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

[Jens Axboe <axboe@kernel.dk>]

On 2/16/23 5:05?AM, Josh Triplett wrote:
> 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!

Indeed!

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

It's still top-of-tree, I just amended it.

-- 
Jens Axboe