path: root/buildscripts/resmokelib/core/programs.py

"""Utility functions to create MongoDB processes.

Handles all the nitty-gritty parameter conversion.
"""

import json
import os
import os.path
import stat

from buildscripts.resmokelib import config
from buildscripts.resmokelib import utils
from buildscripts.resmokelib.core import jasper_process
from buildscripts.resmokelib.core import process
from buildscripts.resmokelib.multiversionconstants import LAST_LTS_MONGOD_BINARY
from buildscripts.resmokelib.multiversionconstants import LAST_LTS_MONGOS_BINARY

# The below parameters define the default 'logComponentVerbosity' object passed to mongod processes
# started either directly via resmoke or those that will get started by the mongo shell. We allow
# this default to be different for tests run locally and tests run in Evergreen. This allows us, for
# example, to keep log verbosity high in Evergreen test runs without polluting the logs for
# developers running local tests.

# The default verbosity setting for any tests that are not started with an Evergreen task id. This
# will apply to any tests run locally.
DEFAULT_MONGOD_LOG_COMPONENT_VERBOSITY = {
    "replication": {"rollback": 2}, "sharding": {"migration": 2}, "transaction": 4,
    "tenantMigration": 4
}

DEFAULT_LAST_LTS_MONGOD_LOG_COMPONENT_VERBOSITY = {"replication": {"rollback": 2}, "transaction": 4}

# The default verbosity setting for any mongod processes running in Evergreen i.e. started with an
# Evergreen task id.
DEFAULT_EVERGREEN_MONGOD_LOG_COMPONENT_VERBOSITY = {
    "replication": {"election": 4, "heartbeats": 2, "initialSync": 2, "rollback": 2},
    "sharding": {"migration": 2}, "storage": {"recovery": 2}, "transaction": 4, "tenantMigration": 4
}

# The default verbosity setting for any last-lts mongod processes running in Evergreen i.e. started
# with an Evergreen task id.
DEFAULT_EVERGREEN_LAST_LTS_MONGOD_LOG_COMPONENT_VERBOSITY = {
    "replication": {"election": 4, "heartbeats": 2, "initialSync": 2, "rollback": 2},
    "storage": {"recovery": 2}, "transaction": 4
}

# The default verbosity setting for any tests that are not started with an Evergreen task id. This
# will apply to any tests run locally.
DEFAULT_MONGOS_LOG_COMPONENT_VERBOSITY = {"transaction": 3}

# The default verbosity setting for any tests running in Evergreen i.e. started with an Evergreen
# task id.
DEFAULT_EVERGREEN_MONGOS_LOG_COMPONENT_VERBOSITY = {"transaction": 3}


def make_process(*args, **kwargs):
    """Choose whether to use python built in process or jasper."""
    process_cls = process.Process
    if config.SPAWN_USING == "jasper":
        process_cls = jasper_process.Process

    # Add the current working directory and /data/multiversion to the PATH.
    env_vars = kwargs.get("env_vars", {}).copy()
    path = [
        os.getcwd(),
        config.DEFAULT_MULTIVERSION_DIR,
    ]

    # If installDir is provided, add it early to the path
    if config.INSTALL_DIR is not None:
        path.append(config.INSTALL_DIR)
        env_vars["INSTALL_DIR"] = config.INSTALL_DIR

    path.append(env_vars.get("PATH", os.environ.get("PATH", "")))

    env_vars["PATH"] = os.pathsep.join(path)
    kwargs["env_vars"] = env_vars
    return process_cls(*args, **kwargs)


def default_mongod_log_component_verbosity():
    """Return the default 'logComponentVerbosity' value to use for mongod processes."""
    if config.EVERGREEN_TASK_ID:
        return DEFAULT_EVERGREEN_MONGOD_LOG_COMPONENT_VERBOSITY
    return DEFAULT_MONGOD_LOG_COMPONENT_VERBOSITY


def default_last_lts_mongod_log_component_verbosity():
    """Return the default 'logComponentVerbosity' value to use for last-lts mongod processes."""
    if config.EVERGREEN_TASK_ID:
        return DEFAULT_EVERGREEN_LAST_LTS_MONGOD_LOG_COMPONENT_VERBOSITY
    return DEFAULT_LAST_LTS_MONGOD_LOG_COMPONENT_VERBOSITY


