Merge tag 'io_uring-5.7-2020-05-22' of git://git.kernel.dk/linux-block

[thirdparty/linux.git] / drivers / block / virtio_blk.c

// SPDX-License-Identifier: GPL-2.0-only
//#define DEBUG
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/hdreg.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/interrupt.h>
#include <linux/virtio.h>
#include <linux/virtio_blk.h>
#include <linux/scatterlist.h>
#include <linux/string_helpers.h>
#include <linux/idr.h>
#include <linux/blk-mq.h>
#include <linux/blk-mq-virtio.h>
#include <linux/numa.h>
#include <uapi/linux/virtio_ring.h>

#define PART_BITS 4
#define VQ_NAME_LEN 16
#define MAX_DISCARD_SEGMENTS 256u

static int major;
static DEFINE_IDA(vd_index_ida);

static struct workqueue_struct *virtblk_wq;

struct virtio_blk_vq {
        struct virtqueue *vq;
        spinlock_t lock;
        char name[VQ_NAME_LEN];
} ____cacheline_aligned_in_smp;

struct virtio_blk {
        /*
         * This mutex must be held by anything that may run after
         * virtblk_remove() sets vblk->vdev to NULL.
         *
         * blk-mq, virtqueue processing, and sysfs attribute code paths are
         * shut down before vblk->vdev is set to NULL and therefore do not need
         * to hold this mutex.
         */
        struct mutex vdev_mutex;
        struct virtio_device *vdev;

        /* The disk structure for the kernel. */
        struct gendisk *disk;

        /* Block layer tags. */
        struct blk_mq_tag_set tag_set;

        /* Process context for config space updates */
        struct work_struct config_work;

        /*
         * Tracks references from block_device_operations open/release and
         * virtio_driver probe/remove so this object can be freed once no
         * longer in use.
         */
        refcount_t refs;

        /* What host tells us, plus 2 for header & tailer. */
        unsigned int sg_elems;

        /* Ida index - used to track minor number allocations. */
        int index;

        /* num of vqs */
        int num_vqs;
        struct virtio_blk_vq *vqs;
};

struct virtblk_req {
        struct virtio_blk_outhdr out_hdr;
        u8 status;
        struct scatterlist sg[];
};

static inline blk_status_t virtblk_result(struct virtblk_req *vbr)
{
        switch (vbr->status) {
        case VIRTIO_BLK_S_OK:
                return BLK_STS_OK;
        case VIRTIO_BLK_S_UNSUPP:
                return BLK_STS_NOTSUPP;
        default:
                return BLK_STS_IOERR;
        }
}

static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr,
                struct scatterlist *data_sg, bool have_data)
{
        struct scatterlist hdr, status, *sgs[3];
        unsigned int num_out = 0, num_in = 0;

        sg_init_one(&hdr, &vbr->out_hdr, sizeof(vbr->out_hdr));
        sgs[num_out++] = &hdr;

        if (have_data) {
                if (vbr->out_hdr.type & cpu_to_virtio32(vq->vdev, VIRTIO_BLK_T_OUT))
                        sgs[num_out++] = data_sg;
                else
                        sgs[num_out + num_in++] = data_sg;
        }

        sg_init_one(&status, &vbr->status, sizeof(vbr->status));
        sgs[num_out + num_in++] = &status;

        return virtqueue_add_sgs(vq, sgs, num_out, num_in, vbr, GFP_ATOMIC);
}

static int virtblk_setup_discard_write_zeroes(struct request *req, bool unmap)
{
        unsigned short segments = blk_rq_nr_discard_segments(req);
        unsigned short n = 0;
        struct virtio_blk_discard_write_zeroes *range;
        struct bio *bio;
        u32 flags = 0;

        if (unmap)
                flags |= VIRTIO_BLK_WRITE_ZEROES_FLAG_UNMAP;

        range = kmalloc_array(segments, sizeof(*range), GFP_ATOMIC);
        if (!range)
                return -ENOMEM;

