gnu: Make 'mount' interface in static Guile consistent with Guix API.

Rather than expecting a pointer, the version of 'mount' in
guile-static-stripped now takes a string for the 'options' argument, just like
the 'mount' procedure in (guix build syscalls).

* gnu/packages/patches/guile-linux-syscalls.patch (mount): Expect a string or
  #f for 'options' argument.
* gnu/build/file-systems.scm (mount-file-system): Use new 'mount' interface.

gnu/build/file-systems.scm

@@ -286,16 +286,13 @@ run a file system check."
        (when check?
          (check-file-system source type))
        (mkdir-p mount-point)
-       (mount source mount-point type flags
-              (if options
-                  (string->pointer options)
-                  %null-pointer))
+       (mount source mount-point type flags options)
 
        ;; For read-only bind mounts, an extra remount is needed, as per
        ;; <http://lwn.net/Articles/281157/>, which still applies to Linux 4.0.
        (when (and (= MS_BIND (logand flags MS_BIND))
                   (= MS_RDONLY (logand flags MS_RDONLY)))
-         (mount source mount-point type (logior MS_BIND MS_REMOUNT MS_RDONLY)
-                %null-pointer))))))
+         (let ((flags (logior MS_BIND MS_REMOUNT MS_RDONLY)))
+           (mount source mount-point type flags #f)))))))
 
 ;;; file-systems.scm ends here

gnu/packages/patches/guile-linux-syscalls.patch

@@ -7,10 +7,10 @@ diff --git a/libguile/posix.c b/libguile/posix.c
 index 324f21b..cbee94d 100644
 --- a/libguile/posix.c
 +++ b/libguile/posix.c
-@@ -2286,6 +2286,261 @@ scm_init_popen (void)
+@@ -2245,6 +2245,267 @@ scm_init_popen (void)
  }
  #endif
- 
+
 +
 +/* Linux! */
 +
@@ -25,15 +25,18 @@ index 324f21b..cbee94d 100644
 +#define FUNC_NAME s_scm_mount
 +{
 +  int err;
-+  char *c_source, *c_target, *c_type;
++  char *c_source, *c_target, *c_type, *c_data;
 +  unsigned long c_flags;
-+  void *c_data;
 +
 +  c_source = scm_to_locale_string (source);
 +  c_target = scm_to_locale_string (target);
 +  c_type = scm_to_locale_string (type);
 +  c_flags = SCM_UNBNDP (flags) ? 0 : scm_to_ulong (flags);
-+  c_data = SCM_UNBNDP (data) ? NULL : scm_to_pointer (data);
++
++  if (SCM_UNBNDP (data) || scm_is_false (data))
++    c_data = NULL;
++  else
++    c_data = scm_to_locale_string (data);
 +
 +  err = mount (c_source, c_target, c_type, c_flags, c_data);
 +  if (err != 0)
@@ -43,6 +46,9 @@ index 324f21b..cbee94d 100644
 +  free (c_target);
 +  free (c_type);
 +
++  if (c_data != NULL)
++    free (c_data);
++
 +  if (err != 0)
 +    {
 +      errno = err;