io_uring: add support for absolute timeouts

This is a pretty trivial addition on top of the relative timeouts
we have now, but it's handy for ensuring tighter timing for those
that are building scheduling primitives on top of io_uring.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1978,13 +1978,17 @@ static int io_timeout(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	unsigned count;
 	struct io_ring_ctx *ctx = req->ctx;
 	struct list_head *entry;
+	enum hrtimer_mode mode;
 	struct timespec64 ts;
 	unsigned span = 0;
+	unsigned flags;
 
 	if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
 		return -EINVAL;
-	if (sqe->flags || sqe->ioprio || sqe->buf_index || sqe->timeout_flags ||
-	    sqe->len != 1)
+	if (sqe->flags || sqe->ioprio || sqe->buf_index || sqe->len != 1)
+		return -EINVAL;
+	flags = READ_ONCE(sqe->timeout_flags);
+	if (flags & ~IORING_TIMEOUT_ABS)
 		return -EINVAL;
 
 	if (get_timespec64(&ts, u64_to_user_ptr(sqe->addr)))
@@ -2042,10 +2046,13 @@ static int io_timeout(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	list_add(&req->list, entry);
 	spin_unlock_irq(&ctx->completion_lock);
 
-	hrtimer_init(&req->timeout.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	if (flags & IORING_TIMEOUT_ABS)
+		mode = HRTIMER_MODE_ABS;
+	else
+		mode = HRTIMER_MODE_REL;
+	hrtimer_init(&req->timeout.timer, CLOCK_MONOTONIC, mode);
 	req->timeout.timer.function = io_timeout_fn;
-	hrtimer_start(&req->timeout.timer, timespec64_to_ktime(ts),
-			HRTIMER_MODE_REL);
+	hrtimer_start(&req->timeout.timer, timespec64_to_ktime(ts), mode);
 	return 0;
 }
 

include/uapi/linux/io_uring.h

@@ -70,6 +70,11 @@ struct io_uring_sqe {
  */
 #define IORING_FSYNC_DATASYNC	(1U << 0)
 
+/*
+ * sqe->timeout_flags
+ */
+#define IORING_TIMEOUT_ABS	(1U << 0)
+
 /*
  * IO completion data structure (Completion Queue Entry)
  */