Kevin Wolf <kw...@redhat.com> writes: > Am 06.06.2011 13:57, schrieb Markus Armbruster: >>>>> Not sure what's the best way of fixing this. Maybe just ignoring >>>>> -snapshot for read-only block devices? >>>> >>>> Why not, the combination is pointless. >>> >>> It could start making a difference in some obscure combinations. Imagine >>> a read-only image with a backing file, -snapshot and the 'commit' >>> monitor command. >>> >>> Sounds pretty insane, but I wouldn't bet that people aren't using it... >> >> People try all kinds of insane things. The question is whether we can >> change it anyway. > > We have a backing file chain like base <- cow [<- tmp], and the drive is > read-only. > > Currently, 'commit' means that tmp is committed to cow (i.e. nothing > happens because it's read-only). After changing it, we would commit the > content of cow to base and possibly corrupt other images that are based > on base. > > We can hope that nobody would be hit by it in practice, but it's not a > change I'd feel very comfortable about.
So the one effect -snapshot has on a read-only drive is to neuter the commit command. Hmm. Naive question: shouldn't commit require the drive to be read/write? It writes both the backing image and the COW... [...]