        __rq_for_each_bio(bio, req) {
                u64 sector = bio->bi_iter.bi_sector;
                u32 num_sectors = bio->bi_iter.bi_size >> SECTOR_SHIFT;

                range[n].flags = cpu_to_le32(flags);
                range[n].num_sectors = cpu_to_le32(num_sectors);
                range[n].sector = cpu_to_le64(sector);
                n++;
        }

        req->special_vec.bv_page = virt_to_page(range);
        req->special_vec.bv_offset = offset_in_page(range);
        req->special_vec.bv_len = sizeof(*range) * segments;
        req->rq_flags |= RQF_SPECIAL_PAYLOAD;

        return 0;
}

static inline void virtblk_request_done(struct request *req)
{
        struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);

        if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
                kfree(page_address(req->special_vec.bv_page) +
                      req->special_vec.bv_offset);
        }

        blk_mq_end_request(req, virtblk_result(vbr));
}

static void virtblk_done(struct virtqueue *vq)
{
        struct virtio_blk *vblk = vq->vdev->priv;
        bool req_done = false;
        int qid = vq->index;
        struct virtblk_req *vbr;
        unsigned long flags;
        unsigned int len;

        spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
        do {
                virtqueue_disable_cb(vq);
                while ((vbr = virtqueue_get_buf(vblk->vqs[qid].vq, &len)) != NULL) {
                        struct request *req = blk_mq_rq_from_pdu(vbr);

                        blk_mq_complete_request(req);
                        req_done = true;
                }
                if (unlikely(virtqueue_is_broken(vq)))
                        break;
        } while (!virtqueue_enable_cb(vq));

        /* In case queue is stopped waiting for more buffers. */
        if (req_done)
                blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
        spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);
}

static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
{
        struct virtio_blk *vblk = hctx->queue->queuedata;
        struct virtio_blk_vq *vq = &vblk->vqs[hctx->queue_num];
        bool kick;

        spin_lock_irq(&vq->lock);
        kick = virtqueue_kick_prepare(vq->vq);
        spin_unlock_irq(&vq->lock);

        if (kick)
                virtqueue_notify(vq->vq);
}

static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
                           const struct blk_mq_queue_data *bd)
{
        struct virtio_blk *vblk = hctx->queue->queuedata;
        struct request *req = bd->rq;
        struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
        unsigned long flags;
        unsigned int num;
        int qid = hctx->queue_num;
        int err;
        bool notify = false;
        bool unmap = false;
        u32 type;

        BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);

        switch (req_op(req)) {
        case REQ_OP_READ:
        case REQ_OP_WRITE:
                type = 0;
                break;
        case REQ_OP_FLUSH:
                type = VIRTIO_BLK_T_FLUSH;
                break;
        case REQ_OP_DISCARD:
                type = VIRTIO_BLK_T_DISCARD;
                break;
        case REQ_OP_WRITE_ZEROES:
                type = VIRTIO_BLK_T_WRITE_ZEROES;
                unmap = !(req->cmd_flags & REQ_NOUNMAP);
                break;
        case REQ_OP_DRV_IN:
                type = VIRTIO_BLK_T_GET_ID;
                break;
        default:
                WARN_ON_ONCE(1);
                return BLK_STS_IOERR;
        }

        vbr->out_hdr.type = cpu_to_virtio32(vblk->vdev, type);
        vbr->out_hdr.sector = type ?
                0 : cpu_to_virtio64(vblk->vdev, blk_rq_pos(req));
        vbr->out_hdr.ioprio = cpu_to_virtio32(vblk->vdev, req_get_ioprio(req));

        blk_mq_start_request(req);

        if (type == VIRTIO_BLK_T_DISCARD || type == VIRTIO_BLK_T_WRITE_ZEROES) {
                err = virtblk_setup_discard_write_zeroes(req, unmap);
                if (err)
                        return BLK_STS_RESOURCE;
        }

        num = blk_rq_map_sg(hctx->queue, req, vbr->sg);
        if (num) {
                if (rq_data_dir(req) == WRITE)
                        vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_OUT);
                else
                        vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_IN);
        }

        spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
        err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg, num);
        if (err) {
                virtqueue_kick(vblk->vqs[qid].vq);
                /* Don't stop the queue if -ENOMEM: we may have failed to
                 * bounce the buffer due to global resource outage.
                 */
                if (err == -ENOSPC)
                        blk_mq_stop_hw_queue(hctx);
                spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);
                switch (err) {
                case -ENOSPC:
                        return BLK_STS_DEV_RESOURCE;
                case -ENOMEM:
                        return BLK_STS_RESOURCE;
                default:
                        return BLK_STS_IOERR;
                }
        }

        if (bd->last && virtqueue_kick_prepare(vblk->vqs[qid].vq))
                notify = true;
        spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);

        if (notify)
                virtqueue_notify(vblk->vqs[qid].vq);
        return BLK_STS_OK;
}

