host/commands/launch/flag_forwarder.cc - device/google/cuttlefish - Git at Google

 //
 // Copyright (C) 2019 The Android Open Source Project
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 #include "flag_forwarder.h"

 #include <cstring>

 #include <sstream>
 #include <map>
 #include <string>
 #include <vector>

 #include <gflags/gflags.h>
 #include <android-base/logging.h>
 #include <libxml/tree.h>

 #include "common/libs/fs/shared_buf.h"
 #include "common/libs/fs/shared_fd.h"
 #include "common/libs/utils/subprocess.h"

 /**
  * Superclass for a flag loaded from another process.
  *
  * An instance of this class defines a flag available either in this subprocess
  * or another flag. If a flag needs to be registered in the current process, see
  * the DynamicFlag subclass. If multiple subprocesses declare a flag with the
  * same name, they all should receive that flag, but the DynamicFlag should only
  * be created zero or one times. Zero times if the parent process defines it as
  * well, one time if the parent does not define it.
  *
  * Notably, gflags itself defines some flags that are present in every binary.
  */
 class SubprocessFlag {
   std::string subprocess_;
   std::string name_;
 public:
   SubprocessFlag(const std::string& subprocess, const std::string& name)
       : subprocess_(subprocess), name_(name) {
   }
   virtual ~SubprocessFlag() = default;
   SubprocessFlag(const SubprocessFlag&) = delete;
   SubprocessFlag& operator=(const SubprocessFlag&) = delete;
   SubprocessFlag(SubprocessFlag&&) = delete;
   SubprocessFlag& operator=(SubprocessFlag&&) = delete;

   const std::string& Subprocess() const { return subprocess_; }
   const std::string& Name() const { return name_; }
 };

 /*
  * A dynamic gflags flag. Creating an instance of this class is equivalent to
  * registering a flag with DEFINE_<type>. Instances of this class should not
  * be deleted while flags are still in use (likely through the end of main).
  *
  * This is implemented as a wrapper around gflags::FlagRegisterer. This class
  * serves a dual purpose of holding the memory for gflags::FlagRegisterer as
  * that normally expects memory to be held statically. The other reason is to
  * subclass class SubprocessFlag to fit into the flag-forwarding scheme.
  */
 template<typename T>
 class DynamicFlag : public SubprocessFlag {
   std::string help_;
   std::string filename_;
   T current_storage_;
   T defvalue_storage_;
   gflags::FlagRegisterer registerer_;
 public:
   DynamicFlag(const std::string& subprocess, const std::string& name,
               const std::string& help, const std::string& filename,
               const T& current, const T& defvalue)
       : SubprocessFlag(subprocess, name), help_(help), filename_(filename),
         current_storage_(current), defvalue_storage_(defvalue),
         registerer_(Name().c_str(), help_.c_str(), filename_.c_str(),
                     &current_storage_, &defvalue_storage_) {
   }
 };

 namespace {

 /**
  * Returns a mapping between flag name and "gflags type" as strings for flags
  * defined in the binary.
  */
 std::map<std::string, std::string> CurrentFlagsToTypes() {
   std::map<std::string, std::string> name_to_type;
   std::vector<gflags::CommandLineFlagInfo> self_flags;
   gflags::GetAllFlags(&self_flags);
   for (auto& flag : self_flags) {
     name_to_type[flag.name] = flag.type;
   }
   return name_to_type;
 }

 /**
  * Returns a pointer to the child of `node` with name `name`.
  *
  * For example, invoking `xmlChildWithName(<foo><bar>abc</bar></foo>, "foo")`
  * will return <bar>abc</bar>.
  */
 xmlNodePtr xmlChildWithName(xmlNodePtr node, const std::string& name) {
   for (xmlNodePtr child = node->children; child != nullptr; child = child->next) {
     if (child->type != XML_ELEMENT_NODE) {
       continue;
     }
     if (std::strcmp((const char*) child->name, name.c_str()) == 0) {
       return child;
     }
   }
   LOG(WARNING) << "no child with name " << name;
   return nullptr;
 }

