path: root/drivers/scsi/virtio_scsi.c

/*
 * 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/interrupt.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 <linux/blkdev.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_tcq.h>
#include <scsi/scsi_devinfo.h>
#include <linux/seqlock.h>
#include <linux/blk-mq-virtio.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_cmd_req_pi    cmd_pi;
		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).
 *
 * tgt_seq is held to serialize reading and writing req_vq.
 *
 * Decrements of reqs are never concurrent with writes of req_vq: before the
 * decrement reqs will be != 0; after the decrement the virtqueue completion
 * routine will not use the req_vq so it can be changed by a new request.
 * Thus they can happen outside the tgt_seq, provided of course we make reqs
 * an atomic_t.
 */
struct virtio_scsi_target_state {
	seqcount_t tgt_seq;

	/* 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;

	struct hlist_node node;

	/* Protected by event_vq lock */
	bool stop_events;

	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;

	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, virtio32_to_cpu(vscsi->vdev, 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(virtio32_to_cpu(vscsi->vdev, resp->sense_len) >
		VIRTIO_SCSI_SENSE_SIZE);
	if (sc->sense_buffer) {
		memcpy(sc->sense_buffer, resp->sense,
		       min_t(u32,
			     virtio32_to_cpu(vscsi->vdev, resp->sense_len),
			     VIRTIO_SCSI_SENSE_SIZE));
		if (resp->sense_len)
			set_driver_byte(sc, DRIVER_SENSE);
	}

	sc->scsi_done(sc);
}

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);

		if (unlikely(virtqueue_is_broken(vq)))
			break;
	} 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];

	virtscsi_vq_done(vscsi, req_vq, virtscsi_complete_cmd);
};

static void virtscsi_poll_requests(struct virtio_scsi *vscsi)
{
	int i, num_vqs;

	num_vqs = vscsi->num_queues;
	for (i = 0; i < num_vqs; i++)
		virtscsi_vq_done(vscsi, &vscsi->req_vqs[i],
				 virtscsi_complete_cmd);
}

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

	if (cmd->comp)
		complete(cmd->comp);
}

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 void virtscsi_handle_event(struct work_struct *work);

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

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

	/* Stop scheduling work before calling cancel_work_sync.  */
	spin_lock_irq(&vscsi->event_vq.vq_lock);
	vscsi->stop_events = true;
	spin_unlock_irq(&vscsi->event_vq.vq_lock);

	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 (virtio32_to_cpu(vscsi->vdev, 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("Unsupported 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 = virtio32_to_cpu(vscsi->vdev, event->reason) & 255;
	u8 ascq = virtio32_to_cpu(vscsi->vdev, 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 &
	    cpu_to_virtio32(vscsi->vdev, VIRTIO_SCSI_T_EVENTS_MISSED)) {
		event->event &= ~cpu_to_virtio32(vscsi->vdev,
						   VIRTIO_SCSI_T_EVENTS_MISSED);
		scsi_scan_host(virtio_scsi_host(vscsi->vdev));
	}

	switch (virtio32_to_cpu(vscsi->vdev, 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("Unsupported 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;

	if (!vscsi->stop_events)
		queue_work(system_freezable_wq, &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
 */
static int virtscsi_add_cmd(struct virtqueue *vq,
			    struct virtio_scsi_cmd *cmd,
			    size_t req_size, size_t resp_size)
{
	struct scsi_cmnd *sc = cmd->sc;
	struct scatterlist *sgs[6], 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) {
		/* Place WRITE protection SGLs before Data OUT payload */
		if (scsi_prot_sg_count(sc))
			sgs[out_num++] = scsi_prot_sglist(sc);
		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) {
		/* Place READ protection SGLs before Data IN payload */
		if (scsi_prot_sg_count(sc))
			sgs[out_num + in_num++] = scsi_prot_sglist(sc);
		sgs[out_num + in_num++] = in->sgl;
	}

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

static int virtscsi_kick_cmd(struct virtio_scsi_vq *vq,
			     struct virtio_scsi_cmd *cmd,
			     size_t req_size, size_t resp_size)
{
	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);
	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 void virtio_scsi_init_hdr(struct virtio_device *vdev,
				 struct virtio_scsi_cmd_req *cmd,
				 struct scsi_cmnd *sc)
{
	cmd->lun[0] = 1;
	cmd->lun[1] = sc->device->id;
	cmd->lun[2] = (sc->device->lun >> 8) | 0x40;
	cmd->lun[3] = sc->device->lun & 0xff;
	cmd->tag = cpu_to_virtio64(vdev, (unsigned long)sc);
	cmd->task_attr = VIRTIO_SCSI_S_SIMPLE;
	cmd->prio = 0;
	cmd->crn = 0;
}

