[RFC] Reed-Solomon Code: Update no_eras to the actual number of errors
From: Aiden Leong
Date: Thu Jun 25 2020 - 00:12:49 EST
Corr and eras_pos are updated to actual correction pattern and erasure
positions, but no_eras is not.
When this library is used to recover lost bytes, we normally memset the
lost trunk of bytes to zero as a placeholder. Unfortunately, if the lost
byte is zero, b[i] is zero too. Without correct no_eras, users won't be
able to determine the valid length of corr and eras_pos.
Signed-off-by: Aiden Leong <aiden.leong@xxxxxxxxx>
---
drivers/md/dm-verity-fec.c | 2 +-
fs/pstore/ram_core.c | 2 +-
include/linux/rslib.h | 4 ++--
lib/reed_solomon/decode_rs.c | 20 ++++++++++++++------
lib/reed_solomon/reed_solomon.c | 4 ++--
lib/reed_solomon/test_rslib.c | 18 ++++++++++++------
6 files changed, 32 insertions(+), 18 deletions(-)
diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c
index fb41b4f23c48..ae8366a50244 100644
--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c
@@ -50,7 +50,7 @@ static int fec_decode_rs8(struct dm_verity *v, struct dm_verity_fec_io *fio,
for (i = 0; i < v->fec->roots; i++)
par[i] = fec[i];
- return decode_rs8(fio->rs, data, par, v->fec->rsn, NULL, neras,
+ return decode_rs8(fio->rs, data, par, v->fec->rsn, NULL, &neras,
fio->erasures, 0, NULL);
}
diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index aa8e0b65ff1a..fcc661a60640 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -115,7 +115,7 @@ static int persistent_ram_decode_rs8(struct persistent_ram_zone *prz,
for (i = 0; i < prz->ecc_info.ecc_size; i++)
prz->ecc_info.par[i] = ecc[i];
- return decode_rs8(prz->rs_decoder, data, prz->ecc_info.par, len,
+ return decode_rs8(prz->rs_decoder, data, prz->ecc_info.par, &len,
NULL, 0, NULL, 0, NULL);
}
diff --git a/include/linux/rslib.h b/include/linux/rslib.h
index 238bb85243d3..80662abc9af7 100644
--- a/include/linux/rslib.h
+++ b/include/linux/rslib.h
@@ -64,7 +64,7 @@ int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
#endif
#ifdef CONFIG_REED_SOLOMON_DEC8
int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
- uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
+ uint16_t *s, int *no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr);
#endif
@@ -75,7 +75,7 @@ int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
#endif
#ifdef CONFIG_REED_SOLOMON_DEC16
int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
- uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
+ uint16_t *s, int *no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr);
#endif
diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
index 805de84ae83d..122bc08eb75f 100644
--- a/lib/reed_solomon/decode_rs.c
+++ b/lib/reed_solomon/decode_rs.c
@@ -24,6 +24,7 @@
int count = 0;
int num_corrected;
uint16_t msk = (uint16_t) rs->nn;
+ int no_eras_orig = no_eras ? *no_eras : 0;
/*
* The decoder buffers are in the rs control struct. They are
@@ -106,11 +107,11 @@
memset(&lambda[1], 0, nroots * sizeof(lambda[0]));
lambda[0] = 1;
- if (no_eras > 0) {
+ if (no_eras_orig > 0) {
/* Init lambda to be the erasure locator polynomial */
lambda[1] = alpha_to[rs_modnn(rs,
prim * (nn - 1 - (eras_pos[0] + pad)))];
- for (i = 1; i < no_eras; i++) {
+ for (i = 1; i < no_eras_orig; i++) {
u = rs_modnn(rs, prim * (nn - 1 - (eras_pos[i] + pad)));
for (j = i + 1; j > 0; j--) {
tmp = index_of[lambda[j - 1]];
@@ -129,8 +130,8 @@
* Begin Berlekamp-Massey algorithm to determine error+erasure
