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[Xen-devel] _domain in page_info structure

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: jeet <jeet_sat12@xxxxxxxxxxx>
  • Date: Tue, 27 Mar 2007 13:55:52 +0530 (IST)
  • Delivery-date: Tue, 27 Mar 2007 01:27:31 -0700
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Hi All,

I am looking into the get_page() function implementation in Xen
where I encounter the reference to _domain

nd = page->u.inuse._domain;

what this field is used for? 

 I found comment in source ode about it

/* Meaning of the _domain field in shadow pages
 * --------------------------------------------
 * In shadow pages, this field will always have its least significant bit
 * set.  This ensures that all attempts to get_page() will fail (as all
 * valid pickled domain pointers have a zero for their least significant bit).
 * Instead, the remaining upper bits are used to record the shadow generation
 * counter when the shadow was created.

But I am not able to understand this.What is actual significance of this 

Please provide your valuable replies.


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