Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper macro

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 21 Dec 2018 12:46:47 -0800
Joe Perches <joe@perches.com> wrote:

> I think all the underscores are unnecessary and confusing.

Here. I removed a beginning and ending underscore from each variable ;-)

-- Steve

diff --git a/include/linux/string.h b/include/linux/string.h
index 27d0482e5e05..7f88444471f7 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -14,6 +14,28 @@ extern void *memdup_user(const void __user *, size_t);
 extern void *vmemdup_user(const void __user *, size_t);
 extern void *memdup_user_nul(const void __user *, size_t);
 
+/**
+ * str_has_prefix - Test if a string has a given prefix
+ * @str: The string to test
+ * @prefix: The string to see if @str starts with
+ *
+ * A common way to test a prefix of a string is to do:
+ *  strncmp(str, prefix, sizeof(prefix) - 1)
+ *
+ * But this can lead to bugs due to typos, or if prefix is a pointer
+ * and not a constant. Instead use str_has_prefix().
+ *
+ * Returns: 0 if @str does not start with @prefix
+         strlen(@prefix) if @str does start with @prefix
+ */
+#define str_has_prefix(str, prefix)					\
+	({								\
+		const char *___prefix___ = (const char *)(prefix);	\
+		int ___len___ = strlen(___prefix___);			\
+		strncmp(str, ___prefix___, ___len___) == 0 ?		\
+			___len___ : 0;					\
+	})
+
 /*
  * Include machine specific inline routines
  */