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diff --git a/src/cls/cmpomap/client.h b/src/cls/cmpomap/client.h
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+++ b/src/cls/cmpomap/client.h
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+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab ft=cpp
+
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2020 Red Hat, Inc
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ */
+
+#pragma once
+
+#include <optional>
+#include "include/rados/librados_fwd.hpp"
+#include "types.h"
+
+namespace cls::cmpomap {
+
+/// requests with too many key comparisons will be rejected with -E2BIG
+static constexpr uint32_t max_keys = 1000;
+
+/// process each of the omap value comparisons according to the same rules as
+/// cmpxattr(), and return -ECANCELED if a comparison is unsuccessful. for
+/// comparisons with Mode::U64, failure to decode an input value is reported
+/// as -EINVAL, an empty stored value is compared as 0, and failure to decode
+/// a stored value is reported as -EIO
+[[nodiscard]] int cmp_vals(librados::ObjectReadOperation& op,
+                           Mode mode, Op comparison, ComparisonMap values,
+                           std::optional<ceph::bufferlist> default_value);
+
+/// process each of the omap value comparisons according to the same rules as
+/// cmpxattr(). any key/value pairs that compare successfully are overwritten
+/// with the corresponding input value. for comparisons with Mode::U64, failure
+/// to decode an input value is reported as -EINVAL. an empty stored value is
+/// compared as 0, while decode failure of a stored value is treated as an
+/// unsuccessful comparison and is not reported as an error
+[[nodiscard]] int cmp_set_vals(librados::ObjectWriteOperation& writeop,
+                               Mode mode, Op comparison, ComparisonMap values,
+                               std::optional<ceph::bufferlist> default_value);
+
+/// process each of the omap value comparisons according to the same rules as
+/// cmpxattr(). any key/value pairs that compare successfully are removed. for
+/// comparisons with Mode::U64, failure to decode an input value is reported as
+/// -EINVAL. an empty stored value is compared as 0, while decode failure of a
+/// stored value is treated as an unsuccessful comparison and is not reported
+/// as an error
+[[nodiscard]] int cmp_rm_keys(librados::ObjectWriteOperation& writeop,
+                              Mode mode, Op comparison, ComparisonMap values);
+
+
+// bufferlist factories for comparison values
+inline ceph::bufferlist string_buffer(std::string_view value) {
+  ceph::bufferlist bl;
+  bl.append(value);
+  return bl;
+}
+inline ceph::bufferlist u64_buffer(uint64_t value) {
+  ceph::bufferlist bl;
+  using ceph::encode;
+  encode(value, bl);
+  return bl;
+}
+
+} // namespace cls::cmpomap