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dm verity: add support for forward error correction

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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: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Sami Tolvanen
2015-12-03 14:26:30 +00:00
committed by Mike Snitzer
parent bb4d73ac5e
commit a739ff3f54
7 changed files with 1071 additions and 9 deletions
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12
drivers/md/Kconfig
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@@ -467,6 +467,18 @@ config DM_VERITY
If unsure, say N.
config DM_VERITY_FEC
bool "Verity forward error correction support"
depends on DM_VERITY
select REED_SOLOMON
select REED_SOLOMON_DEC8
---help---
Add forward error correction support to dm-verity. This option
makes it possible to use pre-generated error correction data to
recover from corrupted blocks.
If unsure, say N.
config DM_SWITCH
tristate "Switch target support (EXPERIMENTAL)"
depends on BLK_DEV_DM