kernel-doc: core-api: include string.h into core-api

core-api should show all the various string functions including the newly
added stracpy and stracpy_pad.

Miscellanea:

o Update the Returns: value for strscpy
o fix a defect with %NUL)

[joe@perches.com: correct return of -E2BIG descriptions]
  Link: http://lkml.kernel.org/r/29f998b4c1a9d69fbeae70500ba0daa4b340c546.1563889130.git.joe@perches.com
Link: http://lkml.kernel.org/r/224a6ebf39955f4107c0c376d66155d970e46733.1563841972.git.joe@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Nitin Gote <nitin.r.gote@intel.com>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/core-api/kernel-api.rst

@@ -42,6 +42,9 @@ String Manipulation
 .. kernel-doc:: lib/string.c
    :export:
 
+.. kernel-doc:: include/linux/string.h
+   :internal:
+
 .. kernel-doc:: mm/util.c
    :functions: kstrdup kstrdup_const kstrndup kmemdup kmemdup_nul memdup_user
                vmemdup_user strndup_user memdup_user_nul

include/linux/string.h

@@ -474,8 +474,9 @@ static inline void memcpy_and_pad(void *dest, size_t dest_len,
  * 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
+ * Returns:
+ * * strlen(@prefix) if @str starts with @prefix
+ * * 0 if @str does not start with @prefix
  */
 static __always_inline size_t str_has_prefix(const char *str, const char *prefix)
 {

lib/string.c

@@ -173,8 +173,9 @@ EXPORT_SYMBOL(strlcpy);
  * doesn't unnecessarily force the tail of the destination buffer to be
  * zeroed.  If zeroing is desired please use strscpy_pad().
  *
- * Return: The number of characters copied (not including the trailing
- *         %NUL) or -E2BIG if the destination buffer wasn't big enough.
+ * Returns:
+ * * The number of characters copied (not including the trailing %NUL)
+ * * -E2BIG if count is 0 or @src was truncated.
  */
 ssize_t strscpy(char *dest, const char *src, size_t count)
 {
@@ -253,8 +254,9 @@ EXPORT_SYMBOL(strscpy);
  * For full explanation of why you may want to consider using the
  * 'strscpy' functions please see the function docstring for strscpy().
  *
- * Return: The number of characters copied (not including the trailing
- *         %NUL) or -E2BIG if the destination buffer wasn't big enough.
+ * Returns:
+ * * The number of characters copied (not including the trailing %NUL)
+ * * -E2BIG if count is 0 or @src was truncated.
  */
 ssize_t strscpy_pad(char *dest, const char *src, size_t count)
 {