Re: light weight user level semaphores

Alexander Viro
2001-04-24T00:42:01Z

On 24 Apr 2001, David Wagner wrote:

> 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?

Yes. Not to mention side effects, it's just plain ugly. Anyone who invents
identifiers of _that_ level of ugliness should be forced to read them
aloud for a week or so, until somebody will shoot him out of mercy.
Out of curiosity: who was the author? It looks unusually nasty, even for
SGI.