Commit 6e76ac59 authored by Josh Triplett's avatar Josh Triplett Committed by Jens Axboe
Browse files

io_uring: Add io_uring_setup flag to pre-register ring fd and never install it 



With IORING_REGISTER_USE_REGISTERED_RING, an application can register
the ring fd and use it via registered index rather than installed fd.
This allows using a registered ring for everything *except* the initial
mmap.

With IORING_SETUP_NO_MMAP, io_uring_setup uses buffers allocated by the
user, rather than requiring a subsequent mmap.

The combination of the two allows a user to operate *entirely* via a
registered ring fd, making it unnecessary to ever install the fd in the
first place. So, add a flag IORING_SETUP_REGISTERED_FD_ONLY to make
io_uring_setup register the fd and return a registered index, without
installing the fd.

This allows an application to avoid touching the fd table at all, and
allows a library to never even momentarily install a file descriptor.

This splits out an io_ring_add_registered_file helper from
io_ring_add_registered_fd, for use by io_uring_setup.

Signed-off-by: default avatarJosh Triplett <josh@joshtriplett.org>
Link: https://lore.kernel.org/r/bc8f431bada371c183b95a83399628b605e978a3.1682699803.git.josh@joshtriplett.org


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 03d89a2d

include/uapi/linux/io_uring.h

+7 −0
Original line number Diff line number Diff line
@@ -178,6 +178,13 @@ enum { 
 */

#define IORING_SETUP_NO_MMAP		(1U << 14)



/*

 * Register the ring fd in itself for use with

 * IORING_REGISTER_USE_REGISTERED_RING; return a registered fd index rather

 * than an fd.

 */

#define IORING_SETUP_REGISTERED_FD_ONLY	(1U << 15)



enum io_uring_op {

	IORING_OP_NOP,

	IORING_OP_READV,

io_uring/io_uring.c

+22 −15
Original line number Diff line number Diff line
@@ -3788,19 +3788,13 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx, 
	return 0;

}



static int io_uring_install_fd(struct io_ring_ctx *ctx, struct file *file)

static int io_uring_install_fd(struct file *file)

{

	int ret, fd;

	int fd;



	fd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);

	if (fd < 0)

		return fd;



	ret = __io_uring_add_tctx_node(ctx);

	if (ret) {

		put_unused_fd(fd);

		return ret;

	}

	fd_install(fd, file);

	return fd;

}
@@ -3840,6 +3834,7 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p, 
				  struct io_uring_params __user *params)

{

	struct io_ring_ctx *ctx;

	struct io_uring_task *tctx;

	struct file *file;

	int ret;
@@ -3851,6 +3846,10 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p, 
		entries = IORING_MAX_ENTRIES;

	}



	if ((p->flags & IORING_SETUP_REGISTERED_FD_ONLY)

	    && !(p->flags & IORING_SETUP_NO_MMAP))

		return -EINVAL;



	/*

	 * Use twice as many entries for the CQ ring. It's possible for the

	 * application to drive a higher depth than the size of the SQ ring,
@@ -4007,22 +4006,30 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p, 
		goto err;

	}



	ret = __io_uring_add_tctx_node(ctx);

	if (ret)

		goto err_fput;

	tctx = current->io_uring;



	/*

	 * Install ring fd as the very last thing, so we don't risk someone

	 * having closed it before we finish setup

	 */

	ret = io_uring_install_fd(ctx, file);

	if (ret < 0) {

		/* fput will clean it up */

		fput(file);

		return ret;

	}

	if (p->flags & IORING_SETUP_REGISTERED_FD_ONLY)

		ret = io_ring_add_registered_file(tctx, file, 0, IO_RINGFD_REG_MAX);

	else

		ret = io_uring_install_fd(file);

	if (ret < 0)

		goto err_fput;



	trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags);

	return ret;

err:

	io_ring_ctx_wait_and_kill(ctx);

	return ret;

err_fput:

	fput(file);

	return ret;

}



/*
@@ -4049,7 +4056,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params) 
			IORING_SETUP_COOP_TASKRUN | IORING_SETUP_TASKRUN_FLAG |

			IORING_SETUP_SQE128 | IORING_SETUP_CQE32 |

			IORING_SETUP_SINGLE_ISSUER | IORING_SETUP_DEFER_TASKRUN |

			IORING_SETUP_NO_MMAP))

			IORING_SETUP_NO_MMAP | IORING_SETUP_REGISTERED_FD_ONLY))

		return -EINVAL;



	return io_uring_create(entries, &p, params);

io_uring/io_uring.h

+3 −0
Original line number Diff line number Diff line
@@ -75,6 +75,9 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd); 
int io_uring_alloc_task_context(struct task_struct *task,

				struct io_ring_ctx *ctx);



int io_ring_add_registered_file(struct io_uring_task *tctx, struct file *file,

				     int start, int end);



int io_poll_issue(struct io_kiocb *req, struct io_tw_state *ts);

int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr);

int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin);

io_uring/tctx.c

+20 −11
Original line number Diff line number Diff line
@@ -208,17 +208,27 @@ void io_uring_unreg_ringfd(void) 
	}

}



static int io_ring_add_registered_fd(struct io_uring_task *tctx, int fd,

int io_ring_add_registered_file(struct io_uring_task *tctx, struct file *file,

				     int start, int end)

{

	struct file *file;

	int offset;



	for (offset = start; offset < end; offset++) {

		offset = array_index_nospec(offset, IO_RINGFD_REG_MAX);

		if (tctx->registered_rings[offset])

			continue;



		tctx->registered_rings[offset] = file;

		return offset;

	}

	return -EBUSY;

}



static int io_ring_add_registered_fd(struct io_uring_task *tctx, int fd,

				     int start, int end)

{

	struct file *file;

	int offset;



	file = fget(fd);

	if (!file) {

		return -EBADF;
@@ -226,13 +236,12 @@ static int io_ring_add_registered_fd(struct io_uring_task *tctx, int fd, 
		fput(file);

		return -EOPNOTSUPP;

	}

		tctx->registered_rings[offset] = file;

	offset = io_ring_add_registered_file(tctx, file, start, end);

	if (offset < 0)

		fput(file);

	return offset;

}



	return -EBUSY;

}



/*

 * Register a ring fd to avoid fdget/fdput for each io_uring_enter()

 * invocation. User passes in an array of struct io_uring_rsrc_update