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| author | Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> | 2021-09-02 12:37:54 +0300 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2022-01-14 12:03:16 +0100 |
| commit | 64631f368115a332bdca32553a430568ecc7761d (patch) | |
| tree | f021ad8fa5dae349eafd7a234407fd06e0a7816c /include | |
| parent | 96054c76ff2db74165385a69f234c57a6bbc941e (diff) | |
| download | qemu-64631f368115a332bdca32553a430568ecc7761d.zip qemu-64631f368115a332bdca32553a430568ecc7761d.tar.gz qemu-64631f368115a332bdca32553a430568ecc7761d.tar.bz2 | |
block: drop BLK_PERM_GRAPH_MOD
First, this permission never protected a node from being changed, as
generic child-replacing functions don't check it.
Second, it's a strange thing: it presents a permission of parent node
to change its child. But generally, children are replaced by different
mechanisms, like jobs or qmp commands, not by nodes.
Graph-mod permission is hard to understand. All other permissions
describe operations which done by parent node on its child: read,
write, resize. Graph modification operations are something completely
different.
The only place where BLK_PERM_GRAPH_MOD is used as "perm" (not shared
perm) is mirror_start_job, for s->target. Still modern code should use
bdrv_freeze_backing_chain() to protect from graph modification, if we
don't do it somewhere it may be considered as a bug. So, it's a bit
risky to drop GRAPH_MOD, and analyzing of possible loss of protection
is hard. But one day we should do it, let's do it now.
One more bit of information is that locking the corresponding byte in
file-posix doesn't make sense at all.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210902093754.2352-1-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/block/block.h | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/include/block/block.h b/include/block/block.h index e5dd22b..9d40502 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -269,12 +269,13 @@ enum { BLK_PERM_RESIZE = 0x08, /** - * This permission is required to change the node that this BdrvChild - * points to. + * There was a now-removed bit BLK_PERM_GRAPH_MOD, with value of 0x10. QEMU + * 6.1 and earlier may still lock the corresponding byte in block/file-posix + * locking. So, implementing some new permission should be very careful to + * not interfere with this old unused thing. */ - BLK_PERM_GRAPH_MOD = 0x10, - BLK_PERM_ALL = 0x1f, + BLK_PERM_ALL = 0x0f, DEFAULT_PERM_PASSTHROUGH = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |