vhost-blk is an in-kernel virito-blk device accelerator.
Due to lack of proper in-kernel AIO interface, this version converts
guest's I/O request to bio and use submit_bio() to submit I/O directly.
So this version any supports raw block device as guest's disk image,
e.g. /dev/sda, /dev/ram0. We can add file based image support to
vhost-blk once we have in-kernel AIO interface. There are some work in
progress for in-kernel AIO interface from Dave Kleikamp and Zach Brown:
http://marc.info/?l=linux-fsdevel&m=133312234313122
Performance evaluation:
-----------------------------
1) LKVM
Fio with libaio ioengine on Fusion IO device using kvm tool
IOPS Before After Improvement
seq-read 107 121 +13.0%
seq-write 130 179 +37.6%
rnd-read 102 122 +19.6%
rnd-write 125 159 +27.0%
2) QEMU
Fio with libaio ioengine on Fusion IO device using QEMU
IOPS Before After Improvement
seq-read 76 123 +61.8%
seq-write 139 173 +24.4%
rnd-read 73 120 +64.3%
rnd-write 75 156 +108.0%
Userspace bits:
-----------------------------
1) LKVM
The latest vhost-blk userspace bits for kvm tool can be found here:
git at github.com:asias/linux-kvm.git blk.vhost-blk
2) QEMU
The latest vhost-blk userspace prototype for QEMU can be found here:
git at github.com:asias/qemu.git blk.vhost-blk
Changes in V3:
- Sending REQ_FLUSH bio instead of vfs_fsync, thanks Christoph!
- Check file passed by user is a raw block device file
Signed-off-by: Asias He <asias at redhat.com>
---
drivers/vhost/Kconfig | 1 +
drivers/vhost/Kconfig.blk | 10 +
drivers/vhost/Makefile | 2 +
drivers/vhost/blk.c | 669 ++++++++++++++++++++++++++++++++++++++++++++++
drivers/vhost/blk.h | 8 +
5 files changed, 690 insertions(+)
create mode 100644 drivers/vhost/Kconfig.blk
create mode 100644 drivers/vhost/blk.c
create mode 100644 drivers/vhost/blk.h
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 202bba6..acd8038 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -11,4 +11,5 @@ config VHOST_NET
if STAGING
source "drivers/vhost/Kconfig.tcm"
+source "drivers/vhost/Kconfig.blk"
endif
diff --git a/drivers/vhost/Kconfig.blk b/drivers/vhost/Kconfig.blk
new file mode 100644
index 0000000..ff8ab76
--- /dev/null
+++ b/drivers/vhost/Kconfig.blk
@@ -0,0 +1,10 @@
+config VHOST_BLK
+ tristate "Host kernel accelerator for virtio blk (EXPERIMENTAL)"
+ depends on BLOCK && EXPERIMENTAL && m
+ ---help---
+ This kernel module can be loaded in host kernel to accelerate
+ guest block with virtio_blk. Not to be confused with virtio_blk
+ module itself which needs to be loaded in guest kernel.
+
+ To compile this driver as a module, choose M here: the module will
+ be called vhost_blk.
diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile
index a27b053..1a8a4a5 100644
--- a/drivers/vhost/Makefile
+++ b/drivers/vhost/Makefile
@@ -2,3 +2,5 @@ obj-$(CONFIG_VHOST_NET) += vhost_net.o
vhost_net-y := vhost.o net.o
obj-$(CONFIG_TCM_VHOST) += tcm_vhost.o
+obj-$(CONFIG_VHOST_BLK) += vhost_blk.o
+vhost_blk-y := blk.o
diff --git a/drivers/vhost/blk.c b/drivers/vhost/blk.c
new file mode 100644
index 0000000..4a4e793
--- /dev/null
+++ b/drivers/vhost/blk.c
@@ -0,0 +1,669 @@
+/*
+ * Copyright (C) 2011 Taobao, Inc.
+ * Author: Liu Yuan <tailai.ly at taobao.com>
+ *
+ * Copyright (C) 2012 Red Hat, Inc.
+ * Author: Asias He <asias at redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ * virtio-blk server in host kernel.
