Re: about serial console problem

[Eric W. Biederman]

"Robert J.Dunlop" <[e-mail]> writes:

> Hi,
> 
> On Tue, Jul 24,  Eric W. Biederman wrote:
> > Barry Wu <[e-mail]> writes:
> > 
> > > I am porting linux 2.4.3 to our mipsel evaluation
> > > board. Now I meet a problem. Because I use edown
> > > to download the linux kernel to evaluation board.
> > > I update the serial baud rate to 115200.
> > > I use serial 0 as our console, and I can use
> > > printk to print debug messages on serial port.
> > > But after kernel call /sbin/init, I can not
> > > see "INIT ...  ..." messages on serial port.
> > > I suppose perhaps I make some mistakes. But when
> > > I use 2.2.12 kernel, it ok.
> > > If someone knows, please help me. Thanks!
> > 
> > It's a bug in init.  INIT clears the CREAD flag which means all reads
> > to the console will be dropped.  Why it /sbin/init works before 2.4.3
> > is a mystery.
> 
> Perhaps because most of the serial drivers didn't implement CREAD (or
> rather !CREAD) until then. 

Hmm.  When I looked it appeared CREAD should have worked in 2.4.2 but I do
know /sbin/init didn't have a problem with that one.  

> Actually more and more have been implementing
> it as we go through 2.4.x, depends when your particular driver got caught.

Do you know the history on how/why ~CREAD support started showing in
in the linux kernels.  I'd like to understand what is going on.

Eric