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[Xen-devel] Easy user-space usage of xenstore

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: Rian Hunter <rian@xxxxxxx>
  • Date: Thu, 29 Jun 2006 16:31:55 -0400
  • Delivery-date: Fri, 30 Jun 2006 03:21:22 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>


I want to write a Xen-aware application but I am encountering some
problems. For my applications to be Xen aware, the ones that are running
in non domain 0 need to be able to obtain some bootstrap information
from the program running in domain 0. This is very petty information (as
most IPC will be done using TCP/IP).

Basically my approach was this:

1. Process in domain-0 writes a key to /local/domain/<DomID>.  (<DomID>
refers to the domain id number assigned to a newly created vm)
2. Process in unprivileged domain reads from /local/domain/<DomID>

Of course you can see my problem: The unprivileged domain has no idea
which /local/domain/<DomID> is his! My first question: Is there a way
for an unprivileged domain to find out his <DomID> in user-space?

My second approached when I ran into this problem was:

1. Process in domain-0 writes a key to /local/domain/<DomID>.
2. Kernel-space driver in the unprivileged domain reads this value (or
watches this key) using the xs_* functions (which i believe already
defaults to the unprivileged domain's home name-space) and exposes a
character device (/dev/my_program_info) which prints out this
3. Process in unprivileged domain just reads /dev/my_program_info

This second solution is too messy though! I believe I can still take the
first approach especially since the xs_* calls in the kernel default to
the home name-space. Why can't there be a user-space method to do this?

Any help would be greatly appreciated, Thank You!

Rian Hunter

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