+ */
+
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/vhost.h>
+#include <linux/virtio_blk.h>
+#include <linux/mutex.h>
+#include <linux/file.h>
+#include <linux/kthread.h>
+#include <linux/blkdev.h>
+
+#include "vhost.c"
+#include "vhost.h"
+#include "blk.h"
+
+#define BLK_HDR 0
+
+static DEFINE_IDA(vhost_blk_index_ida);
+
+enum {
+ VHOST_BLK_VQ_REQ = 0,
+ VHOST_BLK_VQ_MAX = 1,
+};
+
+struct req_page_list {
+ struct page **pages;
+ int pages_nr;
+};
+
+struct vhost_blk_req {
+ struct llist_node llnode;
+ struct req_page_list *pl;
+ struct vhost_blk *blk;
+
+ struct iovec *iov;
+ int iov_nr;
+
+ struct bio **bio;
+ atomic_t bio_nr;
+
+ sector_t sector;
+ int write;
+ u16 head;
+ long len;
+
+ u8 *status;
+};
+
+struct vhost_blk {
+ struct task_struct *host_kick;
+ struct vhost_blk_req *reqs;
+ struct vhost_virtqueue vq;
+ struct llist_head llhead;
+ struct vhost_dev dev;
+ u16 reqs_nr;
+ int index;
+};
+
+static inline int iov_num_pages(struct iovec *iov)
+{
+ return (PAGE_ALIGN((unsigned long)iov->iov_base + iov->iov_len) -
+ ((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT;
+}
+
+static int vhost_blk_setup(struct vhost_blk *blk)
+{
+ blk->reqs_nr = blk->vq.num;
+
+ blk->reqs = kmalloc(sizeof(struct vhost_blk_req) * blk->reqs_nr,
+ GFP_KERNEL);
+ if (!blk->reqs)
+ return -ENOMEM;
+
+ return 0;
+}
+
+static inline int vhost_blk_set_status(struct vhost_blk_req *req, u8 status)
+{
+ struct vhost_blk *blk = req->blk;
+
+ if (copy_to_user(req->status, &status, sizeof(status))) {
+ vq_err(&blk->vq, "Failed to write status\n");
+ vhost_discard_vq_desc(&blk->vq, 1);
+ return -EFAULT;
+ }
+
+ return 0;
+}
+
+static void vhost_blk_enable_vq(struct vhost_blk *blk,
+ struct vhost_virtqueue *vq)
+{
+ wake_up_process(blk->host_kick);
+}
+
+static void vhost_blk_req_done(struct bio *bio, int err)
+{
+ struct vhost_blk_req *req = bio->bi_private;
+ struct vhost_blk *blk = req->blk;
+
+ if (err)
+ req->len = err;
+
+ if (atomic_dec_and_test(&req->bio_nr)) {
+ llist_add(&req->llnode, &blk->llhead);
+ wake_up_process(blk->host_kick);
+ }
+
+ bio_put(bio);
+}
+
+static void vhost_blk_req_umap(struct vhost_blk_req *req)
+{
+ struct req_page_list *pl;
+ int i, j;
+
+
+ if (!req->pl) {
+ kfree(req->bio);
+ return;
+ }
+
+ for (i = 0; i < req->iov_nr; i++) {
+ pl = &req->pl[i];
+ for (j = 0; j < pl->pages_nr; j++) {
+ if (!req->write)
+ set_page_dirty_lock(pl->pages[j]);
+ page_cache_release(pl->pages[j]);
+ }
+ }
+
+ kfree(req->pl);
+}
+
+static int vhost_blk_bio_make(struct vhost_blk_req *req,
+ struct block_device *bdev)
+{
+ int pages_nr_total, i, j, ret;
+ struct iovec *iov = req->iov;
+ int iov_nr = req->iov_nr;
+ struct page **pages, *page;
+ struct bio *bio = NULL;
+ int bio_nr = 0;
+
+ req->len = 0;
+ pages_nr_total = 0;
+ for (i = 0; i < iov_nr; i++) {
+ req->len += iov[i].iov_len;
+ pages_nr_total += iov_num_pages(&iov[i]);
+ }
+
+ if (unlikely(req->write == WRITE_FLUSH)) {
+ req->pl = NULL;
+ req->bio = kmalloc(sizeof(struct bio *), GFP_KERNEL);
