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ceph源码分析：Admin Socket机制

分类： 服务器与存储

2015-05-31 02:05:57


任何一个成熟的项目，必须要提供出接口，就像探针一样，可以让我们探查进程内部的运行情况，进程不能是一个黑盒子。对于ceph而言，Admin Socket 提供了该功能。Admin Socket 不仅可以查看当前的配置，进程运行的状态，而且，还可以修改配置，获取log等。

下面help可以看出，ceph给出了很多命令，来了解ceph内部的运行情况。
  1. root@test3:~# ceph daemon /var/run/ceph/ceph-osd.4.asok help
  2. { "config get": "config get : get the config value",
  3.   "config set": "config set [ ...]: set a config variable",
  4.   "config show": "dump current config settings",
  5.   "dump_blacklist": "dump blacklisted clients and times",
  6.   "dump_historic_ops": "show slowest recent ops",
  7.   "dump_op_pq_state": "dump op priority queue state",
  8.   "dump_ops_in_flight": "show the ops currently in flight",
  9.   "dump_watchers": "show clients which have active watches, and on which objects",
  10.   "get_command_descriptions": "list available commands",
  11.   "getomap": "output entire object map",
  12.   "git_version": "get git sha1",
  13.   "help": "list available commands",
  14.   "injectdataerr": "inject data error into omap",
  15.   "injectmdataerr": "inject metadata error",
  16.   "log dump": "dump recent log entries to log file",
  17.   "log flush": "flush log entries to log file",
  18.   "log reopen": "reopen log file",
  19.   "perf dump": "dump perfcounters value",
  20.   "perf schema": "dump perfcounters schema",
  21.   "rmomapkey": "remove omap key",
  22.   "setomapheader": "set omap header",
  23.   "setomapval": "set omap key",
  24.   "truncobj": "truncate object to length",
  25.   "version": "get ceph version"}
  26. root@test3:~# ceph daemon /var/run/ceph/ceph-mon.*.asok help
  27. { "add_bootstrap_peer_hint": "add peer address as potential bootstrap peer for cluster bringup",
  28.   "config get": "config get : get the config value",
  29.   "config set": "config set [ ...]: set a config variable",
  30.   "config show": "dump current config settings",
  31.   "get_command_descriptions": "list available commands",
  32.   "git_version": "get git sha1",
  33.   "help": "list available commands",
  34.   "log dump": "dump recent log entries to log file",
  35.   "log flush": "flush log entries to log file",
  36.   "log reopen": "reopen log file",
  37.   "mon_status": "show current monitor status",
  38.   "perf dump": "dump perfcounters value",
  39.   "perf schema": "dump perfcounters schema",
  40.   "quorum_status": "show current quorum status",
  41.   "sync_force": "force sync of and clear monitor store",
  42.   "version": "get ceph version"}
  43. root@test3:~# ceph daemon /var/run/ceph/ceph-mds.*.asok help
  44. { "config get": "config get : get the config value",
  45.   "config set": "config set [ ...]: set a config variable",
  46.   "config show": "dump current config settings",
  47.   "get_command_descriptions": "list available commands",
  48.   "git_version": "get git sha1",
  49.   "help": "list available commands",
  50.   "log dump": "dump recent log entries to log file",
  51.   "log flush": "flush log entries to log file",
  52.   "log reopen": "reopen log file",
  53.   "objecter_requests": "show in-progress osd requests",
  54.   "perf dump": "dump perfcounters value",
  55.   "perf schema": "dump perfcounters schema",
  56.   "version": "get ceph version"}

比如可以查看 ceph的各个模块的当前配置

  1. ceph daemon /var/run/ceph/ceph-mds.*.asok config show
  2. ceph daemon /var/run/ceph/ceph-mon.*.asok config show
  3. ceph daemon /var/run/ceph/ceph-osd.4.asok config show
这个是怎么实现的呢？ 这是依靠ceph的AdminSocket机制完成。
CephContext中会创建一个AdminSocket对象，该对象本质是一个线程。ceph-mon/ceph-osd/ceph-mds这些进程都会有创建一个AdminSocket的线程，负责响应用户的探查命令。

