linux-kernel - Re: [RFC][PATCH 6/9] gen_initramfs

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Date:	Tue, 13 Jan 2015 22:34:14 -0600
From:	Rob Landley <rob@...dley.net>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
CC:	Josh Boyer <jwboyer@...oraproject.org>,
	initramfs <initramfs@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-ima-devel@...ts.sourceforge.net,
	linux-security-module <linux-security-module@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Fionnuala Gunter <fin@...ux.vnet.ibm.com>,
	"casey.schaufler" <casey.schaufler@...el.com>,
	Paul Moore <pmoore@...hat.com>
Subject: Re: [RFC][PATCH 6/9] gen_initramfs_list.sh: include xattrs



On 01/13/2015 09:23 PM, Mimi Zohar wrote:
> On Tue, 2015-01-13 at 15:42 -0600, Rob Landley wrote: 
>>> 4 bytes enough?
> 
>> Eh, as long as we're breaking compatibility anyway, we might as well
>> extend the file size. It's gzipped so the extra run of consecutive
>> zeroes isn't really an issue, and if tmpfs is going to support 64 bit
>> file sizes the thing that's populating them should to just to match.
>> (You can already have memory bigger than 4g. Some crazy person is going
>> to put a squashfs in tmpfs and loopback mount it, or have a giant video
>> there, or... Bootloaders being able to cope with this is not my problem. :)
> 
>> Probably having the new fields at the end (and gluing them to the
>> earlier ones) makes more sense than having variable sized fields? I
>> don't have a strong opinion either way.
> 
> The current file data size header field is a 8 character hexidecimal
> string, which is long enough to store 4g (0xFFFFFFFF).

The current header fields are all 32 bits, yes. To get a 64 bit field
we'd have to add a second 32 bit field and add it <<32 to the original
one, or else have the header fields be of varying sizes. That was the
"adding a new one to the end" thing mentioned above.

Then again if we add a new field right before the previous size then the
"treat it as 64 bits vs 2 32 bit ones" is an implementation detail
anyway. And for the moment we can just have it be padding that
compresses away and wait for an actual >4g file.

Unless you think nobody will ever need an archive member >4g in
initramfs, even though servers with ~256g are reasonably common today
already?

Rob
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