linux-kernel - Re: [PATCH] ACPI: Implement overriding of arbitrary ACPI tables via initrd

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Date:	Sat, 24 Mar 2012 15:17:18 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Thomas Renninger <trenn@...e.de>, eric.piel@...mplin-utc.net,
	vojcek@...n.pl, dsdt@...gusch.at, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Lin Ming <ming.m.lin@...el.com>, lenb@...nel.org,
	robert.moore@...el.com, Al Viro <viro@...iv.linux.org.uk>,
	Harald Hoyer <harald@...hat.com>
Subject: Re: [PATCH] ACPI: Implement overriding of arbitrary ACPI tables via
 initrd

On Sat, Mar 24, 2012 at 12:15:59PM -0700, H. Peter Anvin wrote:
> On 03/24/2012 11:42 AM, Konrad Rzeszutek Wilk wrote:
> > 
> > Probably should also have:
> > 		u32 version;
> > 
> > in case we decide to expand this structure in the future, and:
> >> 		u32 type;	/* 1 = file data, 2 = ACPI, 3 = microcode... */
> >> 		u32 length;	/* Length of data object */
> >> 	};
> > 
> > and encapsulate the whole thing in a 4K union?
> > 
> 
> For "version" you'd have to define what happens if you see a version
> number you don't recognize, and why that is in any way better than
> changing the magic number or the type.  It is something that people like
> to throw in without thinking about it, and that is a mistake.

I was thinking of interface version. So the first would be 1, and if
there are extensions (so version 2 for example), it should support 1 and 2.
The idea is to expand past the structure with newer additions without
breaking the binary interface.

> 
> Forcing everything to be page-aligned may be a good idea, although that
> assumes all bootloaders actually align them that way...

Oh, and be 4K.
> 
> > 
> > Perhaps the header should be in big-endian (that is the same as the network
> > byte order, right?) and each sub-type can define its own endian?
> > 
> 
> The content of the encapsulation is its own thing; it will be different
> for different types as most of them already
> 
> 	-hpa
> 
> -- 
> H. Peter Anvin, Intel Open Source Technology Center
> I work for Intel.  I don't speak on their behalf.
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