lei: use RENAME_NOREPLACE on Linux 3.15+

One syscall is better than two for atomicity in Maildirs.  This
means there's no window where another process can see both the
old and new file at the same time (link && unlink), nor a window
where we might inadvertantly clobber an existing file if we were
to do `stat && rename'.

1 files changed, 26 insertions, 0 deletions

diff --git a/t/rename_noreplace.t b/t/rename_noreplace.t
new file mode 100644
index 00000000..bd1c4e92
--- /dev/null
+++ b/t/rename_noreplace.t
@@ -0,0 +1,26 @@
+#!perl -w
+# Copyright (C) all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+use strict;
+use v5.10.1;
+use PublicInbox::TestCommon;
+use_ok 'PublicInbox::Syscall', 'rename_noreplace';
+my ($tmpdir, $for_destroy) = tmpdir;
+
+open my $fh, '>', "$tmpdir/a" or xbail $!;
+my @sa = stat($fh);
+is(rename_noreplace("$tmpdir/a", "$tmpdir/b"), 1, 'rename_noreplace');
+my @sb = stat("$tmpdir/b");
+ok(scalar(@sb), 'new file exists');
+ok(!-e "$tmpdir/a", 'original gone');
+is("@sa[0,1]", "@sb[0,1]", 'same st_dev + st_ino');
+
+is(rename_noreplace("$tmpdir/a", "$tmpdir/c"), undef, 'undef on ENOENT');
+ok($!{ENOENT}, 'ENOENT set when missing');
+
+open $fh, '>', "$tmpdir/a" or xbail $!;
+is(rename_noreplace("$tmpdir/a", "$tmpdir/b"), undef, 'undef on EEXIST');
+ok($!{EEXIST}, 'EEXIST set when missing');
+is_deeply([stat("$tmpdir/b")], \@sb, 'target unchanged on EEXIST');
+
+done_testing;