Modified rc.multi for starting daemons

realturner · 2012-04-08 11:01:15

I'd like to share some of my modification about the daemon starting process here

What I've done is to add an option for DAEMONS in rc.conf, which allows starting a daemon after all the previous dependencies are actually done.

This is done by a creating a named pipe for a before it starts, and removing it after the daemon completes.

Daemons with dependencies are guaranteed to either be blocked by reading the named pipe or fail to find the named pipe (which means it already completed) by some tricks.

Here is the snippet from the rc.multi:

depsd="/var/lock/boot"
mkdir -p "$depsd"
rm -f "$depsd"/*

start_daemon_dep(){
        local dep daemon="$1"
        shift
        for dep; do
                cat "$depsd/$dep" 2>/dev/null
        done
        start_daemon "$daemon"
        /etc/rc.d/daemon_complete "$depsd/$daemon"
}

make_dep(){
        mkfifo "$depsd/$1"
        (cat "$depsd/$1") 2>/dev/null &
        stat_bkgd "Starting daemon $1"
}

# Start daemons
for daemon in "${DAEMONS[@]}"; do
        d=(${daemon//:/ })
        case ${d[0]:0:1} in
                '!') continue;;
                '@')
                        make_dep "${d[0]#@}"
                        (start_daemon_dep ${d[0]#@} ${d[1]//,/ }) 1>/dev/null &
                        ;;
                *)
                        make_dep "${d[0]}"
                        start_daemon_dep ${d[0]} ${d[1]//,/ } 1>/dev/null
                        ;;
        esac
done

/etc/rc.d/daemon_complete is the programing doing the atomic guarantee.
daemon_complete.c:

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
int main(int argc, char **argv){
    int fd;
    if((fd  = open(argv[1], O_WRONLY))< 0)
        return 1;
    if(unlink(argv[1]) < 0)
        return 1;
    if(close(fd) < 0)
        return 1;
    return 0;
}

Then we can write something like the following in rc.conf:

DAEMONS=(hwclock
         rsyslogd
         @network
         @ntpdate:network
         @dnsmasq:network
         dbus
         kdm:dbus,network
         crond)

This means that ntpdate is running in background, but it won't start until its dependency, network, completes in background.
Multiple dependencies can be applied like the one kdm does: it relies on both dbus and network.

However, changing DAEMONS array syntax breaks some functionalities in /etc/rc.d/functions, so we have to accordingly change the file.
The file is here.

edit: I shouldn't put the executable in /etc/rc.d/functions.d/, so now it's in /etc/rc.d/

Last edited by realturner (2012-04-08 11:13:15)

PReP · 2012-04-10 13:54:35

I cannot contribute any specific thoughts yet,
but this is interesting.

I'll just post and follow this thread for the moment

Arch Linux

#1 2012-04-08 11:01:15

Modified rc.multi for starting daemons

#2 2012-04-10 13:54:35

Re: Modified rc.multi for starting daemons

Board footer