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

[Tristan Ye]

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.