Re: [PATCH] hvc_console: returning 0 from put_chars is not an error

Scott Wood
2009-10-16T15:34:29Z

On Fri, Oct 16, 2009 at 03:46:45PM +1100, Benjamin Herrenschmidt wrote:
> On Thu, 2009-10-15 at 13:57 -0500, Scott Wood wrote:
> > I'd say the dropping approach is quite undesirable (significant
> > potential for output loss unless the buffer is huge), unless there's
> > simply no way to safely spin. Hopefully there are no such backends, but
> > if there are perhaps we can have them return some special code to
> > indicate that.
>
> Should never spin.

Why is a hypervisor console different than a serial port in this regard?

> Best is to keep a copy in the upper layer of the pending data and throttle
> (not accept further data from tty layer) until we have managed to flush
> out that "pending" buffer.

The data isn't coming from the tty layer -- we're talking about printk. How
do you throttle that without spinning?

I agree that it shouldn't spin when handling tty I/O.

-Scott