hello_world.cc

// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
/*
 * Ceph - scalable distributed file system
 *
 * This is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License version 2.1, as published by the Free Software
 * Foundation.  See file COPYING.
 * Copyright 2013 Inktank
 */

// install the librados-dev package to get this
#include <rados/librados.hpp>
#include <iostream>
#include <string>

int main(int argc, const char **argv)
{
  int ret = 0;

  // we will use all of these below
  const char *pool_name = "hello_world_pool";
  std::string hello("hello world!");
  std::string object_name("hello_object");
  librados::IoCtx io_ctx;

  // first, we create a Rados object and initialize it
  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! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we just set up a rados cluster object" << std::endl;
  }

  /*
   * Now we need to get the rados object its config info. It can
   * parse argv for us to find the id, monitors, etc, so let's just
   * use that.
   */
  {
    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;
      goto out;
    }

    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;
	  goto out;
	}
	break;
      }
    }
  }

  /*
   * next, we actually connect to the cluster
   */
  {
    ret = rados.connect();
    if (ret < 0) {
      std::cerr << "couldn't connect to cluster! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we just connected to the rados cluster" << std::endl;
  }

  /*
   * let's create our own pool instead of scribbling over real data.
   * Note that this command creates pools with default PG counts specified
   * by the monitors, which may not be appropriate for real use -- it's fine
   * for testing, though.
   */
  {
    ret = rados.pool_create(pool_name);
    if (ret < 0) {
      std::cerr << "couldn't create pool! error " << ret << std::endl;
      return EXIT_FAILURE;
    }
    std::cout << "we just created a new pool named " << pool_name << std::endl;
  }

  /*
   * create an "IoCtx" which is used to do IO to a pool
   */
  {
    ret = rados.ioctx_create(pool_name, io_ctx);
    if (ret < 0) {
      std::cerr << "couldn't set up ioctx! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we just created an ioctx for our pool" << std::endl;
  }

  /*
   * now let's do some IO to the pool! We'll write "hello world!" to a
   * new object.
   */
  {
    /*
     * "bufferlist"s are Ceph's native transfer type, and are carefully
     * designed to be efficient about copying. You can fill them
     * up from a lot of different data types, but strings or c strings
     * are often convenient. Just make sure not to deallocate the memory
     * until the bufferlist goes out of scope and any requests using it
     * have been finished!
     */
    librados::bufferlist bl;
    bl.append(hello);

    /*
     * now that we have the data to write, let's send it to an object.
     * We'll use the synchronous interface for simplicity.
     */
    ret = io_ctx.write_full(object_name, bl);
    if (ret < 0) {
      std::cerr << "couldn't write object! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we just wrote new object " << object_name
              << ", with contents\n" << hello << std::endl;
  }

  /*
   * now let's read that object back! Just for fun, we'll do it using
   * async IO instead of synchronous. (This would be more useful if we
   * wanted to send off multiple reads at once; see
   * http://docs.ceph.com/docs/master/rados/api/librados/#asychronous-io )
   */
  {
    librados::bufferlist read_buf;
    int read_len = 4194304; // this is way more than we need
    // allocate the completion from librados
    librados::AioCompletion *read_completion = librados::Rados::aio_create_completion();
    // send off the request.
    ret = io_ctx.aio_read(object_name, read_completion, &read_buf, read_len, 0);
    if (ret < 0) {
      std::cerr << "couldn't start read object! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    // wait for the request to complete, and check that it succeeded.
    read_completion->wait_for_complete();
    ret = read_completion->get_return_value();
    if (ret < 0) {
      std::cerr << "couldn't read object! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we read our object " << object_name
              << ", and got back " << ret << " bytes with contents\n";
    std::string read_string;
    read_buf.copy(0, ret, read_string);
    std::cout << read_string << std::endl;
  }

  /*
   * We can also use xattrs that go alongside the object.
   */
  {
    librados::bufferlist version_bl;
    version_bl.append('1');
    ret = io_ctx.setxattr(object_name, "version", version_bl);
    if (ret < 0) {
      std::cerr << "failed to set xattr version entry! error "
		<< ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we set the xattr 'version' on our object!" << std::endl;
  }

  /*
   * And if we want to be really cool, we can do multiple things in a single
   * atomic operation. For instance, we can update the contents of our object
   * and set the version at the same time.
   */
  {
    librados::bufferlist bl;
    bl.append(hello);
    bl.append("v2");
    librados::ObjectWriteOperation write_op;
    write_op.write_full(bl);
    librados::bufferlist version_bl;
    version_bl.append('2');
    write_op.setxattr("version", version_bl);
    ret = io_ctx.operate(object_name, &write_op);
    if (ret < 0) {
      std::cerr << "failed to do compound write! error " << ret << std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we overwrote our object " << object_name
              << " with contents\n" << bl.c_str() << std::endl;
  }

  /*
   * And to be even cooler, we can make sure that the object looks the
   * way we expect before doing the write! Notice how this attempt fails
   * because the xattr differs.
   */
  {
    librados::ObjectWriteOperation failed_write_op;
    librados::bufferlist bl;
    bl.append(hello);
    bl.append("v2");
    librados::ObjectWriteOperation write_op;
    write_op.write_full(bl);
    librados::bufferlist version_bl;
    version_bl.append('2');
    librados::bufferlist old_version_bl;
    old_version_bl.append('1');
    failed_write_op.cmpxattr("version", LIBRADOS_CMPXATTR_OP_EQ, old_version_bl);
    failed_write_op.write_full(bl);
    failed_write_op.setxattr("version", version_bl);
    ret = io_ctx.operate(object_name, &failed_write_op);
    if (ret < 0) {
      std::cout << "we just failed a write because the xattr wasn't as specified"
		<< std::endl;
    } else {
      std::cerr << "we succeeded on writing despite an xattr comparison mismatch!"
		<< std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }

    /*
     * Now let's do the update with the correct xattr values so it
     * actually goes through
     */
    bl.clear();
    bl.append(hello);
    bl.append("v3");
    old_version_bl.clear();
    old_version_bl.append('2');
    version_bl.clear();
    version_bl.append('3');
    librados::ObjectWriteOperation update_op;
    update_op.cmpxattr("version", LIBRADOS_CMPXATTR_OP_EQ, old_version_bl);
    update_op.write_full(bl);
    update_op.setxattr("version", version_bl);
    ret = io_ctx.operate(object_name, &update_op);
    if (ret < 0) {
      std::cerr << "failed to do a compound write update! error " << ret
		<< std::endl;
      ret = EXIT_FAILURE;
      goto out;
    }
    std::cout << "we overwrote our object " << object_name
              << " following an xattr test with contents\n" << bl.c_str()
              << std::endl;
  }

  ret = EXIT_SUCCESS;
  out:
  /*
   * And now we're done, so let's remove our pool and then
   * shut down the connection gracefully.
   */
  int delete_ret = rados.pool_delete(pool_name);
  if (delete_ret < 0) {
    // be careful not to
    std::cerr << "We failed to delete our test pool!" << std::endl;
    ret = EXIT_FAILURE;
  }

  rados.shutdown();

  return ret;
}