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[Qemu-devel] [PATCH 6/6] dataplane: refuse to start if device is already

From: Stefan Hajnoczi
Subject: [Qemu-devel] [PATCH 6/6] dataplane: refuse to start if device is already in use
Date: Mon, 29 Jul 2013 17:36:12 +0200

Dataplane must check whether a block device is in use before launching
the dataplane thread.  This is necessary since the thread does not
synchronize with the main loop and I/O requests could cause corruption.

One example is when a drive is added and a block job is started before
hotplugging the virtio-blk-pci adapter.  In this case we must not use
dataplane mode.

Cc: address@hidden
Reviewed-by: Kevin Wolf <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
 hw/block/dataplane/virtio-blk.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 63c3ffa..411becc 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -415,6 +415,14 @@ bool virtio_blk_data_plane_create(VirtIODevice *vdev, 
VirtIOBlkConf *blk,
         return false;
+    /* If dataplane is (re-)enabled while the guest is running there could be
+     * block jobs that can conflict.
+     */
+    if (bdrv_in_use(blk->conf.bs)) {
+        error_report("cannot start dataplane thread while device is in use");
+        return false;
+    }
     fd = raw_get_aio_fd(blk->conf.bs);
     if (fd < 0) {
         error_report("drive is incompatible with x-data-plane, "

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