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Fixed incorrect assumption that weights imply bshrub roots

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rbyd.weight == btree.weight does not imply rbyd is a bshrub root!

This was introduced during a btrv rework, and, unfortunately, works
_most_ of the time. It's extra deceptive because we eagerly collapse
these degenerate roots in lfs3_btree_commit_, but we can't collapse
bshrub roots!

Well, not easily anyways (I guess we could convert to a btree...), but
what's important is that single-entry btree nodes are possible, and
relying on the weight for shrubbed roots is a weak condition.

Instead, we now just check the shrub bit for shrubbed roots. We have a
whole bit for this, so might as well actually use it.

This isn't even the first reliance of the shrub bit in this function!

---

Code changes minimal:

                    code          stack          ctx
  before:          35148           2136          660
  after:           35152 (+0.0%)   2136 (+0.0%)  660 (+0.0%)

                    code          stack          ctx
  gbmap before:    38388           2144          776
  gbmap after:     38388 (+0.0%)   2144 (+0.0%)  776 (+0.0%)

                    code          stack          ctx
  preerase before: 38928           2168          796
  preerase after:  38928 (+0.0%)   2168 (+0.0%)  796 (+0.0%)
This commit is contained in:
Christopher Haster
2025-12-31 12:32:13 -06:00
parent dfc57dda60
commit 15325a3767
1 changed files with 3 additions and 3 deletions
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lfs3.c
+3 -3
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@@ -6332,9 +6332,9 @@ static lfs3_stag_t lfs3_btree_traverse(lfs3_t *lfs3,
// restart from the root? // restart from the root?
if (btrv->bid == -1 if (btrv->bid == -1
|| btrv->rid >= (lfs3_srid_t)btrv->rbyd.weight || btrv->rid >= (lfs3_srid_t)btrv->rbyd.weight
// we do this unconditionally when rbyd == root to avoid // we do this unconditionally when rbyd is a shrub to avoid
// bshrubs falling out-of-sync // bshrub root traversals falling out-of-sync under mutation
|| btrv->rbyd.weight == btree->r.weight) { || lfs3_rbyd_isshrub(&btrv->rbyd)) {
// end of traversal? // end of traversal?
if (btrv->bid >= (lfs3_sbid_t)btree->r.weight) { if (btrv->bid >= (lfs3_sbid_t)btree->r.weight) {
return LFS3_ERR_NOENT; return LFS3_ERR_NOENT;