从上面的OSD MON MDS help的不同输出可以看出，他们支持的命令有共同的，也有各自独立的。
首先是共同支持的命令有：
  • config show        显示所有的配置项
  • config get           获取某个配置项
  • config set           设置某个配置项
  • log flush　　      将log 刷入日志文件
  • log dump           将最近的若干笔log刷入到log文件
  • log reopen         重新打开log文件
  • perf dump         输出统计信息
  • perf schema      输出统计信息的类型
  • version             版本信息
  • git_version   :    git 版本信息
支持的大部分common的命令，注册发生在 CephContext的构造函数：
  1.   _admin_hook = new CephContextHook(this);
  2.   _admin_socket->register_command("perfcounters_dump", "perfcounters_dump", _admin_hook, "");
  3.   _admin_socket->register_command("1", "1", _admin_hook, "");
  4.   _admin_socket->register_command("perf dump", "perf dump", _admin_hook, "dump perfcounters value");
  5.   _admin_socket->register_command("perfcounters_schema", "perfcounters_schema", _admin_hook, "");
  6.   _admin_socket->register_command("2", "2", _admin_hook, "");
  7.   _admin_socket->register_command("perf schema", "perf schema", _admin_hook, "dump perfcounters schema");
  8.   _admin_socket->register_command("config show", "config show", _admin_hook, "dump current config settings");
  9.   _admin_socket->register_command("config set", "config set name=var,type=CephString name=val,type=CephString,n=N", _admin_hook, "config set [ ...]: set a config variable");
  10.   _admin_socket->register_command("config get", "config get name=var,type=CephString", _admin_hook, "config get : get the config value");
  11.   _admin_socket->register_command("log flush", "log flush", _admin_hook, "flush log entries to log file");
  12.   _admin_socket->register_command("log dump", "log dump", _admin_hook, "dump recent log entries to log file");
  13.   _admin_socket->register_command("log reopen", "log reopen", _admin_hook, "reopen log file")

首先定义了个CephContextHook，注册该Hook也作为一个参数传递进去，这个register_command比较简单，就是建立了command字符串和Hook的关联，这个关联有何作用，后面会分析到，暂时按下不表。

  1. int AdminSocket::register_command(std::string command, std::string cmddesc, AdminSocketHook *hook, std::string help)
  2. {
  3.   int ret;
  4.   m_lock.Lock();
  5.   if (m_hooks.count(command)) {
  6.     ldout(m_cct, 5) << "register_command " << command << " hook " << hook << " EEXIST" << dendl;
  7.     ret = -EEXIST;
  8.   } else {
  9.     ldout(m_cct, 5) << "register_command " << command << " hook " << hook << dendl;
  10.     m_hooks[command] = hook;
  11.     m_descs[command] = cmddesc;
  12.     m_help[command] = help;
  13.     ret = 0;
  14.   }
  15.   m_lock.Unlock();
  16.   return ret;
  17. }

后面从注册部分的代码我们可以知道下面三个命令是等效的。

  1. ceph daemon /var/run/ceph/ceph-mds.bfudz.asok perf dump
  2. ceph daemon /var/run/ceph/ceph-mds.bfudz.asok perfcounters_dump
  3. ceph daemon /var/run/ceph/ceph-mds.bfudz.asok 1
还有下面三个命令是等效的：

  1. ceph daemon /var/run/ceph/ceph-mds.bfudz.asok perf schema
  2. ceph daemon /var/run/ceph/ceph-mds.bfudz.asok perfcounters_schema
  3. ceph daemon /var/run/ceph/ceph-mds.bfudz.asok 2
 ceph-osd/ceph-mon/ceph-mds有一些自己的独特的注册函数，大家检索register_command可以检索的到这些独特的命令。


