【分析】Ceph编程实例接口Librbd(C++)--映像创建与数据读写

目前我们有两种路径使用Ceph的块存储：?
- 利用QEMU/KVM通过librbd与 Ceph 块设备交互，主要为虚拟机提供块存储设备，如下图所示；?

- 利用kernel module与Host kernel交互，主要为物理机提供块设备支持。

Librbd 是Ceph提供的块存储接口的抽象，它提供C/C++、Python等多种接口。对于C++，最主要的两个类就是RBD?和?Image。?RBD?主要负责创建、删除、克隆映像等操作，而Image?类负责映像的读写等操作。

准备工作

对于任何客户端应用，都需要首先连接到一个运行良好的Ceph集群。

获取集群句柄

//声明Rados对象，并初始化
librados::Rados rados;
ret = rados.init("admin"); // just use the client.admin keyring
if (ret < 0) { // let's handle any error that might have come back
    std::cerr << "couldn't initialize rados! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "we just set up a rados cluster object" << std::endl;
}

//获取配置文件信息: /etc/ceph/ceph.conf
// 1. 根据命令行参数
/*
ret = rados.conf_parse_argv(argc, argv);
if (ret < 0) {
    // This really can't happen, but we need to check to be a good citizen.
    std::cerr << "failed to parse config options! error " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "we just parsed our config options" << std::endl;
    // We also want to apply the config file if the user specified
    // one, and conf_parse_argv won't do that for us.
    for (int i = 0; i < argc; ++i) {
        if ((strcmp(argv[i], "-c") == 0) || (strcmp(argv[i], "--conf") == 0)) {
            ret = rados.conf_read_file(argv[i+1]);
            if (ret < 0) {
                // This could fail if the config file is malformed, but it'd be hard.
                std::cerr << "failed to parse config file " << argv[i+1]
                        << "! error" << ret << std::endl;
                ret = EXIT_FAILURE;
                return EXIT_FAILURE;
            }
            break;
        }
    }
}
*/
// 2. 程序里面指定
ret = rados.conf_read_file("/etc/ceph/ceph.conf");
if (ret < 0) {
    // This could fail if the config file is malformed, but it'd be hard.
    std::cerr << "failed to parse config file! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
}

连接集群

ret = rados.connect();
if (ret < 0) {
    std::cerr << "couldn't connect to cluster! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "we just connected to the rados cluster" << std::endl;
}

创建I/O上下文环境

如果没有存储池，需要先新建一个存储池。

新建存储池

const char *pool_name = "gnar";
ret = rados.pool_create(pool_name);
if (ret < 0) {
    std::cerr << "couldn't create pool! error " << ret << std::endl;
    ret = EXIT_FAILURE;
    rados.shutdown(); //断开集群连接
    return EXIT_FAILURE;
} else {
    std::cout << "we just created a new pool named " << pool_name << std::endl;
}

新建I/O上下文环境

librados::IoCtx io_ctx; //I/O上下文
const char *pool_name = "gnar";
ret = rados.ioctx_create(pool_name, io_ctx);
if (ret < 0) {
    std::cerr << "couldn't setup ioctx! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    rados.shutdown(); //断开集群连接
    return EXIT_FAILURE; 
} else {
    std::cout << "we just created an ioctx for our pool" << std::endl;
}

若干RBD映像API

声明RBD对象，创建rbd映像

librbd::RBD rbd;
const char *image_name = "rumboo";
uint64_t init_size = (uint64_t) 200 * 1024 * 1024; //映像初始化大小200MB
uint64_t features = 1; //影响feature个数
int order = 22; //默认值为22, 即4MB (1 << 22)
ret = rbd.create2(io_ctx, image_name, init_size, features, &order);
if (ret < 0) {
    std::cerr << "couldn't create rbd image! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    io_ctx.close(); //关闭I/O上下文
    rados.shutdown(); //断开集群连接
    return EXIT_FAILURE;
} else {
    std::cout << "We just created an rbd image" << std::endl;
}

