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

[Dmitry Kadashev <dkadashev@gmail.com>]

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.

>
> > Also, forgot to mention, this is on x86_64, not sure if O_LARGEFILE is
> > necessary to do 2G+ files there?
>
> Internally, yes.
>
> --
> Jens Axboe
>

-- 
Dmitry