Re: io_uring's openat doesn't work with large (2G+) files

[Dmitry Kadashev <dkadashev@gmail.com>]

On Wed, Apr 8, 2020 at 10:49 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 4/8/20 8:41 AM, Dmitry Kadashev wrote:
> > On Wed, Apr 8, 2020 at 10:36 PM Jens Axboe <axboe@kernel.dk> wrote:
> >>
> >> On 4/8/20 8:30 AM, Dmitry Kadashev wrote:
> >>> On Wed, Apr 8, 2020 at 10:19 PM Jens Axboe <axboe@kernel.dk> wrote:
> >>>>
> >>>> On 4/8/20 7:51 AM, Dmitry Kadashev wrote:
> >>>>> Hi,
> >>>>>
> >>>>> io_uring's openat seems to produce FDs that are incompatible with
> >>>>> large files (>2GB). If a file (smaller than 2GB) is opened using
> >>>>> io_uring's openat then writes -- both using io_uring and just sync
> >>>>> pwrite() -- past that threshold fail with EFBIG. If such a file is
> >>>>> opened with sync openat, then both io_uring's writes and sync writes
> >>>>> succeed. And if the file is larger than 2GB then io_uring's openat
> >>>>> fails right away, while the sync one works.
> >>>>>
> >>>>> Kernel versions: 5.6.0-rc2, 5.6.0.
> >>>>>
> >>>>> A couple of reproducers attached, one demos successful open with
> >>>>> failed writes afterwards, and another failing open (in comparison with
> >>>>> sync  calls).
> >>>>>
> >>>>> The output of the former one for example:
> >>>>>
> >>>>> *** sync openat
> >>>>> openat succeeded
> >>>>> sync write at offset 0
> >>>>> write succeeded
> >>>>> sync write at offset 4294967296
> >>>>> write succeeded
> >>>>>
> >>>>> *** sync openat
> >>>>> openat succeeded
> >>>>> io_uring write at offset 0
> >>>>> write succeeded
> >>>>> io_uring write at offset 4294967296
> >>>>> write succeeded
> >>>>>
> >>>>> *** io_uring openat
> >>>>> openat succeeded
> >>>>> sync write at offset 0
> >>>>> write succeeded
> >>>>> sync write at offset 4294967296
> >>>>> write failed: File too large
> >>>>>
> >>>>> *** io_uring openat
> >>>>> openat succeeded
> >>>>> io_uring write at offset 0
> >>>>> write succeeded
> >>>>> io_uring write at offset 4294967296
> >>>>> write failed: File too large
> >>>>
> >>>> Can you try with this one? Seems like only openat2 gets it set,
> >>>> not openat...
> >>>
> >>> I've tried specifying O_LARGEFILE explicitly, that did not change the
> >>> behavior. Is this good enough? Much faster for me to check this way
> >>> that rebuilding the kernel. But if necessary I can do that.
> >>
> >> Not sure O_LARGEFILE settings is going to do it for x86-64, the patch
> >> should fix it though. Might have worked on 32-bit, though.
> >
> > OK, will test.
>
> Great, thanks. FWIW, tested here, and it works for me.

Great, will post results tomorrow.

>
> Any objection to adding your test cases to the liburing regression
> suite?

Feel free to!

>
> --
> Jens Axboe
>

-- 
Dmitry