linux-kernel - Re: [PATCH RFC REPOST 1/2] paravirt: refactor struct paravirt_ops into smaller pv_*

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Message-ID: <470D13CA.3000202@goop.org>
Date:	Wed, 10 Oct 2007 11:02:50 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>, Zachary Amsden <zach@...are.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Avi Kivity <avi@...ranet.com>,
	Glauber de Oliveira Costa <glommer@...il.com>,
	"Nakajima, Jun" <jun.nakajima@...el.com>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>
Subject: Re: [PATCH RFC REPOST 1/2] paravirt: refactor struct paravirt_ops
 into smaller pv_*_ops

Huh, thought I did a more complete reply to this.  Must have farted on it.

Rusty Russell wrote:
> Thanks Jeremy, I've actually taken time to finally review this in detail (I'm 
> assuming you'll refactor as necessary after the x86 arch merger).
>   

Yep.

>> +struct paravirt_ops paravirt_ops;
>> +
>>     
>
> Do you actually need to define this?  See below...
>
>   
>> +DEF_NATIVE(, ud2a, "ud2a");
>>     
>
> Hmm, that's ugly.  It was ugly before, but it's uglier now.  Maybe just 
> use "unsigned char ud2a[] = { 0x0f, 0x0b };" in paravirt_patch_default?
>   

Yeah, its not pretty.  I'll have another go.

>>  }
>>
>>  struct paravirt_ops paravirt_ops = {
>>     
> ...
>   
>> +	.pv_info = {
>> +		.name = "bare hardware",
>> +		.paravirt_enabled = 0,
>> +		.kernel_rpl = 0,
>> +		.shared_kernel_pmd = 1,	/* Only used when CONFIG_X86_PAE is set */
>> +	},
>>     
>
> This is the bit I don't get.  Why not just declare struct pv_info pvinfo, etc, 
> and use the declaration of struct paravirt_ops to get your unique 
> offset-based identifiers for patching?
>   

Given an op id number in .parainstructions, the patching code needs to
be able to index into something to get the corresponding function
pointer.  If each pv_* structure is its own little unrelated structure,
then the id has to be a <structure, id> tuple, which just complicates
things.  If I pack them all into a single structure then it becomes a
simple offset calculation.

That said, there's no need for pv_info to be in that structure, since it
contains no function pointers.  I'll move it out.

    J
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