This is basically a direct port of bfe4037e722e, 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.
Based-on-code-from: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/io_uring.c | 261 +++++++++++++++++++++++++++++++++-
include/uapi/linux/io_uring.h | 3 +
2 files changed, 263 insertions(+), 1 deletion(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index dc5667c53c55..ae51bac078e2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -141,6 +141,7 @@ 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)
@@ -156,8 +157,20 @@ 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 {
- struct kiocb rw;
+ union {
+ struct kiocb rw;
+ struct io_poll_iocb poll;
+ };
struct sqe_submit submit;
@@ -241,6 +254,7 @@ 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;
}
@@ -1034,6 +1048,244 @@ 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) {
+ if (!(mask & poll->events))
+ return 0;
+
+ /* try to complete the iocb inline if we can: */
+ if (spin_trylock(&ctx->completion_lock)) {
+ list_del(&req->list);
+ spin_unlock(&ctx->completion_lock);
+
+ 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)
@@ -1069,6 +1321,12 @@ 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;
@@ -2030,6 +2288,7 @@ 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);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 0ec74bab8dbe..e23408692118 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -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
--
2.17.1
