Add a new sysfs_streq() string comparison function

Add a new sysfs_streq() string comparison function, which ignores
the trailing newlines found in sysfs inputs.  By example:

	sysfs_streq("a", "b")	==> false
	sysfs_streq("a", "a")	==> true
	sysfs_streq("a", "a\n")	==> true
	sysfs_streq("a\n", "a")	==> true

This is intended to simplify parsing of sysfs inputs, letting them
avoid the need to manually strip off newlines from inputs.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/string.h

@@ -109,5 +109,7 @@ extern void *kmemdup(const void *src, size_t len, gfp_t gfp);
 extern char **argv_split(gfp_t gfp, const char *str, int *argcp);
 extern void argv_free(char **argv);
 
+extern bool sysfs_streq(const char *s1, const char *s2);
+
 #endif
 #endif /* _LINUX_STRING_H_ */

lib/string.c

@@ -493,6 +493,33 @@ char *strsep(char **s, const char *ct)
 EXPORT_SYMBOL(strsep);
 #endif
 
+/**
+ * sysfs_streq - return true if strings are equal, modulo trailing newline
+ * @s1: one string
+ * @s2: another string
+ *
+ * This routine returns true iff two strings are equal, treating both
+ * NUL and newline-then-NUL as equivalent string terminations.  It's
+ * geared for use with sysfs input strings, which generally terminate
+ * with newlines but are compared against values without newlines.
+ */
+bool sysfs_streq(const char *s1, const char *s2)
+{
+	while (*s1 && *s1 == *s2) {
+		s1++;
+		s2++;
+	}
+
+	if (*s1 == *s2)
+		return true;
+	if (!*s1 && *s2 == '\n' && !s2[1])
+		return true;
+	if (*s1 == '\n' && !s1[1] && !*s2)
+		return true;
+	return false;
+}
+EXPORT_SYMBOL(sysfs_streq);
+
 #ifndef __HAVE_ARCH_MEMSET
 /**
  * memset - Fill a region of memory with the given value