lib/string: add sysfs_match_string helper

Make a simple helper for matching strings with sysfs
attribute files. In most parts the same as match_string(),
except sysfs_match_string() uses sysfs_streq() instead of
strcmp() for matching. This is more convenient when used
with sysfs attributes.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit e1fe7b6a7b)

include/linux/string.h

@@ -136,6 +136,16 @@ static inline int strtobool(const char *s, bool *res)
 }
 
 int match_string(const char * const *array, size_t n, const char *string);
+int __sysfs_match_string(const char * const *array, size_t n, const char *s);
+
+/**
+ * sysfs_match_string - matches given string in an array
+ * @_a: array of strings
+ * @_s: string to match with
+ *
+ * Helper for __sysfs_match_string(). Calculates the size of @a automatically.
+ */
+#define sysfs_match_string(_a, _s) __sysfs_match_string(_a, ARRAY_SIZE(_a), _s)
 
 #ifdef CONFIG_BINARY_PRINTF
 int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args);

lib/string.c

@@ -656,6 +656,32 @@ int match_string(const char * const *array, size_t n, const char *string)
 }
 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
+ * @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.
+ */
+int __sysfs_match_string(const char * const *array, size_t n, const char *str)
+{
+	const char *item;
+	int index;
+
+	for (index = 0; index < n; index++) {
+		item = array[index];
+		if (!item)
+			break;
+		if (sysfs_streq(item, str))
+			return index;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL(__sysfs_match_string);
+
 #ifndef __HAVE_ARCH_MEMSET
 /**
  * memset - Fill a region of memory with the given value