"RS(n, k)" is by far the most common and standard notation for describing Reed-Solomon codes. Each RS codeword consists of 'n' symbols, divided into 'k' message symbols and 'n - k' parity symbols. 'n - k' is also the number of roots of the generator polynomial.
dm-verity uses "RS(M, N)" instead. I haven't been able to find any other source that uses this convention. This quirk makes the code harder to understand than necessary, especially due to dm-verity's 'N' meaning something different from the standard 'n'. Therefore, update dm-verity-fec.c and dm-verity-fec.h to use the standard parameter names. No functional changes. Signed-off-by: Eric Biggers <[email protected]> --- drivers/md/dm-verity-fec.c | 30 +++++++++++++++--------------- drivers/md/dm-verity-fec.h | 8 ++++---- 2 files changed, 19 insertions(+), 19 deletions(-) diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c index c5f97a49e5b79..8e9482a6df4a1 100644 --- a/drivers/md/dm-verity-fec.c +++ b/drivers/md/dm-verity-fec.c @@ -27,11 +27,11 @@ static inline unsigned int fec_max_nbufs(struct dm_verity *v) */ static inline u64 fec_interleave(struct dm_verity *v, u64 offset) { u32 mod; - mod = do_div(offset, v->fec->rsn); + mod = do_div(offset, v->fec->rs_k); return offset + mod * (v->fec->rounds << v->data_dev_block_bits); } /* Loop over each allocated buffer. */ #define fec_for_each_buffer(io, __i) \ @@ -48,11 +48,11 @@ static inline u64 fec_interleave(struct dm_verity *v, u64 offset) */ static inline u8 *fec_buffer_rs_block(struct dm_verity *v, struct dm_verity_fec_io *fio, unsigned int i, unsigned int j) { - return &fio->bufs[i][j * v->fec->rsn]; + return &fio->bufs[i][j * v->fec->rs_k]; } /* * Return an index to the current RS block when called inside * fec_for_each_buffer_rs_block. @@ -127,11 +127,11 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_io *io, for (; j < v->fec->roots; j++) par_buf[j] = par[parity_pos++]; } /* Decode an RS block using Reed-Solomon */ - res = decode_rs8(fio->rs, block, par_buf, v->fec->rsn, + res = decode_rs8(fio->rs, block, par_buf, v->fec->rs_k, NULL, neras, fio->erasures, 0, NULL); if (res < 0) { r = res; goto error; } @@ -195,19 +195,19 @@ static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io, if (WARN_ON(v->digest_size > sizeof(want_digest))) return -EINVAL; /* - * read each of the rsn data blocks that are part of the RS block, and + * read each of the rs_k data blocks that are part of the RS block, and * interleave contents to available bufs */ - for (i = 0; i < v->fec->rsn; i++) { - ileaved = fec_interleave(v, rsb * v->fec->rsn + i); + for (i = 0; i < v->fec->rs_k; i++) { + ileaved = fec_interleave(v, rsb * v->fec->rs_k + i); /* * target is the data block we want to correct, target_index is - * the index of this block within the rsn RS blocks + * the index of this block within the rs_k RS blocks */ if (ileaved == target) target_index = i; block = ileaved >> v->data_dev_block_bits; @@ -320,11 +320,11 @@ static struct dm_verity_fec_io *fec_alloc_and_init_io(struct dm_verity *v) static void fec_init_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio) { unsigned int n; fec_for_each_buffer(fio, n) - memset(fio->bufs[n], 0, v->fec->rsn << DM_VERITY_FEC_BUF_RS_BITS); + memset(fio->bufs[n], 0, v->fec->rs_k << DM_VERITY_FEC_BUF_RS_BITS); memset(fio->erasures, 