+ bio = bio_alloc(GFP_KERNEL, 1);
+ if (!bio) {
+ kfree(req->bio);
+ return -ENOMEM;
+ }
+ bio->bi_sector = req->sector;
+ bio->bi_bdev = bdev;
+ bio->bi_private = req;
+ bio->bi_end_io = vhost_blk_req_done;
+ req->bio[bio_nr++] = bio;
+
+ goto out;
+ }
+
+ req->pl = kmalloc((iov_nr * sizeof(struct req_page_list)) +
+ (pages_nr_total * sizeof(struct page *)) +
+ (pages_nr_total * sizeof(struct bio *)),
+ GFP_KERNEL);
+ if (!req->pl)
+ return -ENOMEM;
+ pages = (struct page **)&req->pl[iov_nr];
+ req->bio = (struct bio **)&pages[pages_nr_total];
+
+ req->iov_nr = 0;
+ for (i = 0; i < iov_nr; i++) {
+ int pages_nr = iov_num_pages(&iov[i]);
+ unsigned long iov_base, iov_len;
+ struct req_page_list *pl;
+
+ iov_base = (unsigned long)iov[i].iov_base;
+ iov_len = (unsigned long)iov[i].iov_len;
+
+ ret = get_user_pages_fast(iov_base, pages_nr,
+ !req->write, pages);
+ if (ret != pages_nr)
+ goto fail;
+
+ req->iov_nr++;
+ pl = &req->pl[i];
+ pl->pages_nr = pages_nr;
+ pl->pages = pages;
+
+ for (j = 0; j < pages_nr; j++) {
+ unsigned int off, len;
+ page = pages[j];
+ off = iov_base & ~PAGE_MASK;
+ len = PAGE_SIZE - off;
+ if (len > iov_len)
+ len = iov_len;
+
+ while (!bio || bio_add_page(bio, page, len, off) <= 0) {
+ bio = bio_alloc(GFP_KERNEL, pages_nr);
+ if (!bio)
+ goto fail;
+ bio->bi_sector = req->sector;
+ bio->bi_bdev = bdev;
+ bio->bi_private = req;
+ bio->bi_end_io = vhost_blk_req_done;
+ req->bio[bio_nr++] = bio;
+ }
+ req->sector += len >> 9;
+ iov_base += len;
+ iov_len -= len;
+ }
+
+ pages += pages_nr;
+ }
+out:
+ atomic_set(&req->bio_nr, bio_nr);
+ return 0;
+
+fail:
+ for (i = 0; i < bio_nr; i++)
+ bio_put(req->bio[i]);
+ vhost_blk_req_umap(req);
+ return -ENOMEM;
+}
+
+static inline void vhost_blk_bio_send(struct vhost_blk_req *req)
+{
+ struct blk_plug plug;
+ int i, bio_nr;
+
+ bio_nr = atomic_read(&req->bio_nr);
+ blk_start_plug(&plug);
+ for (i = 0; i < bio_nr; i++)
+ submit_bio(req->write, req->bio[i]);
+ blk_finish_plug(&plug);
+}
+
+static int vhost_blk_req_submit(struct vhost_blk_req *req, struct file *file)
+{
+
+ struct inode *inode = file->f_mapping->host;
+ struct block_device *bdev = inode->i_bdev;
+ int ret;
+
+ ret = vhost_blk_bio_make(req, bdev);
+ if (ret < 0)
+ return ret;
+
+ vhost_blk_bio_send(req);
+
+ return ret;
+}
+
+static int vhost_blk_req_done_thread(void *data)
+{
+ mm_segment_t oldfs = get_fs();
+ struct vhost_blk *blk = data;
+ struct vhost_virtqueue *vq;
+ struct llist_node *llnode;
+ struct vhost_blk_req *req;
+ bool added;
+ u8 status;
+ int ret;
+
+ vq = &blk->vq;
+ set_fs(USER_DS);
+ use_mm(blk->dev.mm);
+ for (;;) {
+ llnode = llist_del_all(&blk->llhead);
+ if (!llnode) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule();
+ if (unlikely(kthread_should_stop()))
+ break;
+ continue;
+ }
+ added = false;
+ while (llnode) {
+ req = llist_entry(llnode, struct vhost_blk_req, llnode);
+ llnode = llist_next(llnode);
+
+ vhost_blk_req_umap(req);
+
+ status = req->len > 0 ?
+ VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR;
+ ret = copy_to_user(req->status, &status,
+ sizeof(status));
+ if (unlikely(ret)) {
+ vq_err(&blk->vq, "Failed to write status\n");
+ return -1;
+ }
+ vhost_add_used(&blk->vq, req->head, req->len);
+ added = true;
+ }
+ if (likely(added))
+ vhost_signal(&blk->dev, &blk->vq);
+
+ }
+ unuse_mm(blk->dev.mm);
+ set_fs(oldfs);
+ return 0;
+}
+
+static void vhost_blk_flush(struct vhost_blk *blk)
+{
+ vhost_poll_flush(&blk->vq.poll);
+}
+
+static struct file *vhost_blk_stop_vq(struct vhost_blk *blk,
+ struct vhost_virtqueue *vq)
+{
+ struct file *file;
+
+ mutex_lock(&vq->mutex);
+ file = rcu_dereference_protected(vq->private_data,
+ lockdep_is_held(&vq->mutex));
+ rcu_assign_pointer(vq->private_data, NULL);
+ mutex_unlock(&vq->mutex);
+
+ return file;
+
+}
+
+static inline void vhost_blk_stop(struct vhost_blk *blk, struct file **file)
+{
+
+ *file = vhost_blk_stop_vq(blk, &blk->vq);
+}
+
+/* Handle guest request */
+static int vhost_blk_req_handle(struct vhost_virtqueue *vq,
+ struct virtio_blk_outhdr *hdr,
+ u16 head, u16 out, u16 in,
+ struct file *file)
+{
+ struct vhost_blk *blk = container_of(vq->dev, struct vhost_blk, dev);
+ struct vhost_blk_req *req;
+ int iov_nr, ret;
+ u8 status;
+
+ if (hdr->type == VIRTIO_BLK_T_IN || hdr->type == VIRTIO_BLK_T_GET_ID)
+ iov_nr = in - 1;
+ else
+ iov_nr = out - 1;
+
+ req = &blk->reqs[head];
+ req->head = head;
+ req->status = blk->vq.iov[iov_nr + 1].iov_base;
+ req->blk = blk;
+ req->iov = &vq->iov[BLK_HDR + 1];
+ req->iov_nr = iov_nr;
+ req->sector = hdr->sector;
+
+ switch (hdr->type) {
+ case VIRTIO_BLK_T_OUT:
+ req->write = WRITE;
+ ret = vhost_blk_req_submit(req, file);
+ break;
+ case VIRTIO_BLK_T_IN:
+ req->write = READ;
+ ret = vhost_blk_req_submit(req, file);
+ break;
+ case VIRTIO_BLK_T_FLUSH:
+ req->write = WRITE_FLUSH;
+ ret = vhost_blk_req_submit(req, file);
+ break;
+ case VIRTIO_BLK_T_GET_ID:
+ ret = snprintf(vq->iov[BLK_HDR + 1].iov_base,
+ VIRTIO_BLK_ID_BYTES, "vhost-blk%d", blk->index);
+ status = ret < 0 ? VIRTIO_BLK_S_IOERR : VIRTIO_BLK_S_OK;
+ if (!vhost_blk_set_status(req, status))
+ vhost_add_used_and_signal(&blk->dev, vq, head, ret);
+ break;
+ default:
+ pr_warn("Unsupported request type %d\n", hdr->type);
+ vhost_discard_vq_desc(vq, 1);
+ ret = -EFAULT;
+ break;
+ }
+
+ return ret;
+}
+
+/* Guest kick us for IO request */
+static void vhost_blk_handle_guest_kick(struct vhost_work *work)
+{
+ struct virtio_blk_outhdr hdr;
+ struct vhost_virtqueue *vq;
+ struct vhost_blk *blk;
+ struct blk_plug plug;
+ struct file *f;
+ int in, out;
+ u16 head;
+
+ vq = container_of(work, struct vhost_virtqueue, poll.work);
+ blk = container_of(vq->dev, struct vhost_blk, dev);
+
+ /* TODO: check that we are running from vhost_worker? */
+ f = rcu_dereference_check(vq->private_data, 1);
+ if (!f)
+ return;
+
+ vhost_disable_notify(&blk->dev, vq);
