Re: console driver - How domain0 processes console messages ?

[Andrew Warfield <andrew.warfield@gmail.com>]

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

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
tools/python/xen/xend/server/console.py.

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.

hth,
a.


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