linux-kernel - Re: [PATCH v2 1/3] x86/boot: Introduce the kernel

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Message-ID: <20191001114133.xy5nuhepzzixhuh4@tomti.i.net-space.pl>
Date:   Tue, 1 Oct 2019 13:41:33 +0200
From:   Daniel Kiper <daniel.kiper@...cle.com>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, bp@...en8.de, corbet@....net,
        dpsmith@...rtussolutions.com, eric.snowberg@...cle.com,
        kanth.ghatraju@...cle.com, konrad.wilk@...cle.com,
        mingo@...hat.com, ross.philipson@...cle.com, tglx@...utronix.de
Subject: Re: [PATCH v2 1/3] x86/boot: Introduce the kernel_info

On Mon, Sep 30, 2019 at 10:18:43AM -0700, H. Peter Anvin wrote:
> On 2019-09-30 08:01, Daniel Kiper wrote:
> >
> > OK.
> >
> >> field for the entire .kernel_info section, thus ensuring it is a
> >> single self-contained blob.
> >
> > .rodata.kernel_info contains its total size immediately behind the
> > "InfO" header. Do you suggest that we should add the size of
> > .rodata.kernel_info into setup_header too?
> >
>
> No, what I want is a chunked architecture for kernel_info.
>
> That is:
>
> /* Common chunk header */
> struct kernel_info_header {
> 	uint32_t magic;
> 	uint32_t len;
> };
>
> /* Top-level chunk, always first */
> #define KERNEL_INFO_MAGIC 0x45fdbe4f
>
> struct kernel_info {
> 	struct kernel_info_header hdr;
> 	uint32_t total_size;		/* Total size of all chunks */
>
> 	/* Various fixed-sized data objects, OR offsets to other chunks */
> };

OK, so, this is more or less what I had in my v3 patch before sending
this email. So, it looks that I am on good track. Great! Though I am not
sure that we should have magic for chunked objects. If yes could you
explain why? I would just leave len for chunked objects.

> Also "InfO" is a pretty hideous magic. In general, all-ASCII magics have much
> higher risk of collision than *RANDOM* binary numbers. However, for a chunked
> architecture they do have the advantage that they can be used also as a human
> name or file name for the chunk, e.,g. in sysfs, so maybe something like
> "LnuX" or even "LToP" for the top-level chunk might make sense.
>
> How does that sound?

Well, your proposals are more cryptic, especially the second one, than
mine but I tend to agree that more *RANDOM* magics are better. So,
I would choose "LToP" if you decipher it for me. Linux Top?

Daniel