Comment 22 for bug 1716028

Libvirt will make this "easier" to be avoided by
commit 28907b0043fbf71085a798372ab9c816ba043b93
Author: Peter Krempa <email address hidden>
Date: Wed Nov 15 15:21:14 2017 +0100

    qemu: command: Mark <shared/> disks as such in qemu

    Qemu has now an internal mechanism for locking images to fix specific
    cases of disk corruption. This requires libvirt to mark the image as
    shared so that qemu lifts certain restrictions.

    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1378242

commit 860a3c4bea1d24773d8a495f213d5de3ac48a462
Author: Peter Krempa <email address hidden>
Date: Wed Nov 15 15:02:58 2017 +0100

    qemu: caps: Add capability for 'share-rw' disk option

    'share-rw' for the disk device configures qemu to allow concurrent
    access to the backing storage.

    The capability is checked in various supported disk frontend buses since
    it does not make sense to partially backport it.

Once this is complete in bionic by taking the new upstream I'll take a look at how backportable that is (changes look ok, but might need some testing in the SRU spirit of things).