On 03/09/2012 06:42 PM, Kevin Wolf wrote: > >> > >> While (3) can be worked around, the only way around the other two, > >> unfortunately, is support in the formats and protocols. We will still > >> provide device options to opt out of this, but with raw and qed covered > >> (+ qcow2 without backing file, and qcow3 in the future) it should not > >> be too bad. > > > > Can't qcow2 with a backing file also be supported? Zero out the first > > cluster, and remember it. The following discards can reuse this zero > > cluster, as long as it hasn't been overwritten. > > qcow2 can't handle clusters that are referenced twice from the same L1 > table. This would require a reverse lookup to adjust the QCOW_O_COPIED > flags in the L2 tables containing the other references.
Don't follow, sorry. What adjustment are you talking about? If it's a 1->0 transition, is it mandatory to adjust the flag? That is, it it legal to have a refcount of exactly one, but have the flag clear? -- error compiling committee.c: too many arguments to function
