[Xen-changelog] [qemu-upstream-unstable] Xen PV backend: Disable use of O_DIRECT by default as it results in crashes.

[patchbot@xxxxxxx]

commit 7714986a9896a3ba25612b7d4739365a9932041f
Author:     Alex Bligh <alex@xxxxxxxxxxx>
AuthorDate: Fri Apr 5 15:45:15 2013 +0000
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
CommitDate: Fri Apr 5 23:31:25 2013 +0000

    Xen PV backend: Disable use of O_DIRECT by default as it results in crashes.
    
    Due to what is almost certainly a kernel bug, writes with O_DIRECT may
    continue to reference the page after the write has been marked as
    completed, particularly in the case of TCP retransmit. In other
    scenarios, this "merely" risks data corruption on the write, but with
    Xen pages from domU are only transiently mapped into dom0's memory,
    resulting in kernel panics when they are subsequently accessed.
    
    This brings PV devices in line with emulated devices.  Removing
    O_DIRECT is safe as barrier operations are now correctly passed
    through.
    
    See:
       http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html
    for more details.
    
    upstream-commit-id: c1a88ad1f4ac994cd70695bf08141d161e21533e
    
    Signed-off-by: Alex Bligh <alex@xxxxxxxxxxx>
    Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 hw/xen_disk.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/hw/xen_disk.c b/hw/xen_disk.c
index c3c5904..668cb54 100644
--- a/hw/xen_disk.c
+++ b/hw/xen_disk.c
@@ -783,7 +783,7 @@ static int blk_connect(struct XenDevice *xendev)
     int pers, index, qflags;
 
     /* read-only ? */
-    qflags = BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO;
+    qflags = BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO;
     if (strcmp(blkdev->mode, "w") == 0) {
         qflags |= BDRV_O_RDWR;
     }
--
generated by git-patchbot for /home/xen/git/qemu-upstream-unstable.git

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