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Merge branch 'core-rslib-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Browse source 
Pull Reed-Solomon library updates from Thomas Gleixner:
 "A cleanup and fixes series from Ferdinand Blomqvist who analyzed the
  original Reed-Solomon library from Phil Karn on which the kernel
  implementation is based on.

  This comes with a test module which verifies all the various corner
  cases for correctness"

* 'core-rslib-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rslib: Make some functions static
  rslib: Fix remaining decoder flaws
  rslib: Update documentation
  rslib: Fix handling of of caller provided syndrome
  rslib: decode_rs: Code cleanup
  rslib: decode_rs: Fix length parameter check
  rslib: Fix decoding of shortened codes
  rslib: Add tests for the encoder and decoder
This commit is contained in:
Linus Torvalds 2019-07-08 10:36:07 -07:00
commit 568521d058
5 changed files with 625 additions and 36 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
lib/Kconfig.debug
View file

@ -1754,6 +1754,18 @@ config RBTREE_TEST
A benchmark measuring the performance of the rbtree library.
Also includes rbtree invariant checks.
config REED_SOLOMON_TEST
tristate "Reed-Solomon library test"
depends on DEBUG_KERNEL || m
select REED_SOLOMON
select REED_SOLOMON_ENC16
select REED_SOLOMON_DEC16
help
This option enables the self-test function of rslib at boot,
or at module load time.
If unsure, say N.
config INTERVAL_TREE_TEST
tristate "Interval tree test"
depends on DEBUG_KERNEL

2
lib/reed_solomon/Makefile
View file

@ -4,4 +4,4 @@
#
obj-$(CONFIG_REED_SOLOMON) += reed_solomon.o
obj-$(CONFIG_REED_SOLOMON_TEST) += test_rslib.o

117
lib/reed_solomon/decode_rs.c
View file

@ -22,6 +22,7 @@
uint16_t *index_of = rs->index_of;
uint16_t u, q, tmp, num1, num2, den, discr_r, syn_error;
int count = 0;
int num_corrected;
uint16_t msk = (uint16_t) rs->nn;
/*
@ -39,11 +40,21 @@
/* Check length parameter for validity */
pad = nn - nroots - len;
BUG_ON(pad < 0 || pad >= nn);
BUG_ON(pad < 0 || pad >= nn - nroots);
/* Does the caller provide the syndrome ? */
if (s != NULL)
goto decode;
if (s != NULL) {
for (i = 0; i < nroots; i++) {
/* The syndrome is in index form,
* so nn represents zero
*/
if (s[i] != nn)
goto decode;
}
/* syndrome is zero, no errors to correct */
return 0;
}
/* form the syndromes; i.e., evaluate data(x) at roots of
* g(x) */
@ -88,8 +99,7 @@
/* if syndrome is zero, data[] is a codeword and there are no
* errors to correct. So return data[] unmodified
*/
count = 0;
goto finish;
return 0;
}
decode:
@ -99,9 +109,9 @@
if (no_eras > 0) {
/* Init lambda to be the erasure locator polynomial */
lambda[1] = alpha_to[rs_modnn(rs,
prim * (nn - 1 - eras_pos[0]))];
prim * (nn - 1 - (eras_pos[0] + pad)))];
for (i = 1; i < no_eras; i++) {
u = rs_modnn(rs, prim * (nn - 1 - eras_pos[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]];
if (tmp != nn) {
@ -175,6 +185,15 @@
if (lambda[i] != nn)
deg_lambda = i;
}
if (deg_lambda == 0) {
/*
* deg(lambda) is zero even though the syndrome is non-zero
* => uncorrectable error detected
*/
return -EBADMSG;
}
/* Find roots of error+erasure locator polynomial by Chien search */
memcpy(&reg[1], &lambda[1], nroots * sizeof(reg[0]));
count = 0; /* Number of roots of lambda(x) */
@ -188,6 +207,12 @@
}
if (q != 0)
continue; /* Not a root */
if (k < pad) {
/* Impossible error location. Uncorrectable error. */
return -EBADMSG;
}
/* store root (index-form) and error location number */
root[count] = i;
loc[count] = k;
@ -202,8 +227,7 @@
* deg(lambda) unequal to number of roots => uncorrectable
* error detected
*/
count = -EBADMSG;
goto finish;
return -EBADMSG;
}
/*
* Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo
@ -223,7 +247,9 @@
/*
* Compute error values in poly-form. num1 = omega(inv(X(l))), num2 =
* inv(X(l))**(fcr-1) and den = lambda_pr(inv(X(l))) all in poly-form
* Note: we reuse the buffer for b to store the correction pattern
*/
num_corrected = 0;
for (j = count - 1; j >= 0; j--) {
num1 = 0;
for (i = deg_omega; i >= 0; i--) {
@ -231,6 +257,13 @@
num1 ^= alpha_to[rs_modnn(rs, omega[i] +
i * root[j])];
}
if (num1 == 0) {
/* Nothing to correct at this position */
b[j] = 0;
continue;
}
num2 = alpha_to[rs_modnn(rs, root[j] * (fcr - 1) + nn)];
den = 0;
@ -242,30 +275,52 @@
i * root[j])];
}
}
/* Apply error to data */
if (num1 != 0 && loc[j] >= pad) {
uint16_t cor = alpha_to[rs_modnn(rs,index_of[num1] +
index_of[num2] +
nn - index_of[den])];
/* Store the error correction pattern, if a
* correction buffer is available */
if (corr) {
corr[j] = cor;
} else {
/* If a data buffer is given and the
* error is inside the message,
* correct it */
if (data && (loc[j] < (nn - nroots)))
data[loc[j] - pad] ^= cor;
b[j] = alpha_to[rs_modnn(rs, index_of[num1] +
index_of[num2] +
nn - index_of[den])];
num_corrected++;
}
/*
* We compute the syndrome of the 'error' and check that it matches
* the syndrome of the received word
*/
for (i = 0; i < nroots; i++) {
tmp = 0;
for (j = 0; j < count; j++) {
if (b[j] == 0)
continue;
k = (fcr + i) * prim * (nn-loc[j]-1);
tmp ^= alpha_to[rs_modnn(rs, index_of[b[j]] + k)];
}
if (tmp != alpha_to[s[i]])
return -EBADMSG;
}
/*
* Store the error correction pattern, if a
* correction buffer is available
*/
if (corr && eras_pos) {
j = 0;
for (i = 0; i < count; i++) {
if (b[i]) {
corr[j] = b[i];
eras_pos[j++] = loc[i] - pad;
}
}
} else if (data && par) {
/* Apply error to data and parity */
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];
}
}
finish:
if (eras_pos != NULL) {
for (i = 0; i < count; i++)
eras_pos[i] = loc[i] - pad;
}
return count;
return num_corrected;
}

