serial console problems with 2.4.4

serial console problems with 2.4.4

[Reto Baettig]

Hi

I just installed 2.4.4 on our alpha SMP boxes (ES40) and now I have
problems with the serial console:

sulogin does not accept input from the serial line
mingetty does not accept input from the serial line
agetty works fine

Everything works fine for the 2.4.2 kernel. I took the .config file from
the 2.4.2 kernel to compile the 2.4.4 kernel.

Any ideas?

Reto

Re: serial console problems with 2.4.4

[Fabrice Gautier]

On Wed, 02 May 2001 11:54:11 +0200
Reto Baettig <baettig@scs.ch> wrote:

> Hi
> 
> I just installed 2.4.4 on our alpha SMP boxes (ES40) and now I have
> problems with the serial console:

I get same kind of problem when upgrading from 2.4.2 to 2.4.3 and using
busybox as init/getty 

The problem was a bug in busybox. The console initialisation code was
not correct.
> 
> sulogin does not accept input from the serial line
> mingetty does not accept input from the serial line
> agetty works fine

So this this probably a sulogin/mingetty problem. They should set the
CREAD flag in your tty c_cflag.

the patch for busybox repalced the line
	tty.c_cflag |= HUPCL|CLOCAL
by
	tty.c_cflag |= CREAD|HUPCL|CLOCAL
	
Hope this help.

-- 
Fabrice Gautier <gautier@email.enstfr>

Re: serial console problems with 2.4.4

[Eric W. Biederman]

Fabrice Gautier <gautier@email.enst.fr> writes:

> On Wed, 02 May 2001 11:54:11 +0200
> Reto Baettig <baettig@scs.ch> wrote:
> 
> > Hi
> > 
> > I just installed 2.4.4 on our alpha SMP boxes (ES40) and now I have
> > problems with the serial console:
> 
> I get same kind of problem when upgrading from 2.4.2 to 2.4.3 and using
> busybox as init/getty 
> 
> The problem was a bug in busybox. The console initialisation code was
> not correct.
> > 
> > sulogin does not accept input from the serial line
> > mingetty does not accept input from the serial line
> > agetty works fine
> 
> So this this probably a sulogin/mingetty problem. They should set the
> CREAD flag in your tty c_cflag.
> 
> the patch for busybox repalced the line
> 	tty.c_cflag |= HUPCL|CLOCAL
> by
> 	tty.c_cflag |= CREAD|HUPCL|CLOCAL
> 	
> Hope this help.

This part is correct.  

However the kernel sets CREAD by default.  
sysvinit (and possibly other inits) clears CREAD.
I wish I knew where the breakage actually occured.

And then sulogin/mingetty need to reenable it.

It's not too big of a deal except the serial code doesn't accept SAK's
when CREAD is clear.

Eric

Re: serial console problems with 2.4.4

[Fabrice Gautier]

On 02 May 2001 10:37:21 -0600
ebiederm@xmission.com (Eric W. Biederman) wrote:

> Fabrice Gautier <gautier@email.enst.fr> writes:
> > So this this probably a sulogin/mingetty problem. They should set the
> > CREAD flag in your tty c_cflag.
> > 
> > the patch for busybox repalced the line
> > 	tty.c_cflag |= HUPCL|CLOCAL
> > by
> > 	tty.c_cflag |= CREAD|HUPCL|CLOCAL
> > 	
> > Hope this help.
> 
> This part is correct.  
> 
> However the kernel sets CREAD by default.  

Are your sure? Wasn't this the behaviour for 2.4.2  but changed in 2.4.3

> sysvinit (and possibly other inits) clears CREAD.

In my case I was using busybox as init. So there is no sysinit or any other
init called before this line.


> I wish I knew where the breakage actually occured.

Just look at this diff on serial.c between 2.4.2 and 2.4.3:

--- serial.c	Sat Apr 21 17:22:53 2001
+++ ../../../linux-2.4.2/drivers/char/serial.c	Sat Feb 17 01:02:36 2001
@@ -1764,8 +1765,8 @@
 	/*
 	 * !!! ignore all characters if CREAD is not set
 	 */
-//	if ((cflag & CREAD) == 0)
-//		info->ignore_status_mask |= UART_LSR_DR;
+	if ((cflag & CREAD) == 0)
+		info->ignore_status_mask |= UART_LSR_DR;
 	save_flags(flags); cli();
 	if (uart_config[info->state->type].flags & UART_STARTECH) {
 		serial_outp(info, UART_LCR, 0xBF);


-- 
Fabrice Gautier <gautier@email.enstfr>

Re: serial console problems with 2.4.4

[Eric W. Biederman]

Fabrice Gautier <gautier@email.enst.fr> writes:

> On 02 May 2001 10:37:21 -0600
> ebiederm@xmission.com (Eric W. Biederman) wrote:
> 
> > Fabrice Gautier <gautier@email.enst.fr> writes:
> > > So this this probably a sulogin/mingetty problem. They should set the
> > > CREAD flag in your tty c_cflag.
> > > 
> > > the patch for busybox repalced the line
> > > 	tty.c_cflag |= HUPCL|CLOCAL
> > > by
> > > 	tty.c_cflag |= CREAD|HUPCL|CLOCAL
> > > 	
> > > Hope this help.
> > 
> > This part is correct.  
> > 
> > However the kernel sets CREAD by default.  
> 
> Are your sure? Wasn't this the behaviour for 2.4.2  but changed in 2.4.3

init=/bin/bash works fine over a serial console in 2.4.4.  So I am
certain.

I get the impression that something in 2.4.3 fixed CREAD handling, and we
started noticing the buggy user space.

> > sysvinit (and possibly other inits) clears CREAD.
> 
> In my case I was using busybox as init. So there is no sysinit or any other
> init called before this line.

The busy box init is also clearing CREAD (as of 0.51 anyway).

> > I wish I knew where the breakage actually occured.
> 
> Just look at this diff on serial.c between 2.4.2 and 2.4.3:

If it was a real diff between 2.4.2 and 2.4.3 I would agree, however it looks
like your attempt to fix 2.4.3. 

Eric


> --- serial.c	Sat Apr 21 17:22:53 2001
> +++ ../../../linux-2.4.2/drivers/char/serial.c	Sat Feb 17 01:02:36 2001
> @@ -1764,8 +1765,8 @@
>  	/*
>  	 * !!! ignore all characters if CREAD is not set
>  	 */
> -//	if ((cflag & CREAD) == 0)
> -//		info->ignore_status_mask |= UART_LSR_DR;
> +	if ((cflag & CREAD) == 0)
> +		info->ignore_status_mask |= UART_LSR_DR;
>  	save_flags(flags); cli();
>  	if (uart_config[info->state->type].flags & UART_STARTECH) {
>  		serial_outp(info, UART_LCR, 0xBF);
> 

Re: serial console problems with 2.4.4

[Fabrice Gautier]

On 03 May 2001 02:15:03 -0600
ebiederm@xmission.com (Eric W. Biederman) wrote:

> 
> I get the impression that something in 2.4.3 fixed CREAD handling, and we
> started noticing the buggy user space.

That's my impression too...

> > > I wish I knew where the breakage actually occured.
> > 
> > Just look at this diff on serial.c between 2.4.2 and 2.4.3:
> 
> If it was a real diff between 2.4.2 and 2.4.3 I would agree, however it looks
> like your attempt to fix 2.4.3. 

Err... Yes sorry, in fact this was a workaround proposed by Kanoj, the 
maintener of serial.c (I think)...

Regards.

-- 
Fabrice Gautier <gautier@email.enstfr>