Re: [PATCH v2 13/22] xfs: introduce XFS_FSVERITY_REGION_START constant

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Jan 12, 2026 at 03:51:25PM +0100, Andrey Albershteyn wrote:
> This constant defines location of fsverity metadata in page cache of
> an inode.
> 
> Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
> ---
>  fs/xfs/libxfs/xfs_fs.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
> index 12463ba766..b73458a7c2 100644
> --- a/fs/xfs/libxfs/xfs_fs.h
> +++ b/fs/xfs/libxfs/xfs_fs.h
> @@ -1106,4 +1106,26 @@
>  #define BBTOB(bbs)	((bbs) << BBSHIFT)
>  #endif
>  
> +/* Merkle tree location in page cache. We take memory region from the inode's

Dumb nit: new line after opening the multiline comment.

/*
 * Merkle tree location in page cache...

also, isn't (1U<<53) the location of the Merkle tree ondisk in addition
to its location in the page cache?

That occurs to me, what happens on 32-bit systems where the pagecache
can only address up to 16T of data?  Maybe we just don't allow fsverity
on 32-bit xfs.

> + * address space for Merkle tree.
> + *
> + * At maximum of 8 levels with 128 hashes per block (32 bytes SHA-256) maximum
> + * tree size is ((128^8 − 1)/(128 − 1)) = 567*10^12 blocks. This should fit in 53
> + * bits address space.
> + *
> + * At this Merkle tree size we can cover 295EB large file. This is much larger
> + * than the currently supported file size.
> + *
> + * For sha512 the largest file we can cover ends at 1 << 50 offset, this is also
> + * good.
> + *
> + * The metadata is stored on disk as follows:
> + *
> + *	[merkle tree...][descriptor.............desc_size]
> + *	^ (1 << 53)     ^ (block border)                 ^ (end of the block)
> + *	                ^--------------------------------^
> + *	                Can be FS_VERITY_MAX_DESCRIPTOR_SIZE
> + */
> +#define XFS_FSVERITY_REGION_START (1ULL << 53)

Is this in fsblocks or in bytes?  I think the comment should state that
explicitly.

--D

> +
>  #endif	/* __XFS_FS_H__ */
> 
> -- 
> - Andrey
> 
>