/*
 * 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 VSCSIFRONT_OP_ADD_LUN   1
#define VSCSIFRONT_OP_DEL_LUN   2
#define VSCSIFRONT_OP_READD_LUN 3

/* 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;
        uint8_t nr_segments;
        uint16_t rqid;
        uint16_t ref_rqid;

        bool inflight;

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

        /* 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;
        enum {
                STATE_INACTIVE,
                STATE_ACTIVE,
                STATE_ERROR
        }  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];

        /* Following items are protected by the host lock. */
        wait_queue_head_t wq_sync;
        wait_queue_head_t wq_pause;
        unsigned int wait_ring_available:1;
        unsigned int waiting_pause:1;
        unsigned int pause:1;
        unsigned callers;

        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 int scsifront_do_request(struct vscsifrnt_info *info,
                                struct vscsifrnt_shadow *shadow)
{
        struct vscsiif_front_ring *ring = &(info->ring);
        struct vscsiif_request *ring_req;
        struct scsi_cmnd *sc = shadow->sc;
        uint32_t id;
        int i, notify;

        if (RING_FULL(&info->ring))
                return -EBUSY;

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

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

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

        ring_req->rqid        = id;
        ring_req->act         = shadow->act;
        ring_req->ref_rqid    = shadow->ref_rqid;
        ring_req->nr_segments = shadow->nr_segments;

        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 = scsi_cmd_to_rq(sc)->timeout / HZ;

        for (i = 0; i < (shadow->nr_segments & ~VSCSIIF_SG_GRANT); i++)
                ring_req->seg[i] = shadow->seg[i];

        shadow->inflight = true;

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

        return 0;
}

static void scsifront_set_error(struct vscsifrnt_info *info, const char *msg)
{
        shost_printk(KERN_ERR, info->host, KBUILD_MODNAME "%s\n"
                     "Disabling device for further use\n", msg);
        info->host_active = STATE_ERROR;
}

static void scsifront_gnttab_done(struct vscsifrnt_info *info,
                                  struct vscsifrnt_shadow *shadow)
{
        int i;

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

        for (i = 0; i < shadow->nr_grants; i++) {
                if (unlikely(!gnttab_try_end_foreign_access(shadow->gref[i]))) {
                        scsifront_set_error(info, "grant still in use by backend");
                        return;
                }
        }

        kfree(shadow->sg);
}

static unsigned int scsifront_host_byte(int32_t rslt)
{
        switch (XEN_VSCSIIF_RSLT_HOST(rslt)) {
        case XEN_VSCSIIF_RSLT_HOST_OK:
                return DID_OK;
        case XEN_VSCSIIF_RSLT_HOST_NO_CONNECT:
                return DID_NO_CONNECT;
        case XEN_VSCSIIF_RSLT_HOST_BUS_BUSY:
                return DID_BUS_BUSY;
        case XEN_VSCSIIF_RSLT_HOST_TIME_OUT:
                return DID_TIME_OUT;
        case XEN_VSCSIIF_RSLT_HOST_BAD_TARGET:
                return DID_BAD_TARGET;
        case XEN_VSCSIIF_RSLT_HOST_ABORT:
                return DID_ABORT;
        case XEN_VSCSIIF_RSLT_HOST_PARITY:
                return DID_PARITY;
        case XEN_VSCSIIF_RSLT_HOST_ERROR:
                return DID_ERROR;
        case XEN_VSCSIIF_RSLT_HOST_RESET:
                return DID_RESET;
        case XEN_VSCSIIF_RSLT_HOST_BAD_INTR:
                return DID_BAD_INTR;
        case XEN_VSCSIIF_RSLT_HOST_PASSTHROUGH:
                return DID_PASSTHROUGH;
        case XEN_VSCSIIF_RSLT_HOST_SOFT_ERROR:
                return DID_SOFT_ERROR;
        case XEN_VSCSIIF_RSLT_HOST_IMM_RETRY:
                return DID_IMM_RETRY;
        case XEN_VSCSIIF_RSLT_HOST_REQUEUE:
                return DID_REQUEUE;
        case XEN_VSCSIIF_RSLT_HOST_TRANSPORT_DISRUPTED:
                return DID_TRANSPORT_DISRUPTED;
        case XEN_VSCSIIF_RSLT_HOST_TRANSPORT_FAILFAST:
                return DID_TRANSPORT_FAILFAST;
        case XEN_VSCSIIF_RSLT_HOST_TRANSPORT_MARGINAL:
                return DID_TRANSPORT_MARGINAL;
        default:
                return DID_ERROR;
        }
}