12
lib/reed_solomon/reed_solomon.c
View file

@ -340,7 +340,8 @@ EXPORT_SYMBOL_GPL(encode_rs8);
* @data: data field of a given type
* @par: received parity data field
* @len: data length
* @s: syndrome data field (if NULL, syndrome is calculated)
* @s: syndrome data field, must be in index form
* (if NULL, syndrome is calculated)
* @no_eras: number of erasures
* @eras_pos: position of erasures, can be NULL
* @invmsk: invert data mask (will be xored on data, not on parity!)
@ -354,7 +355,8 @@ EXPORT_SYMBOL_GPL(encode_rs8);
* decoding, so the caller has to ensure that decoder invocations are
* serialized.
*
* Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
* Returns the number of corrected symbols or -EBADMSG for uncorrectable
* 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,
@ -391,7 +393,8 @@ EXPORT_SYMBOL_GPL(encode_rs16);
* @data: data field of a given type
* @par: received parity data field
* @len: data length
* @s: syndrome data field (if NULL, syndrome is calculated)
* @s: syndrome data field, must be in index form
* (if NULL, syndrome is calculated)
* @no_eras: number of erasures
* @eras_pos: position of erasures, can be NULL
* @invmsk: invert data mask (will be xored on data, not on parity!)
@ -403,7 +406,8 @@ EXPORT_SYMBOL_GPL(encode_rs16);
* decoding, so the caller has to ensure that decoder invocations are
* serialized.
*
* Returns the number of corrected bits or -EBADMSG for uncorrectable errors.
* Returns the number of corrected symbols or -EBADMSG for uncorrectable
* 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,

