Hi all! It's an alternative lock-less solution to [PATCH v4 0/3] qcow2: fix parallel rewrite and discard (rw-lock)
It's an updated version of what was don in [PATCH v3 0/6] qcow2: compressed write cache I've split the logic into several patches, add a lot more comments and documentation, I hope it's all now a lot more clean. Main change from v3 is careful handling "freeing" the cluster. The concept of "free cluster" is established. And good thing: now updating inflight-counters it lock-less: we don't need the lock for discard operation, instead we consider this discard as the last one inflight write! The solution is still more complicated then co-rw-lock based one. But it is cool and I hope someone like it. RFC: should we protect reads as well of intersecting with discarding host clusters? I think yes. Reads are not as critical, as they can't corrupt the metadata or data (due to use-after-free like writes), but with reads it's possible that guest reads some metadata cluster. It's a kind of security violation I think. Vladimir Sementsov-Ogievskiy (6): iotests: add qcow2-discard-during-rewrite qcow2: fix cache discarding in update_refcount() qcow2: introduce is_cluster_free() helper qcow2: introduce inflight-write-counters qcow2: consider in-flight-writes when freeing clusters qcow2: do not discard host clusters during in-flight writes block/qcow2.h | 16 ++ block/qcow2-refcount.c | 184 +++++++++++++++++- block/qcow2.c | 26 ++- .../tests/qcow2-discard-during-rewrite | 72 +++++++ .../tests/qcow2-discard-during-rewrite.out | 21 ++ 5 files changed, 308 insertions(+), 11 deletions(-) create mode 100755 tests/qemu-iotests/tests/qcow2-discard-during-rewrite create mode 100644 tests/qemu-iotests/tests/qcow2-discard-during-rewrite.out -- 2.29.2