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, 3 insertions, 4 deletions

diff --git a/lib/PublicInbox/LeiToMail.pm b/lib/PublicInbox/LeiToMail.pm
index ca4e92de..d33d27ae 100644
--- a/lib/PublicInbox/LeiToMail.pm
+++ b/lib/PublicInbox/LeiToMail.pm
@@ -12,6 +12,7 @@ use PublicInbox::Spawn qw(spawn);
 use Symbol qw(gensym);
 use IO::Handle; # ->autoflush
 use Fcntl qw(SEEK_SET SEEK_END O_CREAT O_EXCL O_WRONLY);
+use PublicInbox::Syscall qw(rename_noreplace);
 
 my %kw2char = ( # Maildir characters
         draft => 'D',
@@ -262,10 +263,8 @@ sub _buf2maildir ($$$$) {
                 $rand = '';
                 do {
                         $base = $rand.$common.':2,'.kw2suffix($kw);
-                } while (!($ok = link($tmp, $dst.$base)) && $!{EEXIST} &&
-                        ($rand = _rand.','));
-                die "link($tmp, $dst$base): $!" unless $ok;
-                unlink($tmp) or warn "W: failed to unlink $tmp: $!\n";
+                } while (!($ok = rename_noreplace($tmp, $dst.$base)) &&
+                        $!{EEXIST} && ($rand = _rand.','));
                 \$base;
         } else {
                 my $err = "Error writing $smsg->{blob} to $dst: $!\n";