umount --detach-loop fails but fs is unmounted

umount --detach-loop fails but fs is unmounted

[Alex Deymo]

Hi,

I'm running into a problem when using -d in umount. I'm using
util-linux 2.25.1, but didn't see changes in that code in ToT. When
calling "umount -d" if the passed argument is *not* a loop device (for
example /dev/loopX or /mnt/foo/bar), it will umount it, but the
command will fail (return != 0) and print EINVAL error (22).
Documentation says:

  -d, --detach-loop
    When the unmounted device was a loop device, also free this loop device.

So the command shouldn't fail if you didn't pass a loop device but
still used -d; right? Is this a problem in the documentation or the
code?

* Examples: if you mount your ${image} (an ext4 fs, but whatever) in
${mount_point} this way:

  loop_device=$(sudo losetup --find --show ${image})
  sudo mount -o rw ${loop_device} ${mount_point}


The following command fails (error code 1) and does NOT remove the
loop device, but unmounts the fs properly:
  sudo umount -d ${mount_point}
umount: ${mount_point}: filesystem was unmounted, but mount(8) failed:
Invalid argument

On the other hand, if you run this command instead, it succeeds and
removes the loop device:
  sudo umount -d ${loop_device}


If your loop device has AUTOCLEAN=1 (see "losetup --list --all") the
loop device is removed either way, but the command still fails when
using ${mount_point}:
  sudo mount -o loop,rw ${image} ${mount_point}

This command fails but loop is removed due to the autoclean.
  sudo umount -d ${mount_point}

Thanks,
deymo.

Re: umount --detach-loop fails but fs is unmounted

[Karel Zak]

On Fri, Mar 27, 2015 at 12:03:26PM -0700, Alex Deymo wrote:
> I'm running into a problem when using -d in umount. I'm using
> util-linux 2.25.1, but didn't see changes in that code in ToT. When
> calling "umount -d" if the passed argument is *not* a loop device (for
> example /dev/loopX or /mnt/foo/bar), it will umount it, but the
> command will fail (return != 0) and print EINVAL error (22).
> Documentation says:
> 
>   -d, --detach-loop
>     When the unmounted device was a loop device, also free this loop device.
> 
> So the command shouldn't fail if you didn't pass a loop device but
> still used -d; right? Is this a problem in the documentation or the
> code?
> 
> * Examples: if you mount your ${image} (an ext4 fs, but whatever) in
> ${mount_point} this way:
> 
>   loop_device=$(sudo losetup --find --show ${image})
>   sudo mount -o rw ${loop_device} ${mount_point}
> 
> 
> The following command fails (error code 1) and does NOT remove the
> loop device, but unmounts the fs properly:
>   sudo umount -d ${mount_point}
> umount: ${mount_point}: filesystem was unmounted, but mount(8) failed:
> Invalid argument

I'm not able to reproduce this problem.

        # rpm -q util-linux
        util-linux-2.25.2-2.fc21.x86_64

        # losetup --find --show /home/archive/fs-images/filesystems/ext2.img
        /dev/loop0

        # mount /dev/loop0 /mnt/test

        # losetup 
        NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE
        /dev/loop0         0      0         0  0 /home/archive/fs-images/filesystems/ext2.img

        # findmnt /mnt/test
        TARGET    SOURCE     FSTYPE OPTIONS
        /mnt/test /dev/loop0 ext3   rw,relatime,seclabel,data=ordered

        # umount -d /mnt/test
        # echo $?
        0

Please, try

   LIBMOUNT_DEBUG=0xffff umount -d ${mount_point}

or/and strace output would be also nice.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com