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[Qemu-block] [PATCH v2 1/4] blockdev-backup: don't check aio_context too

From: John Snow
Subject: [Qemu-block] [PATCH v2 1/4] blockdev-backup: don't check aio_context too early
Date: Fri, 10 May 2019 15:03:04 -0400

in blockdev_backup_prepare, we check to make sure that the target is
associated with a compatible aio context. However, do_blockdev_backup is
called later and has some logic to move the target to a compatible
aio_context. The transaction version will fail certain commands
needlessly early as a result.

Allow blockdev_backup_prepare to simply call do_blockdev_backup, which
will ultimately decide if the contexts are compatible or not.

Note: the transaction version has always disallowed this operation since
its initial commit bd8baecd (2014), whereas the version of
qmp_blockdev_backup at the time, from commit c29c1dd312f, tried to
enforce the aio_context switch instead. It's not clear, and I can't see
from the mailing list archives at the time, why the two functions take a
different approach. It wasn't until later in efd7556708b (2016) that the
standalone version tried to determine if it could set the context or

Reported-by: aihua liang <address@hidden>
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1683498
Signed-off-by: John Snow <address@hidden>
 blockdev.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 79fbac8450..a81d88980c 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1872,10 +1872,6 @@ static void blockdev_backup_prepare(BlkActionState 
*common, Error **errp)
     aio_context = bdrv_get_aio_context(bs);
-    if (aio_context != bdrv_get_aio_context(target)) {
-        error_setg(errp, "Backup between two IO threads is not implemented");
-        return;
-    }
     state->bs = bs;

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