#ifdef CONFIG_BLK_DEV_INTEGRITY
static void virtio_scsi_init_hdr_pi(struct virtio_device *vdev,
				    struct virtio_scsi_cmd_req_pi *cmd_pi,
				    struct scsi_cmnd *sc)
{
	struct request *rq = sc->request;
	struct blk_integrity *bi;

	virtio_scsi_init_hdr(vdev, (struct virtio_scsi_cmd_req *)cmd_pi, sc);

	if (!rq || !scsi_prot_sg_count(sc))
		return;

	bi = blk_get_integrity(rq->rq_disk);

	if (sc->sc_data_direction == DMA_TO_DEVICE)
		cmd_pi->pi_bytesout = cpu_to_virtio32(vdev,
						      bio_integrity_bytes(bi,
							blk_rq_sectors(rq)));
	else if (sc->sc_data_direction == DMA_FROM_DEVICE)
		cmd_pi->pi_bytesin = cpu_to_virtio32(vdev,
						     bio_integrity_bytes(bi,
							blk_rq_sectors(rq)));
}
#endif

static struct virtio_scsi_vq *virtscsi_pick_vq_mq(struct virtio_scsi *vscsi,
						  struct scsi_cmnd *sc)
{
	u32 tag = blk_mq_unique_tag(sc->request);
	u16 hwq = blk_mq_unique_tag_to_hwq(tag);

	return &vscsi->req_vqs[hwq];
}

static int virtscsi_queuecommand(struct Scsi_Host *shost,
				 struct scsi_cmnd *sc)
{
	struct virtio_scsi *vscsi = shost_priv(shost);
	struct virtio_scsi_vq *req_vq = virtscsi_pick_vq_mq(vscsi, sc);
	struct virtio_scsi_cmd *cmd = scsi_cmd_priv(sc);
	unsigned long flags;
	int req_size;
	int ret;

	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]);

	cmd->sc = sc;

	BUG_ON(sc->cmd_len > VIRTIO_SCSI_CDB_SIZE);

#ifdef CONFIG_BLK_DEV_INTEGRITY
	if (virtio_has_feature(vscsi->vdev, VIRTIO_SCSI_F_T10_PI)) {
		virtio_scsi_init_hdr_pi(vscsi->vdev, &cmd->req.cmd_pi, sc);
		memcpy(cmd->req.cmd_pi.cdb, sc->cmnd, sc->cmd_len);
		req_size = sizeof(cmd->req.cmd_pi);
	} else
#endif
	{
		virtio_scsi_init_hdr(vscsi->vdev, &cmd->req.cmd, sc);
		memcpy(cmd->req.cmd.cdb, sc->cmnd, sc->cmd_len);
		req_size = sizeof(cmd->req.cmd);
	}

	ret = virtscsi_kick_cmd(req_vq, cmd, req_size, sizeof(cmd->resp.cmd));
	if (ret == -EIO) {
		cmd->resp.cmd.response = VIRTIO_SCSI_S_BAD_TARGET;
		spin_lock_irqsave(&req_vq->vq_lock, flags);
		virtscsi_complete_cmd(vscsi, cmd);
		spin_unlock_irqrestore(&req_vq->vq_lock, flags);
	} else if (ret != 0) {
		return SCSI_MLQUEUE_HOST_BUSY;
	}
	return 0;
}

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) < 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;

	/*
	 * The spec guarantees that all requests related to the TMF have
	 * been completed, but the callback might not have run yet if
	 * we're using independent interrupts (e.g. MSI).  Poll the
	 * virtqueues once.
	 *
	 * In the abort case, sc->scsi_done will do nothing, because
	 * the block layer must have detected a timeout and as a result
	 * REQ_ATOM_COMPLETE has been set.
	 */
	virtscsi_poll_requests(vscsi);

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->req.tmf = (struct virtio_scsi_ctrl_tmf_req){
		.type = VIRTIO_SCSI_T_TMF,
		.subtype = cpu_to_virtio32(vscsi->vdev,
					     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_device_alloc(struct scsi_device *sdevice)
{
	/*
	 * Passed through SCSI targets (e.g. with qemu's 'scsi-block')
	 * may have transfer limits which come from the host SCSI
	 * controller or something on the host side other than the
	 * target itself.
	 *
	 * To make this work properly, the hypervisor can adjust the
	 * target's VPD information to advertise these limits.  But
	 * for that to work, the guest has to look at the VPD pages,
	 * which we won't do by default if it is an SPC-2 device, even
	 * if it does actually support it.
	 *
	 * So, set the blist to always try to read the VPD pages.
	 */
	sdevice->sdev_bflags = BLIST_TRY_VPD_PAGES;

	return 0;
}


/**
 * virtscsi_change_queue_depth() - Change a virtscsi target's queue depth
 * @sdev:	Virtscsi target whose queue depth to change
 * @qdepth:	New queue depth
 */
static int virtscsi_change_queue_depth(struct scsi_device *sdev, int qdepth)
{
	struct Scsi_Host *shost = sdev->host;
	int max_depth = shost->cmd_per_lun;

	return scsi_change_queue_depth(sdev, min(max_depth, qdepth));
}

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->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 = cpu_to_virtio64(vscsi->vdev, (unsigned long)sc),
	};
	return virtscsi_tmf(vscsi, cmd);
}

static int virtscsi_target_alloc(struct scsi_target *starget)
{
	struct Scsi_Host *sh = dev_to_shost(starget->dev.parent);
	struct virtio_scsi *vscsi = shost_priv(sh);

	struct virtio_scsi_target_state *tgt =
				kmalloc(sizeof(*tgt), GFP_KERNEL);
	if (!tgt)
		return -ENOMEM;

	seqcount_init(&tgt->tgt_seq);
	tgt->req_vq = &vscsi->req_vqs[0];

