Split make_system_path_relative_to_its_root into separate file

relpath.c from getroot.c as it's common between unix and haiku
	but otherwise haiku doesn't use any functions from unix getroot.c.

grub-core/osdep/unix/relpath.c

@@ -0,0 +1,168 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 1999,2000,2001,2002,2003,2006,2007,2008,2009,2010,2011,2012,2013  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <config-util.h>
+#include <config.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+
+#include <grub/util/misc.h>
+#include <grub/emu/hostdisk.h>
+#include <grub/emu/getroot.h>
+#include <grub/mm.h>
+
+/* This function never prints trailing slashes (so that its output
+   can be appended a slash unconditionally).  */
+char *
+grub_make_system_path_relative_to_its_root (const char *path)
+{
+  struct stat st;
+  char *p, *buf, *buf2, *buf3, *ret;
+  uintptr_t offset = 0;
+  dev_t num;
+  size_t len;
+  char *poolfs = NULL;
+
+  /* canonicalize.  */
+  p = canonicalize_file_name (path);
+  if (p == NULL)
+    grub_util_error (_("failed to get canonical path of `%s'"), path);
+
+  /* For ZFS sub-pool filesystems, could be extended to others (btrfs?).  */
+  {
+    char *dummy;
+    grub_find_zpool_from_dir (p, &dummy, &poolfs);
+  }
+
+  len = strlen (p) + 1;
+  buf = xstrdup (p);
+  free (p);
+
+  if (stat (buf, &st) < 0)
+    grub_util_error (_("cannot stat `%s': %s"), buf, strerror (errno));
+
+  buf2 = xstrdup (buf);
+  num = st.st_dev;
+
+  /* This loop sets offset to the number of chars of the root
+     directory we're inspecting.  */
+  while (1)
+    {
+      p = strrchr (buf, '/');
+      if (p == NULL)
+	/* This should never happen.  */
+	grub_util_error ("%s",
+			 /* TRANSLATORS: canonical pathname is the
+			    complete one e.g. /etc/fstab. It has
+			    to contain `/' normally, if it doesn't
+			    we're in trouble and throw this error.  */
+			 _("no `/' in canonical filename"));
+      if (p != buf)
+	*p = 0;
+      else
+	*++p = 0;
+
+      if (stat (buf, &st) < 0)
+	grub_util_error (_("cannot stat `%s': %s"), buf, strerror (errno));
+
+      /* buf is another filesystem; we found it.  */
+      if (st.st_dev != num)
+	{
+	  /* offset == 0 means path given is the mount point.
+	     This works around special-casing of "/" in Un*x.  This function never
+	     prints trailing slashes (so that its output can be appended a slash
+	     unconditionally).  Each slash in is considered a preceding slash, and
+	     therefore the root directory is an empty string.  */
+	  if (offset == 0)
+	    {
+	      free (buf);
+#ifdef __linux__
+	      {
+		char *bind;
+		grub_free (grub_find_root_devices_from_mountinfo (buf2, &bind));
+		if (bind && bind[0] && bind[1])
+		  {
+		    buf3 = bind;
+		    goto parsedir;
+		  }
+		grub_free (bind);
+	      }
+#endif
+	      free (buf2);
+	      if (poolfs)
+		return xasprintf ("/%s/@", poolfs);
+	      return xstrdup ("");
+	    }
+	  else
+	    break;
+	}
+
+      offset = p - buf;
+      /* offset == 1 means root directory.  */
+      if (offset == 1)
+	{
+	  /* Include leading slash.  */
+	  offset = 0;
+	  break;
+	}
+    }
+  free (buf);
+  buf3 = xstrdup (buf2 + offset);
+  buf2[offset] = 0;
+#ifdef __linux__
+  {
+    char *bind;
+    grub_free (grub_find_root_devices_from_mountinfo (buf2, &bind));
+    if (bind && bind[0] && bind[1])
+      {
+	char *temp = buf3;
+	buf3 = grub_xasprintf ("%s%s%s", bind, buf3[0] == '/' ?"":"/", buf3);
+	grub_free (temp);
+      }
+    grub_free (bind);
+  }
+#endif
+  
+  free (buf2);
+
+#ifdef __linux__
+ parsedir:
+#endif
+  /* Remove trailing slashes, return empty string if root directory.  */
+  len = strlen (buf3);
+  while (len > 0 && buf3[len - 1] == '/')
+    {
+      buf3[len - 1] = '\0';
+      len--;
+    }
+
+  if (poolfs)
+    {
+      ret = xasprintf ("/%s/@%s", poolfs, buf3);
+      free (buf3);
+    }
+  else
+    ret = buf3;
+
+  return ret;
+}