[PATCH] string.h: Implement strndup

[Uwe Kleine-König]

I implemented this while trying to import mmc-utils into barebox. While
I didn't finish this import this function might still be useful for
someone?!

Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
---
 include/linux/string.h |  3 +++
 lib/string.c           | 20 ++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 5df8c50e579a..ed4eeb5519e6 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -80,6 +80,9 @@ extern __kernel_size_t strnlen(const char *,__kernel_size_t);
 #ifndef __HAVE_ARCH_STRDUP
 extern char * strdup(const char *);
 #endif
+#ifndef __HAVE_ARCH_STRNDUP
+extern char *strndup(const char *, size_t);
+#endif
 #ifndef __HAVE_ARCH_STRSWAB
 extern char * strswab(const char *);
 #endif
diff --git a/lib/string.c b/lib/string.c
index 1d491c9c2fb5..f588933e8191 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -323,6 +323,26 @@ char * strdup(const char *s)
 #endif
 EXPORT_SYMBOL(strdup);
 
+#ifndef __HAVE_ARCH_STRNDUP
+char *strndup(const char *s, size_t n)
+{
+	char *new;
+	size_t len = strnlen(s, n);
+
+	if ((s == NULL) ||
+	    ((new = malloc(len + 1)) == NULL)) {
+		return NULL;
+	}
+
+	memcpy(new, s, len);
+	new[len] = '\0';
+
+	return new;
+}
+
+#endif
+EXPORT_SYMBOL(strndup);
+
 #ifndef __HAVE_ARCH_STRSPN
 /**
  * strspn - Calculate the length of the initial substring of @s which only
-- 
2.11.0