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

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

        BUG_ON(sc == NULL);

        scsifront_gnttab_done(info, shadow);
        if (info->host_active == STATE_ERROR)
                return;
        scsifront_put_rqid(info, id);

        set_host_byte(sc, scsifront_host_byte(ring_rsp->rslt));
        set_status_byte(sc, XEN_VSCSIIF_RSLT_STATUS(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);

        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:
                if (ring_rsp->rslt == XEN_VSCSIIF_RSLT_RESET_SUCCESS)
                        shadow->rslt_reset = SUCCESS;
                else
                        shadow->rslt_reset = FAILED;
                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:
                scsifront_set_error(info, "bad reset state");
                break;
        }
        spin_unlock_irqrestore(&info->shadow_lock, flags);

        wake_up(&shadow->wq_reset);
}

static void scsifront_do_response(struct vscsifrnt_info *info,
                                  struct vscsiif_response *ring_rsp)
{
        struct vscsifrnt_shadow *shadow;

        if (ring_rsp->rqid >= VSCSIIF_MAX_REQS ||
            !info->shadow[ring_rsp->rqid]->inflight) {
                scsifront_set_error(info, "illegal rqid returned by backend!");
                return;
        }
        shadow = info->shadow[ring_rsp->rqid];
        shadow->inflight = false;

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

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

        rp = READ_ONCE(info->ring.sring->rsp_prod);
        virt_rmb();     /* ordering required respective to backend */
        if (RING_RESPONSE_PROD_OVERFLOW(&info->ring, rp)) {
                scsifront_set_error(info, "illegal number of responses");
                return 0;
        }
        for (i = info->ring.rsp_cons; i != rp; i++) {
                RING_COPY_RESPONSE(&info->ring, i, &ring_rsp);
                scsifront_do_response(info, &ring_rsp);
                if (info->host_active == STATE_ERROR)
                        return 0;
                *eoiflag &= ~XEN_EOI_FLAG_SPURIOUS;
        }

        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;

        return more_to_do;
}

static int scsifront_cmd_done(struct vscsifrnt_info *info,
                              unsigned int *eoiflag)
{
        int more_to_do;
        unsigned long flags;

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

        more_to_do = scsifront_ring_drain(info, eoiflag);

        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;
        unsigned int eoiflag = XEN_EOI_FLAG_SPURIOUS;

        if (info->host_active == STATE_ERROR) {
                xen_irq_lateeoi(irq, XEN_EOI_FLAG_SPURIOUS);
                return IRQ_HANDLED;
        }

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

        xen_irq_lateeoi(irq, eoiflag);

        return IRQ_HANDLED;
}

static void scsifront_finish_all(struct vscsifrnt_info *info)
{
        unsigned int i, dummy;
        struct vscsiif_response resp;

        scsifront_ring_drain(info, &dummy);

        for (i = 0; i < VSCSIIF_MAX_REQS; i++) {
                if (test_bit(i, info->shadow_free_bitmap))
                        continue;
                resp.rqid = i;
                resp.sense_len = 0;
                resp.rslt = DID_RESET << 16;
                resp.residual_len = 0;
                scsifront_do_response(info, &resp);
        }
}

static int map_data_for_request(struct vscsifrnt_info *info,
                                struct scsi_cmnd *sc,
                                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;
        struct scsiif_request_segment *seg;

        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 = kzalloc_objs(struct scsiif_request_segment,
                                          data_grants, GFP_ATOMIC);
                if (!shadow->sg)
                        return -ENOMEM;
        }
        seg = shadow->sg ? : shadow->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 = offset_in_page(seg);
                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);

