Re: liburing: expose syscalls?

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

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On 01/02/2020 20:52, Jens Axboe wrote:
> On 2/1/20 10:49 AM, Andres Freund wrote:
>> Hi, 
>>
>> On February 1, 2020 6:39:41 PM GMT+01:00, Jens Axboe <axboe@kernel.dk> wrote:
>>> On 2/1/20 5:53 AM, Andres Freund wrote:
>>>> Hi,
>>>>
>>>> As long as the syscalls aren't exposed by glibc it'd be useful - at
>>>> least for me - to have liburing expose the syscalls without really
>>> going
>>>> through liburing facilities...
>>>>
>>>> Right now I'm e.g. using a "raw"
>>> io_uring_enter(IORING_ENTER_GETEVENTS)
>>>> to be able to have multiple processes safely wait for events on the
>>> same
>>>> uring, without needing to hold the lock [1] protecting the ring [2]. 
>>> It's
>>>> probably a good idea to add a liburing function to be able to do so,
>>> but
>>>> I'd guess there are going to continue to be cases like that. In a bit
>>>> of time it seems likely that at least open source users of uring that
>>>> are included in databases, have to work against multiple versions of
>>>> liburing (as usually embedding libs is not allowed), and sometimes
>>> that
>>>> is easier if one can backfill a function or two if necessary.
>>>>
>>>> That syscall should probably be under a name that won't conflict with
>>>> eventual glibc implementation of the syscall.
>>>>
>>>> Obviously I can just do the syscall() etc myself, but it seems
>>>> unnecessary to have a separate copy of the ifdefs for syscall numbers
>>>> etc.
>>>>
>>>> What do you think?
>>>
>>> Not sure what I'm missing here, but liburing already has
>>> __sys_io_uring_enter() for this purpose, and ditto for the register
>>> and setup functions?
>>
>> Aren't they hidden to the outside by the symbol versioning script?
> 
> So you just want to have them exposed? I'd be fine with that. I'll
> take a patch :-)
> 

Depends on how it's used, but I'd strive to inline __sys_io_uring_enter()
to remove the extra indirect call into the shared lib. Though, not sure about
packaging and all this stuff. May be useful to do that for liburing as well.

-- 
Pavel Begunkov


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