tree 51c82de6e41b4f53f9d41dfe1211c4feba55dc6d
parent c4a69ecdb463a901b4645230613961e134e897cd
author Joe Thornber <ejt@redhat.com> 1332956488 +0100
committer Alasdair G Kergon <agk@redhat.com> 1332956488 +0100

dm thin: support read only external snapshot origins

Support the use of an external _read only_ device as an origin for a thin
device.

Any read to an unprovisioned area of the thin device will be passed
through to the origin.  Writes trigger allocation of new blocks as
usual.

One possible use case for this would be VM hosts that want to run
guests on thinly-provisioned volumes but have the base image on another
device (possibly shared between many VMs).

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>