* locator polynomial
*/
- r = no_eras;
- el = no_eras;
+ r = no_eras_orig;
+ el = no_eras_orig;
while (++r <= nroots) { /* r is the step number */
/* Compute discrepancy at the r-th step in poly-form */
discr_r = 0;
@@ -158,8 +159,8 @@
} else
t[i + 1] = lambda[i + 1];
}
- if (2 * el <= r + no_eras - 1) {
- el = r + no_eras - el;
+ if (2 * el <= r + no_eras_orig - 1) {
+ el = r + no_eras_orig - el;
/*
* 2 lines below: B(x) <-- inv(discr_r) *
* lambda(x)
@@ -312,14 +313,21 @@
eras_pos[j++] = loc[i] - pad;
}
}
+ if (no_eras > 0)
+ *no_eras = j;
} else if (data && par) {
/* Apply error to data and parity */
+ j = 0;
for (i = 0; i < count; i++) {
if (loc[i] < (nn - nroots))
data[loc[i] - pad] ^= b[i];
else
par[loc[i] - pad - len] ^= b[i];
+ if (b[i])
+ j++;
}
+ if (no_eras > 0)
+ *no_eras = j;
}
return num_corrected;
diff --git a/lib/reed_solomon/reed_solomon.c b/lib/reed_solomon/reed_solomon.c
index bbc01bad3053..b2c811674c98 100644
--- a/lib/reed_solomon/reed_solomon.c
+++ b/lib/reed_solomon/reed_solomon.c
@@ -359,7 +359,7 @@ EXPORT_SYMBOL_GPL(encode_rs8);
* errors. The count includes errors in the parity.
*/
int decode_rs8(struct rs_control *rsc, uint8_t *data, uint16_t *par, int len,
- uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
+ uint16_t *s, int *no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr)
{
#include "decode_rs.c"
@@ -410,7 +410,7 @@ EXPORT_SYMBOL_GPL(encode_rs16);
* errors. The count includes errors in the parity.
*/
int decode_rs16(struct rs_control *rsc, uint16_t *data, uint16_t *par, int len,
- uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
+ uint16_t *s, int *no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr)
{
#include "decode_rs.c"
diff --git a/lib/reed_solomon/test_rslib.c b/lib/reed_solomon/test_rslib.c
index 4eb29f365ece..b30a4aea8796 100644
--- a/lib/reed_solomon/test_rslib.c
+++ b/lib/reed_solomon/test_rslib.c
@@ -258,7 +258,7 @@ static void compute_syndrome(struct rs_control *rsc, uint16_t *data,
/* Test up to error correction capacity */
static void test_uc(struct rs_control *rs, int len, int errs,
- int eras, int trials, struct estat *stat,
+ int *eras, int trials, struct estat *stat,
struct wspace *ws, int method)
{
int dlen = len - rs->codec->nroots;
@@ -327,8 +327,11 @@ static int ex_rs_helper(struct rs_control *rs, struct wspace *ws,
pr_info(" %s\n", desc[method]);
for (errs = 0; errs <= nroots / 2; errs++)
- for (eras = 0; eras <= nroots - 2 * errs; eras++)
- test_uc(rs, len, errs, eras, trials, &stat, ws, method);
+ for (eras = 0; eras <= nroots - 2 * errs; eras++) {
+ int no_eras = ers;
+
+ test_uc(rs, len, errs, &no_eras, trials, &stat, ws, method);
+ }
if (v >= V_CSUMMARY) {
pr_info(" Decodes wrong: %d / %d\n",
@@ -364,7 +367,7 @@ static int exercise_rs(struct rs_control *rs, struct wspace *ws,
/* Tests for correct behaviour beyond error correction capacity */
static void test_bc(struct rs_control *rs, int len, int errs,
- int eras, int trials, struct bcstat *stat,
+ int *eras, int trials, struct bcstat *stat,
struct wspace *ws)
{
int nroots = rs->codec->nroots;
@@ -420,8 +423,11 @@ static int exercise_rs_bc(struct rs_control *rs, struct wspace *ws,
eras = 0;
cutoff = nroots <= len - errs ? nroots : len - errs;
- for (; eras <= cutoff; eras++)
- test_bc(rs, len, errs, eras, trials, &stat, ws);
+ for (; eras <= cutoff; eras++) {
+ int no_eras = eras;
+
+ test_bc(rs, len, errs, &no_eras, trials, &stat, ws);
+ }
}
if (v >= V_CSUMMARY) {
--
2.25.1