backport: introduce match_string() for kernels < 4.6

This function was introduced in v4.6 and now the iwlwifi driver uses
it.  Add the function for kernels older than v4.6.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

2 files changed, 30 insertions, 0 deletions

diff --git a/backport/backport-include/linux/string.h b/backport/backport-include/linux/string.h
index 4b35eb9f..2bfdf747 100644
--- a/backport/backport-include/linux/string.h
+++ b/backport/backport-include/linux/string.h
@@ -33,4 +33,8 @@ ssize_t strscpy(char *dest, const char *src, size_t count);
 char *strreplace(char *s, char old, char new);
 #endif
 
+#if LINUX_VERSION_IS_LESS(4,6,0)
+int match_string(const char * const *array, size_t n, const char *string);
+#endif /* LINUX_VERSION_IS_LESS(4,5,0) */
+
 #endif /* __BACKPORT_LINUX_STRING_H */
diff --git a/backport/compat/backport-4.6.c b/backport/compat/backport-4.6.c
index 54ff669d..8d0ecf56 100644
--- a/backport/compat/backport-4.6.c
+++ b/backport/compat/backport-4.6.c
@@ -75,3 +75,29 @@ int kstrtobool_from_user(const char __user *s, size_t count, bool *res)
 	return kstrtobool(buf, res);
 }
 EXPORT_SYMBOL_GPL(kstrtobool_from_user);
+
+/**
+ * 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
+ * @string:	string to match with
+ *
+ * Return:
+ * index of a @string in the @array if matches, or %-EINVAL otherwise.
+ */
+int match_string(const char * const *array, size_t n, const char *string)
+{
+	int index;
+	const char *item;
+
+	for (index = 0; index < n; index++) {
+		item = array[index];
+		if (!item)
+			break;
+		if (!strcmp(item, string))
+			return index;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL(match_string);