这个AdminSocket 对应的线程，在common_init_finish函数中负责创建。

  1. void common_init_finish(CephContext *cct)
  2. {
  3.   ceph::crypto::init(cct);
  4.   cct->start_service_thread();
  5.   if (cct->_conf->lockdep) {
  6.     g_lockdep = true;
  7.     ldout(cct,0) << "lockdep is enabled" << dendl;
  8.     lockdep_register_ceph_context(cct);
  9.   }
  10. }
而在start_service_thread函数中会调用adminsocket的init函数：

  1. void CephContext::start_service_thread()
  2. {
  3.   pthread_spin_lock(&_service_thread_lock);
  4.   if (_service_thread) {
  5.     pthread_spin_unlock(&_service_thread_lock);
  6.     return;
  7.   }
  8.   _service_thread = new CephContextServiceThread(this);
  9.   _service_thread->create();
  10.   pthread_spin_unlock(&_service_thread_lock);
  11.   // make logs flush on_exit()
  12.   if (_conf->log_flush_on_exit)
  13.     _log->set_flush_on_exit();
  14.   // Trigger callbacks on any config observers that were waiting for
  15.   // it to become safe to start threads.
  16.   _conf->set_val("internal_safe_to_start_threads", "true");
  17.   _conf->call_all_observers();
  18.   // start admin socket
  19.   if (_conf->admin_socket.length())
  20.     _admin_socket->init(_conf->admin_socket);
  21. }

接下来可以分析下admin_socket的初始化函数init：

  1. bool AdminSocket::init(const std::string &path)
  2. {
  3.   ldout(m_cct, 5) << "init " << path << dendl;
  4.   /* Set up things for the new thread */
  5.   std::string err;
  6.   int pipe_rd = -1, pipe_wr = -1;
  7.   err = create_shutdown_pipe(&pipe_rd, &pipe_wr);
  8.   if (!err.empty()) {
  9.     lderr(m_cct) << "AdminSocketConfigObs::init: error: " << err << dendl;
  10.     return false;
  11.   }
  12.   int sock_fd;
  13.   err = bind_and_listen(path, &sock_fd);
  14.   if (!err.empty()) {
  15.     lderr(m_cct) << "AdminSocketConfigObs::init: failed: " << err << dendl;
  16.     close(pipe_rd);
  17.     close(pipe_wr);
  18.     return false;
  19.   }
  20.   /* Create new thread */
  21.   m_sock_fd = sock_fd;
  22.   m_shutdown_rd_fd = pipe_rd;
  23.   m_shutdown_wr_fd = pipe_wr;
  24.   m_path = path;
  25.   m_version_hook = new VersionHook;
  26.   register_command("0", "0", m_version_hook, "");
  27.   register_command("version", "version", m_version_hook, "get ceph version");
  28.   register_command("git_version", "git_version", m_version_hook, "get git sha1");
  29.   m_help_hook = new HelpHook(this);
  30.   register_command("help", "help", m_help_hook, "list available commands");
  31.   m_getdescs_hook = new GetdescsHook(this);
  32.   register_command("get_command_descriptions", "get_command_descriptions",
  33.   m_getdescs_hook, "list available commands");
  34.   create();
  35.   add_cleanup_file(m_path.c_str());
  36.   return true;
  37. }

首先是创建了管道，读取端的文件描述符记录在m_shutdown_rd_fd中，写入端的文件描述符记录在m_shutdown_wr_fd中。
从变量名字也可以看出，该文件描述符的作用是收取关闭信息。因为adminsocket一旦创建，必须能够通知到该线程及时退出。
退出的事情会写入管道的写入端，而线程会通过多路复用接口，监听读取端，一旦发现m_shutdown_rd_fd中读出内容，线程就知道，可以退出了。
按下不表。

AdminSocket最重要的是监听发过来的请求，它是用socket来实现的，初始化在bind_and_listen 函数：

  1. std::string AdminSocket::bind_and_listen(const std::string &sock_path, int *fd)
  2. {
  3.   ldout(m_cct, 5) << "bind_and_listen " << sock_path << dendl;