+ blk_start_plug(&plug);
+ for (;;) {
+ head = vhost_get_vq_desc(&blk->dev, vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in, NULL, NULL);
+ if (unlikely(head < 0))
+ break;
+
+ if (unlikely(head == vq->num)) {
+ if (unlikely(vhost_enable_notify(&blk->dev, vq))) {
+ vhost_disable_notify(&blk->dev, vq);
+ continue;
+ }
+ break;
+ }
+
+ if (unlikely(copy_from_user(&hdr, vq->iov[BLK_HDR].iov_base,
+ sizeof(hdr)))) {
+ vq_err(vq, "Failed to get block header!\n");
+ vhost_discard_vq_desc(vq, 1);
+ break;
+ }
+
+ if (vhost_blk_req_handle(vq, &hdr, head, out, in, f) < 0)
+ break;
+ }
+ blk_finish_plug(&plug);
+}
+
+static int vhost_blk_open(struct inode *inode, struct file *file)
+{
+ struct vhost_blk *blk;
+ int ret;
+
+ blk = kzalloc(sizeof(*blk), GFP_KERNEL);
+ if (!blk) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ ret = ida_simple_get(&vhost_blk_index_ida, 0, 0, GFP_KERNEL);
+ if (ret < 0)
+ goto out_dev;
+ blk->index = ret;
+
+ blk->vq.handle_kick = vhost_blk_handle_guest_kick;
+
+ ret = vhost_dev_init(&blk->dev, &blk->vq, VHOST_BLK_VQ_MAX);
+ if (ret < 0)
+ goto out_dev;
+ file->private_data = blk;
+
+ blk->host_kick = kthread_create(vhost_blk_req_done_thread,
+ blk, "vhost-blk-%d", current->pid);
+ if (IS_ERR(blk->host_kick)) {
+ ret = PTR_ERR(blk->host_kick);
+ goto out_dev;
+ }
+
+ return ret;
+out_dev:
+ kfree(blk);
+out:
+ return ret;
+}
+
+static int vhost_blk_release(struct inode *inode, struct file *f)
+{
+ struct vhost_blk *blk = f->private_data;
+ struct file *file;
+
+ ida_simple_remove(&vhost_blk_index_ida, blk->index);
+ vhost_blk_stop(blk, &file);
+ vhost_blk_flush(blk);
+ vhost_dev_cleanup(&blk->dev, false);
+ if (file)
+ fput(file);
+ kthread_stop(blk->host_kick);
+ kfree(blk->reqs);
+ kfree(blk);
+
+ return 0;
+}
+
+static int vhost_blk_set_features(struct vhost_blk *blk, u64 features)
+{
+ mutex_lock(&blk->dev.mutex);
+ blk->dev.acked_features = features;
+ mutex_unlock(&blk->dev.mutex);
+
+ return 0;
+}
+
+static long vhost_blk_set_backend(struct vhost_blk *blk, unsigned index, int
fd)
+{
+ struct vhost_virtqueue *vq = &blk->vq;
+ struct file *file, *oldfile;
+ struct inode *inode;
+ int ret;
+
+ mutex_lock(&blk->dev.mutex);
+ ret = vhost_dev_check_owner(&blk->dev);
+ if (ret)
+ goto out_dev;
+
+ if (index >= VHOST_BLK_VQ_MAX) {
+ ret = -ENOBUFS;
+ goto out_dev;
+ }
+
+ mutex_lock(&vq->mutex);
+
+ if (!vhost_vq_access_ok(vq)) {
+ ret = -EFAULT;
+ goto out_vq;
+ }
+
+ file = fget(fd);
+ if (IS_ERR(file)) {
+ ret = PTR_ERR(file);
+ goto out_vq;
+ }
+
+ /* Only raw block device is supported for now */
+ inode = file->f_mapping->host;
+ if (!S_ISBLK(inode->i_mode)) {
+ ret = -EFAULT;
+ goto out_file;
+ }
+
+ oldfile = rcu_dereference_protected(vq->private_data,
+ lockdep_is_held(&vq->mutex));
+ if (file != oldfile) {
+ rcu_assign_pointer(vq->private_data, file);
+ vhost_blk_enable_vq(blk, vq);
+
+ ret = vhost_init_used(vq);
