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

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Date:	Sat, 24 Mar 2012 14:42:38 -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>
Subject: Re: [PATCH] ACPI: Implement overriding of arbitrary ACPI tables via
 initrd

> 2. We create a new simple header (just a magic number, an identifier
>    for the type of data, and a length) for each of the early-initrd
>    objects:
> 
> 	struct early_initrd_header {
> 		u64 magic;	/* 0xa5a46ce422d8f5a1 */

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?

> 
>    XXX: Should we make this a defined endianness (presumably
>    bigendian), or use host-endianness?  I would guess the former might
>    be better...

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 sub-types could be:
	struct microcode_type {
		u64	magic;
		u32	version;
#define BIG_ENDIAN	1<<1
#define LITTLE_ENDIAN	1<<2
		u32	flags;
	}

and that could be attached to the end of the 'early_initrd_header' ?

> 
> Either of these allow one piece of code to quickly bypass bits that
> doesn't belong to it.
> 
> Thoughts?
> 
> 	-hpa
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