[Qemu-devel] [Bug 1759337] [NEW] 'Failed to get "write" lock' error when trying to run a VM with disk image file on an SMB share

[Adam Williamson]

Public bug reported:

This has been reported and discussed downstream:

https://bugzilla.redhat.com/show_bug.cgi?id=1484130

but doesn't seem to be getting a lot of traction there.

Basically, with qemu since at least 2.10, you cannot use a disk image on
an SMB share that's mounted with protocol version 3 (I think possibly 2
or higher). This is made much more serious because kernel 4.13 upstream
made version 3 the *default* for SMB mounts, because version 1 is
insecure and should not be used.

So basically, anyone with a recent qemu and kernel cannot use disk
images stored on an SMB share. This is a major inconvenience for me
because, well, an SMB share is exactly where I store my VM disk images,
usually: I have a big NAS drive where I keep them all, only now I can't
because of this bug, and I'm manually swapping them in and out of the
very limited space I have on my system drive (SSD).

The error you get is:

qemu-system-x86_64: -drive 
file=/share/data/isos/vms/desktop_test_1.qcow2,format=qcow2,if=none,id=drive-virtio-disk0:
 Failed to get "write" lock
Is another process using the image?

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1759337

Title:
  'Failed to get "write" lock' error when trying to run a VM with disk
  image file on an SMB share

Status in QEMU:
  New

Bug description:
  This has been reported and discussed downstream:

  https://bugzilla.redhat.com/show_bug.cgi?id=1484130

  but doesn't seem to be getting a lot of traction there.

  Basically, with qemu since at least 2.10, you cannot use a disk image
  on an SMB share that's mounted with protocol version 3 (I think
  possibly 2 or higher). This is made much more serious because kernel
  4.13 upstream made version 3 the *default* for SMB mounts, because
  version 1 is insecure and should not be used.

  So basically, anyone with a recent qemu and kernel cannot use disk
  images stored on an SMB share. This is a major inconvenience for me
  because, well, an SMB share is exactly where I store my VM disk
  images, usually: I have a big NAS drive where I keep them all, only
  now I can't because of this bug, and I'm manually swapping them in and
  out of the very limited space I have on my system drive (SSD).

  The error you get is:

  qemu-system-x86_64: -drive 
file=/share/data/isos/vms/desktop_test_1.qcow2,format=qcow2,if=none,id=drive-virtio-disk0:
 Failed to get "write" lock
  Is another process using the image?

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