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block: simplify comment to BDRV_REQ_SERIALISING 

1. BDRV_REQ_NO_SERIALISING doesn't exist already, don't mention it.

2. We are going to add one more user of BDRV_REQ_SERIALISING, so
   comment about backup becomes a bit confusing here. The use case in
   backup is documented in block/backup.c, so let's just drop
   duplication here.

3. The fact that BDRV_REQ_SERIALISING is only for write requests is
   omitted. Add a note.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20201021145859.11201-2-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2020-10-21 17:58:39 +03:00 committed by Max Reitz
parent 071b474f54
commit 2153994e2e
1 changed files with 1 additions and 10 deletions
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11
include/block/block.h
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@ -63,16 +63,7 @@ typedef enum {
* content. */
BDRV_REQ_WRITE_UNCHANGED = 0x40,
/*
* BDRV_REQ_SERIALISING forces request serialisation for writes.
* It is used to ensure that writes to the backing file of a backup process
* target cannot race with a read of the backup target that defers to the
* backing file.
*
* Note, that BDRV_REQ_SERIALISING is _not_ opposite in meaning to
* BDRV_REQ_NO_SERIALISING. A more descriptive name for the latter might be
* _DO_NOT_WAIT_FOR_SERIALISING, except that is too long.
*/
/* Forces request serialisation. Use only with write requests. */
BDRV_REQ_SERIALISING = 0x80,
/* Execute the request only if the operation can be offloaded or otherwise