  5.   struct sockaddr_un address;
  6.   if (sock_path.size() > sizeof(address.sun_path) - 1) {
  7.     ostringstream oss;
  8.     oss << "AdminSocket::bind_and_listen: "
  9.     << "The UNIX domain socket path " << sock_path << " is too long! The "
  10.     << "maximum length on this system is "
  11.     << (sizeof(address.sun_path) - 1);
  12.     return oss.str();
  13.   }
  14.   int sock_fd = socket(PF_UNIX, SOCK_STREAM, 0);
  15.   if (sock_fd < 0) {
  16.     int err = errno;
  17.     ostringstream oss;
  18.     oss << "AdminSocket::bind_and_listen: "
  19.     << "failed to create socket: " << cpp_strerror(err);
  20.     return oss.str();
  21.   }
  22.   int r = fcntl(sock_fd, F_SETFD, FD_CLOEXEC);
  23.   if (r < 0) {
  24.     r = errno;
  25.     TEMP_FAILURE_RETRY(::close(sock_fd));
  26.     ostringstream oss;
  27.     oss << "AdminSocket::bind_and_listen: failed to fcntl on socket: " << cpp_strerror(r);
  28.     return oss.str();
  29.   }
  30.   memset(&address, 0, sizeof(struct sockaddr_un));
  31.   address.sun_family = AF_UNIX;
  32.   snprintf(address.sun_path, sizeof(address.sun_path),
  33.      "%s", sock_path.c_str());
  34.   if (bind(sock_fd, (struct sockaddr*)&address,
  35.      sizeof(struct sockaddr_un)) != 0) {
  36.     int err = errno;
  37.     if (err == EADDRINUSE) {
  38.       AdminSocketClient client(sock_path);
  39.       bool ok;
  40.       client.ping(&ok);
  41.       if (ok) {
  42.     ldout(m_cct, 20) << "socket " << sock_path << " is in use" << dendl;
  43.     err = EEXIST;
  44.       } else {
  45.     ldout(m_cct, 20) << "unlink stale file " << sock_path << dendl;
  46.     TEMP_FAILURE_RETRY(unlink(sock_path.c_str()));
  47.     if (bind(sock_fd, (struct sockaddr*)&address,
  48.          sizeof(struct sockaddr_un)) == 0) {
  49.      err = 0;
  50.     } else {
  51.      err = errno;
  52.     }
  53.       }
  54.     }
  55.     if (err != 0) {
  56.       ostringstream oss;
  57.       oss << "AdminSocket::bind_and_listen: "
  58.      << "failed to bind the UNIX domain socket to '" << sock_path
  59.      << "': " << cpp_strerror(err);
  60.       close(sock_fd);
  61.       return oss.str();
  62.     }
  63.   }
  64.   if (listen(sock_fd, 5) != 0) {
  65.     int err = errno;
  66.     ostringstream oss;
  67.     oss << "AdminSocket::bind_and_listen: "
  68.      << "failed to listen to socket: " << cpp_strerror(err);
  69.     close(sock_fd);
  70.     TEMP_FAILURE_RETRY(unlink(sock_path.c_str()));
  71.     return oss.str();
  72.   }
  73.   *fd = sock_fd;
  74.   return "";
  75. }

这个函数做的事情并不难理解，做的事情比较老套：
1 创建一个socket，该函数需要一个入参，指定socket路径名：
2  bind
3 listen
而传入的路径名是这个
  1. root@test3:/var/run/ceph# ceph daemon /var/run/ceph/ceph-mds.bfudz.asok config get admin_socket
  2. { "admin_socket": "\/var\/run\/ceph\/ceph-mds.bfudz.asok"}
socket建好之后，因为线程还没有创建，所以至今还没有accept接口 。然后我们再次回到init函数，该函数又注册了几个函数：

  1. m_version_hook = new VersionHook;
  2.   register_command("0", "0", m_version_hook, "");
  3.   register_command("version", "version", m_version_hook, "get ceph version");
  4.   register_command("git_version", "git_version", m_version_hook, "get git sha1");
  5.   m_help_hook = new HelpHook(this);
  6.   register_command("help", "help", m_help_hook, "list available commands");
  7.   m_getdescs_hook = new GetdescsHook(this);
  8.   register_command("get_command_descriptions", "get_command_descriptions",
  9.   m_getdescs_hook, "list available commands");
这几个函数的重要性并不大，基本是用来查版本信息的，如下所示，按下不表。

