                  (unsigned long)info->ring.sring);
        unbind_from_irqhandler(info->irq, info);

        scsi_host_put(info->host);

        return 0;
}

static void scsifront_disconnect(struct vscsifrnt_info *info)
{
        struct xenbus_device *dev = info->dev;
        struct Scsi_Host *host = info->host;

        pr_debug("%s: %s disconnect\n", __func__, dev->nodename);

        /*
         * When this function is executed, all devices of
         * Frontend have been deleted.
         * Therefore, it need not block I/O before remove_host.
         */

        mutex_lock(&scsifront_mutex);
        if (info->host_active) {
                scsi_remove_host(host);
                info->host_active = 0;
        }
        mutex_unlock(&scsifront_mutex);

        xenbus_frontend_closed(dev);
}

static void scsifront_do_lun_hotplug(struct vscsifrnt_info *info, int op)
{
        struct xenbus_device *dev = info->dev;
        int i, err = 0;
        char str[64];
        char **dir;
        unsigned int dir_n = 0;
        unsigned int device_state;
        unsigned int hst, chn, tgt, lun;
        struct scsi_device *sdev;

        dir = xenbus_directory(XBT_NIL, dev->otherend, "vscsi-devs", &dir_n);
        if (IS_ERR(dir))
                return;

        /* mark current task as the one allowed to modify device states */
        BUG_ON(info->curr);
        info->curr = current;

        for (i = 0; i < dir_n; i++) {
                /* read status */
                snprintf(str, sizeof(str), "vscsi-devs/%s/state", dir[i]);
                err = xenbus_scanf(XBT_NIL, dev->otherend, str, "%u",
                                   &device_state);
                if (XENBUS_EXIST_ERR(err))
                        continue;

                /* virtual SCSI device */
                snprintf(str, sizeof(str), "vscsi-devs/%s/v-dev", dir[i]);
                err = xenbus_scanf(XBT_NIL, dev->otherend, str,
                                   "%u:%u:%u:%u", &hst, &chn, &tgt, &lun);
                if (XENBUS_EXIST_ERR(err))
                        continue;

                /*
                 * Front device state path, used in slave_configure called
                 * on successfull scsi_add_device, and in slave_destroy called
                 * on remove of a device.
                 */
                snprintf(info->dev_state_path, sizeof(info->dev_state_path),
                         "vscsi-devs/%s/state", dir[i]);

                switch (op) {
                case VSCSIFRONT_OP_ADD_LUN:
                        if (device_state != XenbusStateInitialised)
                                break;

                        if (scsi_add_device(info->host, chn, tgt, lun)) {
                                dev_err(&dev->dev, "scsi_add_device\n");
                                xenbus_printf(XBT_NIL, dev->nodename,
                                              info->dev_state_path,
                                              "%d", XenbusStateClosed);
                        }
                        break;
                case VSCSIFRONT_OP_DEL_LUN:
                        if (device_state != XenbusStateClosing)
                                break;

                        sdev = scsi_device_lookup(info->host, chn, tgt, lun);
                        if (sdev) {
                                scsi_remove_device(sdev);
                                scsi_device_put(sdev);
                        }
                        break;
                default:
                        break;
                }
        }

        info->curr = NULL;

        kfree(dir);
}

static void scsifront_read_backend_params(struct xenbus_device *dev,
                                          struct vscsifrnt_info *info)
{
        unsigned int sg_grant;
        int ret;
        struct Scsi_Host *host = info->host;

        ret = xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg-grant", "%u",
                           &sg_grant);
        if (ret == 1 && sg_grant) {
                sg_grant = min_t(unsigned int, sg_grant, SG_ALL);
                sg_grant = max_t(unsigned int, sg_grant, VSCSIIF_SG_TABLESIZE);
                host->sg_tablesize = min_t(unsigned int, sg_grant,
                        VSCSIIF_SG_TABLESIZE * PAGE_SIZE /
                        sizeof(struct scsiif_request_segment));
                host->max_sectors = (host->sg_tablesize - 1) * PAGE_SIZE / 512;
        }
        dev_info(&dev->dev, "using up to %d SG entries\n", host->sg_tablesize);
}

static void scsifront_backend_changed(struct xenbus_device *dev,
                                      enum xenbus_state backend_state)
{
        struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);

        pr_debug("%s: %p %u %u\n", __func__, dev, dev->state, backend_state);

        switch (backend_state) {
        case XenbusStateUnknown:
        case XenbusStateInitialising:
        case XenbusStateInitWait:
        case XenbusStateInitialised:
                break;

        case XenbusStateConnected:
                scsifront_read_backend_params(dev, info);
                if (xenbus_read_driver_state(dev->nodename) ==
                    XenbusStateInitialised)
                        scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_ADD_LUN);

                if (dev->state != XenbusStateConnected)
                        xenbus_switch_state(dev, XenbusStateConnected);
                break;

        case XenbusStateClosed:
                if (dev->state == XenbusStateClosed)
                        break;
                /* Missed the backend's Closing state -- fallthrough */
        case XenbusStateClosing:
                scsifront_disconnect(info);
                break;

        case XenbusStateReconfiguring:
                scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_DEL_LUN);
                xenbus_switch_state(dev, XenbusStateReconfiguring);
                break;

        case XenbusStateReconfigured:
                scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_ADD_LUN);
                xenbus_switch_state(dev, XenbusStateConnected);
                break;
        }
}

static const struct xenbus_device_id scsifront_ids[] = {
        { "vscsi" },
        { "" }
};

static struct xenbus_driver scsifront_driver = {
        .ids                    = scsifront_ids,
        .probe                  = scsifront_probe,
        .remove                 = scsifront_remove,
        .otherend_changed       = scsifront_backend_changed,
};

static int __init scsifront_init(void)
{
        if (!xen_domain())
                return -ENODEV;

        return xenbus_register_frontend(&scsifront_driver);
}
module_init(scsifront_init);

static void __exit scsifront_exit(void)
{
        xenbus_unregister_driver(&scsifront_driver);
}
module_exit(scsifront_exit);

MODULE_DESCRIPTION("Xen SCSI frontend driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("xen:vscsi");
MODULE_AUTHOR("Juergen Gross <jgross@suse.com>");