0, sizeof(fio->erasures)); } /* @@ -392,16 +392,16 @@ int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io, if (type == DM_VERITY_BLOCK_TYPE_METADATA) block = block - v->hash_start + v->data_blocks; /* - * For RS(M, N), the continuous FEC data is divided into blocks of N - * bytes. Since block size may not be divisible by N, the last block + * For RS(n, k), the continuous FEC data is divided into blocks of k + * bytes. Since block size may not be divisible by k, the last block * is zero padded when decoding. * - * Each byte of the block is covered by a different RS(M, N) code, - * and each code is interleaved over N blocks to make it less likely + * Each byte of the block is covered by a different RS(n, k) code, + * and each code is interleaved over k blocks to make it less likely * that bursty corruption will leave us in unrecoverable state. */ offset = block << v->data_dev_block_bits; res = div64_u64(offset, v->fec->rounds << v->data_dev_block_bits); @@ -648,19 +648,19 @@ int verity_fec_ctr(struct dm_verity *v) if (!f->roots) { ti->error = "Missing " DM_VERITY_OPT_FEC_ROOTS; return -EINVAL; } - f->rsn = DM_VERITY_FEC_RSM - f->roots; + f->rs_k = DM_VERITY_FEC_RS_N - f->roots; if (!f->blocks) { ti->error = "Missing " DM_VERITY_OPT_FEC_BLOCKS; return -EINVAL; } f->rounds = f->blocks; - if (sector_div(f->rounds, f->rsn)) + if (sector_div(f->rounds, f->rs_k)) f->rounds++; /* * Due to optional metadata, f->blocks can be larger than * data_blocks and hash_blocks combined. @@ -728,11 +728,11 @@ int verity_fec_ctr(struct dm_verity *v) ti->error = "Cannot allocate RS pool"; return ret; } f->cache = kmem_cache_create("dm_verity_fec_buffers", - f->rsn << DM_VERITY_FEC_BUF_RS_BITS, + f->rs_k << DM_VERITY_FEC_BUF_RS_BITS, 0, 0, NULL); if (!f->cache) { ti->error = "Cannot create FEC buffer cache"; return -ENOMEM; } diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h index d8d0e81da2701..5afa93f2f1fc7 100644 --- a/drivers/md/dm-verity-fec.h +++ b/drivers/md/dm-verity-fec.h @@ -9,12 +9,12 @@ #define DM_VERITY_FEC_H #include "dm-verity.h" #include <linux/rslib.h> -/* Reed-Solomon(M, N) parameters */ -#define DM_VERITY_FEC_RSM 255 +/* Reed-Solomon(n, k) parameters */ +#define DM_VERITY_FEC_RS_N 255 #define DM_VERITY_FEC_MIN_ROOTS 2 /* RS(255, 253): ~0.8% space overhead */ #define DM_VERITY_FEC_MAX_ROOTS 24 /* RS(255, 231): ~10% space overhead */ /* buffers for deinterleaving and decoding */ #define DM_VERITY_FEC_BUF_RS_BITS 4 /* 1 << RS blocks per buffer */ @@ -32,12 +32,12 @@ struct dm_verity_fec { size_t io_size; /* IO size for roots */ sector_t start; /* parity data start in blocks */ sector_t blocks; /* number of blocks covered */ sector_t rounds; /* number of interleaving rounds */ sector_t hash_blocks; /* blocks covered after v->hash_start */ - unsigned char roots; /* number of parity bytes, M-N of RS(M, N) */ - unsigned char rsn; /* N of RS(M, N) */ + unsigned char roots; /* parity bytes per RS codeword, n-k of RS(n, k) */ + unsigned char rs_k; /* message bytes per RS codeword, k of RS(n, k) */ mempool_t fio_pool; /* mempool for dm_verity_fec_io */ mempool_t rs_pool; /* mempool for fio->rs */ mempool_t prealloc_pool; /* mempool for preallocated buffers */ mempool_t output_pool; /* mempool for output */ struct kmem_cache *cache; /* cache for buffers */ -- 2.52.0
