summaryrefslogtreecommitdiff
path: root/src/mongo/db/feature_flag.cpp
blob: 818df3bfdcc10ed0c74d07508d31da5959e498b3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
/**
 *    Copyright (C) 2020-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#include "mongo/db/feature_flag.h"

#include "mongo/util/debug_util.h"
#include "mongo/util/version/releases.h"

namespace mongo {

// (Generic FCV reference): feature flag support
FeatureFlag::FeatureFlag(bool enabled, StringData versionString, bool shouldBeFCVGated)
    : _enabled(enabled),
      _version(multiversion::GenericFCV::kLatest),
      _shouldBeFCVGated(shouldBeFCVGated) {

    // Verify the feature flag invariants. IDL binder verifies these hold but we add these checks to
    // prevent incorrect direct instantiation.
    //
    // If default is true, then version should be present.
    // If default is false, then no version is allowed.
    if (kDebugBuild) {
        if (enabled && shouldBeFCVGated) {
            dassert(!versionString.empty());
        } else {
            dassert(versionString.empty());
        }
    }

    if (!versionString.empty()) {
        _version = FeatureCompatibilityVersionParser::parseVersionForFeatureFlags(versionString);
    }
}

bool FeatureFlag::isEnabled(const ServerGlobalParams::FeatureCompatibility& fcv) const {
    // If the feature flag is not FCV gated, return whether it is enabled.
    if (!_shouldBeFCVGated) {
        return _enabled;
    }


    // If the FCV is not initialized yet, we check whether the feature flag is enabled on the last
    // LTS FCV, which is the lowest FCV we can have on this server. Because the version of a feature
    // flag is not supposed to change, we are sure that if the feature flag is enabled on the last
    // LTS FCV, it is enabled on all FCVs this server can have.
    if (!fcv.isVersionInitialized()) {
        // (Generic FCV reference): This FCV reference should exist across LTS binary versions.
        return isEnabledOnVersion(multiversion::GenericFCV::kLastLTS);
    }

    if (!_enabled) {
        return false;
    }

    // If the feature flag is enabled, return whether the server's FCV is >= to the version the
    // feature flag was enabled on.
    return fcv.isGreaterThanOrEqualTo(_version);
}

// isEnabledAndIgnoreFCVUnsafe should NOT be used in general, as it checks if the feature flag is
// turned on, regardless of which FCV we are on. It can result in unsafe scenarios
// where we enable a feature on an FCV where it is not supported or where the feature has not been
// fully implemented yet. In order to use isEnabledAndIgnoreFCVUnsafe, you **must** add a comment
// above that line starting with "(Ignore FCV check):" describing why we can safely ignore checking
// the FCV here.
// Note that if the feature flag does not have any upgrade/downgrade concerns, then shouldBeFCVGated
// should be set to false and FeatureFlag::isEnabled() should be used instead of this function.
bool FeatureFlag::isEnabledAndIgnoreFCVUnsafe() const {
    return _enabled;
}

// isEnabledAndIgnoreFCVUnsafeAtStartup should only be used on startup, if we want to check if the
// feature flag if the feature flag is turned on, regardless of which FCV we are on.
// Note that if the feature flag does not have any upgrade/downgrade concerns, then shouldBeFCVGated
// should be set to false and FeatureFlag::isEnabled() should be used instead of this function.
bool FeatureFlag::isEnabledAndIgnoreFCVUnsafeAtStartup() const {
    return _enabled;
}

bool FeatureFlag::isEnabledOnVersion(multiversion::FeatureCompatibilityVersion targetFCV) const {
    if (!_enabled) {
        return false;
    }

    return targetFCV >= _version;
}

bool FeatureFlag::isDisabledOnTargetFCVButEnabledOnOriginalFCV(
    multiversion::FeatureCompatibilityVersion targetFCV,
    multiversion::FeatureCompatibilityVersion originalFCV) const {
    if (!_enabled) {
        return false;
    }

    return originalFCV >= _version && targetFCV < _version;
}

bool FeatureFlag::isEnabledOnTargetFCVButDisabledOnOriginalFCV(
    multiversion::FeatureCompatibilityVersion targetFCV,
    multiversion::FeatureCompatibilityVersion originalFCV) const {
    if (!_enabled) {
        return false;
    }

    return targetFCV >= _version && originalFCV < _version;
}

multiversion::FeatureCompatibilityVersion FeatureFlag::getVersion() const {
    uassert(5111001, "Feature Flag is not enabled, cannot retrieve version", _enabled);

    return _version;
}

void FeatureFlag::set(bool enabled) {
    _enabled = enabled;
}

FeatureFlagServerParameter::FeatureFlagServerParameter(StringData name, FeatureFlag& storage)
    : ServerParameter(name, ServerParameterType::kStartupOnly), _storage(storage) {}

void FeatureFlagServerParameter::append(OperationContext* opCtx,
                                        BSONObjBuilder* b,
                                        StringData name,
                                        const boost::optional<TenantId>&) {
    bool enabled = _storage.isEnabledAndIgnoreFCVUnsafe();

    {
        auto sub = BSONObjBuilder(b->subobjStart(name));
        sub.append("value"_sd, enabled);

        if (enabled) {
            sub.append("version",
                       FeatureCompatibilityVersionParser::serializeVersionForFeatureFlags(
                           _storage.getVersion()));
        }
    }
}

void FeatureFlagServerParameter::appendSupportingRoundtrip(OperationContext* opCtx,
                                                           BSONObjBuilder* b,
                                                           StringData name,
                                                           const boost::optional<TenantId>&) {
    bool enabled = _storage.isEnabledAndIgnoreFCVUnsafe();
    b->append(name, enabled);
}

Status FeatureFlagServerParameter::set(const BSONElement& newValueElement,
                                       const boost::optional<TenantId>&) {
    bool newValue;

    if (auto status = newValueElement.tryCoerce(&newValue); !status.isOK()) {
        return {status.code(),
                str::stream() << "Failed setting " << name() << ": " << status.reason()};
    }

    _storage.set(newValue);

    return Status::OK();
}

Status FeatureFlagServerParameter::setFromString(StringData str, const boost::optional<TenantId>&) {
    auto swNewValue = idl_server_parameter_detail::coerceFromString<bool>(str);
    if (!swNewValue.isOK()) {
        return swNewValue.getStatus();
    }

    _storage.set(swNewValue.getValue());

    return Status::OK();
}

}  // namespace mongo