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

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Message-ID: <291EDFCB1E9E224A99088639C4762022B5988E542E@LONPMAILBOX01.citrite.net>
Date:	Wed, 7 Dec 2011 08:59:54 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	ANNIE LI <annie.li@...cle.com>,
	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>
Subject: RE: [PATCH 1/2] xen/granttable: Support sub-page grants



> -----Original Message-----
> From: ANNIE LI [mailto:annie.li@...cle.com]
> Sent: 07 December 2011 03:36
> To: Ian Campbell
> Cc: xen-devel@...ts.xensource.com; linux-kernel@...r.kernel.org;
> konrad.wilk@...cle.com; jeremy@...p.org; kurt.hackel@...cle.com;
> Paul Durrant
> 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; }
> 


Do you need ops for the ref and non-ref functions? I would have thought you could just have the ref ones since the all the non-ref variants do is allocate and then call the ref variant.

  Paul

> 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