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Commit 221c5eb2 authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring: add support for IORING_OP_POLL 



This is basically a direct port of bfe4037e, which implements a
one-shot poll command through aio. Description below is based on that
commit as well. However, instead of adding a POLL command and relying
on io_cancel(2) to remove it, we mimic the epoll(2) interface of
having a command to add a poll notification, IORING_OP_POLL_ADD,
and one to remove it again, IORING_OP_POLL_REMOVE.

To poll for a file descriptor the application should submit an sqe of
type IORING_OP_POLL. It will poll the fd for the events specified in the
poll_events field.

Unlike poll or epoll without EPOLLONESHOT this interface always works in
one shot mode, that is once the sqe is completed, it will have to be
resubmitted.

Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Based-on-code-from: Christoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent c16361c1

fs/io_uring.c

+262 −1
Original line number Diff line number Diff line
@@ -161,6 +161,7 @@ struct io_ring_ctx { 
		 * manipulate the list, hence no extra locking is needed there.

		 */

		struct list_head	poll_list;

		struct list_head	cancel_list;

	} ____cacheline_aligned_in_smp;



#if defined(CONFIG_UNIX)
@@ -176,8 +177,20 @@ struct sqe_submit { 
	bool				needs_fixed_file;

};



struct io_poll_iocb {

	struct file			*file;

	struct wait_queue_head		*head;

	__poll_t			events;

	bool				woken;

	bool				canceled;

	struct wait_queue_entry		wait;

};



struct io_kiocb {

	union {

		struct kiocb		rw;

		struct io_poll_iocb	poll;

	};



	struct sqe_submit	submit;
@@ -261,6 +274,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p) 
	init_waitqueue_head(&ctx->wait);

	spin_lock_init(&ctx->completion_lock);

	INIT_LIST_HEAD(&ctx->poll_list);

	INIT_LIST_HEAD(&ctx->cancel_list);

	return ctx;

}
@@ -1058,6 +1072,246 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe, 
	return 0;

}



static void io_poll_remove_one(struct io_kiocb *req)

{

	struct io_poll_iocb *poll = &req->poll;



	spin_lock(&poll->head->lock);

	WRITE_ONCE(poll->canceled, true);

	if (!list_empty(&poll->wait.entry)) {

		list_del_init(&poll->wait.entry);

		queue_work(req->ctx->sqo_wq, &req->work);

	}

	spin_unlock(&poll->head->lock);



	list_del_init(&req->list);

}



static void io_poll_remove_all(struct io_ring_ctx *ctx)

{

	struct io_kiocb *req;



	spin_lock_irq(&ctx->completion_lock);

	while (!list_empty(&ctx->cancel_list)) {

		req = list_first_entry(&ctx->cancel_list, struct io_kiocb,list);

		io_poll_remove_one(req);

	}

	spin_unlock_irq(&ctx->completion_lock);

}



/*

 * Find a running poll command that matches one specified in sqe->addr,

 * and remove it if found.

 */

static int io_poll_remove(struct io_kiocb *req, const struct io_uring_sqe *sqe)

{

	struct io_ring_ctx *ctx = req->ctx;

	struct io_kiocb *poll_req, *next;

	int ret = -ENOENT;



	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))

		return -EINVAL;

	if (sqe->ioprio || sqe->off || sqe->len || sqe->buf_index ||

	    sqe->poll_events)

		return -EINVAL;



	spin_lock_irq(&ctx->completion_lock);

	list_for_each_entry_safe(poll_req, next, &ctx->cancel_list, list) {

		if (READ_ONCE(sqe->addr) == poll_req->user_data) {

			io_poll_remove_one(poll_req);

			ret = 0;

			break;

		}

	}

	spin_unlock_irq(&ctx->completion_lock);



	io_cqring_add_event(req->ctx, sqe->user_data, ret, 0);

	io_free_req(req);

	return 0;

}



static void io_poll_complete(struct io_kiocb *req, __poll_t mask)

{

	io_cqring_add_event(req->ctx, req->user_data, mangle_poll(mask), 0);

	io_fput(req);

	io_free_req(req);

}



static void io_poll_complete_work(struct work_struct *work)

{

	struct io_kiocb *req = container_of(work, struct io_kiocb, work);

	struct io_poll_iocb *poll = &req->poll;

	struct poll_table_struct pt = { ._key = poll->events };

	struct io_ring_ctx *ctx = req->ctx;

	__poll_t mask = 0;



	if (!READ_ONCE(poll->canceled))

		mask = vfs_poll(poll->file, &pt) & poll->events;



	/*

	 * Note that ->ki_cancel callers also delete iocb from active_reqs after

	 * calling ->ki_cancel.  We need the ctx_lock roundtrip here to

	 * synchronize with them.  In the cancellation case the list_del_init

	 * itself is not actually needed, but harmless so we keep it in to

	 * avoid further branches in the fast path.

