Re: [PATCH 2/2] zonefs: use zone-append for AIO as well

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

On 21/07/2020 07:54, Christoph Hellwig wrote:
> On Mon, Jul 20, 2020 at 04:48:50PM +0000, Johannes Thumshirn wrote:
>> On 20/07/2020 15:45, Christoph Hellwig wrote:
>>> On Mon, Jul 20, 2020 at 10:21:18PM +0900, Johannes Thumshirn wrote:
>>>> On a successful completion, the position the data is written to is
>>>> returned via AIO's res2 field to the calling application.
>>>
>>> That is a major, and except for this changelog, undocumented ABI
>>> change.  We had the whole discussion about reporting append results
>>> in a few threads and the issues with that in io_uring.  So let's
>>> have that discussion there and don't mix it up with how zonefs
>>> writes data.  Without that a lot of the boilerplate code should
>>> also go away.
>>>
>>
>> OK maybe I didn't remember correctly, but wasn't this all around 
>> io_uring and how we'd report the location back for raw block device
>> access?
> 
> Report the write offset.  The author seems to be hell bent on making
> it block device specific, but that is a horrible idea as it is just
> as useful for normal file systems (or zonefs).

After having looked into io_uring I don't this there is anything that
prevents io_uring from picking up the write offset from ki_complete's
res2 argument. As of now io_uring ignores the filed but that can be 
changed.

The reporting of the write offset to user-space still needs to be 
decided on from an io_uring PoV.

So the only thing that needs to be done from a zonefs perspective is 
documenting the use of res2 and CC linux-aio and linux-abi (including
an update of the io_getevents man page).

Or am I completely off track now?

Thanks,
	Johannes