On Mon, Oct 05, 2020 at 07:51:10PM -0700, Darrick J. Wong wrote:

quoted

quoted

Could /somebody/ please document the ondisk format changes that are
associated with this feature?

I pretty much had to sort it out by looking at a combination of
e2fsprogs and the kernel, and a lot of experimentation, until I ended up
with something that the kernel was completely happy with without a
single complaint.

I'd be happy to write up a summary of the format.

Seems like a good idea, particularly since you're asking for a format
change that requires kernel support and the ondisk format documentation
lives under Documentation/.  That said...

quoted

If you set up the rest of the metadata consistently with it (for
instance, 0 free blocks and 0 free inodes), you'll only get a single
complaint, from the e2fsck equivalent of block_validity. See
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=956509 for details on
that;

...Ted shot down this whole thing six months ago.

The Debian bug database is /not/ the designated forum to discuss changes
to the ondisk format; linux-ext4 is.

What Josh is proposing I'm pretty sure would also break "e2fsck -E
unshare_blocks", so that's another reason not to accept this as a
valid format change.

As far as I'm concerned, contrib/e2fsdroid is the canonical definition
of how to create valid file systems with shared_blocks.

					- Ted