linux-kernel - Re: [PATCH] jffs2: implement mount option to configure endianness

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Date:   Wed, 07 Nov 2018 10:05:38 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Nikunj Kela <nkela@...co.com>
Cc:     xe-linux-external@...co.com, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] jffs2: implement mount option to configure endianness

On Tue, 2018-11-06 at 13:49 -0800, Nikunj Kela wrote:
> This patch allows the endianness of the JFSS2 filesystem to be
> specified by mount option 'force_endian=big|little|native'. If
> endianness is not specified, it defaults to 'native' endianness
> thus retaining the existing behavior.
> 
> Some architectures benefit from having a single known endianness
> of JFFS2 filesystem (for data, not executables) independent of the
> endianness of the processor (ARM processors can be switched to either
> endianness at run-time).
> 
> We have boards that are shipped with BE jffs2 and BE kernel. We are
> now migrating to LE kernel. This mount option helps us in mounting
> BE jffs2 on LE kernel.

Thanks for implementing this. JFFS2 has often been very sensitive to
performance at mount time — I'd love to see how this affects the time
taken to mount a large file system. If it's significant, we may want a
config option to make this conditional?

Also, perhaps we should improve the behaviour when the user
accidentally tries to mount a wrong-endian file system. If we can't
just make it autodetect and use the "correct" endianness, perhaps we
should at least printk a message suggesting that the user try again
with the other endianness?

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