Date: Mon, 02 Jun 1997 16:51:26 -0400 From: Brian McGovern <bmcgover@cisco.com> To: hackers@freebsd.org Cc: questions@freebsd.org Subject: Need help with O_NONBLOCK and pppd in FreeBSD.... Message-ID: <199706022051.QAA00272@bmcgover-pc.cisco.com>
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I've been doing some code-searching as to why, whenever I try to run pppd
with my serial driver, that pppd suddenly starts spinning out of control. I
think I see where this is happening (in pppd), but I'm not sure if I'm
confusing what I think is happening, and what really is happening. If someone
can comment on these code chunks, I'd greatly appreciate it:
>From /usr/src/usr.sbin/pppd/main.c, line 317:
nonblock = (connector || !modem)? O_NONBLOCK: 0;
Now, in my test cases, connector will be 0/NULL (I am not dialing out), and
modem is 1 (I want to use modem control lines). Therefore,
nonblock = (0 || !1)? O_NONBLOCK:0;
nonblock = (0 || 0) ? O_NONBLOCK:0;
nonblock = 0;
Then, on line 326:
if (nonblock) {
initfdflags &= ~O_NONBLOCK;
fcntl(fd, F_SETFL, initfdflags);
}
Which translates in to:
if (0) {
initfdflags &= ~O_NONBLOCK;
fcntl(fd, F_SETFL, initfdflags);
}
which will never get executed. This should turn OFF NON_BLOCKING operation,
which I'm assuming is what pppd really wants. Of course, due to the value of
nonblock, this code will never happen, so O_NONBLOCK is still in the default
case, which appears to be OFF (unset).
However, then we look at line 396, which reads:
if (fcntl(fd, F_SETFL, initfdflags | O_NONBLOCK) == -1) {
syslog(LOG_ERR, "Couldn't set device to non-blocking mode: %m");
die(1);
}
Which seems to tell me to set O_NONBLOCK, reguardless of whether we want to
use modem control lines or not. Once in a non-blocking state, pppd is free
to spin completely out of control. This is the last invokation I've found that
effects the O_NONBLOCK attribute.
Now, in my opinion, this seems backwards. Wouldn't I potentially want to turn
O_NONBLOCK _ON_ first, in order to dial out, then turn it _OFF_
unconditionally? Perhaps I'm missing something, but it seems strange. Please,
set me straight....
-Brian
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