string: factorize skip_spaces and export it to be generally available

On the following sentence:
    while (*s && isspace(*s))
        s++;

If *s == 0, isspace() evaluates to ((_ctype[*s] & 0x20) != 0), which
evaluates to ((0x08 & 0x20) != 0) which equals to 0 as well.
If *s == 1, we depend on isspace() result anyway. In other words,
"a char equals zero is never a space", so remove this check.

Also, *s != 0 is most common case (non-null string).

Fixed const return as noticed by Jan Engelhardt and James Bottomley.
Fixed unnecessary extra cast on strstrip() as noticed by Jan Engelhardt.

Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/ctype.h b/include/linux/ctype.h
index 6dec944a370b..a3d6ee0044f9 100644
--- a/include/linux/ctype.h
+++ b/include/linux/ctype.h
@@ -27,6 +27,7 @@ extern const unsigned char _ctype[];
 #define islower(c)      ((__ismask(c)&(_L)) != 0)
 #define isprint(c)      ((__ismask(c)&(_P|_U|_L|_D|_SP)) != 0)
 #define ispunct(c)      ((__ismask(c)&(_P)) != 0)
+/* Note: isspace() must return false for %NUL-terminator */
 #define isspace(c)      ((__ismask(c)&(_S)) != 0)
 #define isupper(c)      ((__ismask(c)&(_U)) != 0)
 #define isxdigit(c)     ((__ismask(c)&(_D|_X)) != 0)
diff --git a/include/linux/string.h b/include/linux/string.h
index b8508868d5ad..168dad11ae03 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -62,6 +62,7 @@ extern char * strnchr(const char *, size_t, int);
 #ifndef __HAVE_ARCH_STRRCHR
 extern char * strrchr(const char *,int);
 #endif
+extern char * __must_check skip_spaces(const char *);
 extern char * __must_check strstrip(char *);
 #ifndef __HAVE_ARCH_STRSTR
 extern char * strstr(const char *,const char *);