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Re: [Xen-devel] [PATCH] Default serial console to BAUD_AUTO

To: John Levon <john.levon@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Default serial console to BAUD_AUTO
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Mon, 24 Sep 2007 19:12:10 +0100
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On 24/9/07 18:58, "John Levon" <john.levon@xxxxxxx> wrote:

> Indeed, this has changed in xen-unstable compared to 3.0.4, my apologies. So
> with my patch you'll automatically get serial console output in xen-unstable,
> regardless of console=com1

The behaviour was exactly the same in 3.0.4. In fact the current behaviour
has existed forever, pretty much.

> When you say "waste time", what exactly do you mean? Are you concerned about
> printk() performance? Isn't this only debug and early boot? It seems to me
> that
> getting such serial console output by default is pretty useful.
> Otherwise, I'm fine with remove com1 from opt_console, as it matches current
> behaviour.

Actually another reason to not change the current behaviour is that it will
also lock out dom0 from getting at COM1 and COM2. Because any serial ports
that ns16550.c knows about get removed from dom0's io permissions.

I expect we could rework some stuff to get some slightly more sensible
defaults to emerge (e.g., console=...com1... could imply that com1 should be
grabbed by Xen with sensible defaults), but it's more work than your
one-line patch and, really, you can just put 'com1=auto' on your command
line to get the same effect and then noone gets surprised by Xen locking
down serial ports when com1/com2 does not appear on their Xen command line.
The current situation seems quite acceptable to me.

 -- Keir

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