> 2026年10月13日 21:53，Kevin Wolf <[email protected]> 写道：
>
> Am 13.10.2026 um 10:15 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> On 13.10.26 09:05, Haoqian He wrote:
>>> mirror_start_job() inserts a mirror_top filter above the source node
>>> for both mirror and active commit jobs. Previously, the filter was
>>> opened with BDRV_O_RDWR only, even when the source had BDRV_O_UNMAP
>>> enabled.
>>>
>>> The block layer checks BDRV_O_UNMAP before invoking a node's discard
>>> callback. Without this flag on mirror_top, discard requests return
>>> success without reaching bdrv_mirror_top_pdiscard(). Consequently,
>>> starting a job can silently suppress guest UNMAP/TRIM requests that
>>> would otherwise reach the discard-enabled source.
>>>
>>> Initialize the filter's open flags with BDRV_O_RDWR and conditionally
>>> add BDRV_O_UNMAP from bs->open_flags. Pass the resulting flags to
>>> bdrv_new_open_driver() so that mirror_top follows the source node's
>>> discard setting.
>>>
>>> This allows discard requests to reach the existing filter callback,
>>> which forwards them to the source and either tracks the affected
>>> range in the dirty bitmap or synchronously propagates the discard
>>> to the target, depending on the copy mode.
>>>
>>> Signed-off-by: Haoqian He <[email protected]>
>>> ---
>>> block/mirror.c | 10 ++++++++--
>>> 1 file changed, 8 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/block/mirror.c b/block/mirror.c
>>> index 089856f4a8..a551d392c6 100644
>>> --- a/block/mirror.c
>>> +++ b/block/mirror.c
>>> @@ -1854,6 +1854,7 @@ static BlockJob *mirror_start_job(
>>> BlockDriverState *mirror_top_bs;
>>> bool target_is_backing;
>>> uint64_t target_perms, target_shared_perms;
>>> + int flags;
>>> int ret;
>>> GLOBAL_STATE_CODE();
>>> @@ -1886,8 +1887,13 @@ static BlockJob *mirror_start_job(
>>> /* In the case of active commit, add dummy driver to provide consistent
>>> * reads on the top, while disabling it in the intermediate nodes, and
>>> make
>>> * the backing chain writable. */
>>> - mirror_top_bs = bdrv_new_open_driver(&bdrv_mirror_top,
>>> filter_node_name,
>>> - BDRV_O_RDWR, errp);
>>> + flags = BDRV_O_RDWR;
>>> + if (bs->open_flags & BDRV_O_UNMAP) {
>>> + flags |= BDRV_O_UNMAP;
>>> + }
>>> + mirror_top_bs = bdrv_new_open_driver(&bdrv_mirror_top,
>>> + filter_node_name,
>>> + flags, errp);
>>> if (mirror_top_bs == NULL) {
>>> return NULL;
>>> }
>>
>> Cool find!
>>
>> Reviewed-by: Vladimir Sementsov-Ogievskiy <[email protected]>
>>
>> Thanks for fixing, applied to my block branch.
>
> This bug is something that should be relatively easily testable in
> qemu-iotests. Can we please add a test at the same time?
>
> Kevin
>
Okay, i will add qemu-iotests in the subsequent patch ASAP.
Haoqian
