dg@lakart.UUCP (David Goodenough) (04/14/89)
From article <1403@auspex.auspex.com>, by guy@auspex.auspex.com (Guy Harris): > Huh? Its sole purpose is to prevent two programs ("getty" and the > program that's dialing out) from gaining simultaneous access to the same > serial line. I thought tip / uucico did that when they opened the line. Usually an idle getty looks like this: F UID PID PPID CP PRI NI ADDR SZ RSS WCHAN STAT TT TIME COMMAND 1800001 0 4872 1 0 3 0 5d8 40 28 cp_tty I h1 0:00 - std.960 where the cp_tty means it waiting for a tty to do something. I'd do it now but I'm dialed in (catch 22 :-) ), but when uucico / tip are running, the WCHAN changes to a 'u', and the stat goes to a 'S' (short term snooze). So either uucico does some explicit widgetry to nuke the getty, or the open does. I once started writing a term program, and since I'm on a BSD system, I opted to check for a getty on the line, and if there just issue a kill -17 at it. Held that sucker quiet real good :-). If I couldn't, I assumed that the tty was in use and exited the term prog. Anyway what does happen when the WCHAN changes from cp_tty to u?? Enquiring minds want to know. -- dg@lakart.UUCP - David Goodenough +---+ IHS | +-+-+ ....... !harvard!xait!lakart!dg +-+-+ | AKA: dg%lakart.uucp@xait.xerox.com +---+
guy@auspex.auspex.com (Guy Harris) (04/18/89)
>> Huh? Its sole purpose is to prevent two programs ("getty" and the >> program that's dialing out) from gaining simultaneous access to the same >> serial line. > >I thought tip / uucico did that when they opened the line. "It", in this case, refers to the dialin/dialout feature. "tip"/"uucico" do *not* themselves do anything that keeps "getty" from using the line; the serial port driver does so when the line is opened. ("getty" is not running on the same major/minor as "tip" or "uucico", so even if "tip" or "uucico" does a TIOCEXCL that won't stop "getty".) >Usually an idle getty looks like this: > > F UID PID PPID CP PRI NI ADDR SZ RSS WCHAN STAT TT TIME COMMAND > 1800001 0 4872 1 0 3 0 5d8 40 28 cp_tty I h1 0:00 - std.96 > >where the cp_tty means it waiting for a tty to do something. It's presumably waiting for carrier to come up on the serial port. >I'd do it now but I'm dialed in (catch 22 :-) ), but when uucico / tip >are running, the WCHAN changes to a 'u', and the stat goes to a 'S' >(short term snooze). So either uucico does some explicit widgetry to >nuke the getty, or the open does. If you're talking about schemes of the sort used by SunOS, the "open" does - it doesn't nuke the "getty", it just keeps the arrival of carrier on the serial port from waking it up.