[Bug 1077838] Re: qemu-nbd -r -c taints device for subsequent usage, even after -d

[Serge Hallyn]

** Also affects: qemu-kvm (Ubuntu Precise)
   Importance: Undecided
       Status: New

** Also affects: qemu-kvm (Ubuntu Quantal)
   Importance: Undecided
       Status: New

** Changed in: qemu-kvm (Ubuntu Precise)
   Importance: Undecided => High

** Changed in: qemu-kvm (Ubuntu Quantal)
   Importance: Undecided => High

** Changed in: qemu-kvm (Ubuntu Quantal)
       Status: New => Triaged

** Changed in: qemu-kvm (Ubuntu Precise)
       Status: New => Triaged

** Description changed:

  Something about qemu-nbd -r -c /dev/nbd0 someimg leaves cruft behind -
  subsequent connections get marked readonly.
  
  This is on quantal, haven't checked precise or raring.
  
  To demonstrate:
  # use one image
  qemu-img create -f qcow2 /tmp/1.qcow2 100M
  sudo qemu-nbd -c /dev/nbd2 /tmp/1.qcow2
  sudo mkfs -t ext4 /dev/nbd2
  sudo qemu-nbd -d /dev/nbd2
  # use a second one on the same nbd device, shows that reuse works:
  qemu-img create -f qcow2 /tmp/2.qcow2 100M
  sudo qemu-nbd -c /dev/nbd2 /tmp/2.qcow2
  sudo mkfs -t ext4 /dev/nbd2
  sudo qemu-nbd -d /dev/nbd2
  # connect an image in read only mode
  sudo qemu-nbd -r -c /dev/nbd2 /tmp/2.qcow2
  sudo dumpe2fs /dev/nbd2 | head -n 3
  sudo qemu-nbd -d /dev/nbd2
  # now try to reuse in read-write mode again:
  qemu-img create -f qcow2 /tmp/3.qcow2 100M
  sudo qemu-nbd -c /dev/nbd2 /tmp/3.qcow2
  sudo mkfs -t ext4 /dev/nbd2
  # here it goes boom:
  mke2fs 1.42.5 (29-Jul-2012)
  /dev/nbd2: Operation not permitted while setting up superblock
  # still need to cleanup
  sudo qemu-nbd -d /dev/nbd2
+ 
+ ===============================
+ SRU Justification:
+ 1. Impact: mounting an nbd device as read-write after doing so read-only
+ will cause the mount to erroneously (and quietly) be read-only.
+ 2. Development fix: have qemu-nbd set the device to read-write when asked,
+ rather than only setting read-only.
+ 3. Stable fix: same as development fix
+ 4. Test case: See above
+ 5. Regression potential: The patch is localized to the handling of read-only
+ flag in qemu-nbd, so any regression should not affect anything else.
+ ===============================

-- 
You received this bug notification because you are a member of Ubuntu
Server Team, which is subscribed to qemu-kvm in Ubuntu.
https://bugs.launchpad.net/bugs/1077838

Title:
  qemu-nbd -r -c taints device for subsequent usage, even after -d

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1077838/+subscriptions