Am 07.12.2009 12:28, schrieb Jamie Lokier: > Kevin Wolf wrote: >> Am 07.12.2009 11:31, schrieb Jamie Lokier: >>> So the distinction read/write makes more sense. Can anyone think of a >>> situation where a shared lock on an image opened for writing is useful? >> >> I think there are people using shared writable images with cluster file >> systems. > > Yes, they are. Please the following again: > >>> Sometimes shared access to a raw image (partitioned or whole disk >>> filesystem) is ok, and sometimes it is not ok. Only the user knows >>> the difference, because only the user knows if the guests they are >>> running use distinct partitions in the same raw image, or cooperative >>> access to a shard image. >>> >>> But does it make sense to request a shared lock in that case? Not >>> really. If you have a group of guests correctly sharing an image, you >>> still want to prevent running the same group a second time - and a >>> shared lock wouldn't do that, because each group would be requesting >>> shared locks. > > If you run each guest in the disk-sharing cluster with 'lock=shared', > it reflects that they are sharing - but that doesn't actually prevent > mistakes, does it? If you run any of those guests a second time, it > won't prevent that. So what's the point in the shared lock?
Sorry, I apparently misunderstood. I was thinking about shared vs. exclusive whereas you are talking about shared vs. none (vs. something completely different). I think you're right there. Kevin
