Re: [TUHS] Photos of University Computer Labs - now off topic

["Theodore Ts'o" <tytso@mit.edu>]

On Thu, Dec 23, 2021 at 05:13:39PM -0500, Steve Nickolas wrote:
> On Thu, 23 Dec 2021, Larry McVoy wrote:
> 
> > On Thu, Dec 23, 2021 at 10:02:40AM -0600, Warner Losh wrote:
> > > > I had forgotten about control-t - does anything modern still do that
> > > 
> > > FreeBSD does. It's my biggest annoyance with Linux that it doesn't.
> > 
> > Seems like a patch might be nice.
> 
> Yeah, I miss SIGINFO when I'm on Linux.

There have been patches proposed, but it turns out the sticky wicket
is that we're out of signal numbers on most architectures.  There are
code points that potentially could be repurposed, since they aren't
actually signaled from the kernel:

    SIGLOST        -        Term    File lock lost (unused)
    SIGSTKFLT      -        Term    Stack fault on coprocessor (unused)

Howveer, the current behavior if no signal handler is installed is to
terminate the process --- and it's unclear whether there might be some
user space libraries that might be using these signals for their own
nefarious purposes.  So someone would have to deprecate one of these
signals, and then try to do a code search across the internet to see
if there's any evidence that SIGLOST or SIGSTKFLT is being used (at
least in open source software).

It's not impossible to deal with this, but no one has cared enough to
really try to push this through as a new feature.

Cheers,

						- Ted