/*
 * Virtio SCSI HBA driver
 *
 * Copyright IBM Corp. 2010
 * Copyright Red Hat, Inc. 2011
 *
 * Authors:
 *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
 *  Paolo Bonzini   <pbonzini@redhat.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/mempool.h>
#include <linux/virtio.h>
#include <linux/virtio_ids.h>
#include <linux/virtio_config.h>
#include <linux/virtio_scsi.h>
#include <linux/cpu.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_cmnd.h>

#define VIRTIO_SCSI_MEMPOOL_SZ 64
#define VIRTIO_SCSI_EVENT_LEN 8
#define VIRTIO_SCSI_VQ_BASE 2

/* Command queue element */
struct virtio_scsi_cmd {
        struct scsi_cmnd *sc;
        struct completion *comp;
        union {
                struct virtio_scsi_cmd_req       cmd;
                struct virtio_scsi_ctrl_tmf_req  tmf;
                struct virtio_scsi_ctrl_an_req   an;
        } req;
        union {
                struct virtio_scsi_cmd_resp      cmd;
                struct virtio_scsi_ctrl_tmf_resp tmf;
                struct virtio_scsi_ctrl_an_resp  an;
                struct virtio_scsi_event         evt;
        } resp;
} ____cacheline_aligned_in_smp;

struct virtio_scsi_event_node {
        struct virtio_scsi *vscsi;
        struct virtio_scsi_event event;
        struct work_struct work;
};

struct virtio_scsi_vq {
        /* Protects vq */
        spinlock_t vq_lock;

        struct virtqueue *vq;
};

/*
 * Per-target queue state.
 *
 * This struct holds the data needed by the queue steering policy.  When a
 * target is sent multiple requests, we need to drive them to the same queue so
 * that FIFO processing order is kept.  However, if a target was idle, we can
 * choose a queue arbitrarily.  In this case the queue is chosen according to
 * the current VCPU, so the driver expects the number of request queues to be
 * equal to the number of VCPUs.  This makes it easy and fast to select the
 * queue, and also lets the driver optimize the IRQ affinity for the virtqueues
 * (each virtqueue's affinity is set to the CPU that "owns" the queue).
 *
 * An interesting effect of this policy is that only writes to req_vq need to
 * take the tgt_lock.  Read can be done outside the lock because:
 *
 * - writes of req_vq only occur when atomic_inc_return(&tgt->reqs) returns 1.
 *   In that case, no other CPU is reading req_vq: even if they were in
 *   virtscsi_queuecommand_multi, they would be spinning on tgt_lock.
 *
 * - reads of req_vq only occur when the target is not idle (reqs != 0).
 *   A CPU that enters virtscsi_queuecommand_multi will not modify req_vq.
 *
 * Similarly, decrements of reqs are never concurrent with writes of req_vq.
 * Thus they can happen outside the tgt_lock, provided of course we make reqs
 * an atomic_t.
 */
struct virtio_scsi_target_state {
        /* This spinlock never held at the same time as vq_lock. */
        spinlock_t tgt_lock;

        /* Count of outstanding requests. */
        atomic_t reqs;

        /* Currently active virtqueue for requests sent to this target. */
        struct virtio_scsi_vq *req_vq;
};

/* Driver instance state */
struct virtio_scsi {
        struct virtio_device *vdev;

        /* Get some buffers ready for event vq */
        struct virtio_scsi_event_node event_list[VIRTIO_SCSI_EVENT_LEN];

        u32 num_queues;

        /* If the affinity hint is set for virtqueues */
        bool affinity_hint_set;

        /* CPU hotplug notifier */
        struct notifier_block nb;

        struct virtio_scsi_vq ctrl_vq;
        struct virtio_scsi_vq event_vq;
        struct virtio_scsi_vq req_vqs[];
};

static struct kmem_cache *virtscsi_cmd_cache;
static mempool_t *virtscsi_cmd_pool;

static inline struct Scsi_Host *virtio_scsi_host(struct virtio_device *vdev)
{
        return vdev->priv;
}

static void virtscsi_compute_resid(struct scsi_cmnd *sc, u32 resid)
{
        if (!resid)
                return;

        if (!scsi_bidi_cmnd(sc)) {
                scsi_set_resid(sc, resid);
                return;
        }

        scsi_in(sc)->resid = min(resid, scsi_in(sc)->length);
        scsi_out(sc)->resid = resid - scsi_in(sc)->resid;
}

