libdpkg: New atomic file module

lib/dpkg/Makefile.am

@@ -26,6 +26,7 @@ libdpkg_a_SOURCES = \
 	dlist.h \
 	ar.c \
 	arch.c \
+	atomic-file.c \
 	buffer.c \
 	cleanup.c \
 	command.c \
@@ -77,6 +78,7 @@ libdpkg_a_SOURCES = \
 pkginclude_HEADERS = \
 	ar.h \
 	arch.h \
+	atomic-file.h \
 	buffer.h \
 	command.h \
 	compress.h \

lib/dpkg/atomic-file.c

@@ -0,0 +1,124 @@
+/*
+ * libdpkg - Debian packaging suite library routines
+ * atomic-file.c - atomic file helper functions
+ *
+ * Copyright © 2011 Guillem Jover <guillem@debian.org>
+ *
+ * This 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This 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 <config.h>
+#include <compat.h>
+
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include <dpkg/i18n.h>
+#include <dpkg/dpkg.h>
+#include <dpkg/atomic-file.h>
+
+#define ATOMIC_FILE_NEW_EXT "-new"
+#define ATOMIC_FILE_OLD_EXT "-old"
+
+struct atomic_file *
+atomic_file_new(const char *filename, enum atomic_file_flags flags)
+{
+	struct atomic_file *file;
+
+	file = m_malloc(sizeof(*file));
+	file->flags = flags;
+	file->fp = NULL;
+	file->name = m_strdup(filename);
+	m_asprintf(&file->name_new, "%s%s", filename, ATOMIC_FILE_NEW_EXT);
+
+	return file;
+}
+
+void
+atomic_file_open(struct atomic_file *file)
+{
+	file->fp = fopen(file->name_new, "w");
+	if (file->fp == NULL)
+		ohshite(_("unable to create new file '%.250s'"),
+		        file->name_new);
+	fchmod(fileno(file->fp), 0644);
+
+	push_cleanup(cu_closestream, ~ehflag_normaltidy, NULL, 0, 1, file->fp);
+}
+
+void
+atomic_file_sync(struct atomic_file *file)
+{
+	if (ferror(file->fp))
+		ohshite(_("unable to write new file '%.250s'"), file->name_new);
+	if (fflush(file->fp))
+		ohshite(_("unable to flush new file '%.250s'"), file->name_new);
+	if (fsync(fileno(file->fp)))
+		ohshite(_("unable to sync new file '%.250s'"), file->name_new);
+}
+
+void
+atomic_file_close(struct atomic_file *file)
+{
+	pop_cleanup(ehflag_normaltidy); /* fopen */
+
+	if (fclose(file->fp))
+		ohshite(_("unable to close new file `%.250s'"), file->name_new);
+}
+
+static void
+atomic_file_backup(struct atomic_file *file)
+{
+	char *name_old;
+
+	m_asprintf(&name_old, "%s%s", file->name, ATOMIC_FILE_OLD_EXT);
+
+	if (unlink(name_old) && errno != ENOENT)
+		ohshite(_("error removing old backup file '%s'"), name_old);
+	if (link(file->name, name_old) && errno != ENOENT)
+		ohshite(_("error creating new backup file '%s'"), name_old);
+
+	free(name_old);
+}
+
+void
+atomic_file_remove(struct atomic_file *file)
+{
+	if (unlink(file->name_new))
+		ohshite(_("cannot remove `%.250s'"), file->name_new);
+	if (unlink(file->name) && errno != ENOENT)
+		ohshite(_("cannot remove `%.250s'"), file->name);
+}
+
+void
+atomic_file_commit(struct atomic_file *file)
+{
+	if (file->flags & aff_backup)
+		atomic_file_backup(file);
+
+	if (rename(file->name_new, file->name))
+		ohshite(_("error installing new file '%s'"), file->name);
+}
+
+void
+atomic_file_free(struct atomic_file *file)
+{
+	free(file->name_new);
+	free(file->name);
+	free(file);
+}

lib/dpkg/atomic-file.h

@@ -0,0 +1,52 @@
+/*
+ * libdpkg - Debian packaging suite library routines
+ * atomic-file.h - atomic file helper functions
+ *
+ * Copyright © 2011 Guillem Jover <guillem@debian.org>
+ *
+ * This 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This 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 LIBDPKG_ATOMIC_FILE_H
+#define LIBDPKG_ATOMIC_FILE_H
+
+#include <stdio.h>
+
+#include <dpkg/macros.h>
+
+DPKG_BEGIN_DECLS
+
+enum atomic_file_flags {
+	aff_backup = 01,
+};
+
+struct atomic_file {
+	enum atomic_file_flags flags;
+	char *name;
+	char *name_new;
+	FILE *fp;
+};
+
+struct atomic_file *
+atomic_file_new(const char *filename, enum atomic_file_flags flags);
+void atomic_file_open(struct atomic_file *file);
+void atomic_file_sync(struct atomic_file *file);
+void atomic_file_close(struct atomic_file *file);
+void atomic_file_commit(struct atomic_file *file);
+void atomic_file_remove(struct atomic_file *file);
+void atomic_file_free(struct atomic_file *file);
+
+DPKG_END_DECLS
+
+#endif /* LIBDPKG_ATOMIC_FILE_H */

lib/dpkg/dpkg-db.h

@@ -231,6 +231,8 @@ const char *dpkg_db_set_dir(const char *dir);
 const char *dpkg_db_get_dir(void);
 char *dpkg_db_get_path(const char *pathpart);
 
+#include <dpkg/atomic-file.h>
+
 /*** from dbmodify.c ***/
 
 enum modstatdb_rw {

lib/dpkg/libdpkg.map

@@ -91,6 +91,14 @@ LIBDPKG_PRIVATE {
 
 	file_copy_perms;
 
+	atomic_file_new;
+	atomic_file_open;
+	atomic_file_sync;
+	atomic_file_close;
+	atomic_file_commit;
+	atomic_file_remove;
+	atomic_file_free;
+
 	glob_list_prepend;
 	glob_list_free;
 

po/POTFILES.in

@@ -2,6 +2,7 @@
 
 lib/dpkg/ar.c
 lib/dpkg/arch.c
+lib/dpkg/atomic-file.c
 lib/dpkg/buffer.c
 lib/dpkg/cleanup.c
 lib/dpkg/command.c