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Date: Thu, 17 Sep 2009 19:57:42 +0200
From: Christoph Hellwig <hch@....de>
To: rusty@...tcorp.com.au
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] 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: Christoph Hellwig <hch@....de>
Index: linux-2.6/drivers/block/virtio_blk.c
===================================================================
--- linux-2.6.orig/drivers/block/virtio_blk.c 2009-09-17 14:31:58.269278765 -0300
+++ linux-2.6/drivers/block/virtio_blk.c 2009-09-17 14:32:43.228031777 -0300
@@ -91,15 +91,26 @@ static bool do_req(struct request_queue
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();
}
@@ -199,6 +210,12 @@ out:
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)
{
@@ -336,7 +353,10 @@ static int __devinit virtblk_probe(struc
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 */
@@ -423,7 +443,7 @@ 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
};
/*
Index: linux-2.6/include/linux/virtio_blk.h
===================================================================
--- linux-2.6.orig/include/linux/virtio_blk.h 2009-09-02 08:37:31.460714184 -0300
+++ linux-2.6/include/linux/virtio_blk.h 2009-09-17 14:32:03.245004201 -0300
@@ -17,6 +17,7 @@
#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 */
@@ -38,6 +39,17 @@ 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 combinaed with VIRTIO_BLK_T_SCSI_CMD or
+ * VIRTIO_BLK_T_BARRIER. VIRTIO_BLK_T_FLUSH is a command of it's own
+ * and may no be comined with any of the other flags.
+ */
+
/* These two define direction. */
#define VIRTIO_BLK_T_IN 0
#define VIRTIO_BLK_T_OUT 1
@@ -45,6 +57,9 @@ 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
--
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