freebsd stable - Dec 2004 - Fixing Posix semaphores

I have a desire to fix posix semaphores in at least 5.3.  The current
implementation doesn't actually follow the "spirit" of the
standard,
even though it technically qualifies in a somewhat degraded sense.  I
refer to the fact that the current implementation treats posix
semaphores as completely contained inside the kernel and essentially
divorced from the filesystem.  The true "spirit" of the standard
places
the semaphores directly in the file system, similar to named pipes.
However the current implementation treats the supplied "name" as a
14-character identifier, required to begin with a slash and contain no
other slashes.  Pretty weak.

Well, in order to fix this, we need to add file system code and come up
with a new type.  I currently have some time to spend on something like
this and am willing to put in whatever effort it takes.  Does anyone
want to add their own ideas or requirements?

I currently run 5.3, but I suppose I could think about running current
at some point in the future.

/Joe

On Mon, 13 Dec 2004, Joe Kelsey wrote:
> I have a desire to fix posix semaphores in at least 5.3.  The current
> implementation doesn't actually follow the "spirit" of the
standard,
> even though it technically qualifies in a somewhat degraded sense.  I
> refer to the fact that the current implementation treats posix
> semaphores as completely contained inside the kernel and essentially
> divorced from the filesystem.  The true "spirit" of the standard
places
> the semaphores directly in the file system, similar to named pipes. 
> However the current implementation treats the supplied "name" as
a
> 14-character identifier, required to begin with a slash and contain no
> other slashes.  Pretty weak. 
> 
> Well, in order to fix this, we need to add file system code and come up
> with a new type.  I currently have some time to spend on something like
> this and am willing to put in whatever effort it takes.  Does anyone
> want to add their own ideas or requirements? 
>From my perspective, the biggest win here is that it would permit
different name spaces to trivially exist using multiple mountpoints of a
"semfs".  This would make it easy to allow applications in different
jails
to use identical names without colliding. 

FWIW, my only experience with POSIX semaphores on a system other than
FreeBSD is on Darwin, where a similar model is used to that on FreeBSD: a
flat kernel-maintained name space is present.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Principal Research Scientist, McAfee Research