def default_mongos_log_component_verbosity():
    """Return the default 'logComponentVerbosity' value to use for mongos processes."""
    if config.EVERGREEN_TASK_ID:
        return DEFAULT_EVERGREEN_MONGOS_LOG_COMPONENT_VERBOSITY
    return DEFAULT_MONGOS_LOG_COMPONENT_VERBOSITY


def get_default_log_component_verbosity_for_mongod(executable):
    """Return the correct default 'logComponentVerbosity' value for the executable version."""
    if executable == LAST_LTS_MONGOD_BINARY:
        return default_last_lts_mongod_log_component_verbosity()
    return default_mongod_log_component_verbosity()


def _add_testing_set_parameters(suite_set_parameters):
    # Certain behaviors should only be enabled for resmoke usage. These are traditionally new
    # commands, insecure access, and increased diagnostics.
    suite_set_parameters.setdefault("testingDiagnosticsEnabled", True)
    suite_set_parameters.setdefault("enableTestCommands", True)


def mongod_program(  # pylint: disable=too-many-branches,too-many-statements
        logger, executable=None, process_kwargs=None, **kwargs):
    """Return a Process instance that starts mongod arguments constructed from 'kwargs'."""

    executable = utils.default_if_none(executable, config.DEFAULT_MONGOD_EXECUTABLE)
    args = [executable]

    # Apply the --setParameter command line argument. Command line options to resmoke.py override
    # the YAML configuration.
    suite_set_parameters = kwargs.pop("set_parameters", {})

    if config.MONGOD_SET_PARAMETERS is not None:
        suite_set_parameters.update(utils.load_yaml(config.MONGOD_SET_PARAMETERS))

    # Set default log verbosity levels if none were specified.
    if "logComponentVerbosity" not in suite_set_parameters:
        suite_set_parameters[
            "logComponentVerbosity"] = get_default_log_component_verbosity_for_mongod(executable)

    # minNumChunksForSessionsCollection controls the minimum number of chunks the balancer will
    # enforce for the sessions collection. If the actual number of chunks is less, the balancer will
    # issue split commands to create more chunks. As a result, the balancer will also end up moving
    # chunks for the sessions collection to balance the chunks across shards. Unless the suite is
    # explicitly prepared to handle these background migrations, set the parameter to 1.
    if "configsvr" in kwargs and "minNumChunksForSessionsCollection" not in suite_set_parameters:
        suite_set_parameters["minNumChunksForSessionsCollection"] = 1

    # orphanCleanupDelaySecs controls an artificial delay before cleaning up an orphaned chunk
    # that has migrated off of a shard, meant to allow most dependent queries on secondaries to
    # complete first. It defaults to 900, or 15 minutes, which is prohibitively long for tests.
    # Setting it in the .yml file overrides this.
    if "shardsvr" in kwargs and "orphanCleanupDelaySecs" not in suite_set_parameters:
        suite_set_parameters["orphanCleanupDelaySecs"] = 1

    # The LogicalSessionCache does automatic background refreshes in the server. This is
    # race-y for tests, since tests trigger their own immediate refreshes instead. Turn off
    # background refreshing for tests. Set in the .yml file to override this.
    if "disableLogicalSessionCacheRefresh" not in suite_set_parameters:
        suite_set_parameters["disableLogicalSessionCacheRefresh"] = True

    # Set coordinateCommitReturnImmediatelyAfterPersistingDecision to false so that tests do
    # not need to rely on causal consistency or explicity wait for the transaction to finish
    # committing.
    if executable != LAST_LTS_MONGOD_BINARY and \
        "coordinateCommitReturnImmediatelyAfterPersistingDecision" not in suite_set_parameters:
        suite_set_parameters["coordinateCommitReturnImmediatelyAfterPersistingDecision"] = False

    # There's a periodic background thread that checks for and aborts expired transactions.
    # "transactionLifetimeLimitSeconds" specifies for how long a transaction can run before expiring
    # and being aborted by the background thread. It defaults to 60 seconds, which is too short to
    # be reliable for our tests. Setting it to 24 hours, so that it is longer than the Evergreen
    # execution timeout.
    if "transactionLifetimeLimitSeconds" not in suite_set_parameters:
        suite_set_parameters["transactionLifetimeLimitSeconds"] = 24 * 60 * 60

    # Hybrid index builds drain writes received during the build process in batches of 1000 writes
    # by default. Not all tests perform enough writes to exercise the code path where multiple
    # batches are applied, which means certain bugs are harder to encounter. Set this level lower
    # so there are more opportunities to drain writes in multiple batches.
    if "maxIndexBuildDrainBatchSize" not in suite_set_parameters:
        suite_set_parameters["maxIndexBuildDrainBatchSize"] = 10

