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

[Victor Stewart <v@nametag.social>]

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.
>
> --
> Jens Axboe
>