linux-ext4 - Re: fsverity metadata offset, was: Re: [PATCH v2 0/23] fs-verity support for XFS with post EOF merkle tree

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Message-ID: <20260120073218.GA6757@lst.de>
Date: Tue, 20 Jan 2026 08:32:18 +0100
From: Christoph Hellwig <hch@....de>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Eric Biggers <ebiggers@...nel.org>, Christoph Hellwig <hch@....de>,
	Andrey Albershteyn <aalbersh@...hat.com>,
	Matthew Wilcox <willy@...radead.org>, fsverity@...ts.linux.dev,
	linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	aalbersh@...nel.org, david@...morbit.com, tytso@....edu,
	linux-ext4@...r.kernel.org, jaegeuk@...nel.org, chao@...nel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: fsverity metadata offset, was: Re: [PATCH v2 0/23] fs-verity
 support for XFS with post EOF merkle tree

On Mon, Jan 19, 2026 at 11:58:16AM -0800, Darrick J. Wong wrote:
> > >  a) not all architectures are reasonable.  As Darrick pointed out
> > >     hexagon seems to support page size up to 1MiB.  While I don't know
> > >     if they exist in real life, powerpc supports up to 256kiB pages,
> > >     and I know they are used for real in various embedded settings
> 
> They *did* way back in the day, I worked with some seekrit PPC440s early
> in my career.  I don't know that any of them still exist, but the code
> is still there...

Sorry, I meant I don't really know how real the hexagon large page
sizes are.  I know about the ppcs one personally, too.

> > If we do need to fix this, there are a couple things we could consider
> > doing without changing the on-disk format in ext4 or f2fs: putting the
> > data in the page cache at a different offset than it exists on-disk, or
> > using "small" pages for EOF specifically.
> 
> I'd leave the ondisk offset as-is, but change the pagecache offset to
> roundup(i_size_read(), mapping_max_folio_size_supported()) just to keep
> file data and fsverity metadata completely separate.

Can we find a way to do that in common code and make ext4 and f2fs do
the same?