Re: [PATCHv2] io_uring: Support calling io_uring_register with a registered ring fd

[Josh Triplett <josh@joshtriplett.org>]

On Thu, Feb 16, 2023 at 09:35:44AM +0000, Dylan Yudaken wrote:
> On Tue, 2023-02-14 at 16:42 -0800, Josh Triplett wrote:
> > @@ -4177,17 +4177,37 @@ SYSCALL_DEFINE4(io_uring_register, unsigned
> > int, fd, unsigned int, opcode,
> >         struct io_ring_ctx *ctx;
> >         long ret = -EBADF;
> >         struct fd f;
> > +       bool use_registered_ring;
> > +
> > +       use_registered_ring = !!(opcode &
> > IORING_REGISTER_USE_REGISTERED_RING);
> > +       opcode &= ~IORING_REGISTER_USE_REGISTERED_RING;
> >  
> >         if (opcode >= IORING_REGISTER_LAST)
> >                 return -EINVAL;
> >  
> > -       f = fdget(fd);
> > -       if (!f.file)
> > -               return -EBADF;
> > +       if (use_registered_ring) {
> > +               /*
> > +                * Ring fd has been registered via
> > IORING_REGISTER_RING_FDS, we
> > +                * need only dereference our task private array to
> > find it.
> > +                */
> > +               struct io_uring_task *tctx = current->io_uring;
> >  
> > -       ret = -EOPNOTSUPP;
> > -       if (!io_is_uring_fops(f.file))
> > -               goto out_fput;
> > +               if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
> > +                       return -EINVAL;
> > +               fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
> > +               f.file = tctx->registered_rings[fd];
> > +               f.flags = 0;
> > +               if (unlikely(!f.file))
> > +                       return -EBADF;
> > +               opcode &= ~IORING_REGISTER_USE_REGISTERED_RING;
> 
> ^ this line looks duplicated at the top of the function?

Good catch!

Jens, since you've already applied this, can you remove this line or
would you like a patch doing so?

> Also - is there a liburing regression test for this?

Userspace, including test: https://github.com/axboe/liburing/pull/664