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SubjectRe: [PATCH 4/9] virtio-blk: use virtqueue_start_buf on req path
On 02/12/2013 08:23 PM, Paolo Bonzini wrote:
> This is similar to the previous patch, but a bit more radical
> because the bio and req paths now share the buffer construction
> code. Because the req path doesn't use vbr->sg, however, we
> need to add a couple of arguments to __virtblk_add_req.
>
> We also need to teach __virtblk_add_req how to build SCSI command
> requests.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> drivers/block/virtio_blk.c | 74 ++++++++++++++++++++++---------------------
> 1 files changed, 38 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 4a31fcc..22deb65 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -102,18 +102,26 @@ static inline struct virtblk_req *virtblk_alloc_req(struct virtio_blk *vblk,
> }
>
> static int __virtblk_add_req(struct virtqueue *vq,
> - struct virtblk_req *vbr)
> + struct virtblk_req *vbr,
> + struct scatterlist *data_sg,
> + unsigned data_nents)
> {
> struct scatterlist sg;
> enum dma_data_direction dir;
> int ret;
>
> + int type = vbr->out_hdr.type & ~VIRTIO_BLK_T_OUT;
> unsigned int nents = 2;
> unsigned int nsg = 2;
>
> - if (vbr->nents) {
> + if (type == VIRTIO_BLK_T_SCSI_CMD) {
> + BUG_ON(use_bio);

Do we really need the BUG_ON? Even if with use_bio=1,
VIRTIO_BLK_T_SCSI_CMD cmd can be fired. See this:

# cat /proc/cmdline
root=/dev/mapper/rhel-root console=ttyS0 virtio_blk.use_bio=1

# sg_inq /dev/vda
[ 36.042300] ------------[ cut here ]------------
[ 36.043021] kernel BUG at drivers/block/virtio_blk.c:118!
[ 36.043021] invalid opcode: 0000 [#1] SMP
[ 36.043021] Modules linked in:
[ 36.043021] CPU 2
[ 36.043021] Pid: 3311, comm: sg_inq Not tainted 3.8.0-rc7+ #618 Bochs
Bochs
[ 36.043021] RIP: 0010:[<ffffffff816d740d>] [<ffffffff816d740d>]
__virtblk_add_req+0x1cd/0x1e0
[ 36.043021] RSP: 0018:ffff88007b59b9d8 EFLAGS: 00010002
[ 36.043021] RAX: 0000000000000001 RBX: 0000000000000002 RCX:
0000000000000002
[ 36.043021] RDX: 0000000000000002 RSI: ffff88007a430000 RDI:
ffff88007b422000
[ 36.043021] RBP: ffff88007b59ba28 R08: ffff88007b59b9e0 R09:
ffff88007b59b9f4
[ 36.043021] R10: 0000000000000001 R11: ffff88007bf57900 R12:
ffff88007a430000
[ 36.043021] R13: ffff88007b422000 R14: 0000000000000001 R15:
ffff880077d34088
[ 36.043021] FS: 00007eff2efcb740(0000) GS:ffff88007eb00000(0000)
knlGS:0000000000000000
[ 36.043021] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 36.043021] CR2: 0000003f33e0f200 CR3: 000000007f023000 CR4:
00000000000006e0
[ 36.043021] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 36.043021] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
0000000000000400
[ 36.043021] Process sg_inq (pid: 3311, threadinfo ffff88007b59a000,
task ffff88007f47a3f0)
[ 36.043021] Stack:
[ 36.043021] ffff88007b59ba40 ffff880077d34088 ffff88007bf57980
0000000100000001
[ 36.043021] ffff88007fffa6c0 ffff88007a430000 ffff88007f66abc0
ffff880077d34000
[ 36.043021] ffff88007bdab410 0000000000000000 ffff88007b59ba78
ffffffff816d7f6c
[ 36.043021] Call Trace:
[ 36.043021] [<ffffffff816d7f6c>] virtblk_request+0xec/0x1c0
[ 36.043021] [<ffffffff8148b947>] __blk_run_queue+0x37/0x50
[ 36.043021] [<ffffffff81486c10>] __elv_add_request+0xb0/0x230
[ 36.043021] [<ffffffff81491c69>] blk_execute_rq_nowait+0x79/0x100
[ 36.043021] [<ffffffff811f06e1>] ? bio_phys_segments+0x21/0x30
[ 36.043021] [<ffffffff81491d5d>] blk_execute_rq+0x6d/0xf0
[ 36.043021] [<ffffffff81491798>] ? blk_rq_append_bio+0x28/0x70
[ 36.043021] [<ffffffff81491ad0>] ? blk_rq_map_user+0x1a0/0x280
[ 36.043021] [<ffffffff814979c4>] sg_io+0x274/0x3e0
[ 36.043021] [<ffffffff81497f15>] scsi_cmd_ioctl+0x3e5/0x460
[ 36.043021] [<ffffffff8118c816>] ? handle_pte_fault+0xf6/0x9c0
[ 36.043021] [<ffffffff8116e8e0>] ? release_pages+0x190/0x1e0
[ 36.043021] [<ffffffff81497fe1>] scsi_cmd_blk_ioctl+0x51/0x70
[ 36.043021] [<ffffffff816d80ac>] virtblk_ioctl+0x6c/0x90
[ 36.043021] [<ffffffff81494068>] __blkdev_driver_ioctl+0x28/0x30
[ 36.043021] [<ffffffff814946d0>] blkdev_ioctl+0x200/0x7b0
[ 36.043021] [<ffffffff811c0836>] ? cp_new_stat+0x116/0x130
[ 36.043021] [<ffffffff811f232c>] block_ioctl+0x3c/0x40
[ 36.043021] [<ffffffff811cceaa>] do_vfs_ioctl+0x9a/0x550
[ 36.043021] [<ffffffff811cd3b7>] sys_ioctl+0x57/0x90
[ 36.043021] [<ffffffff814b7c4e>] ? trace_hardirqs_on_thunk+0x3a/0x3c
[ 36.043021] [<ffffffff81c6ad99>] system_call_fastpath+0x16/0x1b
[ 36.043021] Code: 24 20 48 8d 7d b0 ba 10 00 00 00 e8 2e 3d de ff 48
8d 75 b0 b9 02 00 00 00 ba 01 00 00 00 4c 89 ef e8 88 bb e6 ff
e9 d9 fe ff ff <0f> 0b eb fe 66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00
00 55 48
[ 36.043021] RIP [<ffffffff816d740d>] __virtblk_add_req+0x1cd/0x1e0
[ 36.043021] RSP <ffff88007b59b9d8>
[ 36.043021] ---[ end trace 93ac0a3ba2789369 ]---