    # The periodic no-op writer writes an oplog entry of type='n' once every 10 seconds. This has
    # the potential to mask issues such as SERVER-31609 because it allows the operationTime of
    # cluster to advance even if the client is blocked for other reasons. We should disable the
    # periodic no-op writer. Set in the .yml file to override this.
    if "replSet" in kwargs and "writePeriodicNoops" not in suite_set_parameters:
        suite_set_parameters["writePeriodicNoops"] = False

    # The default time for stepdown and quiesce mode in response to SIGTERM is 15 seconds. Reduce
    # this to 100ms for faster shutdown. On branches 4.4 and earlier, there is no quiesce mode, but
    # the default time for stepdown is 10 seconds.
    # TODO(SERVER-47797): Remove reference to waitForStepDownOnNonCommandShutdown.
    if ("replSet" in kwargs and "waitForStepDownOnNonCommandShutdown" not in suite_set_parameters
            and "shutdownTimeoutMillisForSignaledShutdown" not in suite_set_parameters):
        if executable == LAST_LTS_MONGOD_BINARY:
            suite_set_parameters["waitForStepDownOnNonCommandShutdown"] = False
        else:
            suite_set_parameters["shutdownTimeoutMillisForSignaledShutdown"] = 100

    if "enableFlowControl" not in suite_set_parameters and config.FLOW_CONTROL is not None:
        suite_set_parameters["enableFlowControl"] = (config.FLOW_CONTROL == "on")

    if ("failpoint.flowControlTicketOverride" not in suite_set_parameters
            and config.FLOW_CONTROL_TICKETS is not None):
        suite_set_parameters["failpoint.flowControlTicketOverride"] = {
            "mode": "alwaysOn", "data": {"numTickets": config.FLOW_CONTROL_TICKETS}
        }

    # TODO(SERVER-48645): Only keep the else block once v4.4 is not longer the last-lts version
    if executable == LAST_LTS_MONGOD_BINARY:
        suite_set_parameters.setdefault("enableTestCommands", True)
    else:
        _add_testing_set_parameters(suite_set_parameters)

    _apply_set_parameters(args, suite_set_parameters)

    shortcut_opts = {
        "enableMajorityReadConcern": config.MAJORITY_READ_CONCERN,
        "nojournal": config.NO_JOURNAL,
        "storageEngine": config.STORAGE_ENGINE,
        "transportLayer": config.TRANSPORT_LAYER,
        "wiredTigerCollectionConfigString": config.WT_COLL_CONFIG,
        "wiredTigerEngineConfigString": config.WT_ENGINE_CONFIG,
        "wiredTigerIndexConfigString": config.WT_INDEX_CONFIG,
    }

    if config.STORAGE_ENGINE == "inMemory":
        shortcut_opts["inMemorySizeGB"] = config.STORAGE_ENGINE_CACHE_SIZE
    elif config.STORAGE_ENGINE == "rocksdb":
        shortcut_opts["rocksdbCacheSizeGB"] = config.STORAGE_ENGINE_CACHE_SIZE
    elif config.STORAGE_ENGINE == "wiredTiger" or config.STORAGE_ENGINE is None:
        shortcut_opts["wiredTigerCacheSizeGB"] = config.STORAGE_ENGINE_CACHE_SIZE

    # These options are just flags, so they should not take a value.
    opts_without_vals = ("nojournal", "logappend")

    # Have the --nojournal command line argument to resmoke.py unset the journal option.
    if shortcut_opts["nojournal"] and "journal" in kwargs:
        del kwargs["journal"]

    # Ensure that config servers run with journaling enabled.
    if "configsvr" in kwargs:
        shortcut_opts["nojournal"] = False
        kwargs["journal"] = ""

    # Command line options override the YAML configuration.
    for opt_name in shortcut_opts:
        opt_value = shortcut_opts[opt_name]
        if opt_name in opts_without_vals:
            # Options that are specified as --flag on the command line are represented by a boolean
            # value where True indicates that the flag should be included in 'kwargs'.
            if opt_value:
                kwargs[opt_name] = ""
        else:
            # Options that are specified as --key=value on the command line are represented by a
            # value where None indicates that the key-value pair shouldn't be included in 'kwargs'.
            if opt_value is not None:
                kwargs[opt_name] = opt_value

