[RFC] Directly mapped xattr data & fs-verity

[Andrey Albershteyn <aalbersh@redhat.com>]

Hi all,

This is a bit different version of fsverity for XFS from one Darrick sent last
time.

This is mostly a half-baked prototype, sending this out to get
feedback/suggesting/discuss on a design. If you think this approach would be
fine and I can go further with polishing it.

I haven't done anything to repair/scrub yet, haven't tested how old xattr leaf
would work with this changes, and fsverity doesn't work with block size != page
size yet...

The reasoning for iomap interface is that it could possibly be used for other
page cache related processing like fscrypt, compression. Cutting a few more
regions for those.

The attributes design is well described in design doc.

This patchset consists of four parts:
1. Design document which describes directly mappped xattr data (dxattr) and how
   fsverity uses it
2. Patchset with iomap_read_region()/iomap_write_region() interface to write
   beyond EOF
3. Patchset implementing dxattr interface
4. Patchset implementing fsverity using dxattr. Using a xattr per merkle tree
   block, not using da tree address space.

Thanks
Andrey

-- 
2.47.0