kern/misc: Implement grub_strtok()

Add the functions grub_strtok() and grub_strtok_r() to help parse strings into
tokens separated by characters in the "delim" parameter. These functions are
present in gnulib but calling them directly from the gnulib code is quite
challenging since the call "#include <string.h>" would include the header file
grub-core/lib/posix_wrap/string.h instead of grub-core/lib/gnulib/string.h,
where strtok() and strtok_r() are declared. Since this overlap is quite
problematic, the simpler solution was to implement the code in the GRUB based
on gnulib's implementation. For more information on these functions, visit the
Linux Programmer's Manual, man strtok.

Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/kern/misc.c

@@ -401,6 +401,68 @@ grub_strword (const char *haystack, const char *needle)
   return 0;
 }
 
+char *
+grub_strtok_r (char *s, const char *delim, char **save_ptr)
+{
+  char *token;
+  const char *c;
+  bool is_delim;
+
+  if (s == NULL)
+    s = *save_ptr;
+
+  /* Scan leading delimiters. */
+  while (*s != '\0')
+    {
+      is_delim = false;
+      for (c = delim; *c != '\0'; c++)
+	{
+	  if (*s == *c)
+	    {
+	      is_delim = true;
+	      break;
+	    }
+	}
+      if (is_delim == true)
+	s++;
+      else
+	break;
+    }
+
+  if (*s == '\0')
+    {
+      *save_ptr = s;
+      return NULL;
+    }
+
+  /* Find the end of the token. */
+  token = s;
+  while (*s != '\0')
+    {
+      for (c = delim; *c != '\0'; c++)
+	{
+	  if (*s == *c)
+	    {
+	      *s = '\0';
+	      *save_ptr = s + 1;
+	      return token;
+	    }
+	}
+      s++;
+    }
+
+  *save_ptr = s;
+  return token;
+}
+
+char *
+grub_strtok (char *s, const char *delim)
+{
+  static char *last;
+
+  return grub_strtok_r (s, delim, &last);
+}
+
 int
 grub_isspace (int c)
 {

include/grub/misc.h

@@ -126,6 +126,9 @@ char *EXPORT_FUNC(grub_strchr) (const char *s, int c);
 char *EXPORT_FUNC(grub_strrchr) (const char *s, int c);
 int EXPORT_FUNC(grub_strword) (const char *s, const char *w);
 
+char *EXPORT_FUNC(grub_strtok_r) (char *s, const char *delim, char **save_ptr);
+char *EXPORT_FUNC(grub_strtok) (char *s, const char *delim);
+
 /* Copied from gnulib.
    Written by Bruno Haible <bruno@clisp.org>, 2005. */
 static inline char *