518
lib/reed_solomon/test_rslib.c Normal file
View file

@ -0,0 +1,518 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Tests for Generic Reed Solomon encoder / decoder library
*
* Written by Ferdinand Blomqvist
* Based on previous work by Phil Karn, KA9Q
*/
#include <linux/rslib.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/random.h>
#include <linux/slab.h>
enum verbosity {
V_SILENT,
V_PROGRESS,
V_CSUMMARY
};
enum method {
CORR_BUFFER,
CALLER_SYNDROME,
IN_PLACE
};
#define __param(type, name, init, msg) \
static type name = init; \
module_param(name, type, 0444); \
MODULE_PARM_DESC(name, msg)
__param(int, v, V_PROGRESS, "Verbosity level");
__param(int, ewsc, 1, "Erasures without symbol corruption");
__param(int, bc, 1, "Test for correct behaviour beyond error correction capacity");
struct etab {
int symsize;
int genpoly;
int fcs;
int prim;
int nroots;
int ntrials;
};
/* List of codes to test */
static struct etab Tab[] = {
{2, 0x7, 1, 1, 1, 100000 },
{3, 0xb, 1, 1, 2, 100000 },
{3, 0xb, 1, 1, 3, 100000 },
{3, 0xb, 2, 1, 4, 100000 },
{4, 0x13, 1, 1, 4, 10000 },
{5, 0x25, 1, 1, 6, 1000 },
{6, 0x43, 3, 1, 8, 1000 },
{7, 0x89, 1, 1, 14, 500 },
{8, 0x11d, 1, 1, 30, 100 },
{8, 0x187, 112, 11, 32, 100 },
{9, 0x211, 1, 1, 33, 80 },
{0, 0, 0, 0, 0, 0},
};
struct estat {
int dwrong;
int irv;
int wepos;
int nwords;
};
struct bcstat {
int rfail;
int rsuccess;
int noncw;
int nwords;
};
struct wspace {
uint16_t *c; /* sent codeword */
uint16_t *r; /* received word */
uint16_t *s; /* syndrome */
uint16_t *corr; /* correction buffer */
int *errlocs;
int *derrlocs;
};
struct pad {
int mult;
int shift;
};
static struct pad pad_coef[] = {
{ 0, 0 },
{ 1, 2 },
{ 1, 1 },
{ 3, 2 },
{ 1, 0 },
};
static void free_ws(struct wspace *ws)
{
if (!ws)
return;
kfree(ws->errlocs);
kfree(ws->c);
kfree(ws);
}
static struct wspace *alloc_ws(struct rs_codec *rs)
{
int nroots = rs->nroots;
struct wspace *ws;
int nn = rs->nn;
ws = kzalloc(sizeof(*ws), GFP_KERNEL);
if (!ws)
return NULL;
ws->c = kmalloc_array(2 * (nn + nroots),
sizeof(uint16_t), GFP_KERNEL);
if (!ws->c)
goto err;
ws->r = ws->c + nn;
ws->s = ws->r + nn;
ws->corr = ws->s + nroots;
ws->errlocs = kmalloc_array(nn + nroots, sizeof(int), GFP_KERNEL);
if (!ws->errlocs)
goto err;
ws->derrlocs = ws->errlocs + nn;
return ws;
err:
free_ws(ws);
return NULL;
}
/*
* Generates a random codeword and stores it in c. Generates random errors and
* erasures, and stores the random word with errors in r. Erasure positions are
* stored in derrlocs, while errlocs has one of three values in every position:
*
* 0 if there is no error in this position;
* 1 if there is a symbol error in this position;
* 2 if there is an erasure without symbol corruption.
*
* Returns the number of corrupted symbols.
*/
static int get_rcw_we(struct rs_control *rs, struct wspace *ws,
int len, int errs, int eras)
{
int nroots = rs->codec->nroots;
int *derrlocs = ws->derrlocs;
int *errlocs = ws->errlocs;
int dlen = len - nroots;
int nn = rs->codec->nn;
uint16_t *c = ws->c;
uint16_t *r = ws->r;
int errval;
int errloc;
int i;
/* Load c with random data and encode */
for (i = 0; i < dlen; i++)
c[i] = prandom_u32() & nn;
memset(c + dlen, 0, nroots * sizeof(*c));
encode_rs16(rs, c, dlen, c + dlen, 0);
/* Make copyand add errors and erasures */
memcpy(r, c, len * sizeof(*r));
memset(errlocs, 0, len * sizeof(*errlocs));
memset(derrlocs, 0, nroots * sizeof(*derrlocs));
