Date: Sun, 11 Oct 2009 13:51:09 +0300 From: Mikolaj Golub <to.my.trociny@gmail.com> To: freebsd-stable@freebsd.org Subject: can't change tty speed and buffer size on 8.0 Message-ID: <861vla2ogy.fsf@kopusha.onet>
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Hi,
On 8.0-RC1 if you run this command:
cat > /dev/null
and try to input a long line, the maximum length you can input is 1920
characters.
I have investigated a bit how I can increase a tty buffer as this is a problem
for me (I have logs with very long lines and I used to copy&past a particular
line into input of some script to structure it).
According to kern/tty.c:tty_watermarks() the input buffer size is set as
ispeed / 5. The default speed is 9600 that is rather low:
/usr/include/sys/ttydefaults.h:#define TTYDEF_SPEED (B9600)
So to increase the buffer size I need to decrease tty speed. But this does not
work:
zhuzha:/tmp% stty
speed 9600 baud;
lflags: echoe echok echoke echoctl
iflags: -ixany -imaxbel
oflags: tab0
cflags: cs8 parenb
eol2 erase status
^@ ^H <undef>
zhuzha:/tmp% stty ispeed 38400
zhuzha:/tmp% stty
speed 9600 baud;
lflags: echoe echok echoke echoctl
iflags: -ixany -imaxbel
oflags: tab0
cflags: cs8 parenb
eol2 erase status
^@ ^H <undef>
I can change tty speed on 7.X but can't on 8.0. I ran this simple dtrace
program to see what is going on:
tty*:entry
/execname == "stty"/
{
printf("%s entered; args0-4: %d %d %d %d %d\n",
probefunc, arg0, arg1, arg2, arg3, arg4);
}
tty*:return
/execname == "stty"/
{
printf("%s returned %d\n", probefunc, arg1);
}
And here is the relevant part of the output:
ttydev_ioctl entered; arguments: 3313875456 2150396948 3363021248 3 3357835264
tty_wait_background entered; arguments: 3354367492 0 3234498062 158 0
tty_wait_background returned 0
tty_ioctl entered; arguments: 3354367488 2150396948 3363021248 3357835264 0
ttydevsw_defioctl entered; arguments: 3354367488 2150396948 3363021248 3357835264 0
ttydevsw_defioctl returned 4294967293
ttydevsw_defparam entered; arguments: 3354367488 3363021248 3363021248 3357835264 0
ttydevsw_defparam returned 0
tty_watermarks entered; arguments: 3354367488 3363021248 3363021248 3357835264 0
ttyinq_setsize entered; arguments: 3354367528 3354367488 1920 0 3875601352
ttyinq_setsize returned 15
ttyoutq_setsize entered; arguments: 3354367572 3354367488 1920 0 3875601352
ttyoutq_setsize returned 3545052638
tty_watermarks returned 858997088
ttydisc_optimize entered; arguments: 3354367488 3363021264 20 3357835264 0
ttydisc_optimize returned 0
tty_ioctl returned 0
ttydev_ioctl returned 0
As you can see, before calling tty_watermarks() and ttyinq_setsize(),
ttydevsw_defparam() is called that do only this thing:
/* Use a fake baud rate, we're not a real device. */
t->c_ispeed = t->c_ospeed = TTYDEF_SPEED;
As a result the speed of terminal is always set to TTYDEF_SPEED and
ttyinq_setsize() is always called with size=1920 (TTYDEF_SPEED/5).
This all happens in tty_generic_ioctl() in this part:
/*
* Only call param() when the flags really change.
*/
if ((t->c_cflag & CIGNORE) == 0 &&
(tp->t_termios.c_cflag != t->c_cflag ||
tp->t_termios.c_ispeed != t->c_ispeed ||
tp->t_termios.c_ospeed != t->c_ospeed)) {
error = ttydevsw_param(tp, t);
if (error)
return (error);
/* XXX: CLOCAL? */
tp->t_termios.c_cflag = t->c_cflag & ~CIGNORE;
tp->t_termios.c_ispeed = t->c_ispeed;
tp->t_termios.c_ospeed = t->c_ospeed;
/* Baud rate has changed - update watermarks. */
tty_watermarks(tp);
}
AFAIR ttydevsw_param() runs tty hooks and ttydevsw_defparam() among them.
So you can't change the speed of terminal and the size of input buffer on
running system. Only by recompiling the kernel with updated TTYDEF_SPEED.
Is this intentional or does it look rather like a bug?
--
Mikolaj Golub
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