[PATCH v2 1/7] lib: string: add functions to case-convert strings

[Markus Mayer <mmayer@xxxxxxxxxxxx>]

Add a collection of generic functions to convert strings to lowercase
or uppercase.

Changing the case of a string (with or without copying it first) seems
to be a recurring requirement in the kernel that is currently being
solved by several duplicated implementations doing the same thing. This
change aims at reducing this code duplication.

The new functions are
    char *strncpytoupper(char *dst, const char *src, size_t len);
    char *strncpytolower(char *dst, const char *src, size_t len);
    char *strcpytoupper(char *dst, const char *src);
    char *strcpytolower(char *dst, const char *src);
    char *strtoupper(char *s);
    char *strtolower(char *s);

The "str[n]cpyto*" versions of the function take a destination string
and a source string as arguments. The "strncpyto*" versions
additionally take a length argument like strncpy() itself. Lastly, the
strto* functions take a single string argument and modify the passed-in
string.

All functions return a pointer to the terminating '\0' character in the
modified string ("dst" or "s", respectively).

Signed-off-by: Markus Mayer <mmayer@xxxxxxxxxxxx>
---
 include/linux/string.h | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 lib/string.c           | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 26b6f6a..c58d510 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -116,6 +116,8 @@ extern void * memchr(const void *,int,__kernel_size_t);
 #endif
 void *memchr_inv(const void *s, int c, size_t n);
 char *strreplace(char *s, char old, char new);
+char *strncpytoupper(char *dst, const char *src, size_t len);
+char *strncpytolower(char *dst, const char *src, size_t len);
 
 extern void kfree_const(const void *x);
 
@@ -169,4 +171,50 @@ static inline const char *kbasename(const char *path)
 	return tail ? tail + 1 : path;
 }
 
+/**
+ * strcpytoupper - Copy string and convert to uppercase.
+ * @dst: The buffer to store the result.
+ * @src: The string to convert to uppercase.
+ *
+ * Returns pointer to terminating '\0' in @dst.
+ */
+static inline char *strcpytoupper(char *dst, const char *src)
+{
+	return strncpytoupper(dst, src, 0);
+}
+
+/**
+ * strcpytolower - Copy string and convert to lowercase.
+ * @dst: The buffer to store the result.
+ * @src: The string to convert to lowercase.
+ *
+ * Returns pointer to terminating '\0' in @dst.
+ */
+static inline char *strcpytolower(char *dst, const char *src)
+{
+	return strncpytolower(dst, src, 0);
+}
+
+/**
+ * strtoupper - Convert string to uppercase.
+ * @s: The string to operate on.
+ *
+ * Returns pointer to terminating '\0' in @s.
+ */
+static inline char *strtoupper(char *s)
+{
+	return strncpytoupper(s, s, 0);
+}
+
+/**
+ * strtolower - Convert string to lowercase.
+ * @s: The string to operate on.
+ *
+ * Returns pointer to terminating '\0' in @s.
+ */
+static inline char *strtolower(char *s)
+{
+	return strncpytolower(s, s, 0);
+}
+
 #endif /* _LINUX_STRING_H_ */
diff --git a/lib/string.c b/lib/string.c
index ed83562..900f357 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -952,3 +952,45 @@ char *strreplace(char *s, char old, char new)
 	return s;
 }
 EXPORT_SYMBOL(strreplace);
+
+/**
+ * strncpytoupper - Copy a length-limited string and convert to uppercase.
+ * @dst: The buffer to store the result.
+ * @src: The string to convert to uppercase.
+ * @len: Maximum string length. May be 0 to set no limit.
+ *
+ * Returns pointer to terminating '\0' in @dst.
+ */
+char *strncpytoupper(char *dst, const char *src, size_t len)
+{
+	size_t i;
+
+	for (i = 0; src[i] != '\0' && (i < len || !len); i++)
+		dst[i] = toupper(src[i]);
+	if (i < len || !len)
+		dst[i] = '\0';
+
+	return dst + i;
+}
+EXPORT_SYMBOL(strncpytoupper);
+
+/**
+ * strncpytolower - Copy a length-limited string and convert to lowercase.
+ * @dst: The buffer to store the result.
+ * @src: The string to convert to lowercase.
+ * @len: Maximum string length. May be 0 to set no limit.
+ *
+ * Returns pointer to terminating '\0' in @dst.
+ */
+char *strncpytolower(char *dst, const char *src, size_t len)
+{
+	size_t i;
+
+	for (i = 0; src[i] != '\0' && (i < len || !len); i++)
+		dst[i] = tolower(src[i]);
+	if (i < len || !len)
+		dst[i] = '\0';
+
+	return dst + i;
+}
+EXPORT_SYMBOL(strncpytolower);
-- 
2.7.4

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