[liuxuezhao]

A recx enumeration resumes from an anchor holding the first unpacked visible extent. evt_iter_probe_find() binary searches the visible extents with an overlap-only compare and returns whichever entry it hits first. If the anchor extent overlaps several entries (the tree was aggregated differently than when the anchor was taken, e.g. the anchor came from another replica, or aggregation above the enumeration epoch split the extent), the hit can be in the middle and the entries before it are silently skipped.

Slide to the lowest overlapping entry (highest for reverse iteration) before returning. Visible extents are disjoint and sorted, so the overlapping entries are contiguous.

Add VOS438 to reproduce the aggregation split case. Run it alone with:
PMEMOBJ_CONF=sds.at_create=0 vos_tests -S /dev/shm/vos -a -f VOS438

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions]

Ticket title is 'VOS recx enumerate possibly lost recx when race with vos aggregation'
Status is 'Open'
https://daosio.atlassian.net/browse/DAOS-19795

[liuxuezhao]

all test cases passed, only with 3 NLT warning in drpc.c, such as
D_ALLOC(chunk_buf, chunk_len);if (chunk_buf == NULL) {      rc = -DER_NOMEM;      D_ERROR("failed to allocate buffer for chunk (idx=%lu, size=%lu): " DF_RCsend_chunked() failed to allocate buffer for chunk (idx=0, size=28): DER_NOMEM(-1009): 'Out of memory'Logging allocation failure

it should unrelated with this pR