/* return id (s/n) string for *disk to *id_str
 */
static int virtblk_get_id(struct gendisk *disk, char *id_str)
{
        struct virtio_blk *vblk = disk->private_data;
        struct request_queue *q = vblk->disk->queue;
        struct request *req;
        int err;

        req = blk_get_request(q, REQ_OP_DRV_IN, 0);
        if (IS_ERR(req))
                return PTR_ERR(req);

        err = blk_rq_map_kern(q, req, id_str, VIRTIO_BLK_ID_BYTES, GFP_KERNEL);
        if (err)
                goto out;

        blk_execute_rq(vblk->disk->queue, vblk->disk, req, false);
        err = blk_status_to_errno(virtblk_result(blk_mq_rq_to_pdu(req)));
out:
        blk_put_request(req);
        return err;
}

static void virtblk_get(struct virtio_blk *vblk)
{
        refcount_inc(&vblk->refs);
}

static void virtblk_put(struct virtio_blk *vblk)
{
        if (refcount_dec_and_test(&vblk->refs)) {
                ida_simple_remove(&vd_index_ida, vblk->index);
                mutex_destroy(&vblk->vdev_mutex);
                kfree(vblk);
        }
}

static int virtblk_open(struct block_device *bd, fmode_t mode)
{
        struct virtio_blk *vblk = bd->bd_disk->private_data;
        int ret = 0;

        mutex_lock(&vblk->vdev_mutex);

        if (vblk->vdev)
                virtblk_get(vblk);
        else
                ret = -ENXIO;

        mutex_unlock(&vblk->vdev_mutex);
        return ret;
}

static void virtblk_release(struct gendisk *disk, fmode_t mode)
{
        struct virtio_blk *vblk = disk->private_data;

        virtblk_put(vblk);
}

/* We provide getgeo only to please some old bootloader/partitioning tools */
static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
{
        struct virtio_blk *vblk = bd->bd_disk->private_data;
        int ret = 0;

        mutex_lock(&vblk->vdev_mutex);

        if (!vblk->vdev) {
                ret = -ENXIO;
                goto out;
        }

        /* see if the host passed in geometry config */
        if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) {
                virtio_cread(vblk->vdev, struct virtio_blk_config,
                             geometry.cylinders, &geo->cylinders);
                virtio_cread(vblk->vdev, struct virtio_blk_config,
                             geometry.heads, &geo->heads);
                virtio_cread(vblk->vdev, struct virtio_blk_config,
                             geometry.sectors, &geo->sectors);
        } else {
                /* some standard values, similar to sd */
                geo->heads = 1 << 6;
                geo->sectors = 1 << 5;
                geo->cylinders = get_capacity(bd->bd_disk) >> 11;
        }
out:
        mutex_unlock(&vblk->vdev_mutex);
        return ret;
}

static const struct block_device_operations virtblk_fops = {
        .owner  = THIS_MODULE,
        .open = virtblk_open,
        .release = virtblk_release,
        .getgeo = virtblk_getgeo,
};

static int index_to_minor(int index)
{
        return index << PART_BITS;
}

static int minor_to_index(int minor)
{
        return minor >> PART_BITS;
}

static ssize_t serial_show(struct device *dev,
                           struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);
        int err;

        /* sysfs gives us a PAGE_SIZE buffer */
        BUILD_BUG_ON(PAGE_SIZE < VIRTIO_BLK_ID_BYTES);

        buf[VIRTIO_BLK_ID_BYTES] = '\0';
        err = virtblk_get_id(disk, buf);
        if (!err)
                return strlen(buf);

        if (err == -EIO) /* Unsupported? Make it empty. */
                return 0;

        return err;
}

static DEVICE_ATTR_RO(serial);

/* The queue's logical block size must be set before calling this */
static void virtblk_update_capacity(struct virtio_blk *vblk, bool resize)
{
        struct virtio_device *vdev = vblk->vdev;
        struct request_queue *q = vblk->disk->queue;
        char cap_str_2[10], cap_str_10[10];
        unsigned long long nblocks;
        u64 capacity;

        /* Host must always specify the capacity. */
        virtio_cread(vdev, struct virtio_blk_config, capacity, &capacity);

