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Date: Mon, 4 Jul 2011 16:24:29 +0200
From: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: hvc_console change results in corrupt oops output
Message-ID: <20110704142429.GA2147@linux.vnet.ibm.com>
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	<1309787787.14501.268.camel@pasglop>
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Cc: borntraeger@de.ibm.com, brueckner@linux.vnet.ibm.com,
	linuxppc-dev@lists.ozlabs.org, Anton Blanchard <anton@samba.org>
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On Mon, Jul 04, 2011 at 11:56:27PM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2011-07-04 at 20:57 +1000, Anton Blanchard wrote:
> 
>  .../...
> 
> > The hypervisor gives us a busy return, so we could retry a number of
> > times instead of dropping it on the floor. We'd need to do it in the
> > hvc_console driver - the tty drivers share the same backend
> > functions so we can't hide it in the pseries put_chars function.
> 
> For kernel console, I don't see why not wait forever ... If the
> underlying backend really lost the connection it can always return a
> negative error no ?
> 
> Or we could have "well defined" return codes for "wait forever" vs.
> "drop this" ... maybe return -EAGAIN.

I will check this again for my hvc_iucv back-end.  Meanwhile a found
an old thread discussing the same issue.  It covers some differences
between console and ttys which actually does not matter for hvc-backend
because of the shared put_chars() routine.

You can read the thread on lkml.org: http://lkml.org/lkml/2009/10/15/149


Kind regards,
  Hendrik