linux-kernel - Re: [PATCH v3 2/2] initramfs: introduce do

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Date:   Fri, 17 May 2019 14:47:31 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Roberto Sassu <roberto.sassu@...wei.com>, viro@...iv.linux.org.uk,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, initramfs@...r.kernel.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
        silviu.vlasceanu@...wei.com, dmitry.kasatkin@...wei.com,
        takondra@...co.com, kamensky@...co.com, arnd@...db.de,
        rob@...dley.net, james.w.mcmechan@...il.com, niveditas98@...il.com
Subject: Re: [PATCH v3 2/2] initramfs: introduce do_readxattrs()

On 5/17/19 2:02 PM, Arvind Sankar wrote:
> On Fri, May 17, 2019 at 01:18:11PM -0700, hpa@...or.com wrote:
>>
>> Ok... I just realized this does not work for a modular initramfs, composed at load time from multiple files, which is a very real problem. Should be easy enough to deal with: instead of one large file, use one companion file per source file, perhaps something like filename..xattrs (suggesting double dots to make it less likely to conflict with a "real" file.) No leading dot, as it makes it more likely that archivers will sort them before the file proper.
> This version of the patch was changed from the previous one exactly to deal with this case --
> it allows for the bootloader to load multiple initramfs archives, each
> with its own .xattr-list file, and to have that work properly.
> Could you elaborate on the issue that you see?
> 

Well, for one thing, how do you define "cpio archive", each with its own
.xattr-list file? Second, that would seem to depend on the ordering, no,
in which case you depend critically on .xattr-list file following the
files, which most archivers won't do.

Either way it seems cleaner to have this per file; especially if/as it
can be done without actually mucking up the format.

I need to run, but I'll post a more detailed explanation of what I did
in a little bit.

	-hpa