/**
 * virtscsi_complete_cmd - finish a scsi_cmd and invoke scsi_done
 *
 * Called with vq_lock held.
 */
static void virtscsi_complete_cmd(struct virtio_scsi *vscsi, void *buf)
{
        struct virtio_scsi_cmd *cmd = buf;
        struct scsi_cmnd *sc = cmd->sc;
        struct virtio_scsi_cmd_resp *resp = &cmd->resp.cmd;
        struct virtio_scsi_target_state *tgt =
                                scsi_target(sc->device)->hostdata;

        dev_dbg(&sc->device->sdev_gendev,
                "cmd %p response %u status %#02x sense_len %u\n",
                sc, resp->response, resp->status, resp->sense_len);

        sc->result = resp->status;
        virtscsi_compute_resid(sc, resp->resid);
        switch (resp->response) {
        case VIRTIO_SCSI_S_OK:
                set_host_byte(sc, DID_OK);
                break;
        case VIRTIO_SCSI_S_OVERRUN:
                set_host_byte(sc, DID_ERROR);
                break;
        case VIRTIO_SCSI_S_ABORTED:
                set_host_byte(sc, DID_ABORT);
                break;
        case VIRTIO_SCSI_S_BAD_TARGET:
                set_host_byte(sc, DID_BAD_TARGET);
                break;
        case VIRTIO_SCSI_S_RESET:
                set_host_byte(sc, DID_RESET);
                break;
        case VIRTIO_SCSI_S_BUSY:
                set_host_byte(sc, DID_BUS_BUSY);
                break;
        case VIRTIO_SCSI_S_TRANSPORT_FAILURE:
                set_host_byte(sc, DID_TRANSPORT_DISRUPTED);
                break;
        case VIRTIO_SCSI_S_TARGET_FAILURE:
                set_host_byte(sc, DID_TARGET_FAILURE);
                break;
        case VIRTIO_SCSI_S_NEXUS_FAILURE:
                set_host_byte(sc, DID_NEXUS_FAILURE);
                break;
        default:
                scmd_printk(KERN_WARNING, sc, "Unknown response %d",
                            resp->response);
                /* fall through */
        case VIRTIO_SCSI_S_FAILURE:
                set_host_byte(sc, DID_ERROR);
                break;
        }

        WARN_ON(resp->sense_len > VIRTIO_SCSI_SENSE_SIZE);
        if (sc->sense_buffer) {
                memcpy(sc->sense_buffer, resp->sense,
                       min_t(u32, resp->sense_len, VIRTIO_SCSI_SENSE_SIZE));
                if (resp->sense_len)
                        set_driver_byte(sc, DRIVER_SENSE);
        }

        mempool_free(cmd, virtscsi_cmd_pool);
        sc->scsi_done(sc);

        atomic_dec(&tgt->reqs);
}

static void virtscsi_vq_done(struct virtio_scsi *vscsi,
                             struct virtio_scsi_vq *virtscsi_vq,
                             void (*fn)(struct virtio_scsi *vscsi, void *buf))
{
        void *buf;
        unsigned int len;
        unsigned long flags;
        struct virtqueue *vq = virtscsi_vq->vq;

        spin_lock_irqsave(&virtscsi_vq->vq_lock, flags);
        do {
                virtqueue_disable_cb(vq);
                while ((buf = virtqueue_get_buf(vq, &len)) != NULL)
                        fn(vscsi, buf);
        } while (!virtqueue_enable_cb(vq));
        spin_unlock_irqrestore(&virtscsi_vq->vq_lock, flags);
}

static void virtscsi_req_done(struct virtqueue *vq)
{
        struct Scsi_Host *sh = virtio_scsi_host(vq->vdev);
        struct virtio_scsi *vscsi = shost_priv(sh);
        int index = vq->index - VIRTIO_SCSI_VQ_BASE;
        struct virtio_scsi_vq *req_vq = &vscsi->req_vqs[index];

        /*
         * Read req_vq before decrementing the reqs field in
         * virtscsi_complete_cmd.
         *
         * With barriers:
         *
         *      CPU #0                  virtscsi_queuecommand_multi (CPU #1)
         *      ------------------------------------------------------------
         *      lock vq_lock
         *      read req_vq
         *      read reqs (reqs = 1)
         *      write reqs (reqs = 0)
         *                              increment reqs (reqs = 1)
         *                              write req_vq
         *
         * Possible reordering without barriers:
         *
         *      CPU #0                  virtscsi_queuecommand_multi (CPU #1)
         *      ------------------------------------------------------------
         *      lock vq_lock
         *      read reqs (reqs = 1)
         *      write reqs (reqs = 0)
         *                              increment reqs (reqs = 1)
         *                              write req_vq
         *      read (wrong) req_vq
         *
         * We do not need a full smp_rmb, because req_vq is required to get
         * to tgt->reqs: tgt is &vscsi->tgt[sc->device->id], where sc is stored
         * in the virtqueue as the user token.
         */
        smp_read_barrier_depends();

