CD-Rom eject by C code

Question

Im trying eject my CD rom via C code.And it dont want to work. ioctl returned "5" I/O error, where could be a problem?

#include <stdio.h>
#include <fcntl.h>
#include <linux/cdrom.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
int eject_cdrom()
{
    char path_to_cdrom[20]="/dev/cdrom";
    int fd = open("/dev/cdrom", O_RDONLY| O_NONBLOCK);
    printf("%d\n",fd );
    int lala = ioctl(fd, CDROMEJECT);
    printf("%d\n",lala);
    close(fd);
    return lala;
}

int main(int argc, char* argv[])
{
    //eject_cdrom_system();
    int value = eject_cdrom();
    printf("%d\n",value );
    if (value == -1) 
    {
        int errsv = errno;
        printf("somecall() failed\n");
        printf("%d\n",errsv );
    }

    return 0;
}

When I tried this function

void eject_cdrom_system()
    {
        system("/usr/bin/eject");
    }

It works perfectly. But I want to do it by first function (eject_cdrom).

Output from strace:

strace -f ./cdrom

execve("./cdrom", ["./cdrom"], [/* 76 vars */]) = 0
brk(0)                                  = 0xf9c000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fcb50cd7000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=131512, ...}) = 0
mmap(NULL, 131512, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fcb50cb6000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\37\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1845024, ...}) = 0
mmap(NULL, 3953344, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fcb506f1000
mprotect(0x7fcb508ad000, 2093056, PROT_NONE) = 0
mmap(0x7fcb50aac000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bb000) = 0x7fcb50aac000
mmap(0x7fcb50ab2000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fcb50ab2000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fcb50cb5000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fcb50cb3000
arch_prctl(ARCH_SET_FS, 0x7fcb50cb3740) = 0
mprotect(0x7fcb50aac000, 16384, PROT_READ) = 0
mprotect(0x600000, 4096, PROT_READ)     = 0
mprotect(0x7fcb50cd9000, 4096, PROT_READ) = 0
munmap(0x7fcb50cb6000, 131512)          = 0
open("/dev/cdrom", O_RDONLY|O_NONBLOCK) = 3
ioctl(3, CDROMEJECT, 0)                 = -1 EIO (Input/output error)
close(3)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++

"strace -f /usr/bin/eject" may be better since -f catches forks. — Juan, Jun 26 '14 at 19:24
I edited my post with strace output ... I see only this i/o error, nothing more — , Jun 26 '14 at 19:35

score 3 · Answer 1 · edited Jun 20 '20 at 09:12

For the benefit of anyone who wanders in off Google, I'll list all of the possible causes I see:

You're explicitly specifying /dev/cdrom in your code but allowing eject to autodetect that.

Some distros don't set up /dev/cdrom as a symlink to /dev/sr0 or equivalent. Sort of an "Is it plugged in?" question, but included for completeness.
I'm not sure if the raw ioctl will resolve symbolic links

It could be that /usr/bin/eject has to make an extra API call in order to achieve success.
You're just assuming that eject will use that API

According to man eject, the /usr/bin/eject utility supports at least four different ejecting APIs, two of which (CDROM and SCSI) could apply to an optical device.

I actually tested this on my system and, when I forced the API you're using by running eject with the -r option, it failed with the same error.

$ eject -r /dev/cdrom
eject: unable to eject, last error: Input/output error

However, forcing the SCSI API (which was expanded to also cover SATA and then PATA) works for me.

$ eject -s /dev/cdrom

CD-Rom eject by C code

1 Answers1