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在CephContext 的构造函数中会新建一个AdminSocket和一个CephContextHookCephContext::CephContext(uint32_t module_type_,                         enum code_environment_t code_env,                         int init_flags_){  #新建一个AdminSocket 用于接收命令  _admin_socket = new AdminSocket(this);  #新建一个CephContextHook，为这个CephContextHook 添加命令，这样我们就可以通过调用这些命令  _admin_hook = new CephContextHook(this);  _admin_socket->register_command("perfcounters_dump", "perfcounters_dump", _admin_hook, "");  _admin_socket->register_command("1", "1", _admin_hook, "");  _admin_socket->register_command("perf dump", "perf dump name=logger,type=CephString,req=false name=counter,type=CephString,req=false", _admin_hook, "dump perfcounters value");  _admin_socket->register_command("perfcounters_schema", "perfcounters_schema", _admin_hook, "");}新建AdminSocket后在start_service_thread中启动这个socketvoid CephContext::start_service_thread(){   // start admin socket  if (_conf->admin_socket.length())    _admin_socket->init(_conf->admin_socket);}bool AdminSocket::init(const std::string &path){#开始绑定并监听  int sock_fd;  err = bind_and_listen(path, &sock_fd);  if (!err.empty()) {    lderr(m_cct) << "AdminSocketConfigObs::init: failed: " << err << dendl;    close(pipe_rd);    close(pipe_wr);    return false;  }}std::string AdminSocket::bind_and_listen(const std::string &sock_path, int *fd){  ldout(m_cct, 5) << "bind_and_listen " << sock_path << dendl;#新建socket  int sock_fd = socket(PF_UNIX, SOCK_STREAM, 0);  if (sock_fd < 0) {    int err = errno;    ostringstream oss;    oss << "AdminSocket::bind_and_listen: "	<< "failed to create socket: " << cpp_strerror(err);    return oss.str();  }#开始bind  if (::bind(sock_fd, (struct sockaddr*)&address,	   sizeof(struct sockaddr_un)) != 0) {    int err = errno;    if (err == EADDRINUSE) {      AdminSocketClient client(sock_path);      bool ok;      client.ping(&ok);      if (ok) {	ldout(m_cct, 20) << "socket " << sock_path << " is in use" << dendl;	err = EEXIST;      } #开始监听  if (listen(sock_fd, 5) != 0) {    int err = errno;    ostringstream oss;    oss << "AdminSocket::bind_and_listen: "	  << "failed to listen to socket: " << cpp_strerror(err);    close(sock_fd);    VOID_TEMP_FAILURE_RETRY(unlink(sock_path.c_str()));    return oss.str();  }}这样当收到命令时就会调用bool AdminSocket::do_accept(){  bufferlist out;  if (p == m_hooks.end()) {    lderr(m_cct) << "AdminSocket: request '" << c << "' not defined" << dendl;  } else {    string args;    if (match != c) {      args = c.substr(match.length() + 1);    }    in_hook = true;    auto match_hook = p->second;    m_lock.Unlock();	#调用命令注册时对应的call函数    bool success = match_hook->call(match, cmdmap, format, out); }这里我们首先看一下hoook的call函数我们首先看下一CephContextHook的构造函数，class CephContextHook : public AdminSocketHook {  CephContext *m_cct;public:  explicit CephContextHook(CephContext *cct) : m_cct(cct) {}  bool call(std::string command, cmdmap_t& cmdmap, std::string format,	    bufferlist& out) override {    m_cct->do_command(command, cmdmap, format, &out);    return true;  }};原来就是调用CephContext的do_commandvoid CephContext::do_command(std::string command, cmdmap_t& cmdmap,			     std::string format, bufferlist *out){  Formatter *f = Formatter::create(format, "json-pretty", "json-pretty");  stringstream ss;  for (cmdmap_t::iterator it = cmdmap.begin(); it != cmdmap.end(); ++it) {    if (it->first != "prefix") {      ss << it->first  << ":" << cmd_vartype_stringify(it->second) << " ";    }  }  lgeneric_dout(this, 1) << "do_command '" << command << "' '"			 << ss.str() << dendl;  if (command == "perfcounters_dump" || command == "1" ||      command == "perf dump") {    std::string logger;    std::string counter;    cmd_getval(this, cmdmap, "logger", logger);    cmd_getval(this, cmdmap, "counter", counter);    _perf_counters_collection->dump_formatted(f, false, logger, counter);  }  }这里根据command 不同来走不同的分支，以前面注册的perfcounters_dump 为例，对比看看就很清楚了_admin_socket->register_command("perfcounters_dump", "perfcounters_dump", _admin_hook, "");

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