[Qemu-devel] Disable image locking for snapshot drive?

[Andrew Baumann]

Hi all,

I'm running a recent Linux build of qemu on Windows Subsystem for Linux (WSL) 
which doesn't appear to implement file locking:

$ qemu-system-aarch64 ... -drive file=test.vhdx,if=none,id=hd0 -device 
virtio-blk-pci,drive=hd0
qemu-system-aarch64: -drive file=test.vhdx,if=none,id=hd0: Failed to unlock 
byte 100
qemu-system-aarch64: -drive file=test.vhdx,if=none,id=hd0: Failed to unlock 
byte 100
qemu-system-aarch64: -drive file=test.vhdx,if=none,id=hd0: Failed to lock byte 
100

That's no big deal; I can switch it off:

$ qemu-system-aarch64 ... -drive file=test.vhdx,if=none,file.locking=off,id=hd0 
...
(all good)

But how can I do the same for a snapshot drive?

$ qemu-system-aarch64 ... -drive file=test.vhdx,if=none,file.locking=off,id=hd0 
-snapshot ...
qemu-system-aarch64: -drive file=test.vhdx,if=none,file.locking=off,id=hd0: 
Failed to unlock byte 100
qemu-system-aarch64: -drive file=test.vhdx,if=none,file.locking=off,id=hd0: 
Failed to unlock byte 100
qemu-system-aarch64: -drive file=test.vhdx,if=none,file.locking=off,id=hd0: 
Could not create temporary overlay '/var/tmp/vl.o83dxn': Failed to lock byte 100

(I also tried the snapshot=on drive option with similar results.)

Thanks,
Andrew