[Xen-devel] Re: IOCTL Command domain 1

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I am porting a tracing tool to Xen (2.0.5).

Cool :-)

> That tool is receiving control 
> messages from a user space (data collector) through IOCTL.
> I need to run my data collecting tool in the userspace of domain 0, send
> control messages to  domain 1 and also collect data from domain 1.
> Is there an easy way to send those control messages from my userspace app ?

You could write a frontend / backend pair of drivers and use those to send 
control messages and collect data.  Unfortunately, writing an FE / BE is a 
fiddly bit of work - especially if you haven't done it before.

What's the bandwidth like for your tool?

If it's low bandwidth, you might be able to add the smarts to Xend to allow 
you to use control messages to control the other domain and receive sampling 
data.  (in the unstable tree, you could use XCS to send and receive the 
messages directly, which would be easier than modifying Xend).

(side note: there was discussion at one stage of a very simple interdomain 
control message framework for sending control messages to another domain 
without modifying Xend.  Does anybody know if this got checked in?)

> That version of Xen is not making use of the grant_table framework for
> sharing pages between domains , any idea why ?

The grant tables work wasn't complete in time for the 2.0 series.  Dom0 is 
privileged so it can map whatever memory it likes, so this doesn't really 
restrict functionality.  It just means placing a little more trust in your 
backend domain ;-)

> Should I use that ?

They're enabled in the unstable tree but they're not necessary as long as the 
backend is in dom0.

Cheers,
Mark

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