  1. root@test3:/var/run/ceph# ceph daemon /var/run/ceph/ceph-mds.bfudz.asok version
  2. {"version":"0.67.9-222-g014b35f"}
  3. root@test3:/var/run/ceph# ceph daemon /var/run/ceph/ceph-mds.bfudz.asok git_version
  4. {"git_version":"014b35fc1ee0a1ad1f699a3705f3481a88614d36"}
  5. root@test3:/var/run/ceph#

init函数最后调用了create函数。create函数是老朋友，前面分析Log的时候已经提到，对于Thread这个类，做的事情无非就是创建线程。关键内容是，线程执行的函数是哪个？
和Log一样，是entry函数。AdminSocket类也有entry函数，该函数是AdminSocket 对应线程指定的函数：

  1. void* AdminSocket::entry()
  2. {
  3.   ldout(m_cct, 5) << "entry start" << dendl;
  4.   while (true) {
  5.     struct pollfd fds[2];
  6.     memset(fds, 0, sizeof(fds));
  7.     fds[0].fd = m_sock_fd;
  8.     fds[0].events = POLLIN | POLLRDBAND;
  9.     fds[1].fd = m_shutdown_rd_fd;
  10.     fds[1].events = POLLIN | POLLRDBAND;
  11.     int ret = poll(fds, 2, -1);
  12.     if (ret < 0) {
  13.       int err = errno;
  14.       if (err == EINTR) {
  15. continue;
  16.       }
  17.       lderr(m_cct) << "AdminSocket: poll(2) error: '"
  18.   << cpp_strerror(err) << dendl;
  19.       return PFL_FAIL;
  20.     }
  21.     if (fds[0].revents & POLLIN) {
  22.       // Send out some data
  23.       do_accept();
  24.     }
  25.     if (fds[1].revents & POLLIN) {
  26.       // Parent wants us to shut down
  27.       return PFL_SUCCESS;
  28.     }
  29.   }
  30.   ldout(m_cct, 5) << "entry exit" << dendl;
  31. }

这个线程函数比较简单，它监听socket fd和管道的读取端。
1 管道的读取端负责管理何时退出
2 socket fd 负责监听用户发过来的指令。

处理用户发过来的命令，是do_accept函数干的事情：

  1. bool AdminSocket::do_accept()
  2. {
  3.   struct sockaddr_un address;
  4.   socklen_t address_length = sizeof(address);
  5.   ldout(m_cct, 30) << "AdminSocket: calling accept" << dendl;
  6.   int connection_fd = accept(m_sock_fd, (struct sockaddr*) &address,
  7.              &address_length);
  8.   ldout(m_cct, 30) << "AdminSocket: finished accept" << dendl;
  9.   if (connection_fd < 0) {
  10.     int err = errno;
  11.     lderr(m_cct) << "AdminSocket: do_accept error: '"
  12.              << cpp_strerror(err) << dendl;
  13.     return false;
  14.   }

  16.   char cmd[1024];
  17.   int pos = 0;
  18.   string c;
  19.   while (1) {
  20.     int ret = safe_read(connection_fd, &cmd[pos], 1);
  21.     if (ret <= 0) {
  22.       lderr(m_cct) << "AdminSocket: error reading request code: "
  23.          << cpp_strerror(ret) << dendl;
  24.       close(connection_fd);
  25.       return false;
  26.     }
  27.     //ldout(m_cct, 0) << "AdminSocket read byte " << (int)cmd[pos] << " pos " << pos << dendl;
  28.     if (cmd[0] == '\0') {
  29.       // old protocol: __be32
  30.       if (pos == 3 && cmd[0] == '\0') {
  31.     switch (cmd[3]) {
  32.     case 0:
  33.      c = "0";
  34.      break;
  35.     case 1:
  36.      c = "perfcounters_dump";
  37.      break;
  38.     case 2:
  39.      c = "perfcounters_schema";
  40.      break;
  41.     default:
  42.      c = "foo";
  43.      break;
  44.     }
  45.     break;
  46.       }
  47.     } else {
  48.       // new protocol: null or \n terminated string
  49.       if (cmd[pos] == '\n' || cmd[pos] == '\0') {
  50.     cmd[pos] = '\0';
  51.     c = cmd;
  52.     break;
  53.       }
  54.     }
  55.     pos++;
  56.   }

