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Re: [Xen-devel] console driver - How domain0 processes console messages ?

  • To: Richard <judicator3@xxxxxxxxx>
  • From: Andrew Warfield <andrew.warfield@xxxxxxxxx>
  • Date: Wed, 16 Feb 2005 07:54:22 +0000
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 16 Feb 2005 07:55:14 +0000
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  • List-id: List for Xen developers <xen-devel.lists.sourceforge.net>

> I am trying to undestand how domain0 processes console
> messages  (i.e messages with type CMSG_CONSOLE and subtype

Console messages currently share the same shared memory rings that
control messages use.  As such, ctrl_if_send_message_noblock(), is a
non-blocking send on these rings, and ctrl_if_notify_controller() is
an event channel notification of a control event.  Aside from console
messages, control messages are exactly that -- things like driver
setup and connection.  See xen/include/public/io/domain_controller.h
for a full list.

The control message rings are mapped to user space in dom0 through
calls to libxc, while the notification is delivered to dom0 via
/dev/evtchn.  If you are using stable or testing, these rings are
accessed directly by xend, see tools/python/xen/lowlevel/xu/xu.c
(especially the notifier and port objects therein).  If you are using
the unstable tree, xcs (tools/xcs/xcs.c) demultiplexes the shared
rings/event channels.

In xend, consol messages are eventually handled in

Hope that helps.  We plan to separate the console messages from the
control rings in the very near future, allowing them to have a
separate driver and be throttled independent of control messages. 
This should make the current interface considerably simpler.


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