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 11:21 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> 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.

i don't have a dev box up right now, but i applied the below changes to 2.0
sans the tags bit...

diff --git a/src/register.c b/src/register.c
index 994aaff..495216a 100644
--- a/src/register.c
+++ b/src/register.c
@@ -7,6 +7,7 @@
 #include <unistd.h>
 #include <errno.h>
 #include <string.h>
+#include <sys/resource.h>

 #include "liburing/compat.h"
 #include "liburing/io_uring.h"
@@ -14,6 +15,22 @@

 #include "syscall.h"

+static int bump_rlimit_nofile(unsigned nr)
+{
+       struct rlimit rlim;
+
+       if (getrlimit(RLIMIT_NOFILE, &rlim) < 0)
+               return -errno;
+       if (rlim.rlim_cur < nr) {
+               if (nr > rlim.rlim_max)
+                       return -EMFILE;
+               rlim.rlim_cur = nr;
+               setrlimit(RLIMIT_NOFILE, &rlim);
+       }
+
+       return 0;
+}
+
 int io_uring_register_buffers(struct io_uring *ring, const struct
iovec *iovecs,
                              unsigned nr_iovecs)
 {
@@ -55,6 +72,10 @@ int io_uring_register_files_update(struct io_uring
*ring, unsigned off,
        };
        int ret;

+       ret = bump_rlimit_nofile(nr_files);
+       if (ret)
+               return ret;
+

and it failed with the same as before...

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)

if you want i can debug it for you tomorrow? (in london)

>
> > 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...

i think a txt file in liburing might be the perfect place given the audience
for it is solely application developers? could start with 5.15 and maintain
it forward.

>
> --
> Jens Axboe
>