	 */

	spin_lock_irq(&ctx->completion_lock);

	if (!mask && !READ_ONCE(poll->canceled)) {

		add_wait_queue(poll->head, &poll->wait);

		spin_unlock_irq(&ctx->completion_lock);

		return;

	}

	list_del_init(&req->list);

	spin_unlock_irq(&ctx->completion_lock);



	io_poll_complete(req, mask);

}



static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,

			void *key)

{

	struct io_poll_iocb *poll = container_of(wait, struct io_poll_iocb,

							wait);

	struct io_kiocb *req = container_of(poll, struct io_kiocb, poll);

	struct io_ring_ctx *ctx = req->ctx;

	__poll_t mask = key_to_poll(key);



	poll->woken = true;



	/* for instances that support it check for an event match first: */

	if (mask) {

		unsigned long flags;



		if (!(mask & poll->events))

			return 0;



		/* try to complete the iocb inline if we can: */

		if (spin_trylock_irqsave(&ctx->completion_lock, flags)) {

			list_del(&req->list);

			spin_unlock_irqrestore(&ctx->completion_lock, flags);



			list_del_init(&poll->wait.entry);

			io_poll_complete(req, mask);

			return 1;

		}

	}



	list_del_init(&poll->wait.entry);

	queue_work(ctx->sqo_wq, &req->work);

	return 1;

}



struct io_poll_table {

	struct poll_table_struct pt;

	struct io_kiocb *req;

	int error;

};



static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,

			       struct poll_table_struct *p)

{

	struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);



	if (unlikely(pt->req->poll.head)) {

		pt->error = -EINVAL;

		return;

	}



	pt->error = 0;

	pt->req->poll.head = head;

	add_wait_queue(head, &pt->req->poll.wait);

}



static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe)

{

	struct io_poll_iocb *poll = &req->poll;

	struct io_ring_ctx *ctx = req->ctx;

	struct io_poll_table ipt;

	unsigned flags;

	__poll_t mask;

	u16 events;

	int fd;



	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))

		return -EINVAL;

	if (sqe->addr || sqe->ioprio || sqe->off || sqe->len || sqe->buf_index)

		return -EINVAL;



	INIT_WORK(&req->work, io_poll_complete_work);

	events = READ_ONCE(sqe->poll_events);

	poll->events = demangle_poll(events) | EPOLLERR | EPOLLHUP;



	flags = READ_ONCE(sqe->flags);

	fd = READ_ONCE(sqe->fd);



	if (flags & IOSQE_FIXED_FILE) {

		if (unlikely(!ctx->user_files || fd >= ctx->nr_user_files))

			return -EBADF;

		poll->file = ctx->user_files[fd];

		req->flags |= REQ_F_FIXED_FILE;

	} else {

		poll->file = fget(fd);

	}

	if (unlikely(!poll->file))

		return -EBADF;



	poll->head = NULL;

	poll->woken = false;

	poll->canceled = false;



	ipt.pt._qproc = io_poll_queue_proc;

	ipt.pt._key = poll->events;

	ipt.req = req;

	ipt.error = -EINVAL; /* same as no support for IOCB_CMD_POLL */



	/* initialized the list so that we can do list_empty checks */

	INIT_LIST_HEAD(&poll->wait.entry);

	init_waitqueue_func_entry(&poll->wait, io_poll_wake);



	/* one for removal from waitqueue, one for this function */

	refcount_set(&req->refs, 2);



	mask = vfs_poll(poll->file, &ipt.pt) & poll->events;

	if (unlikely(!poll->head)) {

		/* we did not manage to set up a waitqueue, done */

		goto out;

	}



	spin_lock_irq(&ctx->completion_lock);

	spin_lock(&poll->head->lock);

	if (poll->woken) {

		/* wake_up context handles the rest */

		mask = 0;

		ipt.error = 0;

	} else if (mask || ipt.error) {

		/* if we get an error or a mask we are done */

		WARN_ON_ONCE(list_empty(&poll->wait.entry));

		list_del_init(&poll->wait.entry);

	} else {

		/* actually waiting for an event */

		list_add_tail(&req->list, &ctx->cancel_list);

	}

	spin_unlock(&poll->head->lock);

	spin_unlock_irq(&ctx->completion_lock);



out:

	if (unlikely(ipt.error)) {

		if (!(flags & IOSQE_FIXED_FILE))

			fput(poll->file);

		/*

		 * Drop one of our refs to this req, __io_submit_sqe() will

		 * drop the other one since we're returning an error.

		 */

		io_free_req(req);

		return ipt.error;

	}



	if (mask)

		io_poll_complete(req, mask);

	io_free_req(req);

	return 0;

}



static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,

			   const struct sqe_submit *s, bool force_nonblock,

			   struct io_submit_state *state)
@@ -1093,6 +1347,12 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req, 
	case IORING_OP_FSYNC:

		ret = io_fsync(req, s->sqe, force_nonblock);

		break;

	case IORING_OP_POLL_ADD:

		ret = io_poll_add(req, s->sqe);

		break;

	case IORING_OP_POLL_REMOVE:

		ret = io_poll_remove(req, s->sqe);

		break;

	default:

		ret = -EINVAL;

		break;
@@ -2131,6 +2391,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx) 
	percpu_ref_kill(&ctx->refs);

	mutex_unlock(&ctx->uring_lock);



	io_poll_remove_all(ctx);

	io_iopoll_reap_events(ctx);

	wait_for_completion(&ctx->ctx_done);

	io_ring_ctx_free(ctx);

include/uapi/linux/io_uring.h

+3 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ struct io_uring_sqe { 
	union {

		__kernel_rwf_t	rw_flags;

		__u32		fsync_flags;

		__u16		poll_events;

	};

	__u64	user_data;	/* data to be passed back at completion time */

	union {
@@ -51,6 +52,8 @@ struct io_uring_sqe { 
#define IORING_OP_FSYNC		3

#define IORING_OP_READ_FIXED	4

#define IORING_OP_WRITE_FIXED	5

#define IORING_OP_POLL_ADD	6

#define IORING_OP_POLL_REMOVE	7



/*

 * sqe->fsync_flags