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Date: Tue, 5 May 2009 14:09:05 +0200
From: Christoph Hellwig <hch@lst.de>
Message-ID: <20090505120905.GC30721@lst.de>
References: <20090505120804.GA30651@lst.de>
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Subject: [Qemu-devel] [PATCH 3/3] barriers: virtio
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To: qemu-devel@nongnu.org

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;
 }