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

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Message-ID: <4EDEDF44.4000307@oracle.com>
Date:	Wed, 07 Dec 2011 11:36:36 +0800
From:	ANNIE LI <annie.li@...cle.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	"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>,
	"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



>> 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

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