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

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Date:	Wed, 07 Dec 2011 11:36:14 +0800
From:	ANNIE LI <annie.li@...cle.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"kurt.hackel@...cle.com" <kurt.hackel@...cle.com>,
	Paul Durrant <Paul.Durrant@...rix.com>
Subject: Re: [PATCH 1/2] xen/granttable: Support sub-page grants

Thanks for your reviewing, Ian.
>>   EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);
>>
>> +int gnttab_grant_foreign_access_subpage_v2(domid_t domid, unsigned long frame,
>> +					   int flags, unsigned page_off,
>> +					   unsigned length)
> Please drop the v2 suffixes on the public functions.
OK, the initial interface is without v2 suffixes. It was added in order 
to reminder user the interfaces are only available for grant table v2.
But I am fine to remove it, and following ops fn pointers are better.
> Any reason not to route these via the ops table for consistency with all
> the other ops? Then your availability check becomes a test for NULL fn
> pointer rather than a specific version.
Ok, it is good.
How about following implements?

gnttab_v1_ops = {
  ...
.access_subpage = NULL;
.access_ref_subpage = NULL;
.access_trans = NULL;
.access_ref_trans = NULL;
}

gnttab_v2_ops = {
  ...
.access_subpage = access_subpage_v2;
.access_ref_subpage = access_ref_subpage_v2;
.access_trans = access_trans_v2;
.access_ref_trans = access_ref_trans_v2;
}

gnttab_request_version()
{
.....
    if(v2)
       gnttab_interface = &gnttab_v2_ops;
    else
       gnttab_interface = &gnttab_v1_ops;
.....
}

int gnttab_grant_foreign_access_subpage()
{
       if(gnttab_interface->access_subpage != NULL)
             return gnttab_interface->access_subpage;
       return Esomething;
}

Same operations for access_ref_subpage, access_trans and access_ref_trans.

bool gnttab_subpage_available()
{
      return (gnttab_interface->access_subpage != NULL);
}

bool gnttab_subpage_available()
{
      return (gnttab_interface->access_trans != NULL);
}

Thanks
Annie
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