sxts, ptys, and ISIG; can they work together?

[t e bennett]

A question regarding sxt's, pty's and ISIG on 5.3 386.

We noticed recently that if a user is logged into a shell layer on a tty
line and then rlogin's into a shell on another machine, that ^Z will not
cause the switch back to shl's '>>>' prompt.  A little investigation showed
the reason was that rlogin/telnet had turned off ISIG which disabled the
check for the switch character (as well as for INTR and QUIT).

Our first attempt to work around this problem (we consider it a problem,
anyway) involved having rlogin not turn off ISIG, but to change its
VINTR and VQUIT to 0377.  This worked, but has the effect of precluding
any type of umodem/kermit file xfer thru the rlogin/telnet (something we
actually do), since 0377 would now hit the rlogin with a SIGQUIT.

Our next thought was this:

    Is it really in the spirit of things for ISIG to control VSWTCH?
    It looks like ISIG was designed to give the process the ability to
    not be subject to interrupts.  Should VSWTCH be considered in the
    same class?  (Note that the 5.3 documentation quite clearly does
    say that ISIG controls VSWTCH)

    The effect of this is that any application program that wants to
    ignore signals will also disable shell layer switching.

Any thoughts on this?
Please respond by mail.

(sxt driver unchanged from 5.3
 pty driver from Micom-Interlan with minor changes)

--tony

t e bennett
{decvax,akgua}!mcnc!rti!scirtp!tony