hi list,

Question about grant table. "The Definitive Guide to the Xen Hypervisor,
Ch 4.3"

struct grant_entry {
/* GTF_xxx: various type and flag information. [XEN,GST] */
uint16_t flags;
/* The domain being granted foreign privileges. [GST] */
domid_t domid;
/*
* GTF_permit_access: Frame that @domid is allowed to map and access. [GST]
* GTF_accept_transfer: Frame whose ownership transferred by @domid. [XEN]
*/
uint32_t frame;
};

The book says :

The last two fields in this are quite simple; they identify the domain
to which the rights are granted, and the page frame the entry refers to.
The domain (domid) is always filled in by the domain creating the entry.
If the domain is granting access to one of its own frames, the relevant
frame must be identified by the guest. _If the entry relates to a
transfer, the hypervisor will fill in the frame number after the transfer._

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I want to know what the last sentence means.
If some page is supposed to be transfered to some domain, why the
sending domain fill in the frame number ?
Why does the hypervisor do this ?