Re: [PATCH 1/2] xen/granttable: Support sub-page grants

[ANNIE LI <annie.li@oracle.com>]

>> Returning -Esomething might be less drastic? ENOSYS perhaps?
> Yeah, BUG_ON shouldn't be used for API misuse unless there's absolutely
> no other way to handle it.
OK, will change it, thanks.
>>> +	gnttab_shared.v2[ref].sub_page.frame = frame;
>>> +	gnttab_shared.v2[ref].sub_page.page_off = page_off;
>>> +	gnttab_shared.v2[ref].sub_page.length = length;
>>> +	gnttab_shared.v2[ref].hdr.domid = domid;
>>> +	wmb();
>>> +	gnttab_shared.v2[ref].hdr.flags =
>>> +				GTF_permit_access | GTF_sub_page | flags;
>>> +}
>>> +EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref_subpage_v2);
>>> +
>>> +bool gnttab_subpage_trans_grants_available(void)
>>> +{
>>> +	return grant_table_version == 2;
>>> +}
>> It's not clear this adds anything over and above letting the user query
>> the grant table version. It's hard to tell since there are no users
>> presented here though. Perhaps separate subpage and transitive functions
>> would be cleaner?
> Well, in general, specifically testing for features rather than
> interface versions is better.
Ok, will split it into 2 functions and check the function pointer 
instead of grant table version, thanks.

Thanks
Annie