From 4cd7a78f3b8c03670e2d77675229472506eee1eb Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Thu, 21 Oct 2021 21:10:32 +0000
Subject: 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'.
---
 t/rename_noreplace.t | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 t/rename_noreplace.t

(limited to 't')

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;
-- 
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