Re: [PATCH] io_uring: uring_cmd: add multishot support without poll

[Jens Axboe <axboe@kernel.dk>]

On 8/19/25 8:28 AM, Ming Lei wrote:
> On Tue, Aug 19, 2025 at 08:01:18AM -0600, Jens Axboe wrote:
>> On 8/19/25 5:19 AM, Ming Lei wrote:
>>>>> @@ -251,6 +264,11 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
>>>>>  	}
>>>>>  
>>>>>  	ret = file->f_op->uring_cmd(ioucmd, issue_flags);
>>>>> +	if (ioucmd->flags & IORING_URING_CMD_MULTISHOT) {
>>>>> +		if (ret >= 0)
>>>>> +			return IOU_ISSUE_SKIP_COMPLETE;
>>>>> +		io_kbuf_recycle(req, issue_flags);
>>>>> +	}
>>>>>  	if (ret == -EAGAIN) {
>>>>>  		ioucmd->flags |= IORING_URING_CMD_REISSUE;
>>>>>  		return ret;
>>>>
>>>> Missing recycle for -EAGAIN?
>>>
>>> io_kbuf_recycle() is done above if `ret < 0`
>>
>> Inside the multishot case. I don't see anywhere where it's forbidden to
>> use IOSQE_BUFFER_SELECT without having multishot set? Either that needs
> 
> REQ_F_BUFFER_SELECT is supposed to be allowed for IORING_URING_CMD_MULTISHOT
> only, and it is checked in io_uring_cmd_prep().
> 
>> to be explicit for now, or the recycling should happen generically.
>> Probably the former I would suspect.
> 
> Yes, the former is exactly what the patch is doing.

Is it? Because looking at v2, you check if IORING_URING_CMD_FIXED is
set, and you fail for that case if REQ_F_BUFFER_SELECT is set. Then you
have a IORING_URING_CMD_MULTISHOT where the opposite is true, which
obviously makes sense.

But no checks if neither is set?

You could add that in io_uring_cmd_select_buffer(), eg fail if
IORING_URING_CMD_MULTISHOT isn't set. Which if done, then the prep side
checking could probably just go away.

-- 
Jens Axboe