linux-kernel - Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed cpio passing

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Message-ID: <500D691C.7010203@zytor.com>
Date:	Mon, 23 Jul 2012 08:09:16 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Renninger <trenn@...e.de>
CC:	linux-kernel@...r.kernel.org, lenb@...nel.org,
	linux-acpi@...r.kernel.org, initramfs@...r.kernel.org,
	bigeasy@...utronix.de, Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH 1/2] init: Introduce early initrd files through uncompressed
 cpio passing

On 07/23/2012 07:40 AM, Thomas Renninger wrote:
> This is another problem and I expect I call:
> early_initrd_find_cpio_data()
> early enough for Fenghua's needs.
> If not, how early exactly is this needed?

We're calling that from arch-specific code before even turning paging 
on.  This has a couple of consequences:

1. ALL STATIC POINTERS ARE FORBIDDEN.  Period.  The code must be able to 
be executed from a nonstandard linear address, and any static pointer 
(like a function pointer) breaks that.

2. Any ideas of doing everything at the same time, or uniform 
architecture, is clearly out the window... we're just barely capable of 
using C at this point at all.

Now, you definitely do have a valid point about being able to iterate 
over multiple files with a common prefix.  We could do that with either 
a callback (where the callback is passed in as an argument), but I think 
it might be nicer to do that as an iterator interface... let me ketch on 
this.

> If (just an example) CPU microcode files get passed via "early initrd",
> the same path could be provided than needed by request_fw().

This will all be obsolete.  request_fw is available way, way, way too late.

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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