On Mon, Dec 17, 2018 at 12:00:39PM -0800, Darrick J. Wong wrote: > FWIW, if I were (hypothetically) working on an xfs implementation, I > likely would have settled on passing a reference to a merkle tree > through a (fd, length) pair, because that allows us plenty of options > on the back end: > > b) we could remap the tree into a new inode fork for merkle trees, or > a) remap it as posteof blocks like ext4/f2fs does, or > c) remap the blocks into the attribute fork as an (unusually large) > extended attribute value. > > If the merkle_fd isn't on the same filesystem as the fd we could at > least use generic_copy_file_range (i.e. page cache copying) to land the > merkle tree wherever we want. I think the fd would have to be on the same fs for this interface to make sense. But it could be an O_TMPFILE one. And given that ext4 already supports a variant of swapext this interface should also work with the existing ext4 on disk format.