 /**
  * Returns a string with the content of an xml node.
  *
  * For example, calling `xmlContent(<bar>abc</bar>)` will return "abc".
  */
 std::string xmlContent(xmlNodePtr node) {
   if (node == nullptr || node->children == NULL
       || node->children->type != xmlElementType::XML_TEXT_NODE) {
     return "";
   }
   return std::string((char*) node->children->content);
 }

 template<typename T>
 T FromString(const std::string& str) {
   std::stringstream stream(str);
   T output;
   stream >> output;
   return output;
 }

 /**
  * Creates a dynamic flag
  */
 std::unique_ptr<SubprocessFlag> MakeDynamicFlag(
     const std::string& subprocess,
     const gflags::CommandLineFlagInfo& flag_info) {
   std::unique_ptr<SubprocessFlag> ptr;
   if (flag_info.type == "bool") {
     ptr.reset(new DynamicFlag<bool>(subprocess, flag_info.name,
                                     flag_info.description,
                                     flag_info.filename,
                                     FromString<bool>(flag_info.default_value),
                                     FromString<bool>(flag_info.current_value)));
   } else if (flag_info.type == "int32") {
     ptr.reset(new DynamicFlag<int32_t>(subprocess, flag_info.name,
                                        flag_info.description,
                                        flag_info.filename,
                                        FromString<int32_t>(flag_info.default_value),
                                        FromString<int32_t>(flag_info.current_value)));
   } else if (flag_info.type == "uint32") {
     ptr.reset(new DynamicFlag<uint32_t>(subprocess, flag_info.name,
                                         flag_info.description,
                                         flag_info.filename,
                                         FromString<uint32_t>(flag_info.default_value),
                                         FromString<uint32_t>(flag_info.current_value)));
   } else if (flag_info.type == "int64") {
     ptr.reset(new DynamicFlag<int64_t>(subprocess, flag_info.name,
                                        flag_info.description,
                                        flag_info.filename,
                                        FromString<int64_t>(flag_info.default_value),
                                        FromString<int64_t>(flag_info.current_value)));
   } else if (flag_info.type == "uint64") {
     ptr.reset(new DynamicFlag<uint64_t>(subprocess, flag_info.name,
                                         flag_info.description,
                                         flag_info.filename,
                                         FromString<uint64_t>(flag_info.default_value),
                                         FromString<uint64_t>(flag_info.current_value)));
   } else if (flag_info.type == "double") {
     ptr.reset(new DynamicFlag<double>(subprocess, flag_info.name,
                                       flag_info.description,
                                       flag_info.filename,
                                       FromString<double>(flag_info.default_value),
                                       FromString<double>(flag_info.current_value)));
   } else if (flag_info.type == "string") {
     ptr.reset(new DynamicFlag<std::string>(subprocess, flag_info.name,
                                            flag_info.description,
                                            flag_info.filename,
                                            flag_info.default_value,
                                            flag_info.current_value));
   } else {
     LOG(FATAL) << "Unknown type \"" << flag_info.type << "\" for flag " << flag_info.name;
   }
   return ptr;
 }

 std::vector<gflags::CommandLineFlagInfo> FlagsForSubprocess(std::string helpxml_output) {
   // Hack to try to filter out log messages that come before the xml
   helpxml_output = helpxml_output.substr(helpxml_output.find("<?xml"));

   xmlDocPtr doc = xmlReadMemory(helpxml_output.c_str(), helpxml_output.size(),
                                 NULL, NULL, 0);
   if (doc == NULL) {
     LOG(FATAL) << "Could not parse xml of subprocess `--helpxml`";
   }
   xmlNodePtr root_element = xmlDocGetRootElement(doc);
   std::vector<gflags::CommandLineFlagInfo> flags;
   for (xmlNodePtr flag = root_element->children; flag != nullptr; flag = flag->next) {
     if (std::strcmp((const char*) flag->name, "flag") != 0) {
       continue;
     }
     gflags::CommandLineFlagInfo flag_info;
     flag_info.name = xmlContent(xmlChildWithName(flag, "name"));
     flag_info.type = xmlContent(xmlChildWithName(flag, "type"));
     flag_info.filename = xmlContent(xmlChildWithName(flag, "file"));
     flag_info.description = xmlContent(xmlChildWithName(flag, "meaning"));
     flag_info.current_value = xmlContent(xmlChildWithName(flag, "current"));
     flag_info.default_value = xmlContent(xmlChildWithName(flag, "default"));
     flags.emplace_back(std::move(flag_info));
   }
   xmlFree(doc);
   xmlCleanupParser();
   return flags;
 }