+ if (ret)
+ goto out_file;
+ }
+
+ mutex_unlock(&vq->mutex);
+
+ if (oldfile) {
+ vhost_blk_flush(blk);
+ fput(oldfile);
+ }
+
+ mutex_unlock(&blk->dev.mutex);
+ return 0;
+
+out_file:
+ fput(file);
+out_vq:
+ mutex_unlock(&vq->mutex);
+out_dev:
+ mutex_unlock(&blk->dev.mutex);
+ return ret;
+}
+
+static long vhost_blk_reset_owner(struct vhost_blk *blk)
+{
+ struct file *file = NULL;
+ int err;
+
+ mutex_lock(&blk->dev.mutex);
+ err = vhost_dev_check_owner(&blk->dev);
+ if (err)
+ goto done;
+ vhost_blk_stop(blk, &file);
+ vhost_blk_flush(blk);
+ err = vhost_dev_reset_owner(&blk->dev);
+done:
+ mutex_unlock(&blk->dev.mutex);
+ if (file)
+ fput(file);
+ return err;
+}
+
+static long vhost_blk_ioctl(struct file *f, unsigned int ioctl,
+ unsigned long arg)
+{
+ struct vhost_blk *blk = f->private_data;
+ void __user *argp = (void __user *)arg;
+ struct vhost_vring_file backend;
+ u64 __user *featurep = argp;
+ u64 features;
+ int ret;
+
+ switch (ioctl) {
+ case VHOST_BLK_SET_BACKEND:
+ if (copy_from_user(&backend, argp, sizeof(backend)))
+ return -EFAULT;
+ return vhost_blk_set_backend(blk, backend.index, backend.fd);
+ case VHOST_GET_FEATURES:
+ features = VHOST_BLK_FEATURES;
+ if (copy_to_user(featurep, &features, sizeof(features)))
+ return -EFAULT;
+ return 0;
+ case VHOST_SET_FEATURES:
+ if (copy_from_user(&features, featurep, sizeof(features)))
+ return -EFAULT;
+ if (features & ~VHOST_BLK_FEATURES)
+ return -EOPNOTSUPP;
+ return vhost_blk_set_features(blk, features);
+ case VHOST_RESET_OWNER:
+ return vhost_blk_reset_owner(blk);
+ default:
+ mutex_lock(&blk->dev.mutex);
+ ret = vhost_dev_ioctl(&blk->dev, ioctl, arg);
+ if (!ret && ioctl == VHOST_SET_VRING_NUM)
+ ret = vhost_blk_setup(blk);
+ vhost_blk_flush(blk);
+ mutex_unlock(&blk->dev.mutex);
+ return ret;
+ }
+}
+
+static const struct file_operations vhost_blk_fops = {
+ .owner = THIS_MODULE,
+ .open = vhost_blk_open,
+ .release = vhost_blk_release,
+ .llseek = noop_llseek,
+ .unlocked_ioctl = vhost_blk_ioctl,
+};
+
+static struct miscdevice vhost_blk_misc = {
+ MISC_DYNAMIC_MINOR,
+ "vhost-blk",
+ &vhost_blk_fops,
+};
+
+int vhost_blk_init(void)
+{
+ return misc_register(&vhost_blk_misc);
+}
+
+void vhost_blk_exit(void)
+{
+ misc_deregister(&vhost_blk_misc);
+}
+
+module_init(vhost_blk_init);
+module_exit(vhost_blk_exit);
+
+MODULE_VERSION("0.0.3");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Asias He");
+MODULE_DESCRIPTION("Host kernel accelerator for virtio_blk");
diff --git a/drivers/vhost/blk.h b/drivers/vhost/blk.h
new file mode 100644
index 0000000..2f674f0
--- /dev/null
+++ b/drivers/vhost/blk.h
@@ -0,0 +1,8 @@
+#include <linux/vhost.h>
+
+enum {
+ VHOST_BLK_FEATURES = (1ULL << VIRTIO_RING_F_INDIRECT_DESC) |
+ (1ULL << VIRTIO_RING_F_EVENT_IDX),
+};
+/* VHOST_BLK specific defines */
+#define VHOST_BLK_SET_BACKEND _IOW(VHOST_VIRTIO, 0x50, struct vhost_vring_file)
--
1.7.11.4
