c - 从 C 代码中弹出 Cd rom 时出现输入/输出错误

Question

我的 CD-Rom 在 Ubuntu 14.10 上有问题。我正在尝试运行这段代码，它写着 ioctl: Input/output error 并且 open() 返回数字 3。应该在哪里出错？我的光驱路径对吗？当我在终端中写入 eject "dev/cdrom"时，它被弹出。

/* eject.c
** Copyright Paul Dwerryhouse, 1997-2004
*/
#include <sys/types.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/cdrom.h>

#define CDDEVICE "/dev/cdrom"           /* CDROM device */

int main(int argc,char **argv)
{
   int cdrom;                           /* CDROM device file descriptor */

   /* Open the CDROM device. The linux/cdrom.h header file specifies that
   ** it must be given the O_NONBLOCK flag when opening. My tests showed
   ** that if this isn't done, this program will not work. 
   */
   if ((cdrom = open(CDDEVICE,O_RDONLY | O_NONBLOCK)) < 0) {
        perror("open");
        exit(1);
   }

   /* Use ioctl to send the CDROMEJECT command to the device
   */
   if (ioctl(cdrom,CDROMEJECT,0)<0) {
        perror("ioctl");
        exit(1);
   }

   close(cdrom);
}

这是 strace 的输出。

execve("./frca", ["./frca"], [/* 76 vars */]) = 0
brk(0)                                  = 0x2015000
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) = 0x7f4240016000
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=136133, ...}) = 0
mmap(NULL, 136133, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f423fff4000
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) = 0x7f423fa30000
mprotect(0x7f423fbeb000, 2097152, PROT_NONE) = 0
mmap(0x7f423fdeb000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bb000) = 0x7f423fdeb000
mmap(0x7f423fdf1000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f423fdf1000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f423fff3000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f423fff1000
arch_prctl(ARCH_SET_FS, 0x7f423fff1740) = 0
mprotect(0x7f423fdeb000, 16384, PROT_READ) = 0
mprotect(0x600000, 4096, PROT_READ)     = 0
mprotect(0x7f4240018000, 4096, PROT_READ) = 0
munmap(0x7f423fff4000, 136133)          = 0
open("/dev/cdrom", O_RDONLY|O_NONBLOCK) = 3
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f4240015000
write(1, "3\n", 23
)                      = 2
ioctl(3, CDROMEJECT, 0)                 = -1 EIO (Input/output error)
dup(2)                                  = 4
fcntl(4, F_GETFL)                       = 0x8002 (flags O_RDWR|O_LARGEFILE)
brk(0)                                  = 0x2015000
brk(0x2036000)                          = 0x2036000
fstat(4, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f4240014000
lseek(4, 0, SEEK_CUR)                   = -1 ESPIPE (Illegal seek)
write(4, "ioctl: Input/output error\n", 26ioctl: Input/output error
) = 26
close(4)                                = 0
munmap(0x7f4240014000, 4096)            = 0
exit_group(1)                           = ?
+++ exited with 1 +++

跟踪系统弹出:

