Message-ID: <50AB25AC.2070606@redhat.com>
Date:	Tue, 20 Nov 2012 14:39:40 +0800
From:	Asias He <asias@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Hellwig <hch@...radead.org>, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, axboe@...nel.dk,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost-blk: Add vhost-blk support v5

On 11/20/2012 04:26 AM, Michael S. Tsirkin wrote:
> On Mon, Nov 19, 2012 at 04:53:42PM +0800, Asias He wrote:
>> 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(k)    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(k)    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%
> 
> Could you compare with dataplane qemu as well please?


Well, I will try to collect it.

> 
>>
>> Userspace bits:
>> -----------------------------
>> 1) LKVM
>> The latest vhost-blk userspace bits for kvm tool can be found here:
>> git@...hub.com:asias/linux-kvm.git blk.vhost-blk
>>
>> 2) QEMU
>> The latest vhost-blk userspace prototype for QEMU can be found here:
>> git@...hub.com:asias/qemu.git blk.vhost-blk
>>
>> Changes in v5:
>> - Do not assume the buffer layout
>> - Fix wakeup race
>>
>> Changes in v4:
>> - Mark req->status as userspace pointer
>> - Use __copy_to_user() instead of copy_to_user() in vhost_blk_set_status()
>> - Add if (need_resched()) schedule() in blk thread
>> - Kill vhost_blk_stop_vq() and move it into vhost_blk_stop()
>> - Use vq_err() instead of pr_warn()
>> - Fail un Unsupported request
>> - Add flush in vhost_blk_set_features()
>>
>> 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@...hat.com>
> 
> Since there are files shared by this and vhost net
> it's easiest for me to merge this all through the
> vhost tree.
> 
> Jens, could you ack this and the bio usage in this driver
> please?
> 
>> ---
>>  drivers/vhost/Kconfig     |   1 +
>>  drivers/vhost/Kconfig.blk |  10 +
>>  drivers/vhost/Makefile    |   2 +
>>  drivers/vhost/blk.c       | 697 ++++++++++++++++++++++++++++++++++++++++++++++
>>  drivers/vhost/blk.h       |   8 +
>>  5 files changed, 718 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..f0f118a
>> --- /dev/null
>> +++ b/drivers/vhost/blk.c
>> @@ -0,0 +1,697 @@
>> +/*
>> + * Copyright (C) 2011 Taobao, Inc.
>> + * Author: Liu Yuan <tailai.ly@...bao.com>
>> + *
>> + * Copyright (C) 2012 Red Hat, Inc.
>> + * Author: Asias He <asias@...hat.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 <linux/llist.h>
>> +
>> +#include "vhost.c"
>> +#include "vhost.h"
>> +#include "blk.h"
>> +
>> +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;
>> +
>> +	struct iovec status[1];
>> +
>> +	sector_t sector;
>> +	int write;
>> +	u16 head;
>> +	long len;
>> +};
>> +
>> +struct vhost_blk {
>> +	struct task_struct *host_kick;
> 
> Could you please add a comment here explaining why
> is this better than using the builtin vhost thread?

With separate thread model, the request submit and request completion
can be handled in parallel. I have measured significant performance
improvement with this model. In the long term, It would be nice if the
vhost core can provide multiple thread support.

>> +	struct iovec iov[UIO_MAXIOV];
>> +	struct vhost_blk_req *reqs;
>> +	struct vhost_virtqueue vq;
>> +	struct llist_head llhead;
>> +	struct vhost_dev dev;
>> +	u16 reqs_nr;
>> +	int index;
>> +};
>> +
>> +static int move_iovec(struct iovec *from, struct iovec *to,
>> +		      size_t len, int iov_count)
>> +{
>> +	int seg = 0;
>> +	size_t size;
>> +
>> +	while (len && seg < iov_count) {
>> +		if (from->iov_len == 0) {
>> +			++from;
>> +			continue;
>> +		}
>> +		size = min(from->iov_len, len);
>> +		to->iov_base = from->iov_base;
>> +		to->iov_len = size;
>> +		from->iov_len -= size;
>> +		from->iov_base += size;
>> +		len -= size;
>> +		++from;
>> +		++to;
>> +		++seg;
>> +	}
>> +	return seg;
>> +}
>> +
>> +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;
>> +	int ret;
>> +
>> +	ret = memcpy_toiovecend(req->status, &status, 0, sizeof(status));
>> +
>> +	if (ret) {
>> +		vq_err(&blk->vq, "Failed to write status\n");
>> +		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 pl_len, page_len, bio_len;
>> +	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;
>> +	void *buf;
>> +
>> +	pages_nr_total = 0;
>> +	for (i = 0; i < iov_nr; i++)
>> +		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;
>> +	}
>> +
>> +	pl_len = iov_nr * sizeof(req->pl[0]);
>> +	page_len = pages_nr_total * sizeof(struct page *);
>> +	bio_len = pages_nr_total * sizeof(struct bio *);
>> +
>> +	buf = kmalloc(pl_len + page_len + bio_len, GFP_KERNEL);
>> +	if (!buf)
>> +		return -ENOMEM;
>> +
>> +	req->pl	= buf;
>> +	pages = buf + pl_len;
>> +	req->bio = buf + pl_len + page_len;
>> +
>> +	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;
>> +
>> +		/* TODO: Limit the total number of pages pinned */
> 
> What's the plan here? Is there some limit if e.g. aio is used?

