Re: [PATCH][RFC] Lightweight user-level semaphores

[Linus Torvalds]

On Mon, 7 Jan 2002, Matthew Kirkwood wrote:
>
>  * It leaks.  How were you going to refcount the kernel
>    portions?  Could they be attached to the VM mapping?
>    Would a lockfs be too expensive?

Yes, I was going to just attach to the vma, along with potentially also
require a flag at mmap time (MAP_SEMAPHORE - some other unixes have
something like it already) to tell the OS about the consistency issues
that might come up on some architectures (on x86 it would be a no-op).

>  * It doesn't have a timeout.  Is there something like a
>    down_timeout() available?

Not as-is, but all the kernel infrastructure should be there in theory.

>  * I don't do the:
>
> 	if (kfs->user_address != fs)
> 		goto bad_sem;
>
>    because it doesn't seem to add anything, and prevents
>    putting these locks in a non-fixed file or SysV SHM
>    map.

Fair enough. I think I suggested that just as another sanity check, and
because some architectures _will_ require address issues (not necessarily
total equality, but at least "modulo X equality").

			Linus