    # Override the storage engine specified on the command line with "wiredTiger" if running a
    # config server replica set.
    if "replSet" in kwargs and "configsvr" in kwargs:
        kwargs["storageEngine"] = "wiredTiger"

    # Apply the rest of the command line arguments.
    _apply_kwargs(args, kwargs)

    _set_keyfile_permissions(kwargs)

    process_kwargs = utils.default_if_none(process_kwargs, {})
    return make_process(logger, args, **process_kwargs)


def mongos_program(logger, executable=None, process_kwargs=None, **kwargs):
    """Return a Process instance that starts a mongos with arguments constructed from 'kwargs'."""

    executable = utils.default_if_none(executable, config.DEFAULT_MONGOS_EXECUTABLE)
    args = [executable]

    # Apply the --setParameter command line argument. Command line options to resmoke.py override
    # the YAML configuration.
    suite_set_parameters = kwargs.pop("set_parameters", {})

    if config.MONGOS_SET_PARAMETERS is not None:
        suite_set_parameters.update(utils.load_yaml(config.MONGOS_SET_PARAMETERS))

    # Set default log verbosity levels if none were specified.
    if "logComponentVerbosity" not in suite_set_parameters:
        suite_set_parameters["logComponentVerbosity"] = default_mongos_log_component_verbosity()

    # TODO(SERVER-48645): Only keep the else block once v4.4 is not longer the last-lts version
    if executable == LAST_LTS_MONGOS_BINARY:
        suite_set_parameters.setdefault("enableTestCommands", True)
    else:
        _add_testing_set_parameters(suite_set_parameters)

    _apply_set_parameters(args, suite_set_parameters)

    # Apply the rest of the command line arguments.
    _apply_kwargs(args, kwargs)

    _set_keyfile_permissions(kwargs)

    process_kwargs = utils.default_if_none(process_kwargs, {})
    return make_process(logger, args, **process_kwargs)


def mongo_shell_program(  # pylint: disable=too-many-branches,too-many-locals,too-many-statements
        logger, executable=None, connection_string=None, filename=None, process_kwargs=None,
        **kwargs):
    """Return a Process instance that starts a mongo shell.

    The shell is started with the given connection string and arguments constructed from 'kwargs'.
    """

    executable = utils.default_if_none(
        utils.default_if_none(executable, config.MONGO_EXECUTABLE), config.DEFAULT_MONGO_EXECUTABLE)
    args = [executable]

    eval_sb = []  # String builder.
    global_vars = kwargs.pop("global_vars", {}).copy()

    if filename is not None:
        test_name = os.path.splitext(os.path.basename(filename))[0]
    else:
        test_name = None
    shortcut_opts = {
        "backupOnRestartDir": (config.BACKUP_ON_RESTART_DIR, None),
        "enableMajorityReadConcern": (config.MAJORITY_READ_CONCERN, True),
        "mixedBinVersions": (config.MIXED_BIN_VERSIONS, ""),
        "noJournal": (config.NO_JOURNAL, False),
        "storageEngine": (config.STORAGE_ENGINE, ""),
        "storageEngineCacheSizeGB": (config.STORAGE_ENGINE_CACHE_SIZE, ""),
        "testName": (test_name, ""),
        "transportLayer": (config.TRANSPORT_LAYER, ""),
        "wiredTigerCollectionConfigString": (config.WT_COLL_CONFIG, ""),
        "wiredTigerEngineConfigString": (config.WT_ENGINE_CONFIG, ""),
        "wiredTigerIndexConfigString": (config.WT_INDEX_CONFIG, ""),
    }

    test_data = global_vars.get("TestData", {}).copy()
    for opt_name in shortcut_opts:
        (opt_value, opt_default) = shortcut_opts[opt_name]
        if opt_value is not None:
            test_data[opt_name] = opt_value
        elif opt_name not in test_data:
            # Only use 'opt_default' if the property wasn't set in the YAML configuration.
            test_data[opt_name] = opt_default

    global_vars["TestData"] = test_data

    if config.EVERGREEN_TASK_ID is not None:
        test_data["inEvergreen"] = True

    # Initialize setParameters for mongod and mongos, to be passed to the shell via TestData. Since
    # they are dictionaries, they will be converted to JavaScript objects when passed to the shell
    # by the _format_shell_vars() function.
    mongod_set_parameters = test_data.get("setParameters", {}).copy()
    mongos_set_parameters = test_data.get("setParametersMongos", {}).copy()

