linux-kernel - [PATCH] dm-crypt: Slightly simplify crypt_set_keyring

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Message-Id: <c3d25e24503d9e625cf46e9fb4ee55f10bfdd398.1674920529.git.christophe.jaillet@wanadoo.fr>
Date:   Sat, 28 Jan 2023 16:43:00 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] dm-crypt: Slightly simplify crypt_set_keyring_key()

Use strchr() instead of strpbrk() when there is only 1 element in the set
of characters to look for.
This potentially saves a few cycles.

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
On my machine, the diff of the .s file shows that the generated code is
the same:

-- drivers/md/dm-crypt.old.s	2023-01-28 16:28:08.968026902 +0100
++ drivers/md/dm-crypt.s	2023-01-28 16:28:32.056027335 +0100
@@ -17950,7 +17950,7 @@
 	call	__sanitizer_cov_trace_const_cmp1	#
 	testb	%bl, %bl	# _56
 	jne	.L928	#,
-# drivers/md/dm-crypt.c:2490: 	key_desc = strpbrk(key_string, ":");
+# drivers/md/dm-crypt.c:2490: 	key_desc = strchr(key_string, ':');
 	call	__sanitizer_cov_trace_pc	#
 	movl	$58, %esi	#,
 	movq	%r12, %rdi	# key_string,

This is done thanks to fold_builtin_strpbrk() in gcc which already
transforms such patterns.
(https://github.com/gcc-mirror/gcc/blob/master/gcc/builtins.cc#L10238)
---
 drivers/md/dm-crypt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 2653516bcdef..b9c41fd42e8a 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -2487,7 +2487,7 @@ static int crypt_set_keyring_key(struct crypt_config *cc, const char *key_string
 	}
 
 	/* look for next ':' separating key_type from key_description */
-	key_desc = strpbrk(key_string, ":");
+	key_desc = strchr(key_string, ':');
 	if (!key_desc || key_desc == key_string || !strlen(key_desc + 1))
 		return -EINVAL;
 
-- 
2.34.1