backup-rename: new module

It is like backupfile, except it avoids some race conditions,
and it does not output to stderr or exit.
* MODULES.html.sh: Add backup-rename.
* lib/backup-find.c, lib/backup-internal.h, lib/backup-rename.c:
* modules/backup-rename: New files.
* lib/backupfile.c: Turn this into an internals file, which
contains code common to backupfile and backup_rename.  Do not
include argmatch.h or xalloc.h: include xalloc-oversized.h.
Include renameat2.h and fcntl.h.
(BACKUP_NOMEM): New constant.
(numbered_backup): New args BASE_OFFSET and *DIRPP.  Do not exit
on memory exhaustion; just return BACKUP_NOMEM.  Caller changed.
(backupfile_internal): Rename from find_backup_file_name.
Support new arg RENAME.
(backup_args, backup_types, get_version, xget_version):
Move to lib/backup-find.c.
* lib/backupfile.h (backup_file_rename): New decl.
* modules/backupfile (Files): Add lib/backup-internal.h,
lib/backup-find.c.
(Depends-on): Add dirfd, fcntl, renameat2.
(lib_SOURCES): Add backup-find.c.

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/backup-rename.c b/lib/backup-rename.c
new file mode 100644
index 0000000000..628542b902
--- /dev/null
+++ b/lib/backup-rename.c
@@ -0,0 +1,31 @@
+/* Rename a file to a backup name, Emacs style.
+
+   Copyright 2017 Free Software Foundation, Inc.
+
+   This program 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.
+
+   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 <config.h>
+
+#include "backup-internal.h"
+
+/* Rename the existing file FILE to a backup name, allocated with
+   malloc, and return the backup name.  On failure return a null
+   pointer, setting errno.  Do not call this function if backup_type
+   == no_backups.  */
+
+char *
+backup_file_rename (char const *file, enum backup_type backup_type)
+{
+  return backupfile_internal (file, backup_type, true);
+}