 } // namespace

 FlagForwarder::FlagForwarder(std::set<std::string> subprocesses)
     : subprocesses_(std::move(subprocesses)) {
   std::map<std::string, std::string> flag_to_type = CurrentFlagsToTypes();

   for (const auto& subprocess : subprocesses_) {
     cuttlefish::Command cmd(subprocess);
     cmd.AddParameter("--helpxml");
     std::string helpxml_input, helpxml_output, helpxml_error;
     cuttlefish::SubprocessOptions options;
     options.Verbose(false);
     int helpxml_ret = cuttlefish::RunWithManagedStdio(std::move(cmd), &helpxml_input,
                                                &helpxml_output, &helpxml_error,
                                                options);
     if (helpxml_ret != 1) {
       LOG(FATAL) << subprocess << " --helpxml returned unexpected response "
                  << helpxml_ret << ". Stderr was " << helpxml_error;
       return;
     }

     auto subprocess_flags = FlagsForSubprocess(helpxml_output);
     for (const auto& flag : subprocess_flags) {
       if (flag_to_type.count(flag.name)) {
         if (flag_to_type[flag.name] == flag.type) {
           flags_.emplace(std::make_unique<SubprocessFlag>(subprocess, flag.name));
         } else {
           LOG(FATAL) << flag.name << "defined as " << flag_to_type[flag.name]
                      << " and " << flag.type;
           return;
         }
       } else {
         flag_to_type[flag.name] = flag.type;
         flags_.emplace(MakeDynamicFlag(subprocess, flag));
       }
     }
   }
 }

 // Destructor must be defined in an implementation file.
 // https://stackoverflow.com/questions/6012157
 FlagForwarder::~FlagForwarder() = default;

 void FlagForwarder::UpdateFlagDefaults() const {

   for (const auto& subprocess : subprocesses_) {
     cuttlefish::Command cmd(subprocess);
     std::vector<std::string> invocation = {subprocess};
     for (const auto& flag : ArgvForSubprocess(subprocess)) {
       cmd.AddParameter(flag);
     }
     // Disable flags that could cause the subprocess to exit before helpxml.
     // See gflags_reporting.cc.
     cmd.AddParameter("--nohelp");
     cmd.AddParameter("--nohelpfull");
     cmd.AddParameter("--nohelpshort");
     cmd.AddParameter("--helpon=");
     cmd.AddParameter("--helpmatch=");
     cmd.AddParameter("--nohelppackage=");
     cmd.AddParameter("--noversion");
     // Ensure this is set on by putting it at the end.
     cmd.AddParameter("--helpxml");
     std::string helpxml_input, helpxml_output, helpxml_error;
     cuttlefish::SubprocessOptions options;
     options.Verbose(false);
     int helpxml_ret = cuttlefish::RunWithManagedStdio(std::move(cmd), &helpxml_input,
                                                &helpxml_output, &helpxml_error,
                                                options);
     if (helpxml_ret != 1) {
       LOG(FATAL) << subprocess << " --helpxml returned unexpected response "
                  << helpxml_ret << ". Stderr was " << helpxml_error;
       return;
     }

     auto subprocess_flags = FlagsForSubprocess(helpxml_output);
     for (const auto& flag : subprocess_flags) {
       gflags::SetCommandLineOptionWithMode(
           flag.name.c_str(),
           flag.default_value.c_str(),
           gflags::FlagSettingMode::SET_FLAGS_DEFAULT);
     }
   }
 }

 std::vector<std::string> FlagForwarder::ArgvForSubprocess(
     const std::string& subprocess) const {
   std::vector<std::string> subprocess_argv;
   for (const auto& flag : flags_) {
     if (flag->Subprocess() == subprocess) {
       gflags::CommandLineFlagInfo flag_info =
           gflags::GetCommandLineFlagInfoOrDie(flag->Name().c_str());
       if (!flag_info.is_default) {
         subprocess_argv.push_back("--" + flag->Name() + "=" + flag_info.current_value);
       }
     }
   }
   return subprocess_argv;
 }
	//
	// Copyright (C) 2019 The Android Open Source Project
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	#include "flag_forwarder.h"

