On 2015-09-02 01:46, Raymond Jennings wrote:

On 09/01/15 20:30, Albino B Neto wrote:

quoted

2015-08-31 23:53 GMT-03:00 Theodore Ts'o [off-list ref]:

quoted

Yes, you can go back to ext3-only.  In fact, we do *not* automatically
upgrade the file system to use ext4-specific features.

quoted

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 [off-list ref]:

quoted

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.