// Copyright 2019 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.

library fuchsia.storage.metrics;

/// Stats for calls. These stats track completed calls - they may or may not have
/// succeeded. Unless specified otherwise , time units are in nanoseconds and
/// data transferred is in bytes
struct CallStatRaw {
    /// Minimum time taken by a request to be served.
    uint64 minimum_latency;

    /// Maximum time taken by a request to be served.
    uint64 maximum_latency;

    /// Total time spent to serve requests.
    uint64 total_time_spent;

    /// Total number of calls.
    uint64 total_calls;

    /// byte_transferred may mean different things in different context. For
    /// example, read and write may use it for bytes read/written, whereas
    /// create/lseek may use bytes_transferred for file name length or number
    /// of bytes lseek-ed from current position.
    /// bytes_transferred has special meaning if the succeeded or failed.
    /// On success:
    ///    Partitally succeeded calls, bytes fetched is less than bytes requested,
    ///    can be considered as successful. To keep latency and time_spent numbers
    ///    accurate, on success, bytes transferred is number bytes returned to
    ///    caller. It is NOT the number of bytes fetched from underlying subsystem
    ///    and it is NOT number of bytes requested by the caller.
    /// On failure:
    ///    On failure, bytes_transferred is the number of bytes requested by the
    ///    caller.
    uint64 bytes_transferred;
};

struct CallStat {
    /// CallStat keeps track of the successful commands and failed commands
    /// seperately as successful commands may generate completely different stats
    /// than failed commands - a write() to read-only file handle may fail
    /// in nanoseconds and if the stats tracked together, it will skew the
    /// numbers.
    CallStatRaw success;
    CallStatRaw failure;
};

struct FsMetrics {
    /// Call stats for create
    CallStat create;

    /// Call stats for read
    CallStat read;

    /// Call stats for write
    CallStat write;

    /// Call stats for truncate
    CallStat truncate;

    /// Call stats for unlink
    CallStat unlink;

    /// Call stats for rename
    CallStat rename;

    /// Call stats for directory lookups
    CallStat lookup;

    /// Call stats for open. This may or may
    /// not include directory lookup during open
    CallStat open;
};