        virtscsi_vq_done(vscsi, req_vq, virtscsi_complete_cmd);
};

static void virtscsi_complete_free(struct virtio_scsi *vscsi, void *buf)
{
        struct virtio_scsi_cmd *cmd = buf;

        if (cmd->comp)
                complete_all(cmd->comp);
        else
                mempool_free(cmd, virtscsi_cmd_pool);
}

static void virtscsi_ctrl_done(struct virtqueue *vq)
{
        struct Scsi_Host *sh = virtio_scsi_host(vq->vdev);
        struct virtio_scsi *vscsi = shost_priv(sh);

        virtscsi_vq_done(vscsi, &vscsi->ctrl_vq, virtscsi_complete_free);
};

static int virtscsi_kick_event(struct virtio_scsi *vscsi,
                               struct virtio_scsi_event_node *event_node)
{
        int err;
        struct scatterlist sg;
        unsigned long flags;

        sg_init_one(&sg, &event_node->event, sizeof(struct virtio_scsi_event));

        spin_lock_irqsave(&vscsi->event_vq.vq_lock, flags);

        err = virtqueue_add_inbuf(vscsi->event_vq.vq, &sg, 1, event_node,
                                  GFP_ATOMIC);
        if (!err)
                virtqueue_kick(vscsi->event_vq.vq);

        spin_unlock_irqrestore(&vscsi->event_vq.vq_lock, flags);

        return err;
}

static int virtscsi_kick_event_all(struct virtio_scsi *vscsi)
{
        int i;

        for (i = 0; i < VIRTIO_SCSI_EVENT_LEN; i++) {
                vscsi->event_list[i].vscsi = vscsi;
                virtscsi_kick_event(vscsi, &vscsi->event_list[i]);
        }

        return 0;
}

static void virtscsi_cancel_event_work(struct virtio_scsi *vscsi)
{
        int i;

        for (i = 0; i < VIRTIO_SCSI_EVENT_LEN; i++)
                cancel_work_sync(&vscsi->event_list[i].work);
}

static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
                                            struct virtio_scsi_event *event)
{
        struct scsi_device *sdev;
        struct Scsi_Host *shost = virtio_scsi_host(vscsi->vdev);
        unsigned int target = event->lun[1];
        unsigned int lun = (event->lun[2] << 8) | event->lun[3];

        switch (event->reason) {
        case VIRTIO_SCSI_EVT_RESET_RESCAN:
                scsi_add_device(shost, 0, target, lun);
                break;
        case VIRTIO_SCSI_EVT_RESET_REMOVED:
                sdev = scsi_device_lookup(shost, 0, target, lun);
                if (sdev) {
                        scsi_remove_device(sdev);
                        scsi_device_put(sdev);
                } else {
                        pr_err("SCSI device %d 0 %d %d not found\n",
                                shost->host_no, target, lun);
                }
                break;
        default:
                pr_info("Unsupport virtio scsi event reason %x\n", event->reason);
        }
}

static void virtscsi_handle_param_change(struct virtio_scsi *vscsi,
                                         struct virtio_scsi_event *event)
{
        struct scsi_device *sdev;
        struct Scsi_Host *shost = virtio_scsi_host(vscsi->vdev);
        unsigned int target = event->lun[1];
        unsigned int lun = (event->lun[2] << 8) | event->lun[3];
        u8 asc = event->reason & 255;
        u8 ascq = event->reason >> 8;

        sdev = scsi_device_lookup(shost, 0, target, lun);
        if (!sdev) {
                pr_err("SCSI device %d 0 %d %d not found\n",
                        shost->host_no, target, lun);
                return;
        }

        /* Handle "Parameters changed", "Mode parameters changed", and
           "Capacity data has changed".  */
        if (asc == 0x2a && (ascq == 0x00 || ascq == 0x01 || ascq == 0x09))
                scsi_rescan_device(&sdev->sdev_gendev);

        scsi_device_put(sdev);
}

static void virtscsi_handle_event(struct work_struct *work)
{
        struct virtio_scsi_event_node *event_node =
                container_of(work, struct virtio_scsi_event_node, work);
        struct virtio_scsi *vscsi = event_node->vscsi;
        struct virtio_scsi_event *event = &event_node->event;

