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

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Message-ID: <591D4732-BC3E-4F85-9277-25E049FFF4BA@cisco.com>
Date:   Wed, 7 Nov 2018 18:04:35 +0000
From:   "Nikunj Kela (nkela)" <nkela@...co.com>
To:     David Woodhouse <dwmw2@...radead.org>
CC:     "xe-linux-external(mailer list)" <xe-linux-external@...co.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] jffs2: implement mount option to configure endianness

On 11/7/18, 1:05 AM, "David Woodhouse" <dwmw2@...radead.org> wrote:

    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?

I had tried to use configs to start with via the following patch however I was advised to have a mount option:
http://lists.infradead.org/pipermail/linux-mtd/2018-November/085126.html

Thanks,
-Nikunj