Date: Sat, 21 Jan 1995 15:20:23 +1100 From: Bruce Evans <bde@zeta.org.au> To: hackers@FreeBSD.org, luigi@labinfo.iet.unipi.it Subject: Re: sio.c... Message-ID: <199501210420.PAA10155@godzilla.zeta.org.au>
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>The first is easy, and deals with avoding the problem with processes
>which are not able to exit in case of hardware problems.
>In sioclose(), on 2.0R the call to the line_close routine is surrounded
>by a timeout/untimeout pair:
> timeout(wakeup, TSA_OCOMPLETE(tp), 60 * hz);
> (*linesw[tp->t_line].l_close)(tp, flag);
> untimeout(wakeup, TSA_OCOMPLETE(tp));
>while 1.1.5R has only the call to l_close. Would it be possible to add
>the calls to timeout/untimeout on 1.1.5, or there are other changes
>needed ?
The timeouts are actually in a version later than 2.0R, and don't work
(wakeup() doesn't cause the tsleep() in ttywait() to return
EWOULDBLOCK). -current has a better fix for the problem. The tsleep()
in ttywait() uses a timeout (tp->t_timeout, default 0) and you can
change the timeout using comcontrol. This involves Simple changes to
<sys/tty.h>, kern/tty.c and comcontrol.[c8].
>On the same 1.1.5 system here, I found out that a process here keeps
>blocking with WCHAN="siotx" (this happens with mgetty, when a
>particolar user drops the session, probably not in the most
>appropriate way). "siotx" seems to be present only in sio.c, function
>comparam(tp, t), in the following section of code, which is exactly the
>same as in 2.0R (I have no current sources handy):
> disable_intr();
>retry:
> com->state &= ~CS_TTGO;
> enable_intr();
> while ((inb(com->line_status_port) & (LSR_TSRE | LSR_TXRDY))
> != (LSR_TSRE | LSR_TXRDY)) {
> error = ttysleep(tp, TSA_OCOMPLETE(tp), TTIPRI | PCATCH,
> "siotx", hz / 100);
>...
>from which it appears that there is no timeout or other way out in case
>the modem is not responding properly. Wouldn't it be better to add an
>emergemcy exit after a proper timeout ?
Perhaps. The LSR_TSRE and LSR_TXRDY bits are guaranteed to go on in
a short time ((transmit_fifo_size + 1) * time_to_transmit_one_char)
if the hardware and software are working. It's not practical to check
for all h/w bugs. I'll check that there are no races in the s/w.
(There used to be a bug involving not fully stopping transmission
(something turned CS_TTGO back on). For transmission to continue
"forever", something must supply new output "forever". The ttysleep()
probably allows other processes to supply output. Echoing of input
creates output.).
Bruce
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