    # Propagate additional setParameters to mongod processes spawned by the mongo shell. Command
    # line options to resmoke.py override the YAML configuration.
    if config.MONGOD_SET_PARAMETERS is not None:
        mongod_set_parameters.update(utils.load_yaml(config.MONGOD_SET_PARAMETERS))

    # Propagate additional setParameters to mongos processes spawned by the mongo shell. Command
    # line options to resmoke.py override the YAML configuration.
    if config.MONGOS_SET_PARAMETERS is not None:
        mongos_set_parameters.update(utils.load_yaml(config.MONGOS_SET_PARAMETERS))

    # If the 'logComponentVerbosity' setParameter for mongod was not already specified, we set its
    # value to a default.
    mongod_set_parameters.setdefault("logComponentVerbosity",
                                     default_mongod_log_component_verbosity())

    # If the 'enableFlowControl' setParameter for mongod was not already specified, we set its value
    # to a default.
    if config.FLOW_CONTROL is not None:
        mongod_set_parameters.setdefault("enableFlowControl", config.FLOW_CONTROL == "on")

    # If the 'logComponentVerbosity' setParameter for mongos was not already specified, we set its
    # value to a default.
    mongos_set_parameters.setdefault("logComponentVerbosity",
                                     default_mongos_log_component_verbosity())

    test_data["setParameters"] = mongod_set_parameters
    test_data["setParametersMongos"] = mongos_set_parameters

    test_data["undoRecorderPath"] = config.UNDO_RECORDER_PATH

    # There's a periodic background thread that checks for and aborts expired transactions.
    # "transactionLifetimeLimitSeconds" specifies for how long a transaction can run before expiring
    # and being aborted by the background thread. It defaults to 60 seconds, which is too short to
    # be reliable for our tests. Setting it to 24 hours, so that it is longer than the Evergreen
    # execution timeout.
    if "transactionLifetimeLimitSeconds" not in test_data:
        test_data["transactionLifetimeLimitSeconds"] = 24 * 60 * 60

    if "eval_prepend" in kwargs:
        eval_sb.append(str(kwargs.pop("eval_prepend")))

    # If nodb is specified, pass the connection string through TestData so it can be used inside the
    # test, then delete it so it isn't given as an argument to the mongo shell.
    if "nodb" in kwargs and connection_string is not None:
        test_data["connectionString"] = connection_string
        connection_string = None

    for var_name in global_vars:
        _format_shell_vars(eval_sb, [var_name], global_vars[var_name])

    if "eval" in kwargs:
        eval_sb.append(str(kwargs.pop("eval")))

    # Load this file to allow a callback to validate collections before shutting down mongod.
    eval_sb.append("load('jstests/libs/override_methods/validate_collections_on_shutdown.js');")

    # Load a callback to check UUID consistency before shutting down a ShardingTest.
    eval_sb.append(
        "load('jstests/libs/override_methods/check_uuids_consistent_across_cluster.js');")

    # Load a callback to check index consistency before shutting down a ShardingTest.
    eval_sb.append(
        "load('jstests/libs/override_methods/check_indexes_consistent_across_cluster.js');")

    # Load a callback to check that all orphans are deleted before shutting down a ShardingTest.
    eval_sb.append("load('jstests/libs/override_methods/check_orphans_are_deleted.js');")

    # Load this file to retry operations that fail due to in-progress background operations.
    eval_sb.append(
        "load('jstests/libs/override_methods/implicitly_retry_on_background_op_in_progress.js');")

    eval_sb.append(
        "(function() { Timestamp.prototype.toString = function() { throw new Error(\"Cannot toString timestamps. Consider using timestampCmp() for comparison or tojson(<variable>) for output.\"); } })();"
    )

    eval_str = "; ".join(eval_sb)
    args.append("--eval")
    args.append(eval_str)

    if config.SHELL_READ_MODE is not None:
        kwargs["readMode"] = config.SHELL_READ_MODE

    if config.SHELL_WRITE_MODE is not None:
        kwargs["writeMode"] = config.SHELL_WRITE_MODE

    if connection_string is not None:
        # The --host and --port options are ignored by the mongo shell when an explicit connection
        # string is specified. We remove these options to avoid any ambiguity with what server the
        # logged mongo shell invocation will connect to.
        if "port" in kwargs:
            kwargs.pop("port")

        if "host" in kwargs:
            kwargs.pop("host")

    # Apply the rest of the command line arguments.
    _apply_kwargs(args, kwargs)

    if connection_string is not None:
        args.append(connection_string)

    # Have the mongo shell run the specified file.
    if filename is not None:
        args.append(filename)

    _set_keyfile_permissions(test_data)

    process_kwargs = utils.default_if_none(process_kwargs, {})
    return make_process(logger, args, **process_kwargs)


def _format_shell_vars(sb, paths, value):
    """
    Format 'value' in a way that can be passed to --eval.

