Re: [PATCH for-4.2? v3 0/8] block: Fix resize (extending) of short overlays

[Vladimir Sementsov-Ogievskiy]

19.12.2019 13:13, Kevin Wolf wrote:
> Am 19.12.2019 um 10:24 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> 10.12.2019 20:46, Kevin Wolf wrote:
>>> Am 22.11.2019 um 17:05 hat Kevin Wolf geschrieben:
>>>> See patch 4 for the description of the bug fixed.
>>>
>>> I'm applying patches 3 and 5-7 to the block branch because they make
>>> sense on their own.
>>>
>>> The real fix will need another approach because the error handling is
>>> broken in this one: If zeroing out fails (either because of NO_FALLBACK
>>> or because of some other I/O error), bdrv_co_truncate() will return
>>> failure, but the image size has already been increased, with potentially
>>> incorrect data in the new area.
>>>
>>> To fix this, we need to make sure that zeros will be read before we
>>> commit the new image size to the image file (e.g. qcow2 header) and to
>>> bs->total_sectors. In other words, it must become the responsibility of
>>> the block driver.
>>>
>>> To this effect, I'm planning to introduce a PREALLOC_MODE_ZERO_INIT flag
>>> that can be or'ed to the preallocation mode. This will fail by default
>>> because it looks like just another unimplemented preallocation mode to
>>> block drivers. It will be requested explicitly by commit jobs and
>>> automatically added by bdrv_co_truncate() if the backing file would
>>> become visible (like in this series, but now for all preallocation
>>> modes). I'm planning to implement it for qcow2 and file-posix for now,
>>> which should cover most interesting cases.
>>>
>>> Does this make sense to you?
>>
>> This should work. Do you still have this plan in a timeline?
> 
> Still planning to do this, but tomorrow is my last working day for this
> year. So I guess I'll get to it sometime in January.
> 

Good. Have a nice holiday!


-- 
Best regards,
Vladimir