linux-ext4 - Re: [PATCH] e2fsck: allow verity files to have initialized blocks past i

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Date:   Tue, 21 Aug 2018 13:41:33 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH] e2fsck: allow verity files to have initialized blocks
 past i_size

On Tue, Aug 21, 2018 at 04:23:52PM -0400, Theodore Y. Ts'o wrote:
> On Tue, Aug 21, 2018 at 10:59:37AM -0700, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@...gle.com>
> > 
> > Since ext4 verity is going to be an RO_COMPAT feature rather than an
> > INCOMPAT one, the on-disk i_size of verity inodes needs to be the data
> > size rather than the full size.  Consequently, verity inodes will have
> > initialized blocks past i_size, containing the Merkle tree and other
> > verity metadata.  So e2fsck must not fix the i_size of such inodes as it
> > normally would.
> > 
> > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> 
> Thanks, applied.
> 
> We should have some tests, in e2fsprogs and/or xfstests that tests
> this.  The work-in-progress verity 9XX xfstests don't seem to have a
> problem with this, probably because we weren't unmounting a file
> system, and then running fsck.  (Since it's a scratch partition,
> the test harness doesn't run fsck after any of the 9XX tests.)
> 
> Thanks for catching this!
> 
> 				- Ted

Actually xfstests does run fsck on the scratch device.  This reason this wasn't
causing problems before is that the ext4 verity kernel patches were leaving the
on-disk i_size as the full size (size of data + verity metadata) rather than
setting it to just the data size.  I actually just changed this today, in order
to match 'verity' being a RO_COMPAT feature, and I've pushed out updates to both
the kernel [1] and xfstests [2] fs-verity patchsets to start using the ext4
feature flag.

So this *is* tested by the work-in-progress xfstests now, though a test could be
added to e2fsprogs too.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=fsverity
[2] https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/xfstests-dev.git/log/?h=fsverity

Note that we also need to decide whether f2fs will set the on-disk i_size to the
data size as well.  Currently I still have it setting i_size to the full size.

- Eric