        if (event->event & VIRTIO_SCSI_T_EVENTS_MISSED) {
                event->event &= ~VIRTIO_SCSI_T_EVENTS_MISSED;
                scsi_scan_host(virtio_scsi_host(vscsi->vdev));
        }

        switch (event->event) {
        case VIRTIO_SCSI_T_NO_EVENT:
                break;
        case VIRTIO_SCSI_T_TRANSPORT_RESET:
                virtscsi_handle_transport_reset(vscsi, event);
                break;
        case VIRTIO_SCSI_T_PARAM_CHANGE:
                virtscsi_handle_param_change(vscsi, event);
                break;
        default:
                pr_err("Unsupport virtio scsi event %x\n", event->event);
        }
        virtscsi_kick_event(vscsi, event_node);
}

static void virtscsi_complete_event(struct virtio_scsi *vscsi, void *buf)
{
        struct virtio_scsi_event_node *event_node = buf;

        INIT_WORK(&event_node->work, virtscsi_handle_event);
        schedule_work(&event_node->work);
}

static void virtscsi_event_done(struct virtqueue *vq)
{
        struct Scsi_Host *sh = virtio_scsi_host(vq->vdev);
        struct virtio_scsi *vscsi = shost_priv(sh);

        virtscsi_vq_done(vscsi, &vscsi->event_vq, virtscsi_complete_event);
};

/**
 * virtscsi_add_cmd - add a virtio_scsi_cmd to a virtqueue
 * @vq          : the struct virtqueue we're talking about
 * @cmd         : command structure
 * @req_size    : size of the request buffer
 * @resp_size   : size of the response buffer
 * @gfp : flags to use for memory allocations
 */
static int virtscsi_add_cmd(struct virtqueue *vq,
                            struct virtio_scsi_cmd *cmd,
                            size_t req_size, size_t resp_size, gfp_t gfp)
{
        struct scsi_cmnd *sc = cmd->sc;
        struct scatterlist *sgs[4], req, resp;
        struct sg_table *out, *in;
        unsigned out_num = 0, in_num = 0;

        out = in = NULL;

        if (sc && sc->sc_data_direction != DMA_NONE) {
                if (sc->sc_data_direction != DMA_FROM_DEVICE)
                        out = &scsi_out(sc)->table;
                if (sc->sc_data_direction != DMA_TO_DEVICE)
                        in = &scsi_in(sc)->table;
        }

        /* Request header.  */
        sg_init_one(&req, &cmd->req, req_size);
        sgs[out_num++] = &req;

        /* Data-out buffer.  */
        if (out)
                sgs[out_num++] = out->sgl;

        /* Response header.  */
        sg_init_one(&resp, &cmd->resp, resp_size);
        sgs[out_num + in_num++] = &resp;

        /* Data-in buffer */
        if (in)
                sgs[out_num + in_num++] = in->sgl;

        return virtqueue_add_sgs(vq, sgs, out_num, in_num, cmd, gfp);
}

static int virtscsi_kick_cmd(struct virtio_scsi_vq *vq,
                             struct virtio_scsi_cmd *cmd,
                             size_t req_size, size_t resp_size, gfp_t gfp)
{
        unsigned long flags;
        int err;
        bool needs_kick = false;

        spin_lock_irqsave(&vq->vq_lock, flags);
        err = virtscsi_add_cmd(vq->vq, cmd, req_size, resp_size, gfp);
        if (!err)
                needs_kick = virtqueue_kick_prepare(vq->vq);

        spin_unlock_irqrestore(&vq->vq_lock, flags);

        if (needs_kick)
                virtqueue_notify(vq->vq);
        return err;
}

static int virtscsi_queuecommand(struct virtio_scsi *vscsi,
                                 struct virtio_scsi_vq *req_vq,
                                 struct scsi_cmnd *sc)
{
        struct virtio_scsi_cmd *cmd;
        int ret;

        struct Scsi_Host *shost = virtio_scsi_host(vscsi->vdev);
        BUG_ON(scsi_sg_count(sc) > shost->sg_tablesize);

        /* TODO: check feature bit and fail if unsupported?  */
        BUG_ON(sc->sc_data_direction == DMA_BIDIRECTIONAL);

        dev_dbg(&sc->device->sdev_gendev,
                "cmd %p CDB: %#02x\n", sc, sc->cmnd[0]);

        ret = SCSI_MLQUEUE_HOST_BUSY;
        cmd = mempool_alloc(virtscsi_cmd_pool, GFP_ATOMIC);
        if (!cmd)
                goto out;

        memset(cmd, 0, sizeof(*cmd));
        cmd->sc = sc;
        cmd->req.cmd = (struct virtio_scsi_cmd_req){
                .lun[0] = 1,
                .lun[1] = sc->device->id,
                .lun[2] = (sc->device->lun >> 8) | 0x40,
                .lun[3] = sc->device->lun & 0xff,
                .tag = (unsigned long)sc,
                .task_attr = VIRTIO_SCSI_S_SIMPLE,
                .prio = 0,
                .crn = 0,
        };

