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Commit f1b0ef06 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Rusty Russell
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virtio_blk: add support for cache flush 



Recent qemu has added a VIRTIO_BLK_F_FLUSH flag to advertise that the
virtual disk has a volatile write cache that needs to be flushed.  In case
we see this feature implement tell the Linux block layer about the fact
and use the new VIRTIO_BLK_T_FLUSH to flush the cache when required.  This
allows for an correct and simple implementation of write barriers.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 3ca4f5ca

drivers/block/virtio_blk.c

+25 −5
Original line number Diff line number Diff line
@@ -92,15 +92,26 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk, 
		return false;



	vbr->req = req;

	if (blk_fs_request(vbr->req)) {

	switch (req->cmd_type) {

	case REQ_TYPE_FS:

		vbr->out_hdr.type = 0;

		vbr->out_hdr.sector = blk_rq_pos(vbr->req);

		vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);

	} else if (blk_pc_request(vbr->req)) {

		break;

	case REQ_TYPE_BLOCK_PC:

		vbr->out_hdr.type = VIRTIO_BLK_T_SCSI_CMD;

		vbr->out_hdr.sector = 0;

		vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);

	} else {

		break;

	case REQ_TYPE_LINUX_BLOCK:

		if (req->cmd[0] == REQ_LB_OP_FLUSH) {

			vbr->out_hdr.type = VIRTIO_BLK_T_FLUSH;

			vbr->out_hdr.sector = 0;

			vbr->out_hdr.ioprio = req_get_ioprio(vbr->req);

			break;

		}

		/*FALLTHRU*/

	default:

		/* We don't put anything else in the queue. */

		BUG();

	}
@@ -200,6 +211,12 @@ static int virtblk_identify(struct gendisk *disk, void *argp) 
	return err;

}



static void virtblk_prepare_flush(struct request_queue *q, struct request *req)

{

	req->cmd_type = REQ_TYPE_LINUX_BLOCK;

	req->cmd[0] = REQ_LB_OP_FLUSH;

}



static int virtblk_ioctl(struct block_device *bdev, fmode_t mode,

			 unsigned cmd, unsigned long data)

{
@@ -338,7 +355,10 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) 
	index++;



	/* If barriers are supported, tell block layer that queue is ordered */

	if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))

	if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))

		blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_DRAIN_FLUSH,

				  virtblk_prepare_flush);

	else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))

		blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);



	/* If disk is read-only in the host, the guest should obey */
@@ -425,7 +445,7 @@ static struct virtio_device_id id_table[] = { 
static unsigned int features[] = {

	VIRTIO_BLK_F_BARRIER, 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_SCSI, VIRTIO_BLK_F_IDENTIFY

	VIRTIO_BLK_F_SCSI, VIRTIO_BLK_F_IDENTIFY, VIRTIO_BLK_F_FLUSH

};



/*

include/linux/virtio_blk.h

+15 −0
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#define VIRTIO_BLK_F_BLK_SIZE	6	/* Block size of disk is available*/

#define VIRTIO_BLK_F_SCSI	7	/* Supports scsi command passthru */

#define VIRTIO_BLK_F_IDENTIFY	8	/* ATA IDENTIFY supported */

#define VIRTIO_BLK_F_FLUSH	9	/* Cache flush command support */



#define VIRTIO_BLK_ID_BYTES	(sizeof(__u16[256]))	/* IDENTIFY DATA */
@@ -35,6 +36,17 @@ struct virtio_blk_config { 
	__u8 identify[VIRTIO_BLK_ID_BYTES];

} __attribute__((packed));



/*

 * Command types

 *

 * Usage is a bit tricky as some bits are used as flags and some are not.

 *

 * Rules:

 *   VIRTIO_BLK_T_OUT may be combined with VIRTIO_BLK_T_SCSI_CMD or

 *   VIRTIO_BLK_T_BARRIER.  VIRTIO_BLK_T_FLUSH is a command of its own

 *   and may not be combined with any of the other flags.

 */



/* These two define direction. */

#define VIRTIO_BLK_T_IN		0

#define VIRTIO_BLK_T_OUT	1
@@ -42,6 +54,9 @@ struct virtio_blk_config { 
/* This bit says it's a scsi command, not an actual read or write. */

#define VIRTIO_BLK_T_SCSI_CMD	2



/* Cache flush command */

#define VIRTIO_BLK_T_FLUSH	4



/* Barrier before this op. */

#define VIRTIO_BLK_T_BARRIER	0x80000000