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Date:	Tue, 1 Sep 2015 22:46:49 -0700
From:	Raymond Jennings <>
To:	Albino B Neto <>,
	Austin S Hemmelgarn <>
Cc:	Linus Torvalds <>,
	Jan Kara <>, LKML <>,
	"" <>,
	linux-fsdevel <>
Subject: Re: [GIT PULL] Ext3 removal, quota & udf fixes

On 09/01/15 20:30, Albino B Neto wrote:
> 2015-08-31 23:53 GMT-03:00 Theodore Ts'o <>:
>> Yes, you can go back to ext3-only.  In fact, we do *not* automatically
>> upgrade the file system to use ext4-specific features.
>>> So it's not just a "you can use ext4 instead" issue. Can you do that
>>> *without* then forcing an upgrade forever on that partition? I'm not
>>> sure the ext4 people are really even willing to guarantee that kind of
>>> backwards compatibility.
>> Actually, we do guarantee this.  It's considered poor form to
>> automatically change the superblock to add new file system features in
>> a way that would break the ability for the user to roll back to an
>> older kernel.  This isn't just for ext3->ext4, but for new ext4
>> features such as metadata checksumming.  The user has to explicitly
>> enable the feature using "tune2fs -O new_feature /dev/sdXX".
> Yeah!
> 2015-09-01 16:39 GMT-03:00 Austin S Hemmelgarn <>:
>> NO, it is not logical.  A vast majority of Android smartphones in the wild
>> use ext2, as do a very significant portion of embedded systems that don't
>> have room for the few hundred kilobytes of extra code that the ext4 driver
>> has in comparison to ext2.
> Ext2 portion embedded and Ext3 many machines.

So basically the game plan is gutting ext3 because code-dupe with ext4, 
but keep ext2 because ext4 is too big for embedded to outright replace ext2?

Hmm...are there any embedded systems out there that use ext3 and can fit 
its code ext3 but not ext4?

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