Subject: blocking tcsetattr in pppd 2.4.0
To: None <>
From: Brad du Plessis <>
List: netbsd-users
Date: 05/31/2004 11:44:37
Hi all,

I've had an issue from time to time with pppd 2.4.0. Unfortunately the
problem is not easily repeatable but it will occur on occasion when I try
and kill a pppd listening process. Having sent the kill signal (SIGTERM),
the process fails to exit. I put printouts in the pppd code to figure out
where exactly the problem lies and it appears that having received the kill
signal and doing all the tty cleanup before exit, pppd fails to return from
the restore_tty() function called from finish_tty() in tty.c . Looking at
restore_tty() in sys-bsd.c, I assume the problems lies with the line:

tcsetattr(fd, TCSAFLUSH, &inittermios)

My thoughts are that before applying the attributes set in the structure
inittermios, tcsetattr attempts to flush all data written to descriptor fd
to the terminal and for some reason it is unable to do this.

Does this indicate a problem with the modem or serial port?

The attribute change turns off echoing to avoid a loop between tty and the
modem, is this line essential, why would echoing be enabled in the first

What effect would changing the TCSAFLUSH flag to TCSANOW have?

Any ideas why TCSAFLUSH was used instead of TCSANOW?

If TCSANOW was used and the attributes were successfully changed, would I
then see a problem when a close is called for this descriptor if the close
tries a flush of some sort?

Any help would be much appreciated.