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Flipped layout of fcrcs to match B-tree branches

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This may seem more complicated to decode, we can't assume crcs start
at the beginning of the data, but this layout of putting the crcs at the
end has the benefit of allowing the size of the crc to be unknown in
certain cases.

The is a bit of optimistic future proofing for the case where we may
support different crc widths.
This commit is contained in:
Christopher Haster
2023-04-09 02:30:13 -05:00
parent a511696bad
commit 774ae676e4
1 changed files with 21 additions and 20 deletions
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lfs.c
+21 -20
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@@ -940,37 +940,38 @@ static void lfs_fcrc_tole32(struct lfs_fcrc *fcrc) {
#endif
// fcrc on-disk encoding
struct lfsr_fcrc {
uint32_t crc;
typedef struct lfsr_fcrc {
lfs_size_t size;
};
uint32_t crc;
} lfsr_fcrc_t;
#define LFSR_FCRC_DSIZE (4+5)
// 1 leb128 + 1 crc32c => 9 bytes (worst case)
#define LFSR_FCRC_DSIZE (5+4)
static lfs_ssize_t lfsr_fcrc_todisk(
const struct lfsr_fcrc *fcrc,
const lfsr_fcrc_t *fcrc,
uint8_t buf[static LFSR_FCRC_DSIZE]) {
lfs_tole32_(fcrc->crc, &buf[0]);
lfs_ssize_t delta = lfs_toleb128(fcrc->size, &buf[4], 5);
if (delta < 0) {
return delta;
lfs_ssize_t d = lfs_toleb128(fcrc->size, &buf[0], 5);
if (d < 0) {
return d;
}
return sizeof(uint32_t) + delta;
lfs_tole32_(fcrc->crc, &buf[d]);
return d + sizeof(uint32_t);
}
static lfs_ssize_t lfsr_fcrc_fromdisk(
struct lfsr_fcrc *fcrc,
lfsr_fcrc_t *fcrc,
const uint8_t buf[static LFSR_FCRC_DSIZE]) {
fcrc->crc = lfs_fromle32_(&buf[0]);
lfs_ssize_t delta = lfs_fromleb128(&fcrc->size, &buf[4], 5);
if (delta < 0) {
return delta;
lfs_ssize_t d = lfs_fromleb128(&fcrc->size, &buf[0], 5);
if (d < 0) {
return d;
}
return sizeof(uint32_t) + delta;
fcrc->crc = lfs_fromle32_(&buf[d]);
return d + sizeof(uint32_t);
}
// other endianness operations
@@ -1321,7 +1322,7 @@ static int lfsr_rbyd_fetch(lfs_t *lfs, lfsr_rbyd_t *rbyd,
lfs_size_t weight = 0;
// assume unerased until proven otherwise
struct lfsr_fcrc fcrc;
lfsr_fcrc_t fcrc;
bool hasfcrc = false;
bool maybeerased = false;
@@ -2478,7 +2479,7 @@ static int lfsr_rbyd_commit(lfs_t *lfs, lfsr_rbyd_t *rbyd,
// find the expected fcrc, don't bother avoiding a reread of the
// perturb byte, as it should still be in our cache
struct lfsr_fcrc fcrc = {.crc=0, .size=lfs->cfg->prog_size};
lfsr_fcrc_t fcrc = {.size=lfs->cfg->prog_size, .crc=0};
err = lfs_bd_crc32c(lfs,
&lfs->pcache, &lfs->rcache, lfs->cfg->prog_size,
rbyd_.block, aligned, fcrc.size, &fcrc.crc);