About read-only feature EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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Hi ext4 guys,

Recently I found an image from android (vendor.img) has this RO feature
set, but kernel doesn't support it, thus no easy way to modify it.
(Although I can just modify the underlying block for my purpose, it's
just one line change, I still want a more elegant way).

Thus it can only be mounted RO. So far so good, as from its name, it's
kinda of deduped (BTW, both XFS and Btrfs supports RW mount for
reflinked/deduped fs).

But the problem is, how to create such image?

Man page of mke2fs has no mention of such thing at all, and obviously
for whoever comes up with such "brilliant" way to block users from
modifying things, the "-E unshare_blocks" will just make the image too
large for the device.

Or we must go the Android rabbit hole to find an exotic tool to modify
even one line of a config file?

Thanks,
Qu


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