On Wed, Feb 15, 2023 at 10:44:38AM -0700, Jens Axboe wrote:
> On 2/14/23 5:42 PM, Josh Triplett wrote:
> > Add a new flag IORING_REGISTER_USE_REGISTERED_RING (set via the high bit
> > of the opcode) to treat the fd as a registered index rather than a file
> > descriptor.
> >
> > This makes it possible for a library to open an io_uring, register the
> > ring fd, close the ring fd, and subsequently use the ring entirely via
> > registered index.
>
> This looks pretty straight forward to me, only real question I had
> was whether using the top bit of the register opcode for this is the
> best choice. But I can't think of better ways to do it, and the space
> is definitely big enough to do that, so looks fine to me.
It seemed like the cleanest way available given the ABI of
io_uring_register, yeah.
> One more comment below:
>
> > + 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;
>
> I need to double check if it's guaranteed we always have current->io_uring
> assigned here. If the ring is registered we certainly will have it, but
> what if someone calls io_uring_register(2) without having a ring setup
> upfront?
>
> IOW, I think we need a NULL check here and failing the request at that
> point.
The next line is:
+ if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
The first part of that condition is the NULL check you're looking for,
right?
- Josh Triplett
