[PATCH v2 04/13] string: implement strv_length helper

[Ahmad Fatoum <a.fatoum@barebox.org>]

For calculating the length of an array of strings with a NULL sentinel,
introduce a strv_length helper.

Signed-off-by: Ahmad Fatoum <a.fatoum@barebox.org>
---
v1 -> v2:
  - no change
---
 include/string.h |  7 +++++++
 lib/string.c     | 17 +++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/include/string.h b/include/string.h
index b54a8fc3f38a..71affe48b640 100644
--- a/include/string.h
+++ b/include/string.h
@@ -57,4 +57,11 @@ static inline bool is_nul_terminated(const char *val, size_t len)
 	return strnlen(val, len) != len;
 }
 
+typedef union {
+	char * const *sl;
+	const char * const *sl_const;
+} strv_t __attribute__((transparent_union));
+
+size_t strv_length(strv_t) __pure;
+
 #endif /* __STRING_H */
diff --git a/lib/string.c b/lib/string.c
index 96eac6d1daf6..73637cd9710a 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -1137,3 +1137,20 @@ char *strreplace(char *str, char old, char new)
 	return str;
 }
 EXPORT_SYMBOL(strreplace);
+
+/**
+ * strv_length - calculate length of string vector
+ * @strv: NULL-terminated array of string
+ *
+ * Return: size of the vector
+ */
+size_t strv_length(const char * const *l)
+{
+	size_t n = 0;
+
+        for (const char *const *s, *const *i = (l); (s = i) && *i; i++)
+		n++;
+
+	return n;
+}
+EXPORT_SYMBOL(strv_length);
-- 
2.39.5