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Date: Sat, 24 Mar 2012 14:42:38 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Renninger <trenn@suse.de>, eric.piel@tremplin-utc.net,
        vojcek@tlen.pl, dsdt@gaugusch.at, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Lin Ming <ming.m.lin@intel.com>, lenb@kernel.org,
        robert.moore@intel.com, Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH] ACPI: Implement overriding of arbitrary ACPI tables via
 initrd
Message-ID: <20120324184238.GB13978@phenom.dumpdata.com>
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> 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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