Xen devel - Jun 2011 - Question on struct grant table hypercall

Hello All,


I am calling the hypercall to map the grant table on a HVM domain, on
the code I have the cmd and struct gnttab_setup_table required to call
the hypercall, yet on the struct you have XEN_GUEST_HANDLE as a type
to a list of frames, my environment does not include the whole of xen,
I have to include manually all the necessary structs and global
variables needed. But the XEN_GUEST_HANDLE gives me an error, can I
substitute the type with a simple array?

This is the code I am referring:

//This code is slightly modified.
/*
 * GNTTABOP_setup_table: Set up a grant table for <dom> comprising at
least
 * <nr_frames> pages. The frame addresses are written to the
<frame_list>.
 * Only <nr_frames> addresses are written, even if the table is larger.
 * NOTES:
 *  1. <dom> may be specified as DOMID_SELF.
 *  2. Only a sufficiently-privileged domain may specify <dom> !=
DOMID_SELF.
 *  3. Xen may not support more than a single grant-table page per domain.
 */
#define GNTTABOP_setup_table          2
struct gnttab_setup_table {
    /* IN parameters. */
    u32  dom;
    u32 nr_frames;
    /* OUT parameters. */
    u16  status;              /* GNTST_* */
    //??????????????XEN_GUEST_HANDLE(ulong) frame_list;
};
typedef struct gnttab_setup_table gnttab_setup_table_t;



Thanks for the help,

Daniel

-- 
+-=====---------------------------+
| +---------------------------------+ | This space intentionally blank
for notetaking.
| |   | Daniel Castro,                |
| |   | Consultant/Programmer.|
| |   | U Andes                         |
+-------------------------------------+

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On Tue, 2011-06-28 at 01:38 +0100, Daniel Castro wrote:
> Hello All,
> 
> 
> I am calling the hypercall to map the grant table on a HVM domain, on
> the code I have the cmd and struct gnttab_setup_table required to call
> the hypercall, yet on the struct you have XEN_GUEST_HANDLE as a type
> to a list of frames, my environment does not include the whole of xen,
> I have to include manually all the necessary structs and global
> variables needed. But the XEN_GUEST_HANDLE gives me an error, can I
> substitute the type with a simple array?
XEN_GUEST_HANDLE is a wrapper for a pointer rather than an array. IIRC
it was originally introduced to encapsulate some oddities of the
guest-pointer on the PPC architecture. These days I think the hypervisor
only uses to enforce alignment constraints on pointers. The tools also
use it to try and enforce type-safety for these pointers when hypercalls
are made from userspace (since the pointers need to be to memory which
is safe to use as a hypercall argument).

Although in principal you could replace the guest handle with a suitably
aligned pointer definition I think it would be wise to pull in the
necessary macros. They are defined in xen/include/public/arch-x86/xen.h.

You want the version corresponding to "__XEN_INTERFACE_VERSION__
>0x00030201". think you can also ignore the bits related to
XEN_GUEST_HANDLE_64 since they are for control domain use only. (IOW you
can ignore the override in xen/include/public/arch-x86/xen-x86_32.h).

You will also want some of the (__)DEFINE_XEN_GUEST_HANDLE calls from
xen/include/public/xen.h to define the baseline types you need. e.g.
your gnttab example below will require the
"__DEFINE_XEN_GUEST_HANDLE(ulong, unsigned long);" so that
XEN_GUEST_HANDLE(ulong) means something.

Ian.
> 
> This is the code I am referring:
> 
> //This code is slightly modified.
> /*
>  * GNTTABOP_setup_table: Set up a grant table for <dom> comprising at
least
>  * <nr_frames> pages. The frame addresses are written to the
<frame_list>.
>  * Only <nr_frames> addresses are written, even if the table is
larger.
>  * NOTES:
>  *  1. <dom> may be specified as DOMID_SELF.
>  *  2. Only a sufficiently-privileged domain may specify <dom> !=
DOMID_SELF.
>  *  3. Xen may not support more than a single grant-table page per domain.
>  */
> #define GNTTABOP_setup_table          2
> struct gnttab_setup_table {
>     /* IN parameters. */
>     u32  dom;
>     u32 nr_frames;
>     /* OUT parameters. */
>     u16  status;              /* GNTST_* */
>     //??????????????XEN_GUEST_HANDLE(ulong) frame_list;
> };
> typedef struct gnttab_setup_table gnttab_setup_table_t;
> 
> 
> 
> Thanks for the help,
> 
> Daniel
> 


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