打开rbd映像

librbd::RBD rbd;
const char *image_name = "rumboo";
librbd::Image image;
ret = rbd.open(io_ctx, image, image_name);
if (ret < 0) {
    std::cerr << "couldn't open rbd image! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    io_ctx.close(); //关闭I/O上下文
    rados.shutdown(); //断开集群连接
    return EXIT_FAILURE;
} else {
    std::cout << "We just opened an rbd image" << std::endl;
}

查看映像大小

uint64_t size = 0;
ret = image.size(&size);
if (ret < 0) {
    std::cerr << "couldn't get image size! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "The size of the image is " << size << std::endl;
}

调整映像大小

size = (uint64_t) 500 * 1024 * 1024; //调整映像大小500MB
ret = image.resize(size);
if (ret < 0) {
    std::cerr << "couldn't change the size of the image! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "We just change the size of the image" << std::endl;
}

查看映像ID

std::string id;
ret = image.get_id(&id);
if (ret < 0) {
    std::cerr << "couldn't get image ID! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "The ID of the image is " << id << std::endl;
}

查看映像features

features = 0;
ret = image.features(&features);
if (ret < 0) {
    std::cerr << "couldn't get image features! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "The features of the image are " << features << std::endl;
}

查看映像状态信息

librbd::image_info_t info;
ret = image.stat(info, sizeof(info));
if (ret < 0) {
    std::cerr << "couldn't get image stat_info! err " << ret << std::endl;
    ret = EXIT_FAILURE;
    return EXIT_FAILURE;
} else {
    std::cout << "info.size is " << info.size << std::endl;
    std::cout << "info.obj_size is " << info.obj_size << std::endl;
    std::cout << "info.num_objs is " << info.num_objs << std::endl;
    std::cout << "info.order is " << info.order << std::endl;
    std::cout << "info.block_name_prefix is " << info.block_name_prefix << std::endl;
}

查看存储池ID

std::cout << "data pool id is " << image.get_data_pool_id() << std::endl;

• 1

  查看block_name_prefix

  std::cout << "block name prefix is " << image.get_block_name_prefix() << std::endl;

  
  

  查看flags

  uint64_t flags = 0;
  ret = image.get_flags(&flags);
  if (ret < 0) {
      std::cerr << "couldn't get image flags! err " << ret << std::endl;
      ret = EXIT_FAILURE;
      return EXIT_FAILURE;
  } else {
      std::cout << "image flags is " << flags << std::endl;
  }

  
  

  查看条带化参数

  std::cout << "image stripe unit is " << image.get_stripe_unit() << std::endl;
  std::cout << "image stripe count is " << image.get_stripe_count() << std::endl;

  
  

  RBD映像数据读写

  数据读写 – synchronous

  uint64_t ofs_w = (uint64_t) 0; //读写偏移量
  uint64_t ofs_r = (uint64_t) 0;
  size_t len_w = 100; //读写长度
  size_t len_r = 100;
  ceph::bufferlist bl_w; //读写bufferlist
  ceph::bufferlist bl_r;
  const char *fn_i = "input"; //读写文件名
  const char *fn_o = "output";
  std::string error;
  
  ret = bl_r.read_file(fn_i, &error);
  std::cout << "read file ret = " << ret << std::endl;
  if (ret < 0) {
      std::cerr << "couldn't read file! err " << ret << std::endl;
      ret = EXIT_FAILURE;
      image.close(); //关闭rbd映像
      io_ctx.close(); //关闭I/O上下文
      rados.shutdown(); //断开集群连接
      return EXIT_FAILURE;
  } else {
      std::cout << "We just read a file" << std::endl;
  }
  ssize_t ret_w = image.write2(ofs_w, len_w, bl_r, 0);
  
  ssize_t ret_r = image.read2(ofs_r, len_r, bl_w, 0);
  ret = bl_w.write_file(fn_o, 0644);
  std::cout << "write file ret = " << ret << std::endl;
  if (ret < 0) {
      std::cerr << "couldn't write file! err " << ret << std::endl;
      ret = EXIT_FAILURE;
      image.close(); //关闭rbd映像
      io_ctx.close(); //关闭I/O上下文
      rados.shutdown(); //断开集群连接
      return EXIT_FAILURE;
  } else {
      std::cout << "We just wrote a file" << std::endl;
  }

