Re: [PATCH 1/1] io_uring/rw: forbid multishot async reads

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/17/25 13:58, Jens Axboe wrote:
> On 2/17/25 6:37 AM, Pavel Begunkov wrote:
>> At the moment we can't sanely handle queuing an async request from a
>> multishot context, so disable them. It shouldn't matter as pollable
>> files / socekts don't normally do async.
> 
> Having something pollable that can return -EIOCBQUEUED is odd, but
> that's just a side comment.
> 
> 
>> diff --git a/io_uring/rw.c b/io_uring/rw.c
>> index 96b42c331267..4bda46c5eb20 100644
>> --- a/io_uring/rw.c
>> +++ b/io_uring/rw.c
>> @@ -878,7 +878,15 @@ static int __io_read(struct io_kiocb *req, unsigned int issue_flags)
>>   	if (unlikely(ret))
>>   		return ret;
>>   
>> -	ret = io_iter_do_read(rw, &io->iter);
>> +	if (unlikely(req->opcode == IORING_OP_READ_MULTISHOT)) {
>> +		void *cb_copy = rw->kiocb.ki_complete;
>> +
>> +		rw->kiocb.ki_complete = NULL;
>> +		ret = io_iter_do_read(rw, &io->iter);
>> +		rw->kiocb.ki_complete = cb_copy;
>> +	} else {
>> +		ret = io_iter_do_read(rw, &io->iter);
>> +	}
> 
> This looks a bit odd. Why can't io_read_mshot() just clear
> ->ki_complete?

Forgot about that one, as for restoring it back, io_uring compares
or calls ->ki_complete in a couple of places, this way the patch
is more contained. It can definitely be refactored on top.

-- 
Pavel Begunkov