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From: Josh Triplett <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Pavel Begunkov <[email protected]>,
	[email protected], [email protected]
Subject: Re: [PATCHv2] io_uring: Support calling io_uring_register with a registered ring fd
Date: Wed, 15 Feb 2023 12:33:08 -0800	[thread overview]
Message-ID: <Y+1BhMgNJVoqYlYf@localhost> (raw)
In-Reply-To: <[email protected]>

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

  reply	other threads:[~2023-02-15 20:33 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-15  0:42 [PATCHv2] io_uring: Support calling io_uring_register with a registered ring fd Josh Triplett
2023-02-15 17:44 ` Jens Axboe
2023-02-15 20:33   ` Josh Triplett [this message]
2023-02-15 21:39     ` Jens Axboe
2023-02-16  3:24 ` Jens Axboe
2023-02-16  9:35 ` Dylan Yudaken
2023-02-16 12:05   ` Josh Triplett
2023-02-16 13:10     ` Jens Axboe

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