Merge "libsnapshot: Verify the ordering of COW operations." into main

bool CowReader::VerifyMergeOps() {

    auto itr = GetMergeOpIter(true);

    std::unordered_map<uint64_t, const CowOperation*> overwritten_blocks;

    bool non_ordered_op_found = false;

    while (!itr->AtEnd()) {

        const auto& op = itr->Get();

        uint64_t offset;

        // Op should not be a metadata

        if (IsMetadataOp(*op)) {

            LOG(ERROR) << "Metadata op: " << op << " found during merge sequence";

            return false;

        }

        // Sequence ops should contain all the ordered ops followed

        // by Replace and Zero ops. If we find the first op which

        // is not ordered, that means all ordered ops processing

        // has been completed.

        if (!IsOrderedOp(*op)) {

            non_ordered_op_found = true;

        }

        // Since, all ordered ops processing has been completed,

        // check that the subsequent ops are not ordered.

        if (non_ordered_op_found && IsOrderedOp(*op)) {

            LOG(ERROR) << "Invalid sequence - non-ordered and ordered ops"

                       << " cannot be mixed during sequence generation";

            return false;

        }

        if (!GetSourceOffset(op, &offset)) {

            itr->Next();

            continue;