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block: Add BDRV_REQ_WRITE_UNCHANGED flag

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This flag signifies that a write request will not change the visible
disk content.  With this flag set, it is sufficient to have the
BLK_PERM_WRITE_UNCHANGED permission instead of BLK_PERM_WRITE.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-4-mreitz@redhat.com
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2018-04-21 15:29:23 +02:00
parent 24b7c538fe
commit c6035964f8
2 changed files with 10 additions and 2 deletions
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6
block/io.c
View File

@ -1504,7 +1504,11 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child,
assert(!waited || !req->serialising);
assert(req->overlap_offset <= offset);
assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
assert(child->perm & BLK_PERM_WRITE);
if (flags & BDRV_REQ_WRITE_UNCHANGED) {
assert(child->perm & (BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE));
} else {
assert(child->perm & BLK_PERM_WRITE);
}
assert(end_sector <= bs->total_sectors || child->perm & BLK_PERM_RESIZE);
ret = notifier_with_return_list_notify(&bs->before_write_notifiers, req);

6
include/block/block.h
View File

@ -54,8 +54,12 @@ typedef enum {
BDRV_REQ_FUA = 0x10,
BDRV_REQ_WRITE_COMPRESSED = 0x20,
/* Signifies that this write request will not change the visible disk
* content. */
BDRV_REQ_WRITE_UNCHANGED = 0x40,
/* Mask of valid flags */
BDRV_REQ_MASK = 0x3f,
BDRV_REQ_MASK = 0x7f,
} BdrvRequestFlags;
typedef struct BlockSizes {