webmap-download: Ensure we always call linkat() not link().

This costs an extra file descriptor when --cachedir is unsed, but

	os.link(f'/proc/self/fd/{fp.fileno()}', newpath,
	    dst_dir_fd=None, follow_symlinks=True)

calls link("/proc/self/fd/…", newpath) rather than

	linkat(AT_FDCWD, "/proc/self/fd/…", AT_FDCWD, newpath, AT_SYMLINK_FOLLOW)

and the former fails with EXDEV (Invalid cross-device link).

1 files changed, 4 insertions, 4 deletions

diff --git a/webmap-download b/webmap-download
index be48bbb..03c05af 100755
--- a/webmap-download
+++ b/webmap-download
@@ -136,8 +136,8 @@ if __name__ == '__main__':
     logging.basicConfig(format='%(levelname)s: %(message)s', level=logging.INFO)
 
     parser = argparse.ArgumentParser(description='Download or update GIS layers.')
-    parser.add_argument('--cachedir', default=None,
-        help='destination directory for downloaded files (default: .)')
+    parser.add_argument('--cachedir', default=os.curdir,
+        help=f'destination directory for downloaded files (default: {os.curdir})')
     parser.add_argument('--lockdir', default=None,
         help='optional directory for lock files')
     parser.add_argument('--debug', action='store_true', help=argparse.SUPPRESS)
@@ -171,8 +171,8 @@ if __name__ == '__main__':
 
     # intentionally leave the dirfd open until the program terminates
     opendir_args = O_RDONLY|O_CLOEXEC|O_PATH|O_DIRECTORY
-    destdir_fd = None if args.cachedir is None else os.open(args.cachedir, opendir_args)
-    lockdir_fd = None if args.lockdir  is None else os.open(args.lockdir, opendir_args)
+    destdir_fd = os.open(args.cachedir, opendir_args)
+    lockdir_fd = None if args.lockdir is None else os.open(args.lockdir, opendir_args)
 
     sessionRequests = requests.Session()