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

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On Sat, Sep 18, 2021 at 9:38 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> On Sat, Sep 18, 2021 at 2:26 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >
> > On 9/18/21 2:13 PM, Victor Stewart wrote:
> > > On Sat, Sep 18, 2021 at 3:41 PM Jens Axboe <axboe@xxxxxxxxx> 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);

> 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?).

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.

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.

>
> --
> Jens Axboe



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