Re: [PATCH v3 4/4] io_uring: add support for zone-append

Jens Axboe
2020-07-09T14:05:54Z

On 7/9/20 8:00 AM, Christoph Hellwig wrote:
> On Thu, Jul 09, 2020 at 07:58:04AM -0600, Jens Axboe wrote:
>>> We don't actually need any new field at all. By the time the write
>>> returned ki_pos contains the offset after the write, and the res
>>> argument to ->ki_complete contains the amount of bytes written, which
>>> allow us to trivially derive the starting position.
>>
>> Then let's just do that instead of jumping through hoops either
>> justifying growing io_rw/io_kiocb or turning kiocb into a global
>> completion thing.
>
> Unfortunately that is a totally separate issue - the in-kernel offset
> can be trivially calculated. But we still need to figure out a way to
> pass it on to userspace. The current patchset does that by abusing
> the flags, which doesn't really work as the flags are way too small.
> So we somewhere need to have an address to do the put_user to.

Right, we're just trading the 'append_offset' for a 'copy_offset_here'
pointer, which are stored in the same spot...

--
Jens Axboe