    :param sb: string builder array for the output string.
    :param paths: path of keys represented as a list.
    :param value: value in the object corresponding to the keys in `paths`
    :return: Nothing.
    """

    # Convert the list ["a", "b", "c"] into the string 'a["b"]["c"]'
    def bracketize(lst):
        return lst[0] + ''.join(f'["{i}"]' for i in lst[1:])

    # Only need to do special handling for JSON objects.
    if not isinstance(value, dict):
        sb.append("%s = %s" % (bracketize(paths), json.dumps(value)))
        return

    # Avoid including curly braces and colons in output so that the command invocation can be
    # copied and run through bash.
    sb.append("%s = new Object()" % bracketize(paths))
    for subkey in value:
        _format_shell_vars(sb, paths + [subkey], value[subkey])


def dbtest_program(logger, executable=None, suites=None, process_kwargs=None, **kwargs):
    """Return a Process instance that starts a dbtest with arguments constructed from 'kwargs'."""

    executable = utils.default_if_none(executable, config.DEFAULT_DBTEST_EXECUTABLE)
    args = [executable]

    if suites is not None:
        args.extend(suites)

    kwargs["enableMajorityReadConcern"] = config.MAJORITY_READ_CONCERN
    if config.STORAGE_ENGINE is not None:
        kwargs["storageEngine"] = config.STORAGE_ENGINE

    if config.FLOW_CONTROL is not None:
        kwargs["flowControl"] = (config.FLOW_CONTROL == "on")

    return generic_program(logger, args, process_kwargs=process_kwargs, **kwargs)


def genny_program(logger, executable=None, process_kwargs=None, **kwargs):
    """Return a Process instance that starts a genny executable with arguments constructed from 'kwargs'."""
    executable = utils.default_if_none(executable, config.DEFAULT_GENNY_EXECUTABLE)
    args = [executable]
    return generic_program(logger, args, process_kwargs, **kwargs)


def generic_program(logger, args, process_kwargs=None, **kwargs):
    """Return a Process instance that starts an arbitrary executable.

    The executable arguments are constructed from 'kwargs'.

    The args parameter is an array of strings containing the command to execute.
    """

    if not utils.is_string_list(args):
        raise ValueError("The args parameter must be a list of command arguments")

    _apply_kwargs(args, kwargs)

    process_kwargs = utils.default_if_none(process_kwargs, {})
    return make_process(logger, args, **process_kwargs)


def _apply_set_parameters(args, set_parameter):
    """Convert key-value pairs from 'kwargs' into --setParameter key=value arguments.

    This result is appended to 'args'.
    """

    for param_name in set_parameter:
        param_value = set_parameter[param_name]
        # --setParameter takes boolean values as lowercase strings.
        if isinstance(param_value, bool):
            param_value = "true" if param_value else "false"
        args.append("--setParameter")
        args.append("%s=%s" % (param_name, param_value))


def _apply_kwargs(args, kwargs):
    """Convert key-value pairs from 'kwargs' into --key value arguments.

    This result is appended to 'args'.
    A --flag without a value is represented with the empty string.
    """

    for arg_name in kwargs:
        arg_value = str(kwargs[arg_name])
        if arg_value:
            args.append("--%s=%s" % (arg_name, arg_value))
        else:
            args.append("--%s" % (arg_name))


def _set_keyfile_permissions(opts):
    """Change the permissions of keyfiles in 'opts' to 600, (only user can read and write the file).

    This necessary to avoid having the mongod/mongos fail to start up
    because "permissions on the keyfiles are too open".

    We can't permanently set the keyfile permissions because git is not
    aware of them.
    """
    if "keyFile" in opts:
        os.chmod(opts["keyFile"], stat.S_IRUSR | stat.S_IWUSR)
    if "encryptionKeyFile" in opts:
        os.chmod(opts["encryptionKeyFile"], stat.S_IRUSR | stat.S_IWUSR)