Re: [PATCH v2 08/20] block/block-copy: add block_copy_cancel

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

22.10.2020 23:50, Vladimir Sementsov-Ogievskiy wrote:
> 22.07.2020 14:28, Max Reitz wrote:
>> On 01.06.20 20:11, Vladimir Sementsov-Ogievskiy wrote:
>>> Add function to cancel running async block-copy call. It will be used
>>> in backup.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>> ---
>>>   include/block/block-copy.h |  7 +++++++
>>>   block/block-copy.c         | 22 +++++++++++++++++++---
>>>   2 files changed, 26 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/block/block-copy.h b/include/block/block-copy.h
>>> index d40e691123..370a194d3c 100644
>>> --- a/include/block/block-copy.h
>>> +++ b/include/block/block-copy.h
>>> @@ -67,6 +67,13 @@ BlockCopyCallState *block_copy_async(BlockCopyState *s,
>>>   void block_copy_set_speed(BlockCopyState *s, BlockCopyCallState *call_state,
>>>                             uint64_t speed);
>>> +/*
>>> + * Cancel running block-copy call.
>>> + * Cancel leaves block-copy state valid: dirty bits are correct and you may use
>>> + * cancel + <run block_copy with same parameters> to emulate pause/resume.
>>> + */
>>> +void block_copy_cancel(BlockCopyCallState *call_state);
>>> +
>>>   BdrvDirtyBitmap *block_copy_dirty_bitmap(BlockCopyState *s);
>>>   void block_copy_set_skip_unallocated(BlockCopyState *s, bool skip);
>>> diff --git a/block/block-copy.c b/block/block-copy.c
>>> index 851d9c8aaf..b551feb6c2 100644
>>> --- a/block/block-copy.c
>>> +++ b/block/block-copy.c
>>> @@ -44,6 +44,8 @@ typedef struct BlockCopyCallState {
>>>       bool failed;
>>>       bool finished;
>>>       QemuCoSleepState *sleep_state;
>>> +    bool cancelled;
>>> +    Coroutine *canceller;
>>>       /* OUT parameters */
>>>       bool error_is_read;
>>> @@ -582,7 +584,7 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state)
>>>       assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
>>>       assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
>>> -    while (bytes && aio_task_pool_status(aio) == 0) {
>>> +    while (bytes && aio_task_pool_status(aio) == 0 && !call_state->cancelled) {
>>>           BlockCopyTask *task;
>>>           int64_t status_bytes;
>>> @@ -693,7 +695,7 @@ static int coroutine_fn block_copy_common(BlockCopyCallState *call_state)
>>>       do {
>>>           ret = block_copy_dirty_clusters(call_state);
>>> -        if (ret == 0) {
>>> +        if (ret == 0 && !call_state->cancelled) {
>>>               ret = block_copy_wait_one(call_state->s, call_state->offset,
>>>                                         call_state->bytes);
>>>           }
>>> @@ -707,13 +709,18 @@ static int coroutine_fn block_copy_common(BlockCopyCallState *call_state)
>>>            * 2. We have waited for some intersecting block-copy request
>>>            *    It may have failed and produced new dirty bits.
>>>            */
>>> -    } while (ret > 0);
>>> +    } while (ret > 0 && !call_state->cancelled);
>>
>> Would it be cleaner if block_copy_dirty_cluster() just returned
>> -ECANCELED?  Or would that pose a problem for its callers or the async
>> callback?
>>
> 
> I'd prefer not to merge io ret with block-copy logic: who knows what underlying operations may return.. Can't it be _another_ ECANCELED?
> And it would be just a sugar for block_copy_dirty_clusters() call, I'll have to check ->cancelled after block_copy_wait_one() anyway.
> Also, for the next version I try to make it more obvious that finished block-copy call is in one of thee states:
>   - success
>   - failed
>   - cancelled
> 
> Hmm. Also, cancelled should be OK for copy-on-write operations in filter, it just mean that we don't need to care anymore.

This is unrelated: actually only async block-copy call may be cancelled.

> 
>>>       if (call_state->cb) {
>>>           call_state->cb(ret, call_state->error_is_read,
>>>                          call_state->s->progress_opaque);
>>>       }
>>> +    if (call_state->canceller) {
>>> +        aio_co_wake(call_state->canceller);
>>> +        call_state->canceller = NULL;
>>> +    }
>>> +
>>>       call_state->finished = true;
>>>       return ret;
>>
> 
> 


-- 
Best regards,
Vladimir