	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 int virtscsi_map_queues(struct Scsi_Host *shost)
{
	struct virtio_scsi *vscsi = shost_priv(shost);

	return blk_mq_virtio_map_queues(&shost->tag_set, vscsi->vdev, 2);
}

/*
 * The host guarantees to respond to each command, although I/O
 * latencies might be higher than on bare metal.  Reset the timer
 * unconditionally to give the host a chance to perform EH.
 */
static enum blk_eh_timer_return virtscsi_eh_timed_out(struct scsi_cmnd *scmnd)
{
	return BLK_EH_RESET_TIMER;
}

static struct scsi_host_template virtscsi_host_template = {
	.module = THIS_MODULE,
	.name = "Virtio SCSI HBA",
	.proc_name = "virtio_scsi",
	.this_id = -1,
	.cmd_size = sizeof(struct virtio_scsi_cmd),
	.queuecommand = virtscsi_queuecommand,
	.change_queue_depth = virtscsi_change_queue_depth,
	.eh_abort_handler = virtscsi_abort,
	.eh_device_reset_handler = virtscsi_device_reset,
	.eh_timed_out = virtscsi_eh_timed_out,
	.slave_alloc = virtscsi_device_alloc,

	.dma_boundary = UINT_MAX,
	.use_clustering = ENABLE_CLUSTERING,
	.target_alloc = virtscsi_target_alloc,
	.target_destroy = virtscsi_target_destroy,
	.map_queues = virtscsi_map_queues,
	.track_queue_depth = 1,
	.force_blk_mq = 1,
};

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

#define virtscsi_config_set(vdev, fld, val) \
	do { \
		typeof(((struct virtio_scsi_config *)0)->fld) __val = (val); \
		virtio_cwrite(vdev, struct virtio_scsi_config, fld, &__val); \
	} while(0)

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_remove_vqs(struct virtio_device *vdev)
{
	/* 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;
	struct irq_affinity desc = { .pre_vectors = 2 };

	num_vqs = vscsi->num_queues + VIRTIO_SCSI_VQ_BASE;
	vqs = kmalloc_array(num_vqs, sizeof(struct virtqueue *), GFP_KERNEL);
	callbacks = kmalloc_array(num_vqs, sizeof(vq_callback_t *),
				  GFP_KERNEL);
	names = kmalloc_array(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 = virtio_find_vqs(vdev, num_vqs, vqs, callbacks, names, &desc);
	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_config_set(vdev, cdb_size, VIRTIO_SCSI_CDB_SIZE);
	virtscsi_config_set(vdev, sense_size, VIRTIO_SCSI_SENSE_SIZE);

	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;

	if (!vdev->config->get) {
		dev_err(&vdev->dev, "%s failure: config access disabled\n",
			__func__);
		return -EINVAL;
	}

	/* 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;

	shost = scsi_host_alloc(&virtscsi_host_template,
		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;

	shost->can_queue = virtqueue_get_vring_size(vscsi->req_vqs[0].vq);

	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;
	shost->nr_hw_queues = num_queues;

#ifdef CONFIG_BLK_DEV_INTEGRITY
	if (virtio_has_feature(vdev, VIRTIO_SCSI_F_T10_PI)) {
		int host_prot;

		host_prot = SHOST_DIF_TYPE1_PROTECTION | SHOST_DIF_TYPE2_PROTECTION |
			    SHOST_DIF_TYPE3_PROTECTION | SHOST_DIX_TYPE1_PROTECTION |
			    SHOST_DIX_TYPE2_PROTECTION | SHOST_DIX_TYPE3_PROTECTION;

		scsi_host_set_prot(shost, host_prot);
		scsi_host_set_guard(shost, SHOST_DIX_GUARD_CRC);
	}
#endif

	err = scsi_add_host(shost, &vdev->dev);
	if (err)
		goto scsi_add_host_failed;

	virtio_device_ready(vdev);

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

	scsi_scan_host(shost);
	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);
	virtscsi_remove_vqs(vdev);
	scsi_host_put(shost);
}

#ifdef CONFIG_PM_SLEEP
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);
	int err;

	err = virtscsi_init(vdev, vscsi);
	if (err)
		return err;

	virtio_device_ready(vdev);

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

	return err;
}
#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,
#ifdef CONFIG_BLK_DEV_INTEGRITY
	VIRTIO_SCSI_F_T10_PI,
#endif
};

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,
#ifdef CONFIG_PM_SLEEP
	.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");