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btrfs-tree: clean up the fetch function's return set

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Commit d32f31f411 ("btrfs-tree: harden
`rlower_bound` against exceptional objects") passes the first btrfs item
in the result set that is above upper_bound up to `seek_backward`.
This is somewhat wasteful as `seek_backward` cannot use such a result.

Reverse that change in behavior, while keeping the rest of the other
commit.

This introduces a new case, where the search ioctl is producing items
that are above upper bound, but there are no items in the result set,
which continues looping until the end of the filesystem is reached.
Handle that by setting an explicit exit variable.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
2025-02-11 00:04:35 -05:00
parent 50e012ad6d
commit 80f9c147f7
1 changed files with 8 additions and 5 deletions
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13
lib/btrfs-tree.cc
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@ -418,6 +418,7 @@ namespace crucible {
++loops;
fill_sk(sk, unscale_logical(min(scaled_max_logical(), lower_bound)));
set<uint64_t> rv;
bool too_far = false;
do {
sk.nr_items = 4;
sk.do_ioctl(fd());
@ -426,6 +427,7 @@ namespace crucible {
next_sk(sk, i);
// If hdr_stop or !hdr_match, don't inspect the item
if (hdr_stop(i)) {
too_far = true;
rv.insert(numeric_limits<uint64_t>::max());
BTFRLB_DEBUG("(stop)");
break;
@ -438,22 +440,23 @@ namespace crucible {
BTFRLB_DEBUG(" " << to_hex(this_logical) << " " << i);
const auto scaled_hdr_logical = scale_logical(this_logical);
BTFRLB_DEBUG(" " << "(match)");
if (scaled_hdr_logical > upper_bound) {
too_far = true;
BTFRLB_DEBUG("(" << to_hex(scaled_hdr_logical) << " >= " << to_hex(upper_bound) << ")");
break;
}
if (this_logical <= logical && this_logical > closest_logical) {
closest_logical = this_logical;
closest_item = i;
BTFRLB_DEBUG("(closest)");
}
rv.insert(scaled_hdr_logical);
if (scaled_hdr_logical > upper_bound) {
BTFRLB_DEBUG("(" << to_hex(scaled_hdr_logical) << " >= " << to_hex(upper_bound) << ")");
break;
}
BTFRLB_DEBUG("(cont'd)");
}
BTFRLB_DEBUG(endl);
// We might get a search result that contains only non-matching items.
// Keep looping until we find any matching item or we run out of tree.
} while (rv.empty() && !sk.m_result.empty());
} while (!too_far && rv.empty() && !sk.m_result.empty());
return rv;
}, scale_logical(lookbehind_size()));
return closest_item;