> From: John Snow [mailto:js...@redhat.com] > Sent: Monday, 17 July 2017 17:34 > On 07/17/2017 07:30 PM, Andrew Baumann via Qemu-devel wrote: > > 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 > > > > Looks like the shorthand "-snapshot" doesn't let you specify any further > options, which is a bummer. > > You may need to do something a little more manual, and create your own > temporary overlay, and launch QEMU pointing to that overlay instead.
Can you give me some more clues what this might look like? > That sounds like a bit of a hassle. > > Can we compile locking support out of QEMU instead for this platform? Or > is there a runtime option for disabling it globally? The compile target is just Linux, so at best it would need to be a runtime choice based on platform detection, and I doubt that is a good idea (WSL may well get around to implementing this syscall in the future). I agree a runtime command-line flag to disable it globally would be ideal, but from a quick look at the code it doesn't seem to exist at present. Thanks, Andrew
