linux-kernel - [PATCH v2] lib/string: update match_string() doc-strings with correct behavior

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Date:   Thu, 13 Feb 2020 09:27:22 +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 v2] 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.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
---
 lib/string.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/lib/string.c b/lib/string.c
index f607b967d978..6012c385fb31 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -699,6 +699,14 @@ EXPORT_SYMBOL(sysfs_streq);
  * @n:		number of strings in the array or -1 for NULL terminated arrays
  * @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.
+ *
+ * Historically the value of -1 for @n, was used to search in arrays that
+ * are NULL terminated. However, the function does not make a distinction
+ * when finishing the search: either @n elements have been compared OR
+ * the first NULL element was found.
+ *
  * Return:
  * index of a @string in the @array if matches, or %-EINVAL otherwise.
  */
@@ -727,6 +735,14 @@ EXPORT_SYMBOL(match_string);
  *
  * 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.
+ *
+ * Historically the value of -1 for @n, was used to search in arrays that
+ * are NULL terminated. However, the function does not make a distinction
+ * when finishing the search: either @n elements have been compared OR
+ * the first NULL element was found.
  */
 int __sysfs_match_string(const char * const *array, size_t n, const char *str)
 {
-- 
2.20.1