        BUG_ON(sc->cmd_len > VIRTIO_SCSI_CDB_SIZE);
        memcpy(cmd->req.cmd.cdb, sc->cmnd, sc->cmd_len);

        if (virtscsi_kick_cmd(req_vq, cmd,
                              sizeof cmd->req.cmd, sizeof cmd->resp.cmd,
                              GFP_ATOMIC) == 0)
                ret = 0;
        else
                mempool_free(cmd, virtscsi_cmd_pool);

out:
        return ret;
}

static int virtscsi_queuecommand_single(struct Scsi_Host *sh,
                                        struct scsi_cmnd *sc)
{
        struct virtio_scsi *vscsi = shost_priv(sh);
        struct virtio_scsi_target_state *tgt =
                                scsi_target(sc->device)->hostdata;

        atomic_inc(&tgt->reqs);
        return virtscsi_queuecommand(vscsi, &vscsi->req_vqs[0], sc);
}

static struct virtio_scsi_vq *virtscsi_pick_vq(struct virtio_scsi *vscsi,
                                               struct virtio_scsi_target_state *tgt)
{
        struct virtio_scsi_vq *vq;
        unsigned long flags;
        u32 queue_num;

        spin_lock_irqsave(&tgt->tgt_lock, flags);

        /*
         * The memory barrier after atomic_inc_return matches
         * the smp_read_barrier_depends() in virtscsi_req_done.
         */
        if (atomic_inc_return(&tgt->reqs) > 1)
                vq = ACCESS_ONCE(tgt->req_vq);
        else {
                queue_num = smp_processor_id();
                while (unlikely(queue_num >= vscsi->num_queues))
                        queue_num -= vscsi->num_queues;

                tgt->req_vq = vq = &vscsi->req_vqs[queue_num];
        }

        spin_unlock_irqrestore(&tgt->tgt_lock, flags);
        return vq;
}

static int virtscsi_queuecommand_multi(struct Scsi_Host *sh,
                                       struct scsi_cmnd *sc)
{
        struct virtio_scsi *vscsi = shost_priv(sh);
        struct virtio_scsi_target_state *tgt =
                                scsi_target(sc->device)->hostdata;
        struct virtio_scsi_vq *req_vq = virtscsi_pick_vq(vscsi, tgt);

        return virtscsi_queuecommand(vscsi, req_vq, sc);
}

static int virtscsi_tmf(struct virtio_scsi *vscsi, struct virtio_scsi_cmd *cmd)
{
        DECLARE_COMPLETION_ONSTACK(comp);
        int ret = FAILED;

        cmd->comp = &comp;
        if (virtscsi_kick_cmd(&vscsi->ctrl_vq, cmd,
                              sizeof cmd->req.tmf, sizeof cmd->resp.tmf,
                              GFP_NOIO) < 0)
                goto out;

        wait_for_completion(&comp);
        if (cmd->resp.tmf.response == VIRTIO_SCSI_S_OK ||
            cmd->resp.tmf.response == VIRTIO_SCSI_S_FUNCTION_SUCCEEDED)
                ret = SUCCESS;

out:
        mempool_free(cmd, virtscsi_cmd_pool);
        return ret;
}

static int virtscsi_device_reset(struct scsi_cmnd *sc)
{
        struct virtio_scsi *vscsi = shost_priv(sc->device->host);
        struct virtio_scsi_cmd *cmd;

        sdev_printk(KERN_INFO, sc->device, "device reset\n");
        cmd = mempool_alloc(virtscsi_cmd_pool, GFP_NOIO);
        if (!cmd)
                return FAILED;

        memset(cmd, 0, sizeof(*cmd));
        cmd->sc = sc;
        cmd->req.tmf = (struct virtio_scsi_ctrl_tmf_req){
                .type = VIRTIO_SCSI_T_TMF,
                .subtype = VIRTIO_SCSI_T_TMF_LOGICAL_UNIT_RESET,
                .lun[0] = 1,
                .lun[1] = sc->device->id,
                .lun[2] = (sc->device->lun >> 8) | 0x40,
                .lun[3] = sc->device->lun & 0xff,
        };
        return virtscsi_tmf(vscsi, cmd);
}

