Re: [PATCH v4 6/6] io_uring: add support for zone-append

Damien Le Moal
2020-07-31T07:00:23Z

On 2020/07/31 15:45, hch@infradead.org wrote:
> On Fri, Jul 31, 2020 at 06:42:10AM +0000, Damien Le Moal wrote:
>>> - We may not be able to use RWF_APPEND, and need exposing a new
>>> type/flag (RWF_INDIRECT_OFFSET etc.) user-space. Not sure if this
>>> sounds outrageous, but is it OK to have uring-only flag which can be
>>> combined with RWF_APPEND?
>>
>> Why ? Where is the problem ? O_APPEND/RWF_APPEND is currently meaningless for
>> raw block device accesses. We could certainly define a meaning for these in the
>> context of zoned block devices.
>
> We can't just add a meaning for O_APPEND on block devices now,
> as it was previously silently ignored. I also really don't think any
> of these semantics even fit the block device to start with. If you
> want to work on raw zones use zonefs, that's what is exists for.

Which is fine with me. Just trying to say that I think this is exactly the
discussion we need to start with. What interface do we implement...

Allowing zone append only through zonefs as the raw block device equivalent, all
the O_APPEND/RWF_APPEND semantic is defined and the "return written offset"
implementation in VFS would be common for all file systems, including regular
ones. Beside that, there is I think the question of short writes... Not sure if
short writes can currently happen with async RWF_APPEND writes to regular files.
I think not but that may depend on the FS.

--
Damien Le Moal
Western Digital Research