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Can QEMU/KVM+OCFS2 be configured to punch holes in sparse image files when files are deleted in the guest?

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http://unix.stackexchange.com – I'm using sparse raw image files for guest VMs and OCFS2 on the host (local-only, not clustered) for the reflink feature. I understand from Googling around that OCFS2 is one of the filesystems that can punch holes back into sparse files. If I understand correctly, it may be possible (and apparently can be achieved with XFS) to combine this feature with TRIM/discard support in the guest machines so that when files in the guest are deleted, space on the host is automatically reclaimed. However despite much experimentation, I haven't been able to demonstrate this working. Is this possible, and (HowTos)