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Moved gcksumdelta append into lfsr_mdir_commit__

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This tweaks lfsr_rbyd_appendcksum_ to take the canonical cksum as an
argument, allowing the caller to append any non-tree tags they'd like
before finalizing the commit.

This lets us calculate our gcksumdelta directly in lfsr_mdir_commit__,
which simplifies things a bit and avoids a redundant cksum copy.

The code cost mostly cancels out due to the extra gcksumdelta append
needed in lfsr_formatinited, but it's worth it for the code
simplification:

           code          stack          ctx
  before: 38664           2648          644
  after:  38668 (+0.0%)   2648 (+0.0%)  644 (+0.0%)
This commit is contained in:
Christopher Haster
2025-01-17 16:35:53 -06:00
parent 3983b5d1a1
commit d93b24e998
1 changed files with 48 additions and 49 deletions
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lfs.c
+48 -49
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@@ -3970,39 +3970,8 @@ leaf:;
// needed in lfsr_rbyd_appendcksum
static uint32_t lfsr_gcksum_cube(uint32_t gcksum);
static int lfsr_rbyd_appendcksum_(lfs_t *lfs,
lfsr_rbyd_t *rbyd, uint32_t *gcksumdelta) {
// begin appending
int err = lfsr_rbyd_appendinit(lfs, rbyd);
if (err) {
return err;
}
// save the canonical checksum
uint32_t cksum = rbyd->cksum;
// append gcksumdelta?
//
// the only requirement for gcksumdelta is we append after
// calculating the canonical checksum, it's a bit more convenient to
// append before the ecksum because of end-of-commit calculations
if (gcksumdelta) {
// figure out changes to our gcksumdelta
uint32_t gcksumdelta_ = *gcksumdelta
^ lfsr_gcksum_cube(lfs->gcksum_p)
^ lfsr_gcksum_cube(lfs->gcksum)
^ lfs->gcksum_d;
*gcksumdelta = gcksumdelta_;
uint8_t gcksumdelta_buf[LFSR_LE32_DSIZE];
err = lfsr_rbyd_appendrat_(lfs, rbyd, LFSR_RAT(
LFSR_TAG_GCKSUMDELTA, 0, LFSR_DATA_LE32(
gcksumdelta_, gcksumdelta_buf)));
if (err) {
return err;
}
}
static int lfsr_rbyd_appendcksum_(lfs_t *lfs, lfsr_rbyd_t *rbyd,
uint32_t cksum) {
// align to the next prog unit
//
// this gets a bit complicated as we have two types of cksums:
@@ -4037,7 +4006,7 @@ static int lfsr_rbyd_appendcksum_(lfs_t *lfs,
// read the leading byte in case we need to perturb the next commit,
// this should hopefully stay in our cache
uint8_t e = 0;
err = lfsr_bd_read(lfs,
int err = lfsr_bd_read(lfs,
rbyd->blocks[0], off_, lfs->cfg->prog_size,
&e, 1);
if (err && err != LFS_ERR_CORRUPT) {
@@ -4115,7 +4084,7 @@ static int lfsr_rbyd_appendcksum_(lfs_t *lfs,
lfs_tole32_(cksum_, &cksum_buf[2+1+4]);
// prog, when this lands on disk commit is committed
err = lfsr_bd_prog(lfs, rbyd->blocks[0], lfsr_rbyd_eoff(rbyd),
int err = lfsr_bd_prog(lfs, rbyd->blocks[0], lfsr_rbyd_eoff(rbyd),
cksum_buf, 2+1+4+4,
NULL, false);
if (err) {
@@ -4138,7 +4107,14 @@ static int lfsr_rbyd_appendcksum_(lfs_t *lfs,
}
static int lfsr_rbyd_appendcksum(lfs_t *lfs, lfsr_rbyd_t *rbyd) {
return lfsr_rbyd_appendcksum_(lfs, rbyd, NULL);
// begin appending
int err = lfsr_rbyd_appendinit(lfs, rbyd);
if (err) {
return err;
}
// append checksum stuff
return lfsr_rbyd_appendcksum_(lfs, rbyd, rbyd->cksum);
}
static int lfsr_rbyd_appendrats(lfs_t *lfs, lfsr_rbyd_t *rbyd,
@@ -7779,23 +7755,40 @@ static int lfsr_mdir_commit__(lfs_t *lfs, lfsr_mdir_t *mdir,
}
}
// TODO should lfsr_rbyd_appendcksum_ revert cksum on failure?
// save cksum in case we fail
// save our canonical cksum
//
// note this is before we calculate gcksumdelta, otherwise
// everything would get all self-referential
uint32_t cksum = mdir->rbyd.cksum;
// xor our new cksum
lfs->gcksum ^= mdir->rbyd.cksum;
// append gkcsumdelta?
if (start_rid <= -2) {
// figure out changes to our gcksumdelta
mdir->gcksumdelta ^= lfsr_gcksum_cube(lfs->gcksum_p)
^ lfsr_gcksum_cube(lfs->gcksum ^ cksum)
^ lfs->gcksum_d;
uint8_t gcksumdelta_buf[LFSR_LE32_DSIZE];
int err = lfsr_rbyd_appendrat_(lfs, &mdir->rbyd, LFSR_RAT(
LFSR_TAG_GCKSUMDELTA, 0, LFSR_DATA_LE32(
mdir->gcksumdelta, gcksumdelta_buf)));
if (err) {
return err;
}
}
// finalize commit
int err = lfsr_rbyd_appendcksum_(lfs, &mdir->rbyd,
// include gcksumdelta if we're not relocating
(start_rid <= -2) ? &mdir->gcksumdelta : NULL);
int err = lfsr_rbyd_appendcksum_(lfs, &mdir->rbyd, cksum);
if (err) {
// undo cksum xor on failure
lfs->gcksum ^= cksum;
return err;
}
// success? flush gstate?
// success?
// xor our new cksum
lfs->gcksum ^= mdir->rbyd.cksum;
// flush gstate?
if (start_rid <= -1) {
// TODO this is a hack
// we only flush gcksumdelta if rid == -2
@@ -14287,9 +14280,15 @@ static int lfsr_formatinited(lfs_t *lfs) {
return err;
}
// prepare initial gcksum and commit
lfs->gcksum = rbyd.cksum;
err = lfsr_rbyd_appendcksum_(lfs, &rbyd, &(uint32_t){0});
// append initial gcksum
uint32_t cksum = rbyd.cksum;
uint8_t gcksumdelta_buf[LFSR_LE32_DSIZE];
err = lfsr_rbyd_appendrat_(lfs, &rbyd, LFSR_RAT(
LFSR_TAG_GCKSUMDELTA, 0, LFSR_DATA_LE32(
lfsr_gcksum_cube(cksum), gcksumdelta_buf)));
// and commit
err = lfsr_rbyd_appendcksum_(lfs, &rbyd, cksum);
if (err) {
return err;
}