add PBD::sys::path::exists_and_writable() method to help replace access(2)

git-svn-id: svn://localhost/ardour2/branches/3.0@9338 d708f5d6-7413-0410-9779-e7cbd77b26cf

libs/pbd/filesystem.cc

@@ -90,6 +90,30 @@ exists (const path & p)
 	return Glib::file_test (p.to_string(), Glib::FILE_TEST_EXISTS);
 }
 
+bool
+exists_and_writable (const path & p)
+{
+	/* writable() really reflects the whole folder, but if for any
+	   reason the session state file can't be written to, still
+	   make us unwritable.
+	*/
+
+	struct stat statbuf;
+
+	if (g_stat (p.to_string().c_str(), &statbuf) != 0) {
+		/* doesn't exist - not writable */
+		return false;
+	} else {
+		if (!(statbuf.st_mode & S_IWUSR)) {
+			/* exists and is not writable */
+			return false;
+		}
+	}
+
+	return true;
+}
+
+
 bool
 is_directory (const path & p)
 {

libs/pbd/pbd/filesystem.h

@@ -119,6 +119,10 @@ inline path operator/ (const path& lhs, const path& rhs)
 /// @return true if path at p exists
 bool exists(const path & p);
 
+
+/// @return true if path at p exists and is writable, false otherwise
+bool exists_and_writable(const path & p);
+
 /// @return true if path at p is a directory.
 bool is_directory(const path & p);