btrbk: add transaction logging to syslog

Add configuration option transaction_syslog, which can be set to a short
name of a syslog facility, like user or local5. Most of the ones besides
localX do not really make sense, but whatever, let the user decide.

The only logging that is relevant for logging to syslog is the logging
generated inside sub action, so it's easy to hijack all messages in
there and also send them to syslog if needed.

All output is done via print_formatted, which expects a file handle.
So, abuse a file handle to a string to be able to change as less code as
needed for this feature.

Since syslog already adds the timestamps for us, I added a syslog
formatting pattern, which is very similar to tlog, omitting the
timestap.

ChangeLog

@@ -2,6 +2,7 @@ btrbk-current
 
   * Bugfix: set correct parent section when propagating targets
     (close: #85).
+  * Add syslog output for transaction log.
 
 btrbk-0.23.0
 

btrbk

@@ -45,6 +45,8 @@ use warnings FATAL => qw( all );
 use Carp qw(confess);
 use Getopt::Long qw(GetOptions);
 use Time::Local qw( timelocal timegm timegm_nocheck );
+use Sys::Syslog;
+use Sys::Syslog qw(:standard :macros);
 
 our $VERSION         = "0.23.1-dev";
 our $AUTHOR          = 'Axel Burri <axel@tty0.ch>';
@@ -69,6 +71,11 @@ my $ssh_cipher_match = qr/[a-z0-9][a-z0-9@.-]+/;
 my $safe_cmd_match = qr/[0-9a-zA-Z_@=\+\-\.\/]+/;  # $file_match plus '=': good enough for our purpose
 
 my %day_of_week_map = ( sunday => 0, monday => 1, tuesday => 2, wednesday => 3, thursday => 4, friday => 5, saturday => 6 );
+my %syslog_facility_map = (
+  user => LOG_USER, mail => LOG_MAIL, daemon => LOG_DAEMON, auth => LOG_AUTH, lpr => LOG_LPR, news => LOG_NEWS,
+  cron => LOG_CRON, authpriv => LOG_AUTHPRIV, local0 => LOG_LOCAL0, local1 => LOG_LOCAL1, local2 => LOG_LOCAL2,
+  local3 => LOG_LOCAL3, local4 => LOG_LOCAL4, local5 => LOG_LOCAL5, local6 => LOG_LOCAL6, local7 => LOG_LOCAL7,
+);
 
 my %config_options = (
   # NOTE: the parser always maps "no" to undef
@@ -94,6 +101,7 @@ my %config_options = (
   ssh_cipher_spec             => { default => "default", accept_regexp => qr/^$ssh_cipher_match(,$ssh_cipher_match)*$/ },
   rate_limit                  => { default => undef,     accept => [ "no" ], accept_regexp => qr/^[0-9]+[kmgt]?$/, require_bin => '/usr/bin/pv' },
   transaction_log             => { default => undef,     accept_file => { absolute => 1 } },
+  transaction_syslog          => { default => undef,     accept => [ keys %syslog_facility_map ] },
 
   raw_target_compress         => { default => undef,     accept => [ "no", "gzip", "bzip2", "xz" ] },
   raw_target_compress_level   => { default => "default", accept => [ "default" ], accept_numeric => 1 },
@@ -178,6 +186,7 @@ my %table_formats = (
                    long  => [ qw( localtime type status duration target_host target_subvol source_host source_subvol parent_subvol message ) ],
                    raw   => [ qw( time localtime type status duration target_url source_url parent_url message ) ],
                    tlog  => [ qw( localtime type status duration target_url source_url parent_url message ) ],
+                   syslog  => [ qw( type status duration target_url source_url parent_url message ) ],
                  },
 
   origin_tree => { table => [ qw( tree uuid parent_uuid received_uuid ) ],
@@ -202,6 +211,7 @@ my $err = "";
 my $abrt = "";  # last ABORTED() message
 my $output_format;
 my $tlog_fh;
+my $syslog_facility;
 my $current_transaction;
 my @transaction_log;
 my %config_override;
@@ -319,7 +329,7 @@ sub ABORTED($;$)
 }
 
