[Qemu-devel] [PATCH 3/3] barriers: virtio

[Christoph Hellwig <hch@lst.de>]

Advertise the barriers feature to virtio guests if the underlying device
supports it, and make sure to pass down the barrier flag on write requests
to the block layer.


Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: qemu/hw/virtio-blk.c
===================================================================
--- qemu.orig/hw/virtio-blk.c	2009-05-05 13:21:24.196784347 +0200
+++ qemu/hw/virtio-blk.c	2009-05-05 13:31:33.654786861 +0200
@@ -211,8 +211,14 @@ static void virtio_blk_handle_scsi(VirtI
 
 static void virtio_blk_handle_write(VirtIOBlockReq *req)
 {
+
+    unsigned flags = 0;
+
+    if (req->out->type & VIRTIO_BLK_T_BARRIER)
+        flags |= BDRV_IO_BARRIER;
+
     bdrv_aio_writev(req->dev->bs, req->out->sector, &req->qiov,
-                    req->qiov.size / 512, virtio_blk_rw_complete, req, 0);
+                    req->qiov.size / 512, virtio_blk_rw_complete, req, flags);
 }
 
 static void virtio_blk_handle_read(VirtIOBlockReq *req)
@@ -304,6 +310,7 @@ static void virtio_blk_update_config(Vir
 
 static uint32_t virtio_blk_get_features(VirtIODevice *vdev)
 {
+    VirtIOBlock *s = to_virtio_blk(vdev);
     uint32_t features = 0;
 
     features |= (1 << VIRTIO_BLK_F_SEG_MAX);
@@ -312,6 +319,9 @@ static uint32_t virtio_blk_get_features(
     features |= (1 << VIRTIO_BLK_F_SCSI);
 #endif
 
+    if (s->bs->barrier_support)
+        features |= (1 << VIRTIO_BLK_F_BARRIER);
+
     return features;
 }