                        gnttab_grant_foreign_access_ref(ref,
                                info->dev->otherend_id,
                                xen_page_to_gfn(page), 1);
                        shadow->gref[ref_cnt] = ref;
                        shadow->seg[ref_cnt].gref   = ref;
                        shadow->seg[ref_cnt].offset = (uint16_t)off;
                        shadow->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);

                        gnttab_grant_foreign_access_ref(ref,
                                info->dev->otherend_id,
                                xen_page_to_gfn(page),
                                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)
                shadow->nr_segments = VSCSIIF_SG_GRANT | seg_grants;
        else
                shadow->nr_segments = (uint8_t)ref_cnt;
        shadow->nr_grants = ref_cnt;

        return 0;
}

static int scsifront_enter(struct vscsifrnt_info *info)
{
        if (info->pause)
                return 1;
        info->callers++;
        return 0;
}

static void scsifront_return(struct vscsifrnt_info *info)
{
        info->callers--;
        if (info->callers)
                return;

        if (!info->waiting_pause)
                return;

        info->waiting_pause = 0;
        wake_up(&info->wq_pause);
}

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

        if (info->host_active == STATE_ERROR)
                return SCSI_MLQUEUE_HOST_BUSY;

        sc->result = 0;

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

        spin_lock_irqsave(shost->host_lock, flags);
        if (scsifront_enter(info)) {
                spin_unlock_irqrestore(shost->host_lock, flags);
                return SCSI_MLQUEUE_HOST_BUSY;
        }

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

        if (scsifront_do_request(info, shadow)) {
                scsifront_gnttab_done(info, shadow);
                goto busy;
        }

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

        return 0;

busy:
        scsifront_return(info);
        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);
        int err = 0;

        if (info->host_active == STATE_ERROR)
                return FAILED;

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

        shadow->act = act;
        shadow->rslt_reset = RSLT_RESET_WAITING;
        shadow->sc = sc;
        shadow->ref_rqid = s->rqid;
        init_waitqueue_head(&shadow->wq_reset);

        spin_lock_irq(host->host_lock);

        for (;;) {
                if (scsifront_enter(info))
                        goto fail;

                if (!scsifront_do_request(info, shadow))
                        break;

                scsifront_return(info);
                if (err)
                        goto fail;
                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);
        }

        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;
        }

        scsifront_return(info);
        spin_unlock_irq(host->host_lock);
        return err;

fail:
        spin_unlock_irq(host->host_lock);
        kfree(shadow);
        return FAILED;
}

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 queue_limits *lim)
{
        struct vscsifrnt_info *info = shost_priv(sdev->host);
        int err;

        if (info->host_active == STATE_ERROR)
                return -EIO;

        if (current == info->curr) {
                err = xenbus_printf(XBT_NIL, info->dev->nodename,
                              info->dev_state_path, "%d", XenbusStateConnected);
                if (err) {
                        xenbus_dev_error(info->dev, err,
                                "%s: writing dev_state_path", __func__);
                        return err;
                }
        }

        return 0;
}

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

        if (current == info->curr) {
                err = xenbus_printf(XBT_NIL, info->dev->nodename,
                              info->dev_state_path, "%d", XenbusStateClosed);
                if (err)
                        xenbus_dev_error(info->dev, err,
                                "%s: writing dev_state_path", __func__);
        }
}

static const 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,
        .sdev_configure         = scsifront_sdev_configure,
        .sdev_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,
        .proc_name              = "scsifront",
};

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

        /***** Frontend to Backend ring start *****/
        err = xenbus_setup_ring(dev, GFP_KERNEL, (void **)&sring, 1,
                                &info->ring_ref);
        if (err)
                return err;

        XEN_FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);

        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_lateeoi(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:
        xenbus_teardown_ring((void **)&sring, 1, &info->ring_ref);

        return err;
}

static void scsifront_free_ring(struct vscsifrnt_info *info)
{
        unbind_from_irqhandler(info->irq, info);
        xenbus_teardown_ring((void **)&info->ring.sring, 1, &info->ring_ref);
}

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:
        scsifront_free_ring(info);

        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 = shost_priv(host);