	#include <cstring>

	#include <sstream>
	#include <map>
	#include <string>
	#include <vector>

	#include <gflags/gflags.h>
	#include <android-base/logging.h>
	#include <libxml/tree.h>

	#include "common/libs/fs/shared_buf.h"
	#include "common/libs/fs/shared_fd.h"
	#include "common/libs/utils/subprocess.h"

	/**
	* Superclass for a flag loaded from another process.
	*
	* An instance of this class defines a flag available either in this subprocess
	* or another flag. If a flag needs to be registered in the current process, see
	* the DynamicFlag subclass. If multiple subprocesses declare a flag with the
	* same name, they all should receive that flag, but the DynamicFlag should only
	* be created zero or one times. Zero times if the parent process defines it as
	* well, one time if the parent does not define it.
	*
	* Notably, gflags itself defines some flags that are present in every binary.
	*/
	class SubprocessFlag {
	std::string subprocess_;
	std::string name_;
	public:
	SubprocessFlag(const std::string& subprocess, const std::string& name)
	: subprocess_(subprocess), name_(name) {
	}
	virtual ~SubprocessFlag() = default;
	SubprocessFlag(const SubprocessFlag&) = delete;
	SubprocessFlag& operator=(const SubprocessFlag&) = delete;
	SubprocessFlag(SubprocessFlag&&) = delete;
	SubprocessFlag& operator=(SubprocessFlag&&) = delete;

	const std::string& Subprocess() const { return subprocess_; }
	const std::string& Name() const { return name_; }
	};

	/*
	* A dynamic gflags flag. Creating an instance of this class is equivalent to
	* registering a flag with DEFINE_<type>. Instances of this class should not
	* be deleted while flags are still in use (likely through the end of main).
	*
	* This is implemented as a wrapper around gflags::FlagRegisterer. This class
	* serves a dual purpose of holding the memory for gflags::FlagRegisterer as
	* that normally expects memory to be held statically. The other reason is to
	* subclass class SubprocessFlag to fit into the flag-forwarding scheme.
	*/
	template<typename T>
	class DynamicFlag : public SubprocessFlag {
	std::string help_;
	std::string filename_;
	T current_storage_;
	T defvalue_storage_;
	gflags::FlagRegisterer registerer_;
	public:
	DynamicFlag(const std::string& subprocess, const std::string& name,
	const std::string& help, const std::string& filename,
	const T& current, const T& defvalue)
	: SubprocessFlag(subprocess, name), help_(help), filename_(filename),
	current_storage_(current), defvalue_storage_(defvalue),
	registerer_(Name().c_str(), help_.c_str(), filename_.c_str(),
	&current_storage_, &defvalue_storage_) {
	}
	};

	namespace {

	/**
	* Returns a mapping between flag name and "gflags type" as strings for flags
	* defined in the binary.
	*/
	std::map<std::string, std::string> CurrentFlagsToTypes() {
	std::map<std::string, std::string> name_to_type;
	std::vector<gflags::CommandLineFlagInfo> self_flags;
	gflags::GetAllFlags(&self_flags);
	for (auto& flag : self_flags) {
	name_to_type[flag.name] = flag.type;
	}
	return name_to_type;
	}

	/**
	* Returns a pointer to the child of `node` with name `name`.
	*
	* For example, invoking `xmlChildWithName(<foo><bar>abc</bar></foo>, "foo")`
	* will return <bar>abc</bar>.
	*/
	xmlNodePtr xmlChildWithName(xmlNodePtr node, const std::string& name) {
	for (xmlNodePtr child = node->children; child != nullptr; child = child->next) {
	if (child->type != XML_ELEMENT_NODE) {
	continue;
	}
	if (std::strcmp((const char*) child->name, name.c_str()) == 0) {
	return child;
	}
	}
	LOG(WARNING) << "no child with name " << name;
	return nullptr;
	}

