[Ocfs2-tools-devel] [PATCH 2/2] o2hbmonitor: add lockfile

[Joel Becker]

On Fri, Nov 12, 2010 at 04:29:10PM -0800, Srinivas Eeda wrote:
> Tristan Ye wrote:
> > Srinivas Eeda wrote:
> >>
> >>> #define O2HB_SEM_MAGIC_KEY    0x4A32594B
> >>>
> >>> int main()
> >>> {
> >>>    ...
> >>>    daemon();
> >>>    semid = semget(O2HB_SEM_MAGIC_KEY, 1, IPC_CREAT|IPC_EXCL);
> >>>    if (semid < 0) {
> >>>       if (errno = EEXIST)
> >>>          syslog(LOG_INFO "o2hbmonitor is already running.\n");
> >>>       else
> >>>            fprintf(stderr, "failed to get semaphore.\n");
> >>>       exit(semid);
> >>>    }
> >>>    openlog();
> >>>    monitor();
> >>>    sem_close();
> >>> }
> >> Tristan,
> >> thanks for the review and the suggestions :)
> >>
> >> If a user kills the process with SIGKILL, then he will be prevented 
> >> from spawning another process until he  explicitly  removes the 
> >> semaphore. I think it adds big inconvenience. If user explicitly 
> >> removes the lock file and starts another process, then it doesn't 
> >> cause much problems. The likely hood of user sending SIGKILL signal 
> >> is much larger than removing the file.
> >
> > There is a known solution for the cleanup of shared semaphore 
> > resources when process gets terminated abnoramlly.
> >
> > Simply using 'SEM_UNDO' in semop() should work, kernel takes over the 
> > cleanup when process was SIGKILLed.
> >
> agreed. I made the changes and resent the patches.

	Lockfiles are a standard system daemon mechanism.  Sure, you can
run two of them if you rm the file, but who cares?  That's not a normal
case.
	Certainly a semaphore works.  But it doesn't store the pid for
the startup scripts ;-)

Joel

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Joel Becker
Senior Development Manager
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127