static int virtscsi_abort(struct scsi_cmnd *sc)
{
        struct virtio_scsi *vscsi = shost_priv(sc->device->host);
        struct virtio_scsi_cmd *cmd;

        scmd_printk(KERN_INFO, sc, "abort\n");
        cmd = mempool_alloc(virtscsi_cmd_pool, GFP_NOIO);
        if (!cmd)
                return FAILED;

        memset(cmd, 0, sizeof(*cmd));
        cmd->sc = sc;
        cmd->req.tmf = (struct virtio_scsi_ctrl_tmf_req){
                .type = VIRTIO_SCSI_T_TMF,
                .subtype = VIRTIO_SCSI_T_TMF_ABORT_TASK,
                .lun[0] = 1,
                .lun[1] = sc->device->id,
                .lun[2] = (sc->device->lun >> 8) | 0x40,
                .lun[3] = sc->device->lun & 0xff,
                .tag = (unsigned long)sc,
        };
        return virtscsi_tmf(vscsi, cmd);
}

static int virtscsi_target_alloc(struct scsi_target *starget)
{
        struct virtio_scsi_target_state *tgt =
                                kmalloc(sizeof(*tgt), GFP_KERNEL);
        if (!tgt)
                return -ENOMEM;

        spin_lock_init(&tgt->tgt_lock);
        atomic_set(&tgt->reqs, 0);
        tgt->req_vq = NULL;

        starget->hostdata = tgt;
        return 0;
}

static void virtscsi_target_destroy(struct scsi_target *starget)
{
        struct virtio_scsi_target_state *tgt = starget->hostdata;
        kfree(tgt);
}

static struct scsi_host_template virtscsi_host_template_single = {
        .module = THIS_MODULE,
        .name = "Virtio SCSI HBA",
        .proc_name = "virtio_scsi",
        .this_id = -1,
        .queuecommand = virtscsi_queuecommand_single,
        .eh_abort_handler = virtscsi_abort,
        .eh_device_reset_handler = virtscsi_device_reset,

        .can_queue = 1024,
        .dma_boundary = UINT_MAX,
        .use_clustering = ENABLE_CLUSTERING,
        .target_alloc = virtscsi_target_alloc,
        .target_destroy = virtscsi_target_destroy,
};

static struct scsi_host_template virtscsi_host_template_multi = {
        .module = THIS_MODULE,
        .name = "Virtio SCSI HBA",
        .proc_name = "virtio_scsi",
        .this_id = -1,
        .queuecommand = virtscsi_queuecommand_multi,
        .eh_abort_handler = virtscsi_abort,
        .eh_device_reset_handler = virtscsi_device_reset,

        .can_queue = 1024,
        .dma_boundary = UINT_MAX,
        .use_clustering = ENABLE_CLUSTERING,
        .target_alloc = virtscsi_target_alloc,
        .target_destroy = virtscsi_target_destroy,
};

#define virtscsi_config_get(vdev, fld) \
        ({ \
                typeof(((struct virtio_scsi_config *)0)->fld) __val; \
                vdev->config->get(vdev, \
                                  offsetof(struct virtio_scsi_config, fld), \
                                  &__val, sizeof(__val)); \
                __val; \
        })

#define virtscsi_config_set(vdev, fld, val) \
        (void)({ \
                typeof(((struct virtio_scsi_config *)0)->fld) __val = (val); \
                vdev->config->set(vdev, \
                                  offsetof(struct virtio_scsi_config, fld), \
                                  &__val, sizeof(__val)); \
        })

static void __virtscsi_set_affinity(struct virtio_scsi *vscsi, bool affinity)
{
        int i;
        int cpu;

        /* In multiqueue mode, when the number of cpu is equal
         * to the number of request queues, we let the qeueues
         * to be private to one cpu by setting the affinity hint
         * to eliminate the contention.
         */
        if ((vscsi->num_queues == 1 ||
             vscsi->num_queues != num_online_cpus()) && affinity) {
                if (vscsi->affinity_hint_set)
                        affinity = false;
                else
                        return;
        }

        if (affinity) {
                i = 0;
                for_each_online_cpu(cpu) {
                        virtqueue_set_affinity(vscsi->req_vqs[i].vq, cpu);
                        i++;
                }

                vscsi->affinity_hint_set = true;
        } else {
                for (i = 0; i < vscsi->num_queues; i++)
                        virtqueue_set_affinity(vscsi->req_vqs[i].vq, -1);

                vscsi->affinity_hint_set = false;
        }
}

static void virtscsi_set_affinity(struct virtio_scsi *vscsi, bool affinity)
{
        get_online_cpus();
        __virtscsi_set_affinity(vscsi, affinity);
        put_online_cpus();
}