 
-sub init_transaction_log($)
+sub init_transaction_log($$)
 {
   my $file = shift;
   if(defined($file) && (not $dryrun)) {
@@ -332,6 +342,11 @@ sub init_transaction_log($)
       ERROR "Failed to open transaction log '$file': $!";
     }
   }
+  my $config_syslog_facility = shift;
+  if(defined($config_syslog_facility) && (not $dryrun)) {
+    $syslog_facility = $syslog_facility_map{$config_syslog_facility};
+    openlog("btrbk", 0, $syslog_facility);
+  }
   action("startup", status => "v$VERSION", message => "$VERSION_INFO");
 }
 
@@ -341,6 +356,7 @@ sub close_transaction_log()
     DEBUG "Closing transaction log";
     close $tlog_fh || ERROR "Failed to close transaction log: $!";
   }
+  closelog if defined $syslog_facility;
 }
 
 sub action($@)
@@ -352,6 +368,16 @@ sub action($@)
   $h->{time} = $time;
   $h->{localtime} = timestamp($time, 'debug-iso');
   print_formatted("transaction", [ $h ], output_format => "tlog", no_header => 1, outfile => $tlog_fh) if($tlog_fh);
+  if (defined($syslog_facility)) {
+    my $msg = q{};
+    open my $msg_fh, '+<', \$msg;
+    print_formatted("transaction", [ $h ], output_format => "syslog", no_header => 1, outfile => $msg_fh);
+    seek($msg_fh, 0, 0);
+    while (my $line = <$msg_fh>) {
+      syslog(LOG_INFO, $line);
+    }
+    close $msg_fh;
+  }
   push @transaction_log, $h;
   return $h;
 }
@@ -3162,7 +3188,7 @@ sub print_formatted(@)
       print $fh join(' ', map { "$_=\"" . ($row->{$_} // "") . "\""; } @$keys) . "\n";
     }
   }
-  elsif($format eq "tlog")
+  elsif($format eq "tlog" || $format eq "syslog")
   {
     # output: value0 value1, ...
     unless($args{no_header}) {
@@ -3619,7 +3645,8 @@ MAIN:
     # thing used from the configuration is the SSH and transaction log
     # stuff.
     #
-    init_transaction_log(config_key($config, "transaction_log"));
+    init_transaction_log(config_key($config, "transaction_log"),
+                         config_key($config, "transaction_syslog"));
 
     my $src_url    = $filter_args[0] || die;
     my $archive_url = $filter_args[1] || die;
@@ -4518,7 +4545,8 @@ MAIN:
     #
     # identify and delete incomplete backups
     #
-    init_transaction_log(config_key($config, "transaction_log"));
+    init_transaction_log(config_key($config, "transaction_log"),
+                         config_key($config, "transaction_syslog"));
 
     my @out;
     foreach my $sroot (vinfo_subsection($config, 'volume')) {
@@ -4615,7 +4643,8 @@ MAIN:
 
   if($action_run)
   {
-    init_transaction_log(config_key($config, "transaction_log"));
+    init_transaction_log(config_key($config, "transaction_log"),
+                         config_key($config, "transaction_syslog"));
 
     if($resume_only) {
       INFO "Skipping snapshot creation (option \"-r\" present)";

doc/btrbk.conf.5

@@ -75,6 +75,15 @@ subvolume delete) as well as abort messages are logged to <file>, in a
 space-separated table format.
 .RE
 .PP
+\fBtransaction_syslog\fR  <facility>
+.RS 4
+If set, all transactions (snapshot create, subvolume send-receive,
+subvolume delete) as well as abort messages are logged to syslog, in a
+space-separated format. The facility parameter accepts a short
+lowercase syslog facility name, like \[lq]daemon\[rq] or \[lq]local7\[rq].
+The program name used in the messages is "btrbk".
+.RE
+.PP
 \fBtimestamp_format\fR  short|long|long-iso
 .RS 4
 Timestamp format used as postfix for new snapshot subvolume