        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);
        init_waitqueue_head(&info->wq_pause);
        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 = STATE_ACTIVE;

        xenbus_switch_state(dev, XenbusStateInitialised);

        return 0;

free_sring:
        scsifront_free_ring(info);
        scsi_host_put(host);
        return err;
}

static int scsifront_resume(struct xenbus_device *dev)
{
        struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);
        struct Scsi_Host *host = info->host;
        int err;

        spin_lock_irq(host->host_lock);

        /* Finish all still pending commands. */
        scsifront_finish_all(info);

        spin_unlock_irq(host->host_lock);

        /* Reconnect to dom0. */
        scsifront_free_ring(info);
        err = scsifront_init_ring(info);
        if (err) {
                dev_err(&dev->dev, "fail to resume %d\n", err);
                scsi_host_put(host);
                return err;
        }

        xenbus_switch_state(dev, XenbusStateInitialised);

        return 0;
}

static int scsifront_suspend(struct xenbus_device *dev)
{
        struct vscsifrnt_info *info = dev_get_drvdata(&dev->dev);
        struct Scsi_Host *host = info->host;
        int err = 0;

        /* No new commands for the backend. */
        spin_lock_irq(host->host_lock);
        info->pause = 1;
        while (info->callers && !err) {
                info->waiting_pause = 1;
                info->wait_ring_available = 0;
                spin_unlock_irq(host->host_lock);
                wake_up(&info->wq_sync);
                err = wait_event_interruptible(info->wq_pause,
                                               !info->waiting_pause);
                spin_lock_irq(host->host_lock);
        }
        spin_unlock_irq(host->host_lock);
        return err;
}

static void 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 != STATE_INACTIVE) {
                /* Scsi_host not yet removed */
                scsi_remove_host(info->host);
                info->host_active = STATE_INACTIVE;
        }
        mutex_unlock(&scsifront_mutex);

        scsifront_free_ring(info);
        scsi_host_put(info->host);
}

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 != STATE_INACTIVE) {
                scsi_remove_host(host);
                info->host_active = STATE_INACTIVE;
        }
        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;

        if (info->host_active == STATE_ERROR)
                return;

        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 sdev_configure called
                 * on successfull scsi_add_device, and in sdev_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");
                                err = xenbus_printf(XBT_NIL, dev->nodename,
                                              info->dev_state_path,
                                              "%d", XenbusStateClosed);
                                if (err)
                                        xenbus_dev_error(dev, err,
                                                "%s: writing dev_state_path", __func__);
                        }
                        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;
                case VSCSIFRONT_OP_READD_LUN:
                        if (device_state == XenbusStateConnected) {
                                err = xenbus_printf(XBT_NIL, dev->nodename,
                                              info->dev_state_path,
                                              "%d", XenbusStateConnected);
                                if (err)
                                        xenbus_dev_error(dev, err,
                                                "%s: writing dev_state_path", __func__);
                        }
                        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, nr_segs;
        struct Scsi_Host *host = info->host;

        sg_grant = xenbus_read_unsigned(dev->otherend, "feature-sg-grant", 0);
        nr_segs = min_t(unsigned int, sg_grant, SG_ALL);
        nr_segs = max_t(unsigned int, nr_segs, VSCSIIF_SG_TABLESIZE);
        nr_segs = min_t(unsigned int, nr_segs,
                        VSCSIIF_SG_TABLESIZE * PAGE_SIZE /
                        sizeof(struct scsiif_request_segment));

        if (!info->pause && sg_grant)
                dev_info(&dev->dev, "using up to %d SG entries\n", nr_segs);
        else if (info->pause && nr_segs < host->sg_tablesize)
                dev_warn(&dev->dev,
                         "SG entries decreased from %d to %u - device may not work properly anymore\n",
                         host->sg_tablesize, nr_segs);

        host->sg_tablesize = nr_segs;
        host->max_sectors = (nr_segs - 1) * PAGE_SIZE / 512;
}

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 (info->pause) {
                        scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_READD_LUN);
                        xenbus_switch_state(dev, XenbusStateConnected);
                        info->pause = 0;
                        return;
                }

                if (xenbus_read_driver_state(dev, 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;
                fallthrough;    /* Missed the backend's Closing state */
        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,
        .resume                 = scsifront_resume,
        .suspend                = scsifront_suspend,
        .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>");