[PATCH v2 1/8] io_uring: leave a comment for drain_next

Pavel Begunkov
2020-01-25T19:55:00Z

Draining the middle of a link is tricky, so leave a comment there

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e79d6e47dc7b..bc1cab6a256a 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4702,6 +4702,13 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
if (*link) {
struct io_kiocb *head = *link;

+ /*
+ * Taking sequential execution of a link, draining both sides
+ * of the link also fullfils IOSQE_IO_DRAIN semantics for all
+ * requests in the link. So, it drains the head and the
+ * next after the link request. The last one is done via
+ * drain_next flag to persist the effect across calls.
+ */
if (sqe_flags & IOSQE_IO_DRAIN) {
head->flags |= REQ_F_IO_DRAIN;
ctx->drain_next = 1;
--
2.24.0