#! perl

# Copyright (C) 2005-2011, Netfors ApS.
#
# Author: Kristian Nielsen <kn@sifira.dk>
#
# This file is part of chan_ss7.
#
# chan_ss7 is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# chan_ss7 is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with chan_ss7; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

# Wrapper for Asterisk to run it with real-time priority, restarting
# it if it crashes, and whacking it to non-realtime priority if it is
# found to starve out normal user-space (infinite loop ...).

use strict;
use warnings;

use POSIX ":sys_wait_h";
use Sys::Syslog();

# ToDo: Specify Inline build directory somewhere convenient.
use Inline 'C';

my $child_pid = open(CHILD, '-|');
die "Cannot fork(): $!.\n" unless defined($child_pid);
if($child_pid == 0) {                 # Child
    if(set_non_rt($$)) {
        log_error("Watchdog child could not remove realtime priority: $!.\n");
    }

    # The child just runs mindlessly writing stuff down the pipe every
    # second. If the parent sees nothing for a long time, that
    # indicates that the non-realtime child is getting starved,
    # presumably by an infinite loop in the asterisk realtime process.
    $| = 1;
    for(;;) {
        print "\n";
        sleep 1;
    }
    # Child runs until kill()'ed by parent.
}

my $asterisk_pid = spawn_asterisk(@ARGV);

# Now set our own realtime priority high, so that we can have priority
# over an asterisk process run wild and get the CPU time necessary to
# whack him over the head.
if(set_rt_prio($$, 20)) {
    log_error("Cannot set realtime priority for parent: $!.\n");
}

my $rin = '';
vec($rin, fileno(CHILD), 1) = 1;
for(;;) {
    if(defined($child_pid)) {
        # Wait up to 5 seconds for a sign of life from the child.
        my $rout = $rin;
        my $nfound = select($rout, undef, undef, 5);
        if(!$nfound) {
            # Timeout; assume the worst.
            log_error("Timeout reading from child; assuming runaway asterisk, setting it back to non-realtime priority.\n");
            whack_pid($asterisk_pid);
        } else {
            my $buf;
            unless(sysread(CHILD, $buf, 255) > 0) {
                # EOF/error on the child process indicate its death, which is bad.
                # Make sure to at least not create an infinite loop at realtime
                # priority here in the parent.
                log_error("Error reading from child, child may have died.\n");
                undef $child_pid;
            }
        }
    } else {
        # Avoid infinite loop if the child dies.
        sleep 1;
    }

    # Check for asterisk termination.
    if(waitpid($asterisk_pid, WNOHANG) > 0) {
        my $sig = $? & 127;
        if($sig) {
            # Asterisk died; attempt a re-spawn.
            log_error("Asterisk process died with signal $sig, respawning ...\n");
            sleep 2;            # Just in case...
            $asterisk_pid = spawn_asterisk(@ARGV);
        } else {
            # Asterisk stopped normally, so we are done.
            print "Normal asterisk stop, exiting...\n";
            last;
        }
    }
}

# Kill off the child.
if(defined($child_pid)) {
    kill TERM => $child_pid;
    waitpid($child_pid, 0);
}

exit 0;


# Log an error to STDERR and syslog.
my $syslog_inited;
sub log_error {
    my ($msg) = @_;
    unless($syslog_inited) {
        Sys::Syslog::setlogsock('unix');
        Sys::Syslog::openlog('asterisk_safe', 'pid', 'daemon');
        $syslog_inited = 1;
    }

    chomp($msg);
    print STDERR "asterisk_safe: ", $msg, "\n";
    Sys::Syslog::syslog('err', '%s', $msg);
}

# Spawn asterisk process. Returns PID of child process.
sub spawn_asterisk {
    my ($exe, @args) = @_;
    my $pid = fork();
    die "Cannot fork(): $!.\n" unless defined($pid);

    if($pid) {
        return $pid;
    } else {
        # Child.
        if(set_rt_prio($$, 10)) {
            log_error("Cannot set realtime priority for asterisk: $!.\n");
        }
        exec $exe, @args;
        die "Cannot exec(): $!.\n";
    }
}

# Remove realtime priority from a process and all of its children.
sub whack_pid {
    my ($pid) = @_;

    # First look in /proc to build a tree of all processes and their
    # parent/child relationships.
    # ToDo: This code is for Linux 2.4; in 2.6 threads do not appear in /proc,
    # and must instead be found in /proc/<pid>/task/.
    unless(opendir PROC, '/proc') {
        log_error("Cannot read /proc: $!\n");
        return;
    }
    my $h = { };
    for (readdir PROC) {
        $h->{$1} = [ ] if /^\.?([0-9]+)$/;
    }
    closedir PROC;

    unless(exists($h->{$pid})) {
        log_error("Cannot find asterisk process in /proc.\n");
        return;
    }

    for my $p (keys %$h) {
        if(open FH, '<', "/proc/$p/status") {
            while(<FH>) {
                push @{$h->{$1}}, $p if /^PPid:\s+([0-9]+)/ && exists $h->{$1};
            }
            close FH;
        }
    }

    recursive_whack($h, $pid);
}

sub recursive_whack {
    my ($h, $pid) = @_;

    my $res = set_non_rt($pid);
    if($res == 0) {
        recursive_whack($h, $_) for (@{$h->{$pid}});
    }
}

__DATA__
__C__
#include <sched.h>

static int set_prio(int pid, int typ, int prio) {
    struct sched_param sp;
    memset(&sp, 0, sizeof(sp));
    sp.sched_priority = prio;
    return sched_setscheduler(pid, typ, &sp);
}

/* Sets realtime priority, returns 0 on ok, -1 on error (setting errno). */
int set_rt_prio(int pid, int prio) {
    return set_prio(pid, SCHED_RR, prio);
}
/* Removes realtime priority, returns 0 on ok, -1 on error (setting errno). */
int set_non_rt(int pid) {
    return set_prio(pid, SCHED_OTHER, 0);
}