lib: Introduce strnstr()

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>
LKML-Reference: <4B4E8743.6030805@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 30 insertions, 2 deletions

diff --git a/include/linux/string.h b/include/linux/string.h
index 651839a2a755..a716ee2a8adb 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -72,7 +72,10 @@ static inline __must_check char *strstrip(char *str)
 }
 
 #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 9f75b4ec50b8..a1cdcfcc42d0 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -667,7 +667,7 @@ EXPORT_SYMBOL(memscan);
  */
 char *strstr(const char *s1, const char *s2)
 {
-        int l1, l2;
+        size_t l1, l2;
 
         l2 = strlen(s2);
         if (!l2)
@@ -684,6 +684,31 @@ 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.