linux-kernel - [RFC PATCH 22/37] iterate_and_advance(): get rid of magic in case when n is 0

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Date:   Sun,  6 Jun 2021 19:10:36 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Sterba <dsterba@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Anton Altaparmakov <anton@...era.com>,
        David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC PATCH 22/37] iterate_and_advance(): get rid of magic in case when n is 0

iov_iter_advance() needs to do some non-trivial work when it's given
0 as argument (skip all empty iovecs, mostly).  We used to implement
it via iterate_and_advance(); we no longer do so and for all other
users of iterate_and_advance() zero length is a no-op.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 lib/iov_iter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 906e9d49c487..ebb907c6393c 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -117,7 +117,7 @@
 #define iterate_and_advance(i, n, v, I, B, K, X) {		\
 	if (unlikely(i->count < n))				\
 		n = i->count;					\
-	if (i->count) {						\
+	if (likely(n)) {					\
 		size_t skip = i->iov_offset;			\
 		if (likely(iter_is_iovec(i))) {			\
 			const struct iovec *iov;		\
-- 
2.11.0