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dcmd.doc
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1990-11-12
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DCMD.DOC
V1.00
Matthew Dillon
DCMD is utility that monitors a CLI's console IO and copies it to
a user specified file. The console IO is unaffected by this
monitoring.
DCMD has one dangerous problem... there is no way for the monitoring
handler to know when there are no more references to its dummy device
port. Thus, when you start a monitoring session with DCMD, you must
NEVER END THE SESSION UNTIL all programs that were *ever* run by the
shell being monitored have exited. UNDER NO CIRCUMSTANCES MAY YOU
START A PROGRAM IN THE BACKGROUND AND THEN EXIT DCMD. Programs which
detach themselves and otherwise have no references to the console
device are safe to leave running.
I suggest that you always specify a file in RAM:, in case of crash.
DCMD munches on the innards of DOS and there is no guarentee that it
will be compatible with everything.
DCMD consists of two programs:
DCMD
L:DCMD-HANDLER
To start a session type DCMD <filename>, where <filename> is the file
to hold the monitored IO. In almost all cases you will want to specify
a file in RAM:, especially because you can type or edit the file while
DCMD is writing to it. If on a floppy or an HD the file can be read
only to the point of the last sync (see below).
1> DCMD <filename> start a monitoring session, the file is
appended to. If DCMD needs to create the
file, it will close-reopen it in shared
mode.
1> DCMD end a monitoring session
1> DCMD sync (or SYNC), forces DCMD to close-reopen the
file, used when the file is not placed in
the RAM: disk to allow reading of the file
up the current point.
EXAMPLE SESSION
1> DCMD T:test.out
BEGIN DCMD002EC4C0.PORT Fri Oct 12 14:34:51 1990
1> ECHO Hello
Hello
1> DIR T:
...
1> DCMD
DCMD ended
1> TYPE T:test.out
(your entire session is printed verbatim)
Source to DCMD is included and compiles under DICE. The code should be
easily portable to other compilers.
OPERATION
DCMD creates a public message port named after the CLI process it is to
monitor, then redirects the console handler and current input and
output file handles for the CLI through this public port.
DCMD then loads and runs DCMD-HANDLER as a separate processs.
DCMD-HANDLER's task name is the same as the port name and this is how
DCMD-HANDLER finds the port. DCMD-HANDLER then sets up the public
port to signal it as messages come in.
Whenever an ACTION_WRITE occurs DCMD-HANDLER does a Write() to the
monitor file before allowing the packet to resume its journey to the
console handler. Whenever an ACTION_READ occurs DCMD-HANDLER routes
the reply port to itself then immediately sends the packet to the
console device. The packet is returned to DCMD-HANDLER which then
Write()s the read data to the monitor file as well before returning
the packet to the originator of the request.
DCMD and DCMD-HANDLER communicate and handshake through the public
message port via the signals SIGBREAKF_CTRL_D through SIGBREAKF_CTRL_F.
When exiting, DCMD sends a signal to DCMD-HANDLER requesting it to
exit, waits for the handshake, and then restore the cli.
DCMD-HANDLER uses the _main entry point which, under DICE, does not
attempt to interpret any passed arguments or whether the process is
CLI or WORKBENCH based, but does initialize all data and BSS and
opens both the exec and DOS libraries.