static int virtscsi_cpu_callback(struct notifier_block *nfb,
                                 unsigned long action, void *hcpu)
{
        struct virtio_scsi *vscsi = container_of(nfb, struct virtio_scsi, nb);
        switch(action) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                __virtscsi_set_affinity(vscsi, true);
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static void virtscsi_init_vq(struct virtio_scsi_vq *virtscsi_vq,
                             struct virtqueue *vq)
{
        spin_lock_init(&virtscsi_vq->vq_lock);
        virtscsi_vq->vq = vq;
}

static void virtscsi_scan(struct virtio_device *vdev)
{
        struct Scsi_Host *shost = (struct Scsi_Host *)vdev->priv;

        scsi_scan_host(shost);
}

static void virtscsi_remove_vqs(struct virtio_device *vdev)
{
        struct Scsi_Host *sh = virtio_scsi_host(vdev);
        struct virtio_scsi *vscsi = shost_priv(sh);

        virtscsi_set_affinity(vscsi, false);

        /* Stop all the virtqueues. */
        vdev->config->reset(vdev);

        vdev->config->del_vqs(vdev);
}

static int virtscsi_init(struct virtio_device *vdev,
                         struct virtio_scsi *vscsi)
{
        int err;
        u32 i;
        u32 num_vqs;
        vq_callback_t **callbacks;
        const char **names;
        struct virtqueue **vqs;

        num_vqs = vscsi->num_queues + VIRTIO_SCSI_VQ_BASE;
        vqs = kmalloc(num_vqs * sizeof(struct virtqueue *), GFP_KERNEL);
        callbacks = kmalloc(num_vqs * sizeof(vq_callback_t *), GFP_KERNEL);
        names = kmalloc(num_vqs * sizeof(char *), GFP_KERNEL);

        if (!callbacks || !vqs || !names) {
                err = -ENOMEM;
                goto out;
        }

        callbacks[0] = virtscsi_ctrl_done;
        callbacks[1] = virtscsi_event_done;
        names[0] = "control";
        names[1] = "event";
        for (i = VIRTIO_SCSI_VQ_BASE; i < num_vqs; i++) {
                callbacks[i] = virtscsi_req_done;
                names[i] = "request";
        }

        /* Discover virtqueues and write information to configuration.  */
        err = vdev->config->find_vqs(vdev, num_vqs, vqs, callbacks, names);
        if (err)
                goto out;

        virtscsi_init_vq(&vscsi->ctrl_vq, vqs[0]);
        virtscsi_init_vq(&vscsi->event_vq, vqs[1]);
        for (i = VIRTIO_SCSI_VQ_BASE; i < num_vqs; i++)
                virtscsi_init_vq(&vscsi->req_vqs[i - VIRTIO_SCSI_VQ_BASE],
                                 vqs[i]);

        virtscsi_set_affinity(vscsi, true);

        virtscsi_config_set(vdev, cdb_size, VIRTIO_SCSI_CDB_SIZE);
        virtscsi_config_set(vdev, sense_size, VIRTIO_SCSI_SENSE_SIZE);

        if (virtio_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG))
                virtscsi_kick_event_all(vscsi);

        err = 0;

out:
        kfree(names);
        kfree(callbacks);
        kfree(vqs);
        if (err)
                virtscsi_remove_vqs(vdev);
        return err;
}

static int virtscsi_probe(struct virtio_device *vdev)
{
        struct Scsi_Host *shost;
        struct virtio_scsi *vscsi;
        int err;
        u32 sg_elems, num_targets;
        u32 cmd_per_lun;
        u32 num_queues;
        struct scsi_host_template *hostt;

        /* We need to know how many queues before we allocate. */
        num_queues = virtscsi_config_get(vdev, num_queues) ? : 1;

        num_targets = virtscsi_config_get(vdev, max_target) + 1;

        if (num_queues == 1)
                hostt = &virtscsi_host_template_single;
        else
                hostt = &virtscsi_host_template_multi;

        shost = scsi_host_alloc(hostt,
                sizeof(*vscsi) + sizeof(vscsi->req_vqs[0]) * num_queues);
        if (!shost)
                return -ENOMEM;

        sg_elems = virtscsi_config_get(vdev, seg_max) ?: 1;
        shost->sg_tablesize = sg_elems;
        vscsi = shost_priv(shost);
        vscsi->vdev = vdev;
        vscsi->num_queues = num_queues;
        vdev->priv = shost;

        err = virtscsi_init(vdev, vscsi);
        if (err)
                goto virtscsi_init_failed;

        vscsi->nb.notifier_call = &virtscsi_cpu_callback;
        err = register_hotcpu_notifier(&vscsi->nb);
        if (err) {
                pr_err("registering cpu notifier failed\n");
                goto scsi_add_host_failed;
        }

        cmd_per_lun = virtscsi_config_get(vdev, cmd_per_lun) ?: 1;
        shost->cmd_per_lun = min_t(u32, cmd_per_lun, shost->can_queue);
        shost->max_sectors = virtscsi_config_get(vdev, max_sectors) ?: 0xFFFF;

