Re: light weight user level semaphores

David Wagner
2001-04-24T00:21:25Z

Linus Torvalds wrote:
>Ehh.. I will bet you $10 USD that if libc allocates the next file
>descriptor on the first "malloc()" in user space (in order to use the
>semaphores for mm protection), programs _will_ break.
>
>You want to take the bet?

Good point. Speaking of which:
ioctl(fd, UIOCATTACHSEMA, ...);
seems to act like dup(fd) if fd was opened on "/dev/usemaclone"
(see drivers/sgi/char/usema.c). According to usema(7), this is
intended to help libraries implement semaphores.

Is this a bad coding? Should the kernel really support an ioctl()
that can silently allocate the next file descriptor? This seems
like asking for trouble. Or, maybe I just misunderstood something.