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Diffstat (limited to 'src/ceph/examples/librados/hello_world.cc')
| -rw-r--r-- | src/ceph/examples/librados/hello_world.cc | 298 |
1 files changed, 298 insertions, 0 deletions
diff --git a/src/ceph/examples/librados/hello_world.cc b/src/ceph/examples/librados/hello_world.cc new file mode 100644 index 0000000..48e1fd1 --- /dev/null +++ b/src/ceph/examples/librados/hello_world.cc @@ -0,0 +1,298 @@ +// -*- 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; + } else { + 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; + } 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; + 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; + } else { + 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; + } else { + 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; + } else { + 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; + } else { + 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; + } else { + 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; + } else { + 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; + } else { + 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; + } else { + 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; +} |