  58.   bool rval = false;

  60.   map<string, cmd_vartype> cmdmap;
  61.   string format;
  62.   vector<string> cmdvec;
  63.   stringstream errss;
  64.   cmdvec.push_back(cmd);
  65.   if (!cmdmap_from_json(cmdvec, &cmdmap, errss)) {
  66.     ldout(m_cct, 0) << "AdminSocket: " << errss << dendl;
  67.     return false;
  68.   }
  69.   cmd_getval(m_cct, cmdmap, "format", format);
  70.   if (format != "json" && format != "json-pretty" &&
  71.       format != "xml" && format != "xml-pretty")
  72.     format = "json-pretty";
  73.   cmd_getval(m_cct, cmdmap, "prefix", c);

  75.   string firstword;
  76.   if (c.find(" ") == string::npos)
  77.     firstword = c;
  78.   else
  79.     firstword = c.substr(0, c.find(" "));

  81.   m_lock.Lock();
  82.   map<string,AdminSocketHook*>::iterator p;
  83.   string match = c;
  84.   while (match.size()) {
  85.     p = m_hooks.find(match);
  86.     if (p != m_hooks.end())
  87.       break;
  88.     
  89.     // drop right-most word
  90.     size_t pos = match.rfind(' ');
  91.     if (pos == std::string::npos) {
  92.       match.clear(); // we fail
  93.       break;
  94.     } else {
  95.       match.resize(pos);
  96.     }
  97.   }

  99.   bufferlist out;
  100.   if (p == m_hooks.end()) {
  101.     lderr(m_cct) << "AdminSocket: request '" << c << "' not defined" << dendl;
  102.   } else {
  103.     string args;
  104.     if (match != c)
  105.       args = c.substr(match.length() + 1);
  106.     bool success = p->second->call(match, cmdmap, format, out);
  107.     if (!success) {
  108.       ldout(m_cct, 0) << "AdminSocket: request '" << match << "' args '" << args
  109.          << "' to " << p->second << " failed" << dendl;
  110.       out.append("failed");
  111.     } else {
  112.       ldout(m_cct, 5) << "AdminSocket: request '" << match << "' '" << args
  113.          << "' to " << p->second
  114.          << " returned " << out.length() << " bytes" << dendl;
  115.     }
  116.     uint32_t len = htonl(out.length());
  117.     int ret = safe_write(connection_fd, &len, sizeof(len));
  118.     if (ret < 0) {
  119.       lderr(m_cct) << "AdminSocket: error writing response length "
  120.          << cpp_strerror(ret) << dendl;
  121.     } else {
  122.       if (out.write_fd(connection_fd) >= 0)
  123.     rval = true;
  124.     }
  125.   }
  126.   m_lock.Unlock();

  128.   TEMP_FAILURE_RETRY(close(connection_fd));
  129.   return rval;
  130. }

这个函数有点长，但是并不复杂。简单说，如果有个client尝试 connect ，该线程就poll就会感知到，然后进入do_accept函数。
do_accept首先执行accept，和client 搭上线，然后开始通信。 

safe_read负责 读取客户发过来的指令。前面已经提到过，AdminSocket支持的命令是有限的，初始化之前都已注册过了。
如果client 发来的指令时注册过的指令，就见招拆招，返回相应的结果给客户端。

每一个命令的字符串，都是和一个AdminSocketHook 的类型关联的，但是一个AdminSocketHook可以对应多个command

  1. std::map<std::string,AdminSocketHook*> m_hooks
比如说 config show  / config get   / perf dump对应的多事 CephContextHook，前面已经提到过。

