Hi, this might have been discussed in the wake of the lock changes that took place in 2.10 but I can't find anything clear enough to follow in the current case. There was an old submission [1] by Fam to make it possible to no-lock qemu-img and others if needed. But it seems nothing like it made it along to the locking we have in 2.10.
One (maybe more) case where missing this causes pain is e.g. running an info check on a running guest. In general info shouldn't need a write lock anyway, but without --no-lock that use case is broken. Repro of the case is rather simple: $ qemu-img create -f qcow2 /tmp/test.qcow2 1M $ qemu-system-x86_64 -hda /tmp/test.qcow2 -enable-kvm -nodefaults -nographic & $ qemu-img info /tmp/test.qcow2 qemu-img: Could not open '/tmp/test.qcow2': Failed to get shared "write" lock Is another process using the image? [1]: https://lists.gnu.org/archive/html/qemu-block/2016-04/msg00349.html -- Christian Ehrhardt Software Engineer, Ubuntu Server Canonical Ltd
