Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
> mknod foo p. Or use sockets (although AF_UNIX sockets are higher latency)
> Thats why I suggested using flock - its name based. Whether you mkstemp()
> stuff and pass it around isnt something I care about
>
> Files give you permissions for free too
I don't want nor need file permissions. A program would look like this:
process 1:
fd = open("somefile")
addr = mmap(fd);
pthread_mutexattr_init(&attr);
pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
pthread_mutex_init ((pthread_mutex_t *) addr, &attr);
pthread_mutex_lock ((pthread_mutex_t *) addr);
pthread_mutex_destroy((pthread_mutex_t *) addr);
process 2:
fd = open("somefile")
addr = mmap(fd);
pthread_mutex_lock ((pthread_mutex_t *) addr);
The shared mem segment can be retrieved in whatever way. The mutex in
this case is anonymous. Everybody who has access to the shared mem
*must* have access to the mutex.
For semaphores it looks similarly. First the anonymous case:
process 1:
fd = open("somefile")
addr = mmap(fd);
sem_init ((sem_t *) addr, 1, 10); // 10 is arbitrary
sem_wait ((sem_t *) addr);
sem_destroy((sem_t *) addr);
process 2:
fd = open("somefile")
addr = mmap(fd);
sem_wait ((sem_t *) addr);
Note that POSIX semaphores could be implemented with global POSIX
mutexes.
Finally, named semaphores:
semp = sem_open("somefile", O_CREAT|O_EXCL, 0600)
sem_wait (semp);
sem_close(semp);
sem_unlink(semp);
This is the only semaphore kind which maps nicely to a pipe or socket.
All the others don't. And even for named semaphores it is best to
have a separate name space like the shmfs.
> So you have unix file permissions on them ?
See above. Permissions are only allowed for named semaphores.
-- ---------------. ,-. 1325 Chesapeake Terrace Ulrich Drepper \ ,-------------------' \ Sunnyvale, CA 94089 USA Red Hat `--' drepper at redhat.com `------------------------ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Mon Apr 23 2001 - 21:00:33 EST