The problem is there is no easy way to find a proper limit number. May
be 16 * vq size number of pages as you sugguested.

With aio, we do not touch this code path at all.

>> +		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 (;;) {
>> +		set_current_state(TASK_INTERRUPTIBLE);
>> +		llnode = llist_del_all(&blk->llhead);
>> +		if (!llnode) {
>> +			schedule();
>> +			if (unlikely(kthread_should_stop()))
>> +				break;
>> +			continue;
>> +		}
>> +		set_current_state(TASK_RUNNING);
>> +
>> +		if (need_resched())
>> +			schedule();
>> +
>> +		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 = vhost_blk_set_status(req, status);
>> +			if (unlikely(ret))
>> +				continue;
>> +			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 inline void vhost_blk_stop(struct vhost_blk *blk, struct file **file)
>> +{
>> +	struct vhost_virtqueue *vq = &blk->vq;
>> +	struct file *f;
>> +
>> +	mutex_lock(&vq->mutex);
>> +	f = rcu_dereference_protected(vq->private_data,
>> +				      lockdep_is_held(&vq->mutex));
>> +	rcu_assign_pointer(vq->private_data, NULL);
>> +	mutex_unlock(&vq->mutex);
>> +
>> +	*file = f;
>> +}
>> +
>> +/* 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);
>> +	unsigned char id[VIRTIO_BLK_ID_BYTES];
>> +	struct vhost_blk_req *req;
>> +	int ret, len;
>> +	u8 status;
>> +
>> +	req		= &blk->reqs[head];
>> +	req->head	= head;
>> +	req->blk	= blk;
>> +	req->sector	= hdr->sector;
>> +	req->iov	= blk->iov;
>> +
>> +	req->len	= iov_length(vq->iov, out + in) - sizeof(status);
>> +	req->iov_nr	= move_iovec(vq->iov, req->iov, req->len, out + in);
>> +
>> +	move_iovec(vq->iov, req->status, sizeof(status), out + in);
>> +
>> +	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(id, VIRTIO_BLK_ID_BYTES,
>> +			       "vhost-blk%d", blk->index);
>> +		if (ret < 0)
>> +			break;
>> +		len = ret;
>> +		ret = memcpy_toiovecend(req->iov, id, 0, len);
>> +		status = ret < 0 ? VIRTIO_BLK_S_IOERR : VIRTIO_BLK_S_OK;
>> +		ret = vhost_blk_set_status(req, status);
>> +		if (ret)
>> +			break;
>> +		vhost_add_used_and_signal(&blk->dev, vq, head, len);
>> +		break;
>> +	default:
>> +		vq_err(vq, "Unsupported request type %d\n", hdr->type);
>> +		status = VIRTIO_BLK_S_UNSUPP;
>> +		ret = vhost_blk_set_status(req, status);
>> +		if (ret)
>> +			break;
>> +		vhost_add_used_and_signal(&blk->dev, vq, head, 0);
>> +	}
>> +
>> +	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;
>> +	int in, out, ret;
>> +	struct file *f;
>> +	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);
>> +	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;
>> +		}
>> +		move_iovec(vq->iov, vq->hdr, sizeof(hdr), out);
>> +		ret = memcpy_fromiovecend((unsigned char *)&hdr, vq->hdr, 0,
>> +					   sizeof(hdr));
>> +		if (ret < 0) {
>> +			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;
>> +	}
>> +}
>> +
>> +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;
>> +	vhost_blk_flush(blk);
>> +	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,
>> +};
>> +
>> +static int vhost_blk_init(void)
>> +{
>> +	return misc_register(&vhost_blk_misc);
>> +}
>> +
>> +static void vhost_blk_exit(void)
>> +{
>> +	misc_deregister(&vhost_blk_misc);
>> +}
>> +
>> +module_init(vhost_blk_init);
>> +module_exit(vhost_blk_exit);
>> +
>> +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)
>> -- 
>> 1.7.11.7


-- 
Asias
--
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