Re: dummy's guide to emulation?

[Edward Roper <edro%wanfear.net@localhost>]

On Tue, Jun 03, 2008 at 04:10:08PM +1000, Carl Brewer wrote:
> 
> Hello, I want to try and replace a SCO box (OS 5.0.5 I think, it's old
> and hairy) with something modern for a client, I've given up on xen,
> VMware etc to run SCO in, it's just too hard to get SCO working in
> a VM.
> 
> Anyway, NetBSD seems like it can emulate SCO, but is there any doco on
> how to set up an environment such that an application that looks for
> things in certain places finds them?  Is something like a big chroot
> environment suitable?  Is there some magic that the emulation layer
> does to help?  Things like printers etc? Or simple things like where
> to find database files and the like?
> 
> Any pointers to a beginner's guide to using emulation in NetBSD much
> appreciated!
> 
> Thankyou
> 
> Carl

Hi Carl,

I'll start  by saying that I  have no experience with  the NetBSD binary
emulation system. I believe however that it works by mapping system call
parameters between  the emulated binary  and the native system.  I would
assume that it also does some work with signal handlers.

Regardless the  net result  should be  that a  SCO binary  running under
NetBSD will not know  that it isn't running under a  SCO kernel. I would
imagine that there  are a class of applications that  wouldn't work very
well.  For  example, userland  utilities  for  controlling route  tables
probably wouldn't  be much  use running  emulated on  a NetBSD  box. For
things that  aren't tightly coupled to  the kernel, you'll need  to have
copies of any shared libraries that they need. If the programs expect to
be able to find files in a certain path, you'll need to make sure it can
find them  there. If you  wanted to build out  a chroot jail  to isolate
things I'm  sure that  you could.  Keep in  mind that  running emulating
binaries isn't like running them in a virtual machine or container, they
run in the same process space as native binaries, and thus have the same
"view of the world."

http://www.netbsd.org/docs/compat.html is probably a reasonable place to
start looking.  I hope  that made sense,  and I hope  I didn't  make any
egregious misrepresentations about things. I'm sure someone will correct
me if I did ;)

Ed