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

[Dylan Yudaken <dylany@meta.com>]

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?


Also - is there a liburing regression test for this?