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Date:	Wed, 2 Sep 2015 09:28:37 -0400
From:	Austin S Hemmelgarn <ahferroin7@...il.com>
To:	Raymond Jennings <shentino@...il.com>,
	Albino B Neto <bino@...eup.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [GIT PULL] Ext3 removal, quota & udf fixes

On 2015-09-02 01:46, Raymond Jennings wrote:
> On 09/01/15 20:30, Albino B Neto wrote:
>> 2015-08-31 23:53 GMT-03:00 Theodore Ts'o <tytso@....edu>:
>>> 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 <ahferroin7@...il.com>:
>>> 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?
Probably, but I don't know of any myself.  TBH, the systems that use 
ext2 because of space savings are usually ones with less than 64M of 
RAM, which is becoming a smaller and smaller market share.



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