Kevin Wolf <kw...@redhat.com> wrote: >> What I took from the feedback was that Kevin wanted to defer open until the >> device model started. That eliminates the need to reopen or have a >> invalidation >> callback. >> >> I think it