do_div was replaced with div64_u64 at some point, causing a bug with
block calculation due to incompatible semantics of the two functions.
Signed-off-by: NSami Tolvanen <samitolvanen@google.com>
Fixes: a739ff3f ("dm verity: add support for forward error correction")
Cc: stable@vger.kernel.org # v4.5+
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

Request-based DM will also make use of per_bio_data_size.
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

If ignore_zero_blocks is enabled dm-verity will return zeroes for blocks
matching a zero hash without validating the content.
Signed-off-by: NSami Tolvanen <samitolvanen@google.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

Add support for correcting corrupted blocks using Reed-Solomon.

This code uses RS(255, N) interleaved across data and hash
blocks. Each error-correcting block covers N bytes evenly
distributed across the combined total data, so that each byte is a
maximum distance away from the others. This makes it possible to
recover from several consecutive corrupted blocks with relatively
small space overhead.

In addition, using verity hashes to locate erasures nearly doubles
the effectiveness of error correction. Being able to detect
corrupted blocks also improves performance, because only corrupted
blocks need to corrected.

For a 2 GiB partition, RS(255, 253) (two parity bytes for each
253-byte block) can correct up to 16 MiB of consecutive corrupted
blocks if erasures can be located, and 8 MiB if they cannot, with
16 MiB space overhead.
Signed-off-by: NSami Tolvanen <samitolvanen@google.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>