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[Qemu-devel] [Bug 1077838] Re: qemu-nbd -r -c taints device for subseque
From: |
Serge Hallyn |
Subject: |
[Qemu-devel] [Bug 1077838] Re: qemu-nbd -r -c taints device for subsequent usage, even after -d |
Date: |
Thu, 20 Dec 2012 18:14:00 -0000 |
Verified on precise.
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https://bugs.launchpad.net/bugs/1077838
Title:
qemu-nbd -r -c taints device for subsequent usage, even after -d
Status in QEMU:
In Progress
Status in “qemu-kvm” package in Ubuntu:
Fix Released
Status in “qemu-kvm” source package in Precise:
Fix Committed
Status in “qemu-kvm” source package in Quantal:
Fix Committed
Bug description:
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.
===============================
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- [Qemu-devel] [Bug 1077838] Re: qemu-nbd -r -c taints device for subsequent usage, even after -d,
Serge Hallyn <=