  
  

  数据读写 – asynchronous

  std::string data = "foo"; 
  uint64_t ofs_aiow = (uint64_t) 100; //读写偏移量
  uint64_t ofs_aior = (uint64_t) 100;
  size_t len_aiow = 600; //读写长度
  size_t len_aior = 600;
  ceph::bufferlist bl_aiow; //读写bufferlist
  ceph::bufferlist bl_aior;
  librbd::RBD::AioCompletion *write_completion = new librbd::RBD::AioCompletion(
      NULL, (librbd::callback_t) simple_write_cb); //读写AioCompletion
  librbd::RBD::AioCompletion *read_completion = new librbd::RBD::AioCompletion(
      NULL, (librbd::callback_t) simple_read_cb);
  
  for (int i = 0; i < 200; ++i) {
      bl_aior.append(data);
  }
  std::cout << bl_aior.to_str() << std::endl;
  
  ret = image.aio_write2(ofs_aiow, len_aiow, bl_aior, write_completion, 0);
  if (ret < 0) {
      std::cerr << "couldn't start write! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      image.close(); //关闭rbd映像
      io_ctx.close(); //关闭I/O上下文
      rados.shutdown(); //断开集群连接
      return EXIT_FAILURE;
  }
  write_completion->wait_for_complete(); //等待写完成
  ret_w = write_completion->get_return_value();
  if (ret_w < 0) {
      std::cerr << "couldn't write! error " << ret << std::endl;
      ret_w = EXIT_FAILURE;
      image.close(); //关闭rbd映像
      io_ctx.close(); //关闭I/O上下文
      rados.shutdown(); //断开集群连接
      return EXIT_FAILURE;
  } else {
      std::cout << "we just write data successfully, return value is " << ret_w << std::endl;
  }
  
  ret = image.aio_read2(ofs_aior, len_aior, bl_aiow, read_completion, 0);
  if (ret < 0) {
      std::cerr << "couldn't start read! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      image.close(); //关闭rbd映像
      io_ctx.close(); //关闭I/O上下文
      rados.shutdown(); //断开集群连接
      return EXIT_FAILURE;
  }
  read_completion->wait_for_complete(); //等待读完成
  ret_r = read_completion->get_return_value();
  if (ret_r < 0) {
      std::cerr << "couldn't read! error " << ret << std::endl;
      ret_r = EXIT_FAILURE;
      image.close(); //关闭rbd映像
      io_ctx.close(); //关闭I/O上下文
      rados.shutdown(); //断开集群连接
      return EXIT_FAILURE;
  } else {
      std::cout << "we just read data successfully, return value is " << ret_r << std::endl;
  }
  std::cout << bl_aiow.to_str() << std::endl;
  
  write_completion->release();
  read_completion->release();
  
  void simple_write_cb(librbd::completion_t cb, void *arg) {
      std::cout << "write completion cb called!" << std::endl;
  }
  
  //简单的回调函数，用于librbd::RBD::AioCompletion
  void simple_read_cb(librbd::completion_t cb, void *arg) {
      std::cout << "read completion cb called!" << std::endl;
  }

  
  

  收尾工作

  在最后，一定不能忘记关闭rbd映像、I/O上下文，断开集群连接。

  ret = image.close(); //关闭rbd映像
  if (ret < 0) {
      std::cerr << "couldn't close rbd image! err " << ret << std::endl;
      ret = EXIT_FAILURE;
      return EXIT_FAILURE;
  } else {
      std::cout << "we just closed an rbd image" << std::endl;
  }
  io_ctx.close(); //关闭I/O上下文
  rados.shutdown(); //断开集群连接
  return EXIT_SUCCESS;