loop-test.cpp

gistfile1.txt

/*
 * loop-test
 *
 * Copyright (c) 2021 Damian Wrobel <dwrobel@ertelnet.rybnik.pl>
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose, provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 *
 */

#include <sstream>
#include <string.h>
#include <stdio.h>
#include <assert.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/loop.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
    const int dev_min = 100;
          int dev_max = dev_min + 16;

    const int cfd = open("/dev/loop-control", O_RDWR);
    assert(cfd >=0);
#if 0
    // free all unused loop devices
    while (true) {
        const int dev = ioctl(cfd, LOOP_CTL_GET_FREE);
        if (dev >= 0) {
            std::stringstream lo_path;
            lo_path << "/dev/loop" << dev;

            struct stat st;
            const int rv = stat(lo_path.str().c_str(), &st);

            if (rv != -1) {
                const int err = ioctl(cfd, LOOP_CTL_REMOVE, dev);

                if (err == 0 || err == dev) {
                    printf("loop-test: freeing unused /dev/loop%d\n", dev);
                } else {
                    printf("loop-test: freeing unused /dev/loop%d failed - %s (rv: %d, errno: %d)\n", dev, strerror(errno), err, errno);
                    break;
                }
            }
        }
    }
#endif    
    for (int dev = dev_min; dev < dev_max; dev++) {     
        usleep(1000); // needed for 3.10 kernel
        // add a new loop devices
        const int rv = ioctl(cfd, LOOP_CTL_ADD, dev);

        if (rv == 0 || rv == dev) {
            printf("loop-test: added /dev/loop%d\n", dev);
        } else {
            printf("loop-test: adding /dev/loop%d failed - %s (rv: %d, errno: %d)\n", dev, strerror(errno), rv, errno);
        }
    }
    
    for (int dev = dev_min; dev < dev_max; dev++) {
        usleep(1000); // needed for 3.10 kernel
        // remove a loop devices
        const int rv = ioctl(cfd, LOOP_CTL_REMOVE, dev);
        if (rv == 0 || rv == dev) {
            printf("loop-test: removed /dev/loop%d\n", dev);
        } else {
            printf("loop-test: removing /dev/loop%d failed - %s (rv: %d, errno: %d)\n", dev, strerror(errno), rv, errno);
        }
    }

    return 0;
}