        /* If capacity is too big, truncate with warning. */
        if ((sector_t)capacity != capacity) {
                dev_warn(&vdev->dev, "Capacity %llu too large: truncating\n",
                         (unsigned long long)capacity);
                capacity = (sector_t)-1;
        }

        nblocks = DIV_ROUND_UP_ULL(capacity, queue_logical_block_size(q) >> 9);

        string_get_size(nblocks, queue_logical_block_size(q),
                        STRING_UNITS_2, cap_str_2, sizeof(cap_str_2));
        string_get_size(nblocks, queue_logical_block_size(q),
                        STRING_UNITS_10, cap_str_10, sizeof(cap_str_10));

        dev_notice(&vdev->dev,
                   "[%s] %s%llu %d-byte logical blocks (%s/%s)\n",
                   vblk->disk->disk_name,
                   resize ? "new size: " : "",
                   nblocks,
                   queue_logical_block_size(q),
                   cap_str_10,
                   cap_str_2);

        set_capacity_revalidate_and_notify(vblk->disk, capacity, true);
}

static void virtblk_config_changed_work(struct work_struct *work)
{
        struct virtio_blk *vblk =
                container_of(work, struct virtio_blk, config_work);

        virtblk_update_capacity(vblk, true);
}

static void virtblk_config_changed(struct virtio_device *vdev)
{
        struct virtio_blk *vblk = vdev->priv;

        queue_work(virtblk_wq, &vblk->config_work);
}

static int init_vq(struct virtio_blk *vblk)
{
        int err;
        int i;
        vq_callback_t **callbacks;
        const char **names;
        struct virtqueue **vqs;
        unsigned short num_vqs;
        struct virtio_device *vdev = vblk->vdev;
        struct irq_affinity desc = { 0, };

        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_MQ,
                                   struct virtio_blk_config, num_queues,
                                   &num_vqs);
        if (err)
                num_vqs = 1;

        num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);

        vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
        if (!vblk->vqs)
                return -ENOMEM;

        names = kmalloc_array(num_vqs, sizeof(*names), GFP_KERNEL);
        callbacks = kmalloc_array(num_vqs, sizeof(*callbacks), GFP_KERNEL);
        vqs = kmalloc_array(num_vqs, sizeof(*vqs), GFP_KERNEL);
        if (!names || !callbacks || !vqs) {
                err = -ENOMEM;
                goto out;
        }

        for (i = 0; i < num_vqs; i++) {
                callbacks[i] = virtblk_done;
                snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
                names[i] = vblk->vqs[i].name;
        }

        /* Discover virtqueues and write information to configuration.  */
        err = virtio_find_vqs(vdev, num_vqs, vqs, callbacks, names, &desc);
        if (err)
                goto out;

        for (i = 0; i < num_vqs; i++) {
                spin_lock_init(&vblk->vqs[i].lock);
                vblk->vqs[i].vq = vqs[i];
        }
        vblk->num_vqs = num_vqs;

out:
        kfree(vqs);
        kfree(callbacks);
        kfree(names);
        if (err)
                kfree(vblk->vqs);
        return err;
}

/*
 * Legacy naming scheme used for virtio devices.  We are stuck with it for
 * virtio blk but don't ever use it for any new driver.
 */
static int virtblk_name_format(char *prefix, int index, char *buf, int buflen)
{
        const int base = 'z' - 'a' + 1;
        char *begin = buf + strlen(prefix);
        char *end = buf + buflen;
        char *p;
        int unit;

        p = end - 1;
        *p = '\0';
        unit = base;
        do {
                if (p == begin)
                        return -EINVAL;
                *--p = 'a' + (index % unit);
                index = (index / unit) - 1;
        } while (index >= 0);

        memmove(begin, p, end - p);
        memcpy(buf, prefix, strlen(prefix));

        return 0;
}

static int virtblk_get_cache_mode(struct virtio_device *vdev)
{
        u8 writeback;
        int err;

        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_CONFIG_WCE,
                                   struct virtio_blk_config, wce,
                                   &writeback);

