Feedback-ID: i83e94755:Fastmail
Date:   Thu, 16 Feb 2023 04:05:47 -0800
From:   Josh Triplett <josh@joshtriplett.org>
To:     Dylan Yudaken <dylany@meta.com>
Cc:     "axboe@kernel.dk" <axboe@kernel.dk>,
        "asml.silence@gmail.com" <asml.silence@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "io-uring@vger.kernel.org" <io-uring@vger.kernel.org>
Subject: Re: [PATCHv2] io_uring: Support calling io_uring_register with a
 registered ring fd
Message-ID: <Y+4cG5yy8U0XGHP6@localhost>
References: <f2396369e638284586b069dbddffb8c992afba95.1676419314.git.josh@joshtriplett.org>
 <be9f297f68ee3149f67f781fd291b657cfe4166b.camel@meta.com>
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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