> + nsg += 3;
> + nents += 3;
> + }
> + if (data_nents) {
> nsg++;
> - nents += vbr->nents;
> + nents += data_nents;
> }
>
> ret = virtqueue_start_buf(vq, vbr, nents, nsg, GFP_ATOMIC);
> @@ -124,14 +132,32 @@ static int __virtblk_add_req(struct virtqueue *vq,
> sg_init_one(&sg, &vbr->out_hdr, sizeof(vbr->out_hdr));
> virtqueue_add_sg(vq, &sg, 1, dir);
>
> - if (vbr->nents) {
> + /*
> + * If this is a packet command we need a couple of additional headers.
> + * Behind the normal outhdr we put a segment with the scsi command
> + * block, and before the normal inhdr we put the sense data and the
> + * inhdr with additional status information.
> + */
> + if (type == VIRTIO_BLK_T_SCSI_CMD) {
> + sg_init_one(&sg, vbr->req->cmd, vbr->req->cmd_len);
> + virtqueue_add_sg(vq, &sg, 1, dir);
> + }
> +
> + if (data_nents) {
> if ((vbr->out_hdr.type & VIRTIO_BLK_T_OUT) == 0)
> dir = DMA_FROM_DEVICE;
>
> - virtqueue_add_sg(vq, vbr->sg, vbr->nents, dir);
> + virtqueue_add_sg(vq, data_sg, data_nents, dir);
> }
>
> dir = DMA_FROM_DEVICE;
> + if (type == VIRTIO_BLK_T_SCSI_CMD) {
> + sg_init_one(&sg, vbr->req->sense, SCSI_SENSE_BUFFERSIZE);
> + virtqueue_add_sg(vq, &sg, 1, dir);
> + sg_init_one(&sg, &vbr->in_hdr, sizeof(vbr->in_hdr));
> + virtqueue_add_sg(vq, &sg, 1, dir);
> + }
> +
> sg_init_one(&sg, &vbr->status, sizeof(vbr->status));
> virtqueue_add_sg(vq, &sg, 1, dir);
>
> @@ -146,7 +172,8 @@ static void virtblk_add_req(struct virtblk_req *vbr)
> int ret;
>
> spin_lock_irq(vblk->disk->queue->queue_lock);
> - while (unlikely((ret = __virtblk_add_req(vblk->vq, vbr)) < 0)) {
> + while (unlikely((ret = __virtblk_add_req(vblk->vq, vbr, vbr->sg,
> + vbr->nents)) < 0)) {
> prepare_to_wait_exclusive(&vblk->queue_wait, &wait,
> TASK_UNINTERRUPTIBLE);
>
> @@ -299,7 +326,7 @@ static void virtblk_done(struct virtqueue *vq)
> static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
> struct request *req)
> {
> - unsigned long num, out = 0, in = 0;
> + unsigned int num;
> struct virtblk_req *vbr;
>
> vbr = virtblk_alloc_req(vblk, GFP_ATOMIC);
> @@ -336,40 +363,15 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
> }
> }
>
> - sg_set_buf(&vblk->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));
> -
> - /*
> - * If this is a packet command we need a couple of additional headers.
> - * Behind the normal outhdr we put a segment with the scsi command
> - * block, and before the normal inhdr we put the sense data and the
> - * inhdr with additional status information before the normal inhdr.
> - */
> - if (vbr->req->cmd_type == REQ_TYPE_BLOCK_PC)
> - sg_set_buf(&vblk->sg[out++], vbr->req->cmd, vbr->req->cmd_len);
> -
> - num = blk_rq_map_sg(q, vbr->req, vblk->sg + out);
> -
> - if (vbr->req->cmd_type == REQ_TYPE_BLOCK_PC) {
> - sg_set_buf(&vblk->sg[num + out + in++], vbr->req->sense, SCSI_SENSE_BUFFERSIZE);
> - sg_set_buf(&vblk->sg[num + out + in++], &vbr->in_hdr,
> - sizeof(vbr->in_hdr));
> - }
> -
> - sg_set_buf(&vblk->sg[num + out + in++], &vbr->status,
> - sizeof(vbr->status));
> -
> + num = blk_rq_map_sg(q, vbr->req, vblk->sg);
> if (num) {
> - if (rq_data_dir(vbr->req) == WRITE) {
> + if (rq_data_dir(vbr->req) == WRITE)
> vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
> - out += num;
> - } else {
> + else
> vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
> - in += num;
> - }
> }
>
> - if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr,
> - GFP_ATOMIC) < 0) {
> + if (__virtblk_add_req(vblk->vq, vbr, vblk->sg, num) < 0) {
> mempool_free(vbr, vblk->pool);
> return false;
> }
>


--
Asias


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