Re: [Qemu-devel] need to resurrect no-lock option?

[Fam Zheng <famz@redhat.com>]

On Wed, 09/20 11:26, Christian Ehrhardt wrote:
> 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.

The --no-lock option was later revised into --force-share, so...

> 
> 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?

... you can do this:

$ qemu-img info --force-share /tmp/test.qcow2
image: /tmp/test.qcow2
file format: qcow2
virtual size: 1.0M (1048576 bytes)
disk size: 196K
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

Fam