diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/block/block.h | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/include/block/block.h b/include/block/block.h index 706ef00..f7ddff4 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -50,6 +50,18 @@ typedef enum { * opened with BDRV_O_UNMAP. */ BDRV_REQ_MAY_UNMAP = 0x4, + + /* + * The BDRV_REQ_NO_SERIALISING flag is only valid for reads and means that + * we don't want wait_serialising_requests() during the read operation. + * + * This flag is used for backup copy-on-write operations, when we need to + * read old data before write (write notifier triggered). It is okay since + * we already waited for other serializing requests in the initiating write + * (see bdrv_aligned_pwritev), and it is necessary if the initiating write + * is already serializing (without the flag, the read would deadlock + * waiting for the serialising write to complete). + */ BDRV_REQ_NO_SERIALISING = 0x8, BDRV_REQ_FUA = 0x10, BDRV_REQ_WRITE_COMPRESSED = 0x20, |