On Tue, Apr 30, 2024 at 11:47:23PM -0700, Christoph Hellwig wrote: > On Mon, Apr 29, 2024 at 08:29:03PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > Now that fsverity tells our merkle tree io functions about what a hash > > of a data block full of zeroes looks like, we can use this information > > to avoid writing out merkle tree blocks for sparse regions of the file. > > For verified gold master images this can save quite a bit of overhead. > > Is this something that fsverity should be doing in a generic way? I don't think it's all that useful for ext4/f2fs because they always write out full merkle tree blocks even if it's the zerohash over and over again. Old kernels aren't going to know how to deal with that. > It feels odd to have XFS behave different from everyone else here, > even if this does feel useful. Do we also need any hash validation > that no one tampered with the metadata and added a new extent, or > is this out of scope for fsverity? If they wrote a new extent with nonzero contents, then the validation will fail, right? If they added a new unwritten extent (or a written one full of zeroes), then the file data hasn't changed and validation would still pass, correct? --D
