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: <5tse47xskuaofuworccgwhyftyymx5xj3mc6opwz7nfxa225u6@uvbk4gc2rktd>
Date: Tue, 20 Jan 2026 12:44:19 +0100
From: Andrey Albershteyn <aalbersh@...hat.com>
To: Christoph Hellwig <hch@....de>
Cc: "Darrick J. Wong" <djwong@...nel.org>, 
	Eric Biggers <ebiggers@...nel.org>, 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 2026-01-20 08:32:18, Christoph Hellwig wrote:
> 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?

hmm I don't see what else we could do except providing common offset
and then use it to map blocks

loff_t fsverity_metadata_offset(struct inode *inode)
{
	return roundup(i_size_read(), mapping_max_folio_size_supported());
}

-- 
- Andrey