Re: [PATCH nilfs-utils v2 2/4] cleanerd: call _exit(2) twice for ensuring not being a session leader

[Michael Conrad <mconrad-HsDW+lVSy7tZ66HEZ9PjWw@public.gmane.org>]

On 1/5/2014 1:28 PM, Ryusuke Konishi wrote:
> Oh no, I found this series has a critical issue after I applied them.
>
> The current umount.nilfs2 (and mount.nilfs2 -o remount,nogc) uses pid
> of cleanerd to shutdown it, and this series breaks the logic since the
> fork of cleanerd changes its pid.  That was the true reason why nofork
> option is required.
>
> We need to fix it by reverting the series or other means.
>
> Regards,
> Ryusuke Konishi

 From what I've learned of writing daemons, good practice is:

   * Allow an option for writing a PID file, but don't by default 
(location is often distro-specific)
   * To daemonize, double-fork, chdir("/"), and then redirect stdin, 
stdout, stderr to /dev/null
   * Allow users to request messages to syslog, since stdout is lost.
   * If you want to capture the PID, have an option to print it on 
stderr before redirecting to /dev/null.  The caller can read a pipe to 
find the final PID of the daemon.
   * Allow the option to run the program in the foreground (i.e. do not 
daemonize at all) for debugging or in case you want to run the daemon 
from a monitoring program which wait()s on it.  In this case do not 
close stdout, so that debugging messages may be seen on the terminal, or 
the messages can be piped to a logger.

Until now, I had thought "-n" was the "no-daemonize" option, which I 
thought was strange for mount to use.

-Mike
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