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io_uring: add comment for drain_next

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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>
This commit is contained in:
Pavel Begunkov 2020-01-25 00:40:24 +03:00 committed by Jens Axboe
parent 980ad26304
commit 8cdf2193a3
1 changed files with 7 additions and 0 deletions
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7
fs/io_uring.c
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@ -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;