[RFC 1/9] lib/string: Add function to trim duplicate WS

[Tony Asleson <tasleson@redhat.com>]

Adds function strim_dupe which trims leading & trailing whitespace and
duplicate adjacent.  Initial use case is to shorten T10 storage IDs.

Signed-off-by: Tony Asleson <tasleson@redhat.com>
---
 include/linux/string.h |  2 ++
 lib/string.c           | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index b6ccdc2c7f02..bcca6bfab6ab 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -72,6 +72,8 @@ extern char * __must_check skip_spaces(const char *);
 
 extern char *strim(char *);
 
+extern size_t strim_dupe(char *s);
+
 static inline __must_check char *strstrip(char *str)
 {
 	return strim(str);
diff --git a/lib/string.c b/lib/string.c
index 08ec58cc673b..1186cce1f66b 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -515,6 +515,41 @@ char *strim(char *s)
 }
 EXPORT_SYMBOL(strim);
 
+/**
+ * Removes leading and trailing whitespace and removes duplicate
+ * adjacent whitespace in a string, modifies string in place.
+ * @s The %NUL-terminated string to have spaces removed
+ * Returns the new length
+ */
+size_t strim_dupe(char *s)
+{
+	size_t ret = 0;
+	char *w = s;
+	char *p;
+
+	/*
+	 * This will remove all leading and duplicate adjacent, but leave
+	 * 1 space at the end if one or more are present.
+	 */
+	for (p = s; *p != '\0'; ++p) {
+		if (!isspace(*p) || (p != s && !isspace(*(p - 1)))) {
+			*w = *p;
+			++w;
+			ret += 1;
+		}
+	}
+
+	*w = '\0';
+
+	/* Take off the last character if it's a space too */
+	if (ret && isspace(*(w - 1))) {
+		ret--;
+		*(w - 1) = '\0';
+	}
+	return ret;
+}
+EXPORT_SYMBOL(strim_dupe);
+
 #ifndef __HAVE_ARCH_STRLEN
 /**
  * strlen - Find the length of a string
-- 
2.21.0