Xen devel - Jan 2007 - What happens when turning off CONFIG_XEN_DISABLE_SERIAL?

This option seems fairly odd, especially because it doesn''t only
disable access to
the serial port in use by Xen (and even that only optionally), but to all 8250
style
ones. I would want to reach a state where all ports are available to guests
except for the at most one port Xen may use for its console (plus perhaps any
others sharing the IRQ with it, although I can''t see how Xen would be
able to
properly show their unavailability).
But due to the lack of experience with the xen console code (and also more
generally the Linux one) I can''t really judge whether turning off
$subject config
option will have any ill effect here, while I''m pretty convinced that
it would help
the situation described above. In particular I wonder whether xc_mode
shouldn''t default to XC_OFF in dom0 when that config option is off.

Thanks for any suggestions or hints,
Jan

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I think there were two reasons:
 1. To prevent accidental usage of serial ports before we added support to
Xen to disallow port accesses to UARTs that Xen is using.
 2. Xencons wants to have the ttyS major for itself, and I think the 8250
driver gets in earlier and grabs the major if it is compiled into the
kernel.

Reason (1) is obsolete. Reason (2) ought to be (we should move to xvc0 for
dom0 and domU before Xen-3.0.5).

Apart from that, yes it is safe to do away with CONFIG_XEN_DISABLE_SERIAL.

 -- Keir

On 30/1/07 3:39 pm, "Jan Beulich" <jbeulich@novell.com> wrote:
> This option seems fairly odd, especially because it doesn''t only
disable
> access to
> the serial port in use by Xen (and even that only optionally), but to all
8250
> style
> ones. I would want to reach a state where all ports are available to guests
> except for the at most one port Xen may use for its console (plus perhaps
any
> others sharing the IRQ with it, although I can''t see how Xen would
be able to
> properly show their unavailability).
> But due to the lack of experience with the xen console code (and also more
> generally the Linux one) I can''t really judge whether turning off
$subject
> config
> option will have any ill effect here, while I''m pretty convinced
that it would
> help
> the situation described above. In particular I wonder whether xc_mode
> shouldn''t default to XC_OFF in dom0 when that config option is
off.
> 
> Thanks for any suggestions or hints,


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