        /* LUNs > 256 are reported with format 1, so they go in the range
         * 16640-32767.
         */
        shost->max_lun = virtscsi_config_get(vdev, max_lun) + 1 + 0x4000;
        shost->max_id = num_targets;
        shost->max_channel = 0;
        shost->max_cmd_len = VIRTIO_SCSI_CDB_SIZE;
        err = scsi_add_host(shost, &vdev->dev);
        if (err)
                goto scsi_add_host_failed;
        /*
         * scsi_scan_host() happens in virtscsi_scan() via virtio_driver->scan()
         * after VIRTIO_CONFIG_S_DRIVER_OK has been set..
         */
        return 0;

scsi_add_host_failed:
        vdev->config->del_vqs(vdev);
virtscsi_init_failed:
        scsi_host_put(shost);
        return err;
}

static void virtscsi_remove(struct virtio_device *vdev)
{
        struct Scsi_Host *shost = virtio_scsi_host(vdev);
        struct virtio_scsi *vscsi = shost_priv(shost);

        if (virtio_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG))
                virtscsi_cancel_event_work(vscsi);

        scsi_remove_host(shost);

        unregister_hotcpu_notifier(&vscsi->nb);

        virtscsi_remove_vqs(vdev);
        scsi_host_put(shost);
}

#ifdef CONFIG_PM
static int virtscsi_freeze(struct virtio_device *vdev)
{
        virtscsi_remove_vqs(vdev);
        return 0;
}

static int virtscsi_restore(struct virtio_device *vdev)
{
        struct Scsi_Host *sh = virtio_scsi_host(vdev);
        struct virtio_scsi *vscsi = shost_priv(sh);

        return virtscsi_init(vdev, vscsi);
}
#endif

static struct virtio_device_id id_table[] = {
        { VIRTIO_ID_SCSI, VIRTIO_DEV_ANY_ID },
        { 0 },
};

static unsigned int features[] = {
        VIRTIO_SCSI_F_HOTPLUG,
        VIRTIO_SCSI_F_CHANGE,
};

static struct virtio_driver virtio_scsi_driver = {
        .feature_table = features,
        .feature_table_size = ARRAY_SIZE(features),
        .driver.name = KBUILD_MODNAME,
        .driver.owner = THIS_MODULE,
        .id_table = id_table,
        .probe = virtscsi_probe,
        .scan = virtscsi_scan,
#ifdef CONFIG_PM
        .freeze = virtscsi_freeze,
        .restore = virtscsi_restore,
#endif
        .remove = virtscsi_remove,
};

static int __init init(void)
{
        int ret = -ENOMEM;

        virtscsi_cmd_cache = KMEM_CACHE(virtio_scsi_cmd, 0);
        if (!virtscsi_cmd_cache) {
                pr_err("kmem_cache_create() for virtscsi_cmd_cache failed\n");
                goto error;
        }


        virtscsi_cmd_pool =
                mempool_create_slab_pool(VIRTIO_SCSI_MEMPOOL_SZ,
                                         virtscsi_cmd_cache);
        if (!virtscsi_cmd_pool) {
                pr_err("mempool_create() for virtscsi_cmd_pool failed\n");
                goto error;
        }
        ret = register_virtio_driver(&virtio_scsi_driver);
        if (ret < 0)
                goto error;

        return 0;

error:
        if (virtscsi_cmd_pool) {
                mempool_destroy(virtscsi_cmd_pool);
                virtscsi_cmd_pool = NULL;
        }
        if (virtscsi_cmd_cache) {
                kmem_cache_destroy(virtscsi_cmd_cache);
                virtscsi_cmd_cache = NULL;
        }
        return ret;
}

static void __exit fini(void)
{
        unregister_virtio_driver(&virtio_scsi_driver);
        mempool_destroy(virtscsi_cmd_pool);
        kmem_cache_destroy(virtscsi_cmd_cache);
}
module_init(init);
module_exit(fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio SCSI HBA driver");
MODULE_LICENSE("GPL");