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'.
---
 lib/PublicInbox/LeiExportKw.pm | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

(limited to 'lib/PublicInbox/LeiExportKw.pm')

diff --git a/lib/PublicInbox/LeiExportKw.pm b/lib/PublicInbox/LeiExportKw.pm
index 0b65c276..ceeef7f2 100644
--- a/lib/PublicInbox/LeiExportKw.pm
+++ b/lib/PublicInbox/LeiExportKw.pm
@@ -7,6 +7,7 @@ use strict;
 use v5.10.1;
 use parent qw(PublicInbox::IPC PublicInbox::LeiInput);
 use Errno qw(EEXIST ENOENT);
+use PublicInbox::Syscall qw(rename_noreplace);
 
 sub export_kw_md { # LeiMailSync->each_src callback
 	my ($oidbin, $id, $self, $mdir) = @_;
@@ -30,30 +31,22 @@ sub export_kw_md { # LeiMailSync->each_src callback
 	my $lei = $self->{lei};
 	for my $d (@try) {
 		my $src = "$mdir/$d/$$id";
-
-		# we use link(2) + unlink(2) since rename(2) may
-		# inadvertently clobber if the "uniquefilename" part wasn't
-		# actually unique.
-		if (link($src, $dst)) { # success
-			# unlink(2) may ENOENT from parallel invocation,
-			# ignore it, but not other serious errors
-			if (!unlink($src) and $! != ENOENT) {
-				$lei->child_error(1, "E: unlink($src): $!");
-			}
+		if (rename_noreplace($src, $dst)) { # success
 			$self->{lms}->mv_src("maildir:$mdir",
 						$oidbin, $id, $bn);
-			return; # success anyways if link(2) worked
+			return; # success
 		} elsif ($! == EEXIST) { # lost race with lei/store?
 			return;
 		} elsif ($! != ENOENT) {
-			$lei->child_error(1, "E: link($src -> $dst): $!");
+			$lei->child_error(1,
+				"E: rename_noreplace($src -> $dst): $!");
 		} # else loop @try
 	}
 	my $e = $!;
 	# both tries failed
 	my $oidhex = unpack('H*', $oidbin);
 	my $src = "$mdir/{".join(',', @try)."}/$$id";
-	$lei->child_error(1, "link($src -> $dst) ($oidhex): $e");
+	$lei->child_error(1, "rename_noreplace($src -> $dst) ($oidhex): $e");
 	for (@try) { return if -e "$mdir/$_/$$id" }
 	$self->{lms}->clear_src("maildir:$mdir", $id);
 }
-- 
cgit v1.2.3-24-ge0c7