by I have a problem with Streams, as follows. I'm working on a SysV.4
system which, if I interpret the release numbers right, is ICL's
version 6 level 3 of AT&T i386 V.4.0 release 3.0.
There exists on this system an old executable program which is
hard-coded for a particular terminal type. I'm writing a front end for
it which will interpret the screen codes and, using Curses, translate
them to work on other video types.
My program works by creating a pipe and forking/execvping the old
program. One end of the pipe is the program's stdin/stdout. The other
end is read/written in my program. This all works fine for ordinary
screen/keyboard data.
I need to catch the program's IOCTLs in order to know when it wants me
to echo keyboard input and when I mustn't. I read up on Streams and
modules and thought I could do it by creating a pipe like this:
myprog <--> pckt <--> ptem <--> ldterm <--> ttycompat <--> oldprog
I do it as follows: after I fork the child but before I exec, I push
ptem, ldterm and ttycompat onto its end of the pipe, then dup it to
stdin and stdout. After I fork the parent, I push pckt onto *its* end.
The parent reads with getmsg() and I expect the control portion of
returned messages to be M_DATA or M_IOCTL. But I only ever see M_DATA,
except for one final ioctl when the pipe is being closed. If I replace
'oldprog' by a shell script which contains stty commands, then I *do*
see M_IOCTLs for it.
I have also tried pushing 'pipemod' both before pushing pckt and before
ptem. The manual was most unclear on whether this was Essential,
Optional or a Bad Idea. But it didn't make any difference, anyway :-(
It may or may not be relevant that there seems to be a timing problem.
The child starts writing to stdout before the parent has pushed pckt. I
tried avoiding this by doing all the pushed before the fork, but it
appears that pushed modules are not inherited by the child. I don't
really want to use a semaphore, but I fear it may be unavoidable.
It's more likely, though, that I've misinterpretted the manual. I'd
really appreciate any help. I'm the only person I know who's gone into
Streams at this depth and I'm having to learn to swim real fast :-) All
suggestions, either for the Streams problem or for better ways of doing
it, gratefully welcomed.
Many thanks
Nick Leverton
--
"Politician! Where's your credibility ?
You promised to lay down your life to set your people free" - Hugh Masekela.