[Pkg-virtualbox-devel] Bug#799668: encountering umount.nfs: /mnt: is not an NFS filesystem for vboxsf

[Shaddy Baddah]

Package: virtualbox-guest-dkms
Version: 4.3.18-dfsg-3+deb8u3
Severity: important
Tags: upstream

As per the subject, since jessie, if I try to umount a vboxsf I
encounter an error:

$ sudo mount -t vboxsf sw /mnt -o ro
$ sudo umount /mnt
umount.nfs: /mnt: is not an NFS filesystem for vboxsf

I've already looked into this. It seems that since jessie, mount
package has changed so that it looks at the f_type member of the struct
statfs, maps to a filesystem label based on the magic no., and then
will use the relevant mount/umount helper, such as umount.nfs here, if
it is available.

Now, I don't necessarily agree with what has been done to the
mount/umount tools, but not knowing if an alternative is easy or
feasible (instead of mapping, using the label that comes out of the
mount output), I think this means that the vboxsf fs module needs to be
a bit cleverer.

I believe the safety blanket afforded by just using NFS_SUPER_MAGIC
f_type (see below) is no longer ok (in fact the line is marked XXX to
indicate something better could be done):

/usr/src/virtualbox-guest-4.3.18/vboxsf/utils.c:841:    stat->f_type  = 
NFS_SUPER_MAGIC; /* XXX vboxsf type? */

I had a look at what open-vm-tools-dkms does here, and even though the
magic number is bogus against /usr/include/linux/magic.h (where mount
find its C defs), it means that no helper is found, and native umount
is performed:

/usr/src/open-vm-tools-9.4.6/vmblock/linux/super.c:139:   stat->f_type = 
VMBLOCK_SUPER_MAGIC;

I propose that we propose this upstream.

-- 
Regards,
Shaddy

-- System Information:
Debian Release: 8.2
   APT prefers stable
   APT policy: (500, 'stable')
Architecture: i386 (i686)

Kernel: Linux 3.16.0-4-586
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Versions of packages virtualbox-guest-dkms depends on:
ii  dkms                    2.2.0.3-2
ii  dpkg                    1.17.25
ii  virtualbox-guest-utils  4.3.18-dfsg-3+deb8u3

virtualbox-guest-dkms recommends no packages.

virtualbox-guest-dkms suggests no packages.

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