zircon/system/ulib/fs/include/fs/metrics.h

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#pragma once

#include <stdint.h>

#include <cobalt-client/cpp/collector.h>
#include <cobalt-client/cpp/histogram.h>

namespace fs {
// Vnode related histograms.
struct VnodeMetrics {
    // Number of buckets used for the vnode metrics.
    static constexpr uint32_t kHistogramBuckets = 10;

    VnodeMetrics(cobalt_client::Collector* collector, const fbl::String& fs_name,
                 bool local_metrics);

    cobalt_client::Histogram<kHistogramBuckets> close;
    cobalt_client::Histogram<kHistogramBuckets> read;
    cobalt_client::Histogram<kHistogramBuckets> write;
    cobalt_client::Histogram<kHistogramBuckets> append;
    cobalt_client::Histogram<kHistogramBuckets> truncate;
    cobalt_client::Histogram<kHistogramBuckets> set_attr;
    cobalt_client::Histogram<kHistogramBuckets> get_attr;
    cobalt_client::Histogram<kHistogramBuckets> sync;
    cobalt_client::Histogram<kHistogramBuckets> read_dir;
    cobalt_client::Histogram<kHistogramBuckets> look_up;
    cobalt_client::Histogram<kHistogramBuckets> create;
    cobalt_client::Histogram<kHistogramBuckets> unlink;
    cobalt_client::Histogram<kHistogramBuckets> link;

    // Mirrors |Metrics::IsEnabled|, such that |VnodeMetrics| is self sufficient
    // to determine whether metrics should be logged or not.
    bool metrics_enabled = false;
};

// Provides a base class for collecting metrics in FS implementations. This is optional, but
// provides a source of truth of how data is collected for filesystems. Specific filesystem
// implementations with custom APIs can extend and collect more data, but for basic operations, this
// class provides the base infrastructure.
//
// TODO(gevalentino): Define the |event_code| per metric. Currently is ignored.
class Metrics {
public:
    Metrics() = delete;
    Metrics(cobalt_client::CollectorOptions collector_options, bool local_metrics,
            const fbl::String& fs_name);
    Metrics(const Metrics&) = delete;
    Metrics(Metrics&&) = delete;
    Metrics& operator=(const Metrics&) = delete;
    Metrics& operator=(Metrics&&) = delete;
    virtual ~Metrics() = default;

    // Sets metric collection status to |should_collect|.
    void EnableMetrics(bool should_enable);

    // Returns true if the Logger is collecting.
    bool IsEnabled() const;

    // Returns the collector.
    const cobalt_client::Collector& collector() const { return collector_; }

    // Returns the collector.
    cobalt_client::Collector* mutable_collector() { return &collector_; }

    const VnodeMetrics& vnode_metrics() const;
    VnodeMetrics* mutable_vnode_metrics();

protected:
    cobalt_client::Collector collector_;

    VnodeMetrics vnode_metrics_;

    bool is_enabled_ = false;
};

} // namespace fs