见招拆招的函数，就记录在对应的Hook上：

  1. class CephContextHook : public AdminSocketHook {
  2.   CephContext *m_cct;
  3. public:
  4.   CephContextHook(CephContext *cct) : m_cct(cct) {}
  5.   bool call(std::string command, cmdmap_t& cmdmap, std::string format,
  6.    bufferlist& out) {
  7.     m_cct->do_command(command, cmdmap, format, &out);
  8.     return true;
  9.   }
  10. };


do_accept函数中黄色的一行，具体是实现，就是对应Hook的call函数，对于CephContextHook，就是这个类的call方法。

下面我们看下CephContextHook的call方法：即它的do_command函数：

  1. void CephContext::do_command(std::string command, cmdmap_t& cmdmap,
  2.              std::string format, bufferlist *out)
  3. {
  4.   Formatter *f = new_formatter(format);
  5.   if (!f)
  6.     f = new_formatter("json-pretty");
  7.   stringstream ss;
  8.   for (cmdmap_t::iterator it = cmdmap.begin(); it != cmdmap.end(); ++it) {
  9.     if (it->first != "prefix") {
  10.       ss << it->first << ":" << cmd_vartype_stringify(it->second) << " ";
  11.     }
  12.   }
  13.   lgeneric_dout(this, 1) << "do_command '" << command << "' '"
  14.              << ss.str() << dendl;
  15.   if (command == "perfcounters_dump" || command == "1" ||
  16.       command == "perf dump") {
  17.     _perf_counters_collection->dump_formatted(f, false);
  18.   }
  19.   else if (command == "perfcounters_schema" || command == "2" ||
  20.     command == "perf schema") {
  21.     _perf_counters_collection->dump_formatted(f, true);
  22.   }
  23.   else {
  24.     f->open_object_section(command.c_str());
  25.     if (command == "config show") {
  26.       _conf->show_config(f);
  27.     }
  28.     else if (command == "config set") {
  29.       std::string var;
  30.       std::vector<std::string> val;

  32.       if (!(cmd_getval(this, cmdmap, "var", var)) ||
  33.           !(cmd_getval(this, cmdmap, "val", val))) {
  34.         f->dump_string("error", "syntax error: 'config set '");
  35.       } else {
  36.     // val may be multiple words
  37.     string valstr = str_join(val, " ");
  38.         int r = _conf->set_val(var.c_str(), valstr.c_str());
  39.         if (r < 0) {
  40.           f->dump_stream("error") << "error setting '" << var << "' to '" << valstr << "': " << cpp_strerror(r);
  41.         } else {
  42.           ostringstream ss;
  43.           _conf->apply_changes(&ss);
  44.           f->dump_string("success", ss.str());
  45.         }
  46.       }
  47.     } else if (command == "config get") {
  48.       std::string var;
  49.       if (!cmd_getval(this, cmdmap, "var", var)) {
  50.     f->dump_string("error", "syntax error: 'config get '");
  51.       } else {
  52.     char buf[4096];
  53.     memset(buf, 0, sizeof(buf));
  54.     char *tmp = buf;
  55.     int r = _conf->get_val(var.c_str(), &tmp, sizeof(buf));
  56.     if (r < 0) {
  57.      f->dump_stream("error") << "error getting '" << var << "': " << cpp_strerror(r);
  58.     } else {
  59.      f->dump_string(var.c_str(), buf);
  60.     }
  61.       }
  62.     } else if (command == "log flush") {
  63.       _log->flush();
  64.     }
  65.     else if (command == "log dump") {
  66.       _log->dump_recent();
  67.     }
  68.     else if (command == "log reopen") {
  69.       _log->reopen_log_file();
  70.     }
  71.     else {
  72.       assert(0 == "registered under wrong command?");
  73.     }
  74.     f->close_section();
  75.   }
  76.   f->flush(*out);
  77.   delete f;
  78.   lgeneric_dout(this, 1) << "do_command '" << command << "' '" << ss.str()
  79.          << "result is " << out->length() << " bytes" << dendl;
  80. };
  毫不意外，前面注册的每一个方法，在do_command函数中都做了处理。
  
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