bo@bo-ThinkPad-Edge-E530:~$ strace eject 
execve("/usr/bin/eject", ["eject"], [/* 75 vars */]) = 0
brk(0)                                  = 0x7f3dbd946000
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) = 0x7f3dbd094000
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=136133, ...}) = 0
mmap(NULL, 136133, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3dbd072000
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) = 0x7f3dbcaae000
mprotect(0x7f3dbcc69000, 2097152, PROT_NONE) = 0
mmap(0x7f3dbce69000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bb000) = 0x7f3dbce69000
mmap(0x7f3dbce6f000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f3dbce6f000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3dbd071000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3dbd06f000
arch_prctl(ARCH_SET_FS, 0x7f3dbd06f740) = 0
mprotect(0x7f3dbce69000, 16384, PROT_READ) = 0
mprotect(0x7f3dbd29f000, 4096, PROT_READ) = 0
mprotect(0x7f3dbd096000, 4096, PROT_READ) = 0
munmap(0x7f3dbd072000, 136133)          = 0
brk(0)                                  = 0x7f3dbd946000
brk(0x7f3dbd967000)                     = 0x7f3dbd967000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=4427728, ...}) = 0
mmap(NULL, 4427728, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3dbc675000
close(3)                                = 0
access("/dev/cdrom", F_OK)              = 0
readlink("/dev/cdrom", "sr0", 4095)     = 3
lstat("/dev", {st_mode=S_IFDIR|0755, st_size=4300, ...}) = 0
lstat("/dev/sr0", {st_mode=S_IFBLK|0660, st_rdev=makedev(11, 0), ...}) = 0
readlink("/dev/sr0", 0x7fff014d9428, 4095) = -1 EINVAL (Invalid argument)
stat("/dev/sr0", {st_mode=S_IFBLK|0660, st_rdev=makedev(11, 0), ...}) = 0
open("/etc/mtab", O_RDONLY)             = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=911, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3dbd093000
read(3, "/dev/sda5 / ext4 rw,errors=remou"..., 4096) = 911
stat("/dev/sda5", {st_mode=S_IFBLK|0660, st_rdev=makedev(8, 5), ...}) = 0
stat("proc", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("sysfs", 0x7fff014dc740)           = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("udev", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("devpts", 0x7fff014dc740)          = -1 ENOENT (No such file or directory)
stat("tmpfs", 0x7fff014dc740)           = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("none", 0x7fff014dc740)            = -1 ENOENT (No such file or directory)
stat("/dev/sda6", {st_mode=S_IFBLK|0660, st_rdev=makedev(8, 6), ...}) = 0
stat("binfmt_misc", 0x7fff014dc740)     = -1 ENOENT (No such file or directory)
stat("systemd", 0x7fff014dc740)         = -1 ENOENT (No such file or directory)
stat("gvfsd-fuse", 0x7fff014dc740)      = -1 ENOENT (No such file or directory)
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7f3dbd093000, 4096)            = 0
open("/etc/fstab", O_RDONLY)            = 3
fstat(3, {st_mode=S_IFREG|0664, st_size=595, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3dbd093000
read(3, "# /etc/fstab: static file system"..., 4096) = 595
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7f3dbd093000, 4096)            = 0
stat("/dev/sr0", {st_mode=S_IFBLK|0660, st_rdev=makedev(11, 0), ...}) = 0
open("/usr/lib/x86_64-linux-gnu/gconv/gconv-modules.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=26258, ...}) = 0
mmap(NULL, 26258, PROT_READ, MAP_SHARED, 3, 0) = 0x7f3dbd08d000
close(3)                                = 0
geteuid()                               = 1000
open("/dev/sr0", O_RDWR|O_NONBLOCK)     = 3
ioctl(3, CDROMEJECT, 0x7f3dbd9490e0)    = -1 EIO (Input/output error)
ioctl(3, SG_GET_VERSION_NUM, 0x7fff014dd4b8) = 0
ioctl(3, SG_IO, {'S', SG_DXFER_NONE, cmd[6]=[1e, 00, 00, 00, 00, 00], mx_sb_len=32, iovec_count=0, dxfer_len=0, timeout=10000, flags=0, status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=16, info=0}) = 0
ioctl(3, SG_IO, {'S', SG_DXFER_NONE, cmd[6]=[1b, 00, 00, 00, 01, 00], mx_sb_len=32, iovec_count=0, dxfer_len=0, timeout=10000, flags=0, status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=856, info=0}) = 0
ioctl(3, SG_IO, {'S', SG_DXFER_NONE, cmd[6]=[1b, 00, 00, 00, 02, 00], mx_sb_len=32, iovec_count=0, dxfer_len=0, timeout=10000, flags=0, status=02, masked_status=01, sb[18]=[70, 00, 05, 00, 00, 00, 00, 0a, 00, 00, 00, 00, 53, 02, 00, 00, 00, 00], host_status=0, driver_status=0x8, resid=0, duration=4, info=0x1}) = 0
ioctl(3, FDEJECT, 0x7fff014dd4c8)       = -1 ENOTTY (Inappropriate ioctl for device)
ioctl(3, MGSL_IOCGPARAMS or MMTIMER_GETRES or MTIOCTOP or SNDCTL_MIDI_MPUMODE, 0x7fff014dd4c8) = -1 ENOTTY (Inappropriate ioctl for device)
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3dbd08c000
read(4, "# Locale name alias data base.\n#"..., 4096) = 2570
read(4, "", 4096)                       = 0
close(4)                                = 0
munmap(0x7f3dbd08c000, 4096)            = 0
open("/usr/share/locale/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/eject.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/eject.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US/LC_MESSAGES/eject.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en/LC_MESSAGES/eject.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
write(2, "eject: unable to eject, last err"..., 67eject: unable to eject, last error: Inappropriate ioctl for device
) = 67
exit_group(1)                           = ?
+++ exited with 1 +++

Answer 1

由于某些原因，您的 cdrom 拒绝了 CDROMEJECT ioctl 但它接受了 sg (SCSI Generic ) 旨在弹出托盘的命令。

open("/dev/sr0", O_RDWR|O_NONBLOCK)     = 3
ioctl(3, CDROMEJECT, 0x7f3dbd9490e0)    = -1 EIO (Input/output error)
ioctl(3, SG_GET_VERSION_NUM, 0x7fff014dd4b8) = 0
ioctl(3, SG_IO, {'S', SG_DXFER_NONE, cmd[6]=[1e, 00, 00, 00, 00, 00], mx_sb_len=32, iovec_count=0, dxfer_len=0, timeout=10000, flags=0, status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=16, info=0}) = 0
ioctl(3, SG_IO, {'S', SG_DXFER_NONE, cmd[6]=[1b, 00, 00, 00, 01, 00], mx_sb_len=32, iovec_count=0, dxfer_len=0, timeout=10000, flags=0, status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=856, info=0}) = 0
ioctl(3, SG_IO, {'S', SG_DXFER_NONE, cmd[6]=[1b, 00, 00, 00, 02, 00], mx_sb_len=32, iovec_count=0, dxfer_len=0, timeout=10000, flags=0, status=02, masked_status=01, sb[18]=[70, 00, 05, 00, 00, 00, 00, 0a, 00, 00, 00, 00, 53, 02, 00, 00, 00, 00], host_status=0, driver_status=0x8, resid=0, duration=4, info=0x1}) = 0
ioctl(3, FDEJECT, 0x7fff014dd4c8)       = -1 ENOTTY (Inappropriate ioctl for device)

“ioctl(3, SG_IO, ...”命令序列执行以下操作:

• ALLOW_MEDIUM_REMOVAL
• START_STOP 负载 1
• START_STOP 负载 2

---

引用资料:

https://github.com/karelzak/util-linux/blob/master/sys-utils/eject.c#L590 http://git.buildroot.net/busybox/plain/miscutils/eject.c?h=1_17_stable https://github.com/dylex/android_external_busybox/blob/master/miscutils/eject.c#L35