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/**
* 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
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