Re: [BUG? liburing] io_uring_register_files_update with liburing 2.0 on 5.13.17

[Jens Axboe <axboe@kernel.dk>]

On 9/18/21 3:55 PM, Victor Stewart wrote:
> On Sat, Sep 18, 2021 at 9:38 PM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> On Sat, Sep 18, 2021 at 2:26 PM Jens Axboe <axboe@kernel.dk> wrote:
>>>
>>> On 9/18/21 2:13 PM, Victor Stewart wrote:
>>>> On Sat, Sep 18, 2021 at 3:41 PM Jens Axboe <axboe@kernel.dk> wrote:
>>>>>
>>>>> On 9/18/21 7:41 AM, Victor Stewart wrote:
>>>>>> just auto updated from 5.13.16 to 5.13.17, and suddenly my fixed
>>>>>> file registrations fail with EOPNOTSUPP using liburing 2.0.
>>>>>>
>>>>>> static inline struct io_uring ring;
>>>>>> static inline int *socketfds;
>>>>>>
>>>>>> // ...
>>>>>>
>>>>>> void enableFD(int fd)
>>>>>> {
>>>>>>    int result = io_uring_register_files_update(&ring, fd,
>>>>>>                       &(socketfds[fd] = fd), 1);
>>>>>>    printf("enableFD, result = %d\n", result);
>>>>>> }
>>>>>>
>>>>>> maybe this is due to the below and related work that
>>>>>> occurred at the end of 5.13 and liburing got out of sync?
>>>>>>
>>>>>> https://github.com/torvalds/linux/commit/992da01aa932b432ef8dc3885fa76415b5dbe43f#diff-79ffab63f24ef28eec3badbc8769e2a23e0475ab1fbe390207269ece944a0824
>>>>>>
>>>>>> and can't use liburing 2.1 because of the api changes since 5.13.
>>>>>
>>>>> That's very strange, the -EOPNOTSUPP should only be possible if you
>>>>> are not passing in the ring fd for the register syscall. You should
>>>>> be able to mix and match liburing versions just fine, the only exception
>>>>> is sometimes between releases (of both liburing and the kernel) where we
>>>>> have the liberty to change the API of something that was added before
>>>>> release.
>>>>>
>>>>> Can you do an strace of it and attach?
>>>>
>>>> oh ya the EOPNOTSUPP was my bug introduced trying to debug.
>>>>
>>>> here's the real bug...
>>>>
>>>> io_uring_register(13, IORING_REGISTER_FILES, [-1, -1, -1, 3, 4, 5, 6, 7,
>>>> 8, 9, 10, 11, 12, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
>>>> -1, -1, -1, -1, -1,
>>>> -1, ...], 32768) = -1 EMFILE (Too many open files)
>>>>
>>>> 32,768 is 1U << 15 aka IORING_MAX_FIXED_FILES, but i tried
>>>> 16,000 just to try and same issue.
>>>>
>>>> maybe you're not allowed to have pre-filled (aka non negative 1)
>>>> entries upon the initial io_uring_register_files call anymore?
>>>>
>>>> this was working until the 5.13.16 -> 5.13.17 transition.
>>>
>>> Ah yes that makes more sense. You need to up RLIMIT_NOFILE, the
>>> registered files are under that protection now too. This is also why it
>>> was brought back to stable. A bit annoying, but it was needed for the
>>> direct file support to have some sanity there.
>>>
>>> So use rlimit(RLIMIT_NOFILE,...) from the app or ulimit -n to bump the
>>> limit.
>>
> 
> perfect got it working with..
> 
> struct rlimit maxFilesLimit = {N_IOURING_MAX_FIXED_FILES,
> N_IOURING_MAX_FIXED_FILES};
> setrlimit(RLIMIT_NOFILE, &maxFilesLimit);

Good!

>> BTW, this could be incorporated into io_uring_register_files and
>> io_uring_register_files_tags(), might not be a bad idea in general. Just
>> have it check rlim.rlim_cur for RLIMIT_NOFILE, and if it's smaller than
>> 'nr_files', then bump it. That'd hide it nicely, instead of throwing a
>> failure.
> 
> the implicit bump sounds like a good idea (at least in theory?).

Can you try current liburing -git? Remove your own RLIMIT_NOFILE and
just verify that it works. I pushed a change for it.

> another thing i think might be a good idea is an io_uring
> change/migration log that we update with every kernel release covering
> new features but also new restrictions/requirements/tweaks etc.

Yes, that is a good idea. The man pages do tend to reference what
version included what, but a highlight per release would be a great idea
to have without having to dig for it.

> something that would take 1 minute to skim and see if relevant.
> 
> because at this point to stay fully updated requires reading all of the
> mailing list or checking pulls on your branch + running to binaries
> to see if anything breaks.

Question is where to post it? Because I would post it here anyway...

-- 
Jens Axboe