linux-kernel - [PATCH] lib/string: update match_string() doc-strings with correct behavior

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Date:   Wed, 12 Feb 2020 16:47:23 +0200
From:   Alexandru Ardelean <alexandru.ardelean@...log.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <akpm@...ux-foundation.org>, <keescook@...omium.org>,
        <andriy.shevchenko@...ux.intel.com>, <tobin@...nel.org>,
        <gregkh@...uxfoundation.org>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>
Subject: [PATCH] lib/string: update match_string() doc-strings with correct behavior

There were a few attempts at changing behavior of the match_string()
helpers (i.e. 'match_string()' & 'sysfs_match_string()'), to change &
extend the behavior according to the doc-string.

But the simplest approach is to just fix the doc-strings. The current
behavior is fine as-is, and some bugs were introduced trying to fix it.

As for extending the behavior, new helpers can always be introduced if
needed.

The match_string() helpers behave more like 'strncmp()' in the sense that
they go up to n elements or until the first NULL element in the array of
strings.

This change updates the doc-strings with this info.

Some references to the previous attempts (in no particular order):
  https://lore.kernel.org/lkml/20190508111913.7276-1-alexandru.ardelean@analog.com/
  https://lore.kernel.org/lkml/20190625130104.29904-1-alexandru.ardelean@analog.com/
  https://lore.kernel.org/lkml/20190422083257.21805-1-alexandru.ardelean@analog.com/
  

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
---
 lib/string.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/string.c b/lib/string.c
index f607b967d978..061a17b062b1 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -696,9 +696,12 @@ EXPORT_SYMBOL(sysfs_streq);
 /**
  * match_string - matches given string in an array
  * @array:	array of strings
- * @n:		number of strings in the array or -1 for NULL terminated arrays
+ * @n:		number of strings in the array to compare
  * @string:	string to match with
  *
+ * This routine will look for a string in an array of strings up to the
+ * n-th element in the array or until the first NULL element.
+ *
  * Return:
  * index of a @string in the @array if matches, or %-EINVAL otherwise.
  */
@@ -722,11 +725,14 @@ EXPORT_SYMBOL(match_string);
 /**
  * __sysfs_match_string - matches given string in an array
  * @array: array of strings
- * @n: number of strings in the array or -1 for NULL terminated arrays
+ * @n: number of strings in the array to compare
  * @str: string to match with
  *
  * Returns index of @str in the @array or -EINVAL, just like match_string().
  * Uses sysfs_streq instead of strcmp for matching.
+ *
+ * This routine will look for a string in an array of strings up to the
+ * n-th element in the array or until the first NULL element.
  */
 int __sysfs_match_string(const char * const *array, size_t n, const char *str)
 {
-- 
2.20.1