	/**
	* Returns a string with the content of an xml node.
	*
	* For example, calling `xmlContent(<bar>abc</bar>)` will return "abc".
	*/
	std::string xmlContent(xmlNodePtr node) {
	if (node == nullptr \|\| node->children == NULL
	\|\| node->children->type != xmlElementType::XML_TEXT_NODE) {
	return "";
	}
	return std::string((char*) node->children->content);
	}

	template<typename T>
	T FromString(const std::string& str) {
	std::stringstream stream(str);
	T output;
	stream >> output;
	return output;
	}

	/**
	* Creates a dynamic flag
	*/
	std::unique_ptr<SubprocessFlag> MakeDynamicFlag(
	const std::string& subprocess,
	const gflags::CommandLineFlagInfo& flag_info) {
	std::unique_ptr<SubprocessFlag> ptr;
	if (flag_info.type == "bool") {
	ptr.reset(new DynamicFlag<bool>(subprocess, flag_info.name,
	flag_info.description,
	flag_info.filename,
	FromString<bool>(flag_info.default_value),
	FromString<bool>(flag_info.current_value)));
	} else if (flag_info.type == "int32") {
	ptr.reset(new DynamicFlag<int32_t>(subprocess, flag_info.name,
	flag_info.description,
	flag_info.filename,
	FromString<int32_t>(flag_info.default_value),
	FromString<int32_t>(flag_info.current_value)));
	} else if (flag_info.type == "uint32") {
	ptr.reset(new DynamicFlag<uint32_t>(subprocess, flag_info.name,
	flag_info.description,
	flag_info.filename,
	FromString<uint32_t>(flag_info.default_value),
	FromString<uint32_t>(flag_info.current_value)));
	} else if (flag_info.type == "int64") {
	ptr.reset(new DynamicFlag<int64_t>(subprocess, flag_info.name,
	flag_info.description,
	flag_info.filename,
	FromString<int64_t>(flag_info.default_value),
	FromString<int64_t>(flag_info.current_value)));
	} else if (flag_info.type == "uint64") {
	ptr.reset(new DynamicFlag<uint64_t>(subprocess, flag_info.name,
	flag_info.description,
	flag_info.filename,
	FromString<uint64_t>(flag_info.default_value),
	FromString<uint64_t>(flag_info.current_value)));
	} else if (flag_info.type == "double") {
	ptr.reset(new DynamicFlag<double>(subprocess, flag_info.name,
	flag_info.description,
	flag_info.filename,
	FromString<double>(flag_info.default_value),
	FromString<double>(flag_info.current_value)));
	} else if (flag_info.type == "string") {
	ptr.reset(new DynamicFlag<std::string>(subprocess, flag_info.name,
	flag_info.description,
	flag_info.filename,
	flag_info.default_value,
	flag_info.current_value));
	} else {
	LOG(FATAL) << "Unknown type \"" << flag_info.type << "\" for flag " << flag_info.name;
	}
	return ptr;
	}

	std::vector<gflags::CommandLineFlagInfo> FlagsForSubprocess(std::string helpxml_output) {
	// Hack to try to filter out log messages that come before the xml
	helpxml_output = helpxml_output.substr(helpxml_output.find("<?xml"));

	xmlDocPtr doc = xmlReadMemory(helpxml_output.c_str(), helpxml_output.size(),
	NULL, NULL, 0);
	if (doc == NULL) {
	LOG(FATAL) << "Could not parse xml of subprocess `--helpxml`";
	}
	xmlNodePtr root_element = xmlDocGetRootElement(doc);
	std::vector<gflags::CommandLineFlagInfo> flags;
	for (xmlNodePtr flag = root_element->children; flag != nullptr; flag = flag->next) {
	if (std::strcmp((const char*) flag->name, "flag") != 0) {
	continue;
	}
	gflags::CommandLineFlagInfo flag_info;
	flag_info.name = xmlContent(xmlChildWithName(flag, "name"));
	flag_info.type = xmlContent(xmlChildWithName(flag, "type"));
	flag_info.filename = xmlContent(xmlChildWithName(flag, "file"));
	flag_info.description = xmlContent(xmlChildWithName(flag, "meaning"));
	flag_info.current_value = xmlContent(xmlChildWithName(flag, "current"));
	flag_info.default_value = xmlContent(xmlChildWithName(flag, "default"));
	flags.emplace_back(std::move(flag_info));
	}
	xmlFree(doc);
	xmlCleanupParser();
	return flags;
	}

