Re: [PATCH 2/2] io_uring/kbuf: support min length left for incremental buffers

[Gabriel Krisman Bertazi <krisman@suse.de>]

Jens Axboe <axboe@kernel.dk> writes:

>> Honest question, isn't this a property of the specific operation and/or
>> fd being operated, instead of the buffer_reg?
>
> It kind of is, in that some users may not care. But it's not currently
> possible to pass this in on a per-op basis, and while I did hack that
> up initially, it's almost impossible as you end up with layering
> violations. In practice, this is really mostly a recvmsg multishot
> issue, because we need to store the headers. Hence the solution to
> stuff it in the io_uring_buf_reg instead, and make it a fixed property
> of the buffer group. In practice, you may even want a larger min_left
> than what the recvmsg requires, as you don't want a tiny truncated
> transfer at the end, regardless of what type of recv or read operation
> this is. Hence it works generically as well.
>
> Also see the linked GH issue, that's where most of the discussion
> around this have happened already.
>
>>> -		if (buf_len || !this_len) {
>>> +		if (buf_len > bl->min_left_sub_one || !this_len) {
>> 
>> Cosmetic, but perhaps store min_left_sub_one instead of min_left itself? the
>> buf_len must be >= min_left, and that is easier to read.  (buf_len &&
>> buf_len >= min_left || !this_len)
>
> Also see GH issue.

Ack. Thanks.  Feel free to add:

Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>


-- 
Gabriel Krisman Bertazi