pmirror: Add option --noatime

Open source file with O_NOATIME if option --noatime is given.

If pmirror is used for backup purpose, we don't want to trigger metadata
writes on the source filesystem. This needs to be optional, because
O_NOATIME only works for the owner of a file or for a privileged user.

As --cksum is implemented by an external command, we can't do this with
out potentially touching the access time.

pmirror/pmirror

@@ -155,7 +155,7 @@ use Getopt::Long;
 use Sys::Hostname;
 use IO::File;
 use IO::Socket::INET;
-use Fcntl ':mode';
+use Fcntl qw(:mode O_NOATIME);
 import My::Escaper;
 
 use Time::HiRes;
@@ -172,7 +172,8 @@ our ($debug,$quiet,$fileop_noop,$fileop_debug,$delete);
 our ($slave_mode,$local_slave,$slave_unprivileged,
 	$lockident,$safety,$identity_file,$mkdir_slave,
 	$reduce,$force_status,$bandwidth,$allowremotefs,
-	$ssh_opt , $cksum , $nice , $unix_socket, $unix_socket_name);
+	$ssh_opt , $cksum , $nice , $unix_socket, $unix_socket_name,
+	$noatime);
 
 # globals
 
@@ -466,7 +467,7 @@ sub send_file
 	my $data_buf;
 	my $len;
 
-	my $fh=IO::File->new($filename,O_RDONLY);
+	my $fh=IO::File->new($filename, O_RDONLY + ($noatime ? O_NOATIME : 0) );
 	unless (defined $fh) {
 		# one reason to get here is that the file was deleted after it has been offered to
 		# and requested by the client.
@@ -1047,6 +1048,7 @@ usage: $0 [options] path [node:]path
    --nice		EXPERIMENTAL nice
    --unix-socket        EXPERIMENTAL establish data channel over ssh via AF unix sockets
    --socket-name PATH   EXPERIMENTAL use PATH as name for AF unix sockets
+   --noatime            don't touch atime on sender
 
 __EOF__
 
@@ -1075,13 +1077,17 @@ use constant OPTIONS => (
 	'nice'            => \$nice,
 	'unix-socket'     => \$unix_socket,
 	'socket-name=s'   => \$unix_socket_name,
+	'noatime'         => \$noatime,
 );
 
 if ($ENV{SSH_ORIGINAL_COMMAND}) {
 	($_,@ARGV)=split ' ',$ENV{SSH_ORIGINAL_COMMAND};
 }
 
 GetOptions(OPTIONS) or die USAGE;
+if ($noatime && $cksum) {
+	die "$0: --cksum together with --noatime not implemented\n";
+}
 
 if ($nice) {
 	system "ionice -c idle -p $$ 2>/dev/null"