get-device-blocks.c

#include <stdio.h>
#include <stdint.h>
#include <unistd.h>
#include <inttypes.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/utsname.h>

#define BLKGETSIZE64 _IOR(0x12,114,size_t)  /* return device size in bytes (u64 *arg) */

int get_device_blocks(const char *file, int blocksize, uint64_t *retblocks)
{
    int fd, rc = 0;
    int valid_blkgetsize64 = 1;
    struct utsname ut;
    unsigned long long size64;

    fd = open64(file, O_RDONLY);
    if (fd < 0)
        return errno;

    if ((uname(&ut) == 0) &&
            ((ut.release[0] == '2') && (ut.release[1] == '.') &&
             (ut.release[2] < '6') && (ut.release[3] == '.')))
        valid_blkgetsize64 = 0;

    if (valid_blkgetsize64 &&
            ioctl(fd, BLKGETSIZE64, &size64) >= 0) {
        if ((sizeof(*retblocks) < sizeof(unsigned long long)) &&
                ((size64 / blocksize) > 0xFFFFFFFF)) {
            rc = EFBIG;
            goto out;
        }
        *retblocks = size64 / blocksize;
        goto out;
    }

out:
    close(fd);
    return rc;
}

/**
 * gcc get-dev-blocks.c -g -Wall -o get-dev-blocks
 * usage: ./get-dev-blocks /dev/sda
 */
int main(int argc, char *argv[])
{
    int err;
    uint64_t retblocks;

    err = get_device_blocks(argv[1], 4096, &retblocks);
    printf("err: %d, %s: %"PRIu64" blocks\n", err, argv[1], retblocks);

    return 0;
}