/* Generating random errors */
for (i = 0; i < errs; i++) {
do {
/* Error value must be nonzero */
errval = prandom_u32() & nn;
} while (errval == 0);
do {
/* Must not choose the same location twice */
errloc = prandom_u32() % len;
} while (errlocs[errloc] != 0);
errlocs[errloc] = 1;
r[errloc] ^= errval;
}
/* Generating random erasures */
for (i = 0; i < eras; i++) {
do {
/* Must not choose the same location twice */
errloc = prandom_u32() % len;
} while (errlocs[errloc] != 0);
derrlocs[i] = errloc;
if (ewsc && (prandom_u32() & 1)) {
/* Erasure with the symbol intact */
errlocs[errloc] = 2;
} else {
/* Erasure with corrupted symbol */
do {
/* Error value must be nonzero */
errval = prandom_u32() & nn;
} while (errval == 0);
errlocs[errloc] = 1;
r[errloc] ^= errval;
errs++;
}
}
return errs;
}
static void fix_err(uint16_t *data, int nerrs, uint16_t *corr, int *errlocs)
{
int i;
for (i = 0; i < nerrs; i++)
data[errlocs[i]] ^= corr[i];
}
static void compute_syndrome(struct rs_control *rsc, uint16_t *data,
int len, uint16_t *syn)
{
struct rs_codec *rs = rsc->codec;
uint16_t *alpha_to = rs->alpha_to;
uint16_t *index_of = rs->index_of;
int nroots = rs->nroots;
int prim = rs->prim;
int fcr = rs->fcr;
int i, j;
/* Calculating syndrome */
for (i = 0; i < nroots; i++) {
syn[i] = data[0];
for (j = 1; j < len; j++) {
if (syn[i] == 0) {
syn[i] = data[j];
} else {
syn[i] = data[j] ^
alpha_to[rs_modnn(rs, index_of[syn[i]]
+ (fcr + i) * prim)];
}
}
}
/* Convert to index form */
for (i = 0; i < nroots; i++)
syn[i] = rs->index_of[syn[i]];
}
/* 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,
struct wspace *ws, int method)
{
int dlen = len - rs->codec->nroots;
int *derrlocs = ws->derrlocs;
int *errlocs = ws->errlocs;
uint16_t *corr = ws->corr;
uint16_t *c = ws->c;
uint16_t *r = ws->r;
uint16_t *s = ws->s;
int derrs, nerrs;
int i, j;
for (j = 0; j < trials; j++) {
nerrs = get_rcw_we(rs, ws, len, errs, eras);
switch (method) {
case CORR_BUFFER:
derrs = decode_rs16(rs, r, r + dlen, dlen,
NULL, eras, derrlocs, 0, corr);
fix_err(r, derrs, corr, derrlocs);
break;
case CALLER_SYNDROME:
compute_syndrome(rs, r, len, s);
derrs = decode_rs16(rs, NULL, NULL, dlen,
s, eras, derrlocs, 0, corr);
fix_err(r, derrs, corr, derrlocs);
break;
case IN_PLACE:
derrs = decode_rs16(rs, r, r + dlen, dlen,
NULL, eras, derrlocs, 0, NULL);
break;
default:
continue;
}
if (derrs != nerrs)
stat->irv++;
if (method != IN_PLACE) {
for (i = 0; i < derrs; i++) {
if (errlocs[derrlocs[i]] != 1)
stat->wepos++;
}
}
if (memcmp(r, c, len * sizeof(*r)))
stat->dwrong++;
}
stat->nwords += trials;
}
static int ex_rs_helper(struct rs_control *rs, struct wspace *ws,
int len, int trials, int method)
{
static const char * const desc[] = {
"Testing correction buffer interface...",
"Testing with caller provided syndrome...",
"Testing in-place interface..."
};
struct estat stat = {0, 0, 0, 0};
int nroots = rs->codec->nroots;
int errs, eras, retval;
if (v >= V_PROGRESS)
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);
if (v >= V_CSUMMARY) {
pr_info(" Decodes wrong: %d / %d\n",
stat.dwrong, stat.nwords);
pr_info(" Wrong return value: %d / %d\n",
stat.irv, stat.nwords);
if (method != IN_PLACE)
pr_info(" Wrong error position: %d\n", stat.wepos);
}
retval = stat.dwrong + stat.wepos + stat.irv;
if (retval && v >= V_PROGRESS)
pr_warn(" FAIL: %d decoding failures!\n", retval);
return retval;
}
