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This is an microsd ext4 card on a rooted Android, where I want to use

busybox chattr  -R +u /mypath

I know what +u means but does anyone have an idea about how the undo option is implemented for ext4 and specifically in case my hardware to what extent undo will let me in datarecovery. If I use extundelete & ext4magic would these get back my data in case it's deleted by the app ?

corollary to that if : -- ext4 does honor +u and other extended attributes any mount level option that will gimme a good chance of recovery in case of deletion ? -- what file system then does +u work with after all chattr is a linux / unix command there is a mention

ext_attr This feature enables the use of extended attributes. This feature is supported by ext2, ext3, and ext4. here I wondered if that op mount activate the +u attribute

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As indicated in man chattr:

The 'c', 's', and 'u' attributes are not honored by the ext2, ext3, and ext4 file systems as implemented in the current mainline Linux kernels.

The u attribute has no effect on Ext4, and won’t help with data recovery. As far as I can tell no file system supports this attribute on Linux (look for UNRM_FL in the source code; it is referenced in a number of file systems but those references aren’t used anywhere).

That doesn’t affect extundelete and ext4magic; you can still attempt recovery with those, with the usual caveats (in particular, they haven’t been updated in a long while, so I don’t know if they support all the features currently in Ext4).

Extended attributes are a different thing entirely, and enabling them on mount won’t add support for the u attribute. See man 5 attr for details.

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