linux-kernel - CONFIG_EXT4_USE_FOR_EXT23: rootfs shows as ext2 instead of ext4

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Message-ID: <4DA48AF4.5080803@teksavvy.com>
Date:	Tue, 12 Apr 2011 13:25:08 -0400
From:	Mark Lord <kernel@...savvy.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Subject: CONFIG_EXT4_USE_FOR_EXT23:  rootfs shows as ext2 instead of ext4

Ted et al.

I've only just noticed this, so I have no idea how long it has been this way.

When I build a kernel with CONFIG_EXT4_USE_FOR_EXT23=y and boot from it,
the ext4 root filesystem shows up as "ext2" mode, rather than "ext4".

This looks very wrong to me, and quite dangerous.

Eg.  I test it by building my own kernel (2.6.38.2), with ext4 built-in,
no initramfs required, and boot:

    root=/dev/sda1 init=/bin/bash
    ...
    $ mount /proc
    $ cat /proc/mounts
    /dev/root / ext2 ro,relatime,barrier=1,data=ordered 0 0

So.. it shows "ext2" instead of "ext4".  That really looks like a bug.
Especially since it appears to be using journaling regardless.

Building the kernel without CONFIG_EXT4_USE_FOR_EXT23
results in a proper "ext4" mount entry in /proc/mounts.

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