[B2-devel] patch: subprocess as serial port

[Brian J. <bjj...@us...>]

Everyone,

I have a (very) preliminary version of a patch which provides a way to
pipe serial input/output to programs instead of actual ports, as
requested in the second-to-last item of the "TODO" file.  Here's a
URL:

  ftp://ftp.frontiernet.net/pub/users/brianj1/B2_pty_020506.patch

(I'm not sure if this will work directly as input to patch; I had some
trouble with "cvs rdiff" and had to manually edit things a bit.)

Just put a pipe character ("|") at the beginning of the port device
file name, and BII will allocate a pseudoterminal, connect the master
side to the BII serial infrastructure, and run the rest of the port
device file name as a program using "/bin/sh -c", with the slave side
of the pty as its standard input, output, and error.  I.e. BII will
treat the process as a serial port, and the process will think it's
talking to a normal terminal.

On IRIX, the only platform I've tried, I can (sort of) open tcsh and
get a shell prompt.  I think the pty needs some slave-side
configuration to get everything working right.  But I can open a PPP
daemon (via a shell script to set the correct environment variables)
and talk TCP/IP between the Mac and the host.  It works great:  the
host takes care of routing among the Mac, the host, and remote
machines, so the Mac can connect to any machine the host can.  Now all
I have to do is upgrade to a version of MacOS which supports Appletalk
over IP....  Way cool.

The code in pty.c is stolen from GNU screen.  I probably need to steal
their slave-side setup code as well... it's big and ugly, though.  I
just hope it doesn't lead to too much autoconf madness.

Some questions:
- How should BII call wait() to clean up after the subprocess exits?
  From the serial port close handler?  From a separate pthread (so it
  can block)?  Currently I don't call it at all.
- Should I automatically drop privileges in the subprocess if BII is
  running setuid?  What's the philosophy for making BII
  security-conscious vs. just documenting the issues and saying, "if
  you install BII as setuid, you do so at your own risk"?
- Any other security concerns?
- Is the current code structure OK, or would you prefer that I move
  the PTY setup/fork/exec/etc. into a subroutine?

I also added a hook for midi support:  if the device name is "midi",
it's treated specially (returns an error for now).  I have no idea if
Mac MIDI drivers actually use the serial manager, or if this is the
best way to add MIDI to BasiliskII.  Or if I'll get around to finding
out within the next couple of years....

						Brian J. Johnson

--------------------------------------------------------------------

   "The public needs NREN because 300 baud used to be fast and low-
    resolution graphics used to be pretty....  We wait impatiently,
    sure that we spend half our lives waiting for printers, and the
    other half waiting for disk drives.  Time is a commodity."
                                           -- Jean Armour Polly