fsverity: support enabling with tree block size < PAGE_SIZE
Make FS_IOC_ENABLE_VERITY support values of fsverity_enable_arg::block_size other than PAGE_SIZE. To make this possible, rework build_merkle_tree(), which was reading data and hash pages from the file and assuming that they were the same thing as "blocks". For reading the data blocks, just replace the direct pagecache access with __kernel_read(), to naturally read one block at a time. (A disadvantage of the above is that we lose the two optimizations of hashing the pagecache pages in-place and forcing the maximum readahead. That shouldn't be very important, though.) The hash block reads are a bit more difficult to handle, as the only way to do them is through fsverity_operations::read_merkle_tree_page(). Instead, let's switch to the single-pass tree construction algorithm that fsverity-utils uses. This eliminates the need to read back any hash blocks while the tree is being built, at the small cost of an extra block-sized memory buffer per Merkle tree level. This is probably what I should have done originally. Taken together, the above two changes result in page-size independent code that is also a bit simpler than what we had before. Signed-off-by:Eric Biggers <ebiggers@google.com> Reviewed-by:
Andrey Albershteyn <aalbersh@redhat.com> Tested-by:
Ojaswin Mujoo <ojaswin@linux.ibm.com> Link: https://lore.kernel.org/r/20221223203638.41293-8-ebiggers@kernel.org
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