        /*
         * If WCE is not configurable and flush is not available,
         * assume no writeback cache is in use.
         */
        if (err)
                writeback = virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH);

        return writeback;
}

static void virtblk_update_cache_mode(struct virtio_device *vdev)
{
        u8 writeback = virtblk_get_cache_mode(vdev);
        struct virtio_blk *vblk = vdev->priv;

        blk_queue_write_cache(vblk->disk->queue, writeback, false);
        revalidate_disk(vblk->disk);
}

static const char *const virtblk_cache_types[] = {
        "write through", "write back"
};

static ssize_t
cache_type_store(struct device *dev, struct device_attribute *attr,
                 const char *buf, size_t count)
{
        struct gendisk *disk = dev_to_disk(dev);
        struct virtio_blk *vblk = disk->private_data;
        struct virtio_device *vdev = vblk->vdev;
        int i;

        BUG_ON(!virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_CONFIG_WCE));
        i = sysfs_match_string(virtblk_cache_types, buf);
        if (i < 0)
                return i;

        virtio_cwrite8(vdev, offsetof(struct virtio_blk_config, wce), i);
        virtblk_update_cache_mode(vdev);
        return count;
}

static ssize_t
cache_type_show(struct device *dev, struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);
        struct virtio_blk *vblk = disk->private_data;
        u8 writeback = virtblk_get_cache_mode(vblk->vdev);

        BUG_ON(writeback >= ARRAY_SIZE(virtblk_cache_types));
        return snprintf(buf, 40, "%s\n", virtblk_cache_types[writeback]);
}

static DEVICE_ATTR_RW(cache_type);

static struct attribute *virtblk_attrs[] = {
        &dev_attr_serial.attr,
        &dev_attr_cache_type.attr,
        NULL,
};

static umode_t virtblk_attrs_are_visible(struct kobject *kobj,
                struct attribute *a, int n)
{
        struct device *dev = container_of(kobj, struct device, kobj);
        struct gendisk *disk = dev_to_disk(dev);
        struct virtio_blk *vblk = disk->private_data;
        struct virtio_device *vdev = vblk->vdev;

        if (a == &dev_attr_cache_type.attr &&
            !virtio_has_feature(vdev, VIRTIO_BLK_F_CONFIG_WCE))
                return S_IRUGO;

        return a->mode;
}

static const struct attribute_group virtblk_attr_group = {
        .attrs = virtblk_attrs,
        .is_visible = virtblk_attrs_are_visible,
};

static const struct attribute_group *virtblk_attr_groups[] = {
        &virtblk_attr_group,
        NULL,
};

static int virtblk_init_request(struct blk_mq_tag_set *set, struct request *rq,
                unsigned int hctx_idx, unsigned int numa_node)
{
        struct virtio_blk *vblk = set->driver_data;
        struct virtblk_req *vbr = blk_mq_rq_to_pdu(rq);

        sg_init_table(vbr->sg, vblk->sg_elems);
        return 0;
}

static int virtblk_map_queues(struct blk_mq_tag_set *set)
{
        struct virtio_blk *vblk = set->driver_data;

        return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
                                        vblk->vdev, 0);
}

static const struct blk_mq_ops virtio_mq_ops = {
        .queue_rq       = virtio_queue_rq,
        .commit_rqs     = virtio_commit_rqs,
        .complete       = virtblk_request_done,
        .init_request   = virtblk_init_request,
        .map_queues     = virtblk_map_queues,
};

static unsigned int virtblk_queue_depth;
module_param_named(queue_depth, virtblk_queue_depth, uint, 0444);

static int virtblk_probe(struct virtio_device *vdev)
{
        struct virtio_blk *vblk;
        struct request_queue *q;
        int err, index;

        u32 v, blk_size, max_size, sg_elems, opt_io_size;
        u16 min_io_size;
        u8 physical_block_exp, alignment_offset;

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

        err = ida_simple_get(&vd_index_ida, 0, minor_to_index(1 << MINORBITS),
                             GFP_KERNEL);
        if (err < 0)
                goto out;
        index = err;

        /* We need to know how many segments before we allocate. */
        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SEG_MAX,
                                   struct virtio_blk_config, seg_max,
                                   &sg_elems);

        /* We need at least one SG element, whatever they say. */
        if (err || !sg_elems)
                sg_elems = 1;

        /* We need an extra sg elements at head and tail. */
        sg_elems += 2;
        vdev->priv = vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
        if (!vblk) {
                err = -ENOMEM;
                goto out_free_index;
        }

        /* This reference is dropped in virtblk_remove(). */
        refcount_set(&vblk->refs, 1);
        mutex_init(&vblk->vdev_mutex);

        vblk->vdev = vdev;
        vblk->sg_elems = sg_elems;