	} // namespace

	FlagForwarder::FlagForwarder(std::set<std::string> subprocesses)
	: subprocesses_(std::move(subprocesses)) {
	std::map<std::string, std::string> flag_to_type = CurrentFlagsToTypes();

	for (const auto& subprocess : subprocesses_) {
	cuttlefish::Command cmd(subprocess);
	cmd.AddParameter("--helpxml");
	std::string helpxml_input, helpxml_output, helpxml_error;
	cuttlefish::SubprocessOptions options;
	options.Verbose(false);
	int helpxml_ret = cuttlefish::RunWithManagedStdio(std::move(cmd), &helpxml_input,
	&helpxml_output, &helpxml_error,
	options);
	if (helpxml_ret != 1) {
	LOG(FATAL) << subprocess << " --helpxml returned unexpected response "
	<< helpxml_ret << ". Stderr was " << helpxml_error;
	return;
	}

	auto subprocess_flags = FlagsForSubprocess(helpxml_output);
	for (const auto& flag : subprocess_flags) {
	if (flag_to_type.count(flag.name)) {
	if (flag_to_type[flag.name] == flag.type) {
	flags_.emplace(std::make_unique<SubprocessFlag>(subprocess, flag.name));
	} else {
	LOG(FATAL) << flag.name << "defined as " << flag_to_type[flag.name]
	<< " and " << flag.type;
	return;
	}
	} else {
	flag_to_type[flag.name] = flag.type;
	flags_.emplace(MakeDynamicFlag(subprocess, flag));
	}
	}
	}
	}

	// Destructor must be defined in an implementation file.
	// https://stackoverflow.com/questions/6012157
	FlagForwarder::~FlagForwarder() = default;

	void FlagForwarder::UpdateFlagDefaults() const {

	for (const auto& subprocess : subprocesses_) {
	cuttlefish::Command cmd(subprocess);
	std::vector<std::string> invocation = {subprocess};
	for (const auto& flag : ArgvForSubprocess(subprocess)) {
	cmd.AddParameter(flag);
	}
	// Disable flags that could cause the subprocess to exit before helpxml.
	// See gflags_reporting.cc.
	cmd.AddParameter("--nohelp");
	cmd.AddParameter("--nohelpfull");
	cmd.AddParameter("--nohelpshort");
	cmd.AddParameter("--helpon=");
	cmd.AddParameter("--helpmatch=");
	cmd.AddParameter("--nohelppackage=");
	cmd.AddParameter("--noversion");
	// Ensure this is set on by putting it at the end.
	cmd.AddParameter("--helpxml");
	std::string helpxml_input, helpxml_output, helpxml_error;
	cuttlefish::SubprocessOptions options;
	options.Verbose(false);
	int helpxml_ret = cuttlefish::RunWithManagedStdio(std::move(cmd), &helpxml_input,
	&helpxml_output, &helpxml_error,
	options);
	if (helpxml_ret != 1) {
	LOG(FATAL) << subprocess << " --helpxml returned unexpected response "
	<< helpxml_ret << ". Stderr was " << helpxml_error;
	return;
	}

	auto subprocess_flags = FlagsForSubprocess(helpxml_output);
	for (const auto& flag : subprocess_flags) {
	gflags::SetCommandLineOptionWithMode(
	flag.name.c_str(),
	flag.default_value.c_str(),
	gflags::FlagSettingMode::SET_FLAGS_DEFAULT);
	}
	}
	}

	std::vector<std::string> FlagForwarder::ArgvForSubprocess(
	const std::string& subprocess) const {
	std::vector<std::string> subprocess_argv;
	for (const auto& flag : flags_) {
	if (flag->Subprocess() == subprocess) {
	gflags::CommandLineFlagInfo flag_info =
	gflags::GetCommandLineFlagInfoOrDie(flag->Name().c_str());
	if (!flag_info.is_default) {
	subprocess_argv.push_back("--" + flag->Name() + "=" + flag_info.current_value);
	}
	}
	}
	return subprocess_argv;
	}