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Date: Thu, 13 Aug 2009 16:49:56 +0200
From: Christoph Hellwig <hch@lst.de>
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Subject: [Qemu-devel] [PATCH] virtio-blk: handle NULL returns from
	bdrv_aio_{read, write}
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To: qemu-devel@nongnu.org

The bdrv_aio_{read,write} routines can return a NULL pointer when the
I/O submission fails.  Currently we ignore this and will wait forever
for an I/O completion and leading to a hang of the guest.

I can easily reproduce this using the native Linux AIO patch, but it's
also possible using normal pthreads-based AIO.


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

Index: qemu-kvm/hw/virtio-blk.c
===================================================================
--- qemu-kvm.orig/hw/virtio-blk.c
+++ qemu-kvm/hw/virtio-blk.c
@@ -254,14 +254,24 @@ static void virtio_blk_handle_scsi(VirtI
 
 static void virtio_blk_handle_write(VirtIOBlockReq *req)
 {
-    bdrv_aio_writev(req->dev->bs, req->out->sector, &req->qiov,
-                    req->qiov.size / 512, virtio_blk_rw_complete, req);
+    BlockDriverAIOCB *acb;
+
+    acb = bdrv_aio_writev(req->dev->bs, req->out->sector, &req->qiov,
+                          req->qiov.size / 512, virtio_blk_rw_complete, req);
+    if (!acb) {
+        virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
+    }
 }
 
 static void virtio_blk_handle_read(VirtIOBlockReq *req)
 {
-    bdrv_aio_readv(req->dev->bs, req->out->sector, &req->qiov,
-                   req->qiov.size / 512, virtio_blk_rw_complete, req);
+    BlockDriverAIOCB *acb;
+
+    acb = bdrv_aio_readv(req->dev->bs, req->out->sector, &req->qiov,
+                         req->qiov.size / 512, virtio_blk_rw_complete, req);
+    if (!acb) {
+        virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
+    }
 }
 
 static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)