        INIT_WORK(&vblk->config_work, virtblk_config_changed_work);

        err = init_vq(vblk);
        if (err)
                goto out_free_vblk;

        /* FIXME: How many partitions?  How long is a piece of string? */
        vblk->disk = alloc_disk(1 << PART_BITS);
        if (!vblk->disk) {
                err = -ENOMEM;
                goto out_free_vq;
        }

        /* Default queue sizing is to fill the ring. */
        if (!virtblk_queue_depth) {
                virtblk_queue_depth = vblk->vqs[0].vq->num_free;
                /* ... but without indirect descs, we use 2 descs per req */
                if (!virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC))
                        virtblk_queue_depth /= 2;
        }

        memset(&vblk->tag_set, 0, sizeof(vblk->tag_set));
        vblk->tag_set.ops = &virtio_mq_ops;
        vblk->tag_set.queue_depth = virtblk_queue_depth;
        vblk->tag_set.numa_node = NUMA_NO_NODE;
        vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
        vblk->tag_set.cmd_size =
                sizeof(struct virtblk_req) +
                sizeof(struct scatterlist) * sg_elems;
        vblk->tag_set.driver_data = vblk;
        vblk->tag_set.nr_hw_queues = vblk->num_vqs;

        err = blk_mq_alloc_tag_set(&vblk->tag_set);
        if (err)
                goto out_put_disk;

        q = blk_mq_init_queue(&vblk->tag_set);
        if (IS_ERR(q)) {
                err = -ENOMEM;
                goto out_free_tags;
        }
        vblk->disk->queue = q;

        q->queuedata = vblk;

        virtblk_name_format("vd", index, vblk->disk->disk_name, DISK_NAME_LEN);

        vblk->disk->major = major;
        vblk->disk->first_minor = index_to_minor(index);
        vblk->disk->private_data = vblk;
        vblk->disk->fops = &virtblk_fops;
        vblk->disk->flags |= GENHD_FL_EXT_DEVT;
        vblk->index = index;

        /* configure queue flush support */
        virtblk_update_cache_mode(vdev);

        /* If disk is read-only in the host, the guest should obey */
        if (virtio_has_feature(vdev, VIRTIO_BLK_F_RO))
                set_disk_ro(vblk->disk, 1);

        /* We can handle whatever the host told us to handle. */
        blk_queue_max_segments(q, vblk->sg_elems-2);

        /* No real sector limit. */
        blk_queue_max_hw_sectors(q, -1U);

        max_size = virtio_max_dma_size(vdev);

        /* Host can optionally specify maximum segment size and number of
         * segments. */
        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
                                   struct virtio_blk_config, size_max, &v);
        if (!err)
                max_size = min(max_size, v);

        blk_queue_max_segment_size(q, max_size);

        /* Host can optionally specify the block size of the device */
        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
                                   struct virtio_blk_config, blk_size,
                                   &blk_size);
        if (!err)
                blk_queue_logical_block_size(q, blk_size);
        else
                blk_size = queue_logical_block_size(q);

        /* Use topology information if available */
        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
                                   struct virtio_blk_config, physical_block_exp,
                                   &physical_block_exp);
        if (!err && physical_block_exp)
                blk_queue_physical_block_size(q,
                                blk_size * (1 << physical_block_exp));

        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
                                   struct virtio_blk_config, alignment_offset,
                                   &alignment_offset);
        if (!err && alignment_offset)
                blk_queue_alignment_offset(q, blk_size * alignment_offset);

        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
                                   struct virtio_blk_config, min_io_size,
                                   &min_io_size);
        if (!err && min_io_size)
                blk_queue_io_min(q, blk_size * min_io_size);

        err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
                                   struct virtio_blk_config, opt_io_size,
                                   &opt_io_size);
        if (!err && opt_io_size)
                blk_queue_io_opt(q, blk_size * opt_io_size);

        if (virtio_has_feature(vdev, VIRTIO_BLK_F_DISCARD)) {
                q->limits.discard_granularity = blk_size;

                virtio_cread(vdev, struct virtio_blk_config,
                             discard_sector_alignment, &v);
                q->limits.discard_alignment = v ? v << SECTOR_SHIFT : 0;

                virtio_cread(vdev, struct virtio_blk_config,
                             max_discard_sectors, &v);
                blk_queue_max_discard_sectors(q, v ? v : UINT_MAX);

