From: Pavel Begunkov <asml.silence@gmail.com>
Date: Fri, 24 Jan 2020 21:40:24 +0000 (+0300)
Subject: io_uring: add comment for drain_next
X-Git-Tag: v5.15~4609^2~11
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=8cdf2193a3335b4cfb6e023b41ac293d0843d287;p=mirror_ubuntu-kernels.git

io_uring: add comment for drain_next

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

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 4bde5da2c2f5..a700ee5fc89d 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4629,6 +4629,13 @@ err_req:
 	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;