Switch to get_current_dir_name()

This patch changes getcwd to get_current_dir_name and does a tiny
refactor to move cleanup functions to a dedicated module so that they
can be shared.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>

src/Makefile.am

@@ -10,7 +10,9 @@ snap_confine_SOURCES = \
 	mount-support.c \
 	mount-support.h \
 	mount-support-nvidia.c \
-	mount-support-nvidia.h
+	mount-support-nvidia.h \
+	cleanup-funcs.c \
+	cleanup-funcs.h
 snap_confine_CFLAGS = -Wall -Werror $(AM_CFLAGS)
 snap_confine_LDFLAGS = $(AM_LDFLAGS)
 snap_confine_LDADD =

src/cleanup-funcs.c

@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2015 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <stdlib.h>
+
+void sc_cleanup_string(char **ptr)
+{
+	free(*ptr);
+}

src/cleanup-funcs.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2015 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef SNAP_CONFINE_CLEANUP_FUNCS_H
+#define SNAP_CONFINE_CLEANUP_FUNCS_H
+
+/**
+ * Free a dynamically allocated string.
+ *
+ * This function is designed to be used with
+ * __attribute__((cleanup(sc_cleanup_string))).
+ **/
+void sc_cleanup_string(char **ptr);
+
+#endif

src/main.c

@@ -32,6 +32,7 @@
 #include "seccomp-support.h"
 #include "udev-support.h"
 #endif				// ifdef STRICT_CONFINEMENT
+#include "cleanup-funcs.h"
 
 int main(int argc, char **argv)
 {
@@ -89,8 +90,10 @@ int main(int argc, char **argv)
 		// Get the current working directory before we start fiddling with
 		// mounts and possibly pivot_root.  At the end of the whole process, we
 		// will try to re-locate to the same directory (if possible).
-		char vanilla_cwd[512];
-		if (getcwd(vanilla_cwd, sizeof vanilla_cwd) == NULL) {
+		char *vanilla_cwd __attribute__ ((cleanup(sc_cleanup_string))) =
+		    NULL;
+		vanilla_cwd = get_current_dir_name();
+		if (vanilla_cwd == NULL) {
 			die("cannot get the current working directory");
 		}
 		// do the mounting if run on a non-native snappy system

src/mount-support-nvidia.c

@@ -78,11 +78,6 @@ static const char *nvidia_globs[] = {
 static const size_t nvidia_globs_len =
     sizeof nvidia_globs / sizeof *nvidia_globs;
 
-static void cleanup_string(char **ptr)
-{
-	free(*ptr);
-}
-
 // Populate libgl_dir with a symlink farm to files matching glob_list.
 //
 // The symbolic links are made in one of two ways. If the library found is a
@@ -113,7 +108,8 @@ static void sc_populate_libgl_with_hostfs_symlinks(const char *libgl_dir,
 		char symlink_name[512];
 		char symlink_target[512];
 		const char *pathname = glob_res.gl_pathv[i];
-		char *pathname_copy __attribute__ ((cleanup(cleanup_string))) =
+		char *pathname_copy
+		    __attribute__ ((cleanup(sc_cleanup_string))) =
 		    strdup(pathname);
 		char *filename = basename(pathname_copy);
 		struct stat stat_buf;