                virtio_cread(vdev, struct virtio_blk_config, max_discard_seg,
                             &v);
                blk_queue_max_discard_segments(q,
                                               min_not_zero(v,
                                                            MAX_DISCARD_SEGMENTS));

                blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
        }

        if (virtio_has_feature(vdev, VIRTIO_BLK_F_WRITE_ZEROES)) {
                virtio_cread(vdev, struct virtio_blk_config,
                             max_write_zeroes_sectors, &v);
                blk_queue_max_write_zeroes_sectors(q, v ? v : UINT_MAX);
        }

        virtblk_update_capacity(vblk, false);
        virtio_device_ready(vdev);

        device_add_disk(&vdev->dev, vblk->disk, virtblk_attr_groups);
        return 0;

out_free_tags:
        blk_mq_free_tag_set(&vblk->tag_set);
out_put_disk:
        put_disk(vblk->disk);
out_free_vq:
        vdev->config->del_vqs(vdev);
out_free_vblk:
        kfree(vblk);
out_free_index:
        ida_simple_remove(&vd_index_ida, index);
out:
        return err;
}

static void virtblk_remove(struct virtio_device *vdev)
{
        struct virtio_blk *vblk = vdev->priv;

        /* Make sure no work handler is accessing the device. */
        flush_work(&vblk->config_work);

        del_gendisk(vblk->disk);
        blk_cleanup_queue(vblk->disk->queue);

        blk_mq_free_tag_set(&vblk->tag_set);

        mutex_lock(&vblk->vdev_mutex);

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

        /* Virtqueues are stopped, nothing can use vblk->vdev anymore. */
        vblk->vdev = NULL;

        put_disk(vblk->disk);
        vdev->config->del_vqs(vdev);
        kfree(vblk->vqs);

        mutex_unlock(&vblk->vdev_mutex);

        virtblk_put(vblk);
}

#ifdef CONFIG_PM_SLEEP
static int virtblk_freeze(struct virtio_device *vdev)
{
        struct virtio_blk *vblk = vdev->priv;

        /* Ensure we don't receive any more interrupts */
        vdev->config->reset(vdev);

        /* Make sure no work handler is accessing the device. */
        flush_work(&vblk->config_work);

        blk_mq_quiesce_queue(vblk->disk->queue);

        vdev->config->del_vqs(vdev);
        return 0;
}

static int virtblk_restore(struct virtio_device *vdev)
{
        struct virtio_blk *vblk = vdev->priv;
        int ret;

        ret = init_vq(vdev->priv);
        if (ret)
                return ret;

        virtio_device_ready(vdev);

        blk_mq_unquiesce_queue(vblk->disk->queue);
        return 0;
}
#endif

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

static unsigned int features_legacy[] = {
        VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
        VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
        VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
        VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
}
;
static unsigned int features[] = {
        VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
        VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
        VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
        VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
};

static struct virtio_driver virtio_blk = {
        .feature_table                  = features,
        .feature_table_size             = ARRAY_SIZE(features),
        .feature_table_legacy           = features_legacy,
        .feature_table_size_legacy      = ARRAY_SIZE(features_legacy),
        .driver.name                    = KBUILD_MODNAME,
        .driver.owner                   = THIS_MODULE,
        .id_table                       = id_table,
        .probe                          = virtblk_probe,
        .remove                         = virtblk_remove,
        .config_changed                 = virtblk_config_changed,
#ifdef CONFIG_PM_SLEEP
        .freeze                         = virtblk_freeze,
        .restore                        = virtblk_restore,
#endif
};

static int __init init(void)
{
        int error;

        virtblk_wq = alloc_workqueue("virtio-blk", 0, 0);
        if (!virtblk_wq)
                return -ENOMEM;

        major = register_blkdev(0, "virtblk");
        if (major < 0) {
                error = major;
                goto out_destroy_workqueue;
        }

        error = register_virtio_driver(&virtio_blk);
        if (error)
                goto out_unregister_blkdev;
        return 0;

out_unregister_blkdev:
        unregister_blkdev(major, "virtblk");
out_destroy_workqueue:
        destroy_workqueue(virtblk_wq);
        return error;
}

static void __exit fini(void)
{
        unregister_virtio_driver(&virtio_blk);
        unregister_blkdev(major, "virtblk");
        destroy_workqueue(virtblk_wq);
}
module_init(init);
module_exit(fini);

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