persistent ptys

persistent ptys

[Steve Underwood]

Hi,

It seems BSD style ptys are on the way out, and most systems will soon 
have just Unix98 style ptys. This makes me want to move something to 
Unix98 ptys, but I'm not sure of the appropriate way. The issue is that 
things like HylaFAX expect to work with well known, persistent, names 
for modem ports. A 100% soft modem in user space can easily provide that 
with BSD ptys. With Unix98 ptys it is not so obvious what to do. Most 
commercial soft modems don't have this issue, as they are part kernel 
space/part user space designs. Obviously creating a link to a 
dynamically generated pty with a well known name, and various other 
things could be done. However, I assume other people have had to do 
similar persistent pty things, and there is a well defined common 
practice for it. Can anyone tell me what it is? :-\

Regards,
Steve

Re: persistent ptys

[Pavel Machek]

Hi!

> It seems BSD style ptys are on the way out, and most systems will soon 
> have just Unix98 style ptys. This makes me want to move something to 
> Unix98 ptys, but I'm not sure of the appropriate way. The issue is that 
> things like HylaFAX expect to work with well known, persistent, names 
> for modem ports. A 100% soft modem in user space can easily provide that 
> with BSD ptys. With Unix98 ptys it is not so obvious what to
> do. Most 

Do you actually have user-space softmodem implementation? Is it
open-source? I guess it would be very interesting for remaining modem
users :-).
								Pavel
-- 
When do you have heart between your knees?

Re: persistent ptys

[H. Peter Anvin]

Followup to:  <4139F3FA.1070107@coppice.org>
By author:	Steve Underwood <steveu@coppice.org>
In newsgroup: linux.dev.kernel
>
> Hi,
> 
> It seems BSD style ptys are on the way out, and most systems will soon 
> have just Unix98 style ptys. This makes me want to move something to 
> Unix98 ptys, but I'm not sure of the appropriate way. The issue is that 
> things like HylaFAX expect to work with well known, persistent, names 
> for modem ports. A 100% soft modem in user space can easily provide that 
> with BSD ptys. With Unix98 ptys it is not so obvious what to do. Most 
> commercial soft modems don't have this issue, as they are part kernel 
> space/part user space designs. Obviously creating a link to a 
> dynamically generated pty with a well known name, and various other 
> things could be done. However, I assume other people have had to do 
> similar persistent pty things, and there is a well defined common 
> practice for it. Can anyone tell me what it is? :-\
> 

Two options: either continue to use BSD ptys (the kinds of stuff you
describe above is actually the one case where BSD ptys is a better
choice than Unix98 ptys) *or* create symlinks -- or if that doesn't
work for you, device nodes -- dynamically.

I.e. have a program which opens /dev/ptmx, gets a slave pty with a
specific ptsname(), then does a symlink() into a suitable directory.
The symlink is your persistent name.

	-hpa