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

[Dmitry Kadashev <dkadashev@gmail.com>]

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.

Also, forgot to mention, this is on x86_64, not sure if O_LARGEFILE is
necessary to do 2G+ files there?

>
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 79bd22289d73..63eb7efe10f2 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2957,6 +2957,8 @@ static int io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>         req->open.how.mode = READ_ONCE(sqe->len);
>         fname = u64_to_user_ptr(READ_ONCE(sqe->addr));
>         req->open.how.flags = READ_ONCE(sqe->open_flags);
> +       if (force_o_largefile())
> +               req->open.how.flags |= O_LARGEFILE;
>
>         req->open.filename = getname(fname);
>         if (IS_ERR(req->open.filename)) {
>
> --
> Jens Axboe
>

-- 
Dmitry