linux-ext4 - Re: [PATCH v2 00/23] fs-verity support for XFS

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Date:   Wed, 12 Apr 2023 05:42:07 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Andrey Albershteyn <aalbersh@...hat.com>, djwong@...nel.org,
        dchinner@...hat.com, linux-xfs@...r.kernel.org,
        fsverity@...ts.linux.dev, rpeterso@...hat.com, agruenba@...hat.com,
        xiang@...nel.org, chao@...nel.org,
        damien.lemoal@...nsource.wdc.com, jth@...nel.org,
        linux-erofs@...ts.ozlabs.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        cluster-devel@...hat.com
Subject: Re: [PATCH v2 00/23] fs-verity support for XFS

On Wed, Apr 12, 2023 at 01:18:26PM +1000, Dave Chinner wrote:
> Right. It's not entirely simple to store metadata on disk beyond EOF
> in XFS because of all the assumptions throughout the IO path and
> allocator interfaces that it can allocate space beyond EOF at will
> and something else will clean it up later if it is not needed. This
> impacts on truncate, delayed allocation, writeback, IO completion,
> EOF block removal on file close, background garbage collection,
> ENOSPC/EDQUOT driven space freeing, etc.  Some of these things cross
> over into iomap infrastructure, too.

To me that actually makes it easier to support the metadata beyond
i_size.  Remember that the file is immutable after add fsverity
hash is added.  So basically we just need to skip freeing the
eofblocks if that flag is set.