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RE: [Xen-devel] determining dom0 version and bit size from domU

  • To: "xen-devel" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
  • Date: Sat, 2 Feb 2008 14:24:28 +1100
  • Delivery-date: Fri, 01 Feb 2008 19:24:55 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AchlRQYpcQr7K5pVTZi8TpkCkQ4v3gABM8XQ
  • Thread-topic: [Xen-devel] determining dom0 version and bit size from domU

> Unfortunately, it doesn't look like I can determine the version of Xen
> that the Dom0 kernel was compiled against, nor the bit width of Dom0.
> think I can get some indication of the hypervisor version, but that is
> irrelevant.

The more I look at this the more I think that Dom0 just doesn't make
this information available.

So another possible solution I have for determining what is going on is:

1. Write a request (op = 0xff, id = 0) to the ring, and fill all the
seg[] entries with 0xff too.
2. Wait for the response from Dom0, confirm that we get a failure (I'm
assuming that Dom0 will just return 'BLKIF_RSP_ERROR' here)
3. Write another request (op = 0xff, id = 0xffffffffffffffff to the
4. Wait for the response from Dom0, if we get the same response as
before then we are done and can continue as normal.
5. If we didn't get the same response, then switch bit widths (32 -> 64,
or 64 -> 32), then continue as normal.

Sounds like it might work in theory, as long as Dom0 doesn't have a huge
panic attack when it gets op=0xff, or a completely misaligned request
(the id = 0xffffffffffffffff and seg[..] = 0xff is so that if we have
our alignments wrong, the backend still see's a request of 0xff and not
a bizarre read operation).

Any thoughts?


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