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[Qemu-devel] [PULL 16/42] blockdev: document transactional shortcomings

From: Max Reitz
Subject: [Qemu-devel] [PULL 16/42] blockdev: document transactional shortcomings
Date: Tue, 25 Sep 2018 17:15:15 +0200

From: John Snow <address@hidden>

Presently only the backup job really guarantees what one would consider
transactional semantics. To guard against someone helpfully adding them
in the future, document that there are shortcomings in the model that
would need to be audited at that time.

Signed-off-by: John Snow <address@hidden>
Message-id: address@hidden
Reviewed-by: Jeff Cody <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
Signed-off-by: Max Reitz <address@hidden>
 blockdev.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 0cf8febe6c..d4b42403df 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2182,7 +2182,13 @@ static const BlkActionOps actions[] = {
         .instance_size = sizeof(BlockDirtyBitmapState),
         .prepare = block_dirty_bitmap_disable_prepare,
         .abort = block_dirty_bitmap_disable_abort,
-     }
+    },
+    /* Where are transactions for MIRROR, COMMIT and STREAM?
+     * Although these blockjobs use transaction callbacks like the backup job,
+     * these jobs do not necessarily adhere to transaction semantics.
+     * These jobs may not fully undo all of their actions on abort, nor do they
+     * necessarily work in transactions with more than one job in them.
+     */

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