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opening tty devices with getty attached

opening tty devices with getty attached

Post by Sean Sheridan Coleman X56 » Wed, 30 Jan 1991 15:50:26



I want to first thank Guy Harris for all of his help he has
given me concerning these tty devices.

I need just a little bit more info ( I hope) to figure all
of this out.

The manual states that open will block when opening a device
that is a communication device with no carrier. I confirmed
that this works. It also states that when O_NDELAY is set,
the open will not block.

I also confirmed this. QUESTION: Does the open suppose to succeed?
My open did with no carrier and O_NDELAY.

Now for the confusion. With login ( ie getty engaged) turned on`
in /etc/ttytab, the open will block with O_NDELAY set. Reading
through the man pages for the zs devices, I got the idea it was
suppose to, but I want some confirmation because the man pages
are not clear about this point. If it is suppose to hang, has
getty done something to make this happen?

Thanks

Sean Coleman

 
 
 
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opening tty devices with getty attached

Post by Y. Rock L » Wed, 06 Feb 1991 23:38:33



Quote:

>Now for the confusion. With login ( ie getty engaged) turned on`
>in /etc/ttytab, the open will block with O_NDELAY set. Reading
>through the man pages for the zs devices, I got the idea it was
>suppose to, but I want some confirmation because the man pages
>are not clear about this point. If it is suppose to hang, has
>getty done something to make this happen?

Yes, it is supposed to hang because the standard line discipline
used by the character tty driver doesn't support O_NDELAY.
On the other hand, O_NDELAY is supported by the streamhead in SVR4.

Y. Rock Lee, att!cblph!rock


 
 
 
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1. getty attaches tty to future shell?

I recently tried to write a screen saver for a terminal which would be
run by init and would exec getty when a user presses return.
Originally, getty would run fine, but login wouldn't, immediatedly
respawning the screensaver.  Another version put its output on the
wrong tty. We checked the source for getty_ps and figured out how to
open std[in|out|err] on the right tty.  This got us a shell, but there
was no job control due to "tty: invalid argument (null)."  Yet running
as a shell a little program that logged the ttyname() of 0, 1, and 2
showed the correct tty. PIDs shouldn't be a problem since everthing is
exec'ed.  

I've now put the screensaver code into getty, and got the same missing
tty error the first time I ran it on each tty.  Since then there's
been no problems.  

Why didn't it work as a standalone program, what does getty do besides
open stdin, and why didn't it only work the first time I ran it as a
part of getty?

Many thanks,
+Jonas Klein

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