[PATCH 4/7] lib: Introduce strnstr()

[Li Zefan <lizf@cn.fujitsu.com>]

It differs strstr() in that it limits the length to be searched
in the first string.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 include/linux/string.h |    5 ++++-
 lib/string.c           |   27 ++++++++++++++++++++++++++-
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index b850886..fa6a5ba 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -64,7 +64,10 @@ extern char * strrchr(const char *,int);
 #endif
 extern char * __must_check strstrip(char *);
 #ifndef __HAVE_ARCH_STRSTR
-extern char * strstr(const char *,const char *);
+extern char * strstr(const char *, const char *);
+#endif
+#ifndef __HAVE_ARCH_STRNSTR
+extern char * strnstr(const char *, const char *, size_t);
 #endif
 #ifndef __HAVE_ARCH_STRLEN
 extern __kernel_size_t strlen(const char *);
diff --git a/lib/string.c b/lib/string.c
index e96421a..a5fff51 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -656,7 +656,7 @@ EXPORT_SYMBOL(memscan);
  */
 char *strstr(const char *s1, const char *s2)
 {
-	int l1, l2;
+	size_t l1, l2;
 
 	l2 = strlen(s2);
 	if (!l2)
@@ -673,6 +673,31 @@ char *strstr(const char *s1, const char *s2)
 EXPORT_SYMBOL(strstr);
 #endif
 
+#ifndef __HAVE_ARCH_STRNSTR
+/**
+ * strnstr - Find the first substring in a length-limited string
+ * @s1: The string to be searched
+ * @s2: The string to search for
+ * @len: the maximum number of characters to search
+ */
+char *strnstr(const char *s1, const char *s2, size_t len)
+{
+	size_t l1 = len, l2;
+
+	l2 = strlen(s2);
+	if (!l2)
+		return (char *)s1;
+	while (l1 >= l2) {
+		l1--;
+		if (!memcmp(s1, s2, l2))
+			return (char *)s1;
+		s1++;
+	}
+	return NULL;
+}
+EXPORT_SYMBOL(strnstr);
+#endif
+
 #ifndef __HAVE_ARCH_MEMCHR
 /**
  * memchr - Find a character in an area of memory.
-- 
1.6.3