static int exercise_rs(struct rs_control *rs, struct wspace *ws,
int len, int trials)
{
int retval = 0;
int i;
if (v >= V_PROGRESS)
pr_info("Testing up to error correction capacity...\n");
for (i = 0; i <= IN_PLACE; i++)
retval |= ex_rs_helper(rs, ws, len, trials, i);
return retval;
}
/* 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,
struct wspace *ws)
{
int nroots = rs->codec->nroots;
int dlen = len - nroots;
int *derrlocs = ws->derrlocs;
uint16_t *corr = ws->corr;
uint16_t *r = ws->r;
int derrs, j;
for (j = 0; j < trials; j++) {
get_rcw_we(rs, ws, len, errs, eras);
derrs = decode_rs16(rs, r, r + dlen, dlen,
NULL, eras, derrlocs, 0, corr);
fix_err(r, derrs, corr, derrlocs);
if (derrs >= 0) {
stat->rsuccess++;
/*
* We check that the returned word is actually a
* codeword. The obious way to do this would be to
* compute the syndrome, but we don't want to replicate
* that code here. However, all the codes are in
* systematic form, and therefore we can encode the
* returned word, and see whether the parity changes or
* not.
*/
memset(corr, 0, nroots * sizeof(*corr));
encode_rs16(rs, r, dlen, corr, 0);
if (memcmp(r + dlen, corr, nroots * sizeof(*corr)))
stat->noncw++;
} else {
stat->rfail++;
}
}
stat->nwords += trials;
}
static int exercise_rs_bc(struct rs_control *rs, struct wspace *ws,
int len, int trials)
{
struct bcstat stat = {0, 0, 0, 0};
int nroots = rs->codec->nroots;
int errs, eras, cutoff;
if (v >= V_PROGRESS)
pr_info("Testing beyond error correction capacity...\n");
for (errs = 1; errs <= nroots; errs++) {
eras = nroots - 2 * errs + 1;
if (eras < 0)
eras = 0;
cutoff = nroots <= len - errs ? nroots : len - errs;
for (; eras <= cutoff; eras++)
test_bc(rs, len, errs, eras, trials, &stat, ws);
}
if (v >= V_CSUMMARY) {
pr_info(" decoder gives up: %d / %d\n",
stat.rfail, stat.nwords);
pr_info(" decoder returns success: %d / %d\n",
stat.rsuccess, stat.nwords);
pr_info(" not a codeword: %d / %d\n",
stat.noncw, stat.rsuccess);
}
if (stat.noncw && v >= V_PROGRESS)
pr_warn(" FAIL: %d silent failures!\n", stat.noncw);
return stat.noncw;
}
static int run_exercise(struct etab *e)
{
int nn = (1 << e->symsize) - 1;
int kk = nn - e->nroots;
struct rs_control *rsc;
int retval = -ENOMEM;
int max_pad = kk - 1;
int prev_pad = -1;
struct wspace *ws;
int i;
rsc = init_rs(e->symsize, e->genpoly, e->fcs, e->prim, e->nroots);
if (!rsc)
return retval;
ws = alloc_ws(rsc->codec);
if (!ws)
goto err;
retval = 0;
for (i = 0; i < ARRAY_SIZE(pad_coef); i++) {
int pad = (pad_coef[i].mult * max_pad) >> pad_coef[i].shift;
int len = nn - pad;
if (pad == prev_pad)
continue;
prev_pad = pad;
if (v >= V_PROGRESS) {
pr_info("Testing (%d,%d)_%d code...\n",
len, kk - pad, nn + 1);
}
retval |= exercise_rs(rsc, ws, len, e->ntrials);
if (bc)
retval |= exercise_rs_bc(rsc, ws, len, e->ntrials);
}
free_ws(ws);
err:
free_rs(rsc);
return retval;
}
static int __init test_rslib_init(void)
{
int i, fail = 0;
for (i = 0; Tab[i].symsize != 0 ; i++) {
int retval;
retval = run_exercise(Tab + i);
if (retval < 0)
return -ENOMEM;
fail |= retval;
}
if (fail)
pr_warn("rslib: test failed\n");
else
pr_info("rslib: test ok\n");
return -EAGAIN; /* Fail will directly unload the module */
}
static void __exit test_rslib_exit(void)
{
}
module_init(test_rslib_init)
module_exit(test_rslib_exit)
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Ferdinand Blomqvist");
MODULE_DESCRIPTION("Reed-Solomon library test");