rbd_read.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <rados/librados.h>
#include <rbd/librbd.h>

int main (int argc, const char* argv[])
{

        /* Declare the cluster handle and required arguments. */
        rados_t cluster;
        //char cluster_name[] = "ceph";
        char cluster_name[] = "6ff29c93-4568-40a4-a8dc-e2749f4ae22c";
        char user_name[] = "client.admin";
        uint64_t flags;

        /* Initialize the cluster handle with the "ceph" cluster name and the "client.admin" user */
        int err;
        err = rados_create2(&cluster, cluster_name, user_name, flags);

        if (err < 0) {
                fprintf(stderr, "%s: Couldn't create the cluster handle! %s\n", argv[0], strerror(-err));
                exit(EXIT_FAILURE);
        } else {
                printf("\nCreated a cluster handle.\n");
        }

        /* Read a Ceph configuration file to configure the cluster handle. */
        //err = rados_conf_read_file(cluster, "/etc/ceph/ceph.conf");
        err = rados_conf_read_file(cluster, "/opt/ceph_test_script/ceph.conf");
        if (err < 0) {
                fprintf(stderr, "%s: cannot read config file: %s\n", argv[0], strerror(-err));
                exit(EXIT_FAILURE);
        } else {
                printf("\nRead the config file.\n");
        }

        /* Read command line arguments */
        err = rados_conf_parse_argv(cluster, argc, argv);
        if (err < 0) {
                fprintf(stderr, "%s: cannot parse command line arguments: %s\n", argv[0], strerror(-err));
                exit(EXIT_FAILURE);
        } else {
                printf("\nRead the command line arguments.\n");
        }

        /* Connect to the cluster */
        err = rados_connect(cluster);
        if (err < 0) {
                fprintf(stderr, "%s: cannot connect to cluster: %s\n", argv[0], strerror(-err));
                exit(EXIT_FAILURE);
        } else {
                printf("\nConnected to the cluster.\n");
        }

	/*
         * Continued from previous C example, where cluster handle and
         * connection are established. First declare an I/O Context.
         */

        rados_ioctx_t io;
        //char *poolname = "data";
        char *poolname = "rbd";

        err = rados_ioctx_create(cluster, poolname, &io);
        if (err < 0) {
                fprintf(stderr, "%s: cannot open rados pool %s: %s\n", argv[0], poolname, strerror(-err));
                rados_shutdown(cluster);
                exit(EXIT_FAILURE);
        } else {
                printf("\nCreated I/O context.\n");
        }

        rbd_image_t image;
        err = rbd_open(io, "rbd0", &image, NULL);
        if (err < 0) {
		fprintf(stderr, "%s: cannot open image rbd0: %s\n", argv[0], strerror(-err));
                rados_ioctx_destroy(io);
                rados_shutdown(cluster);
                exit(EXIT_FAILURE);
        } else {
                printf("\nOpen image.\n");
        }
        
        rbd_completion_t comp;
        err = rbd_aio_create_completion(NULL, NULL, &comp);
        /*
         * Read data from the cluster asynchronously.
         * First, set up asynchronous I/O completion.
         */
        if (err < 0) {
                fprintf(stderr, "%s: Could not create aio completion: %s\n", argv[0], strerror(-err));
                rbd_aio_release(comp);
                rbd_close(image);
                rados_ioctx_destroy(io);
                rados_shutdown(cluster);

                exit(1);
        } else {
                printf("\nCreated AIO completion.\n");
        }

        /* Next, read data using rados_aio_read. */
        char read_res[50];
        
        err = rbd_aio_read(image, 0, 50, read_res, comp);

        /* Wait for the operation to complete */
//      rados_wait_for_complete(comp);
        err = rbd_aio_wait_for_complete(comp);
        ssize_t value = rbd_aio_get_return_value(comp);
        int ret_value = value;
        printf("\nThe length is %d.\n", ret_value);
	//sleep(1);

        if (err < 0) {
                fprintf(stderr, "%s: Cannot read object. %s %s\n", argv[0], poolname, strerror(-err));
        } else {
                printf("\nThe data is:\n");
                int i = 0;
                for(; i<ret_value; i++)
                    printf("%c", read_res[i]);
                printf("\n");
                //printf("\nRead object \"neo-obj\". The contents are:\n%s\n", read_res);
        }

        /* Release the asynchronous I/O complete handle to avoid memory leaks. */
        rbd_aio_release(comp);
        rbd_close(image);
        rados_ioctx_destroy(io);
        rados_shutdown(cluster);
}