Re: [Qemu-block] [PATCH v6 16/42] block: Flush all children in generic code

[Max Reitz]

On 10.08.19 17:36, Vladimir Sementsov-Ogievskiy wrote:
> 09.08.2019 19:13, Max Reitz wrote:
>> If the driver does not support .bdrv_co_flush() so bdrv_co_flush()
>> itself has to flush the children of the given node, it should not flush
>> just bs->file->bs, but in fact all children.
>>
>> In any case, the BLKDBG_EVENT() should be emitted on the primary child,
>> because that is where a blkdebug node would be if there is any.
>>
>> Suggested-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>> Signed-off-by: Max Reitz <address@hidden>
>> ---
>>   block/io.c | 23 +++++++++++++++++------
>>   1 file changed, 17 insertions(+), 6 deletions(-)
>>
>> diff --git a/block/io.c b/block/io.c
>> index c5a8e3e6a3..bcc770d336 100644
>> --- a/block/io.c
>> +++ b/block/io.c
>> @@ -2572,6 +2572,8 @@ static void coroutine_fn bdrv_flush_co_entry(void 
>> *opaque)
>>   
>>   int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>>   {
>> +    BdrvChild *primary_child = bdrv_primary_child(bs);
>> +    BdrvChild *child;
>>       int current_gen;
>>       int ret = 0;
>>   
>> @@ -2601,7 +2603,7 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>>       }
>>   
>>       /* Write back cached data to the OS even with cache=unsafe */
>> -    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_OS);
>> +    BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_OS);
>>       if (bs->drv->bdrv_co_flush_to_os) {
>>           ret = bs->drv->bdrv_co_flush_to_os(bs);
>>           if (ret < 0) {
>> @@ -2611,15 +2613,15 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>>   
>>       /* But don't actually force it to the disk with cache=unsafe */
>>       if (bs->open_flags & BDRV_O_NO_FLUSH) {
>> -        goto flush_parent;
>> +        goto flush_children;
>>       }
>>   
>>       /* Check if we really need to flush anything */
>>       if (bs->flushed_gen == current_gen) {
>> -        goto flush_parent;
>> +        goto flush_children;
>>       }
>>   
>> -    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_DISK);
>> +    BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_DISK);
>>       if (!bs->drv) {
>>           /* bs->drv->bdrv_co_flush() might have ejected the BDS
>>            * (even in case of apparent success) */
>> @@ -2663,8 +2665,17 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>>       /* Now flush the underlying protocol.  It will also have 
>> BDRV_O_NO_FLUSH
>>        * in the case of cache=unsafe, so there are no useless flushes.
>>        */
>> -flush_parent:
>> -    ret = bs->file ? bdrv_co_flush(bs->file->bs) : 0;
>> +flush_children:
>> +    ret = 0; > +    QLIST_FOREACH(child, &bs->children, next) {
>> +        int this_child_ret;
>> +
>> +        this_child_ret = bdrv_co_flush(child->bs);
>> +        if (!ret) {
>> +            ret = this_child_ret;
>> +        }
>> +    }
> 
> Hmm, you said that we want to flush only children with write-access from 
> parent..

Good that you remember it, I must have overlooked it (when reading the
replies to the previous version). :-)

> Shouldn't we check it? Or we assume that it's always safe to call 
> bdrv_co_flush on
> a node?

I think it’s always safe.  But checking it seems like a nice touch, yes.

Max

>> +
>>   out:
>>       /* Notify any pending flushes that we have completed */
>>       if (ret == 0) {
>>
> 
>

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