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[Qemu-block] [PATCH] block: Fix snapshot=on with aio=native

From: Kevin Wolf
Subject: [Qemu-block] [PATCH] block: Fix snapshot=on with aio=native
Date: Thu, 16 Jun 2016 13:03:20 +0200

snapshot=on creates a temporary overlay that is always opened with
cache=unsafe (the cache mode specified by the user is only for the
actual image file and its children). This means that we must not inherit
the BDRV_O_NATIVE_AIO flag for the temporary overlay because trying to
use Linux AIO with cache=unsafe results in an error.

Reproducer without this patch:

$ x86_64-softmmu/qemu-system-x86_64 -drive 
qemu-system-x86_64: -drive 
file=/tmp/test.qcow2,cache=none,aio=native,snapshot=on: aio=native was
specified, but it requires cache.direct=on, which was not specified.

Signed-off-by: Kevin Wolf <address@hidden>
 block.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block.c b/block.c
index b350794..8104225 100644
--- a/block.c
+++ b/block.c
@@ -684,6 +684,10 @@ static void bdrv_temp_snapshot_options(int *child_flags, 
QDict *child_options,
     /* For temporary files, unconditional cache=unsafe is fine */
     qdict_set_default_str(child_options, BDRV_OPT_CACHE_DIRECT, "off");
     qdict_set_default_str(child_options, BDRV_OPT_CACHE_NO_FLUSH, "on");
+    /* aio=native doesn't work for cache.direct=off, so disable it for the
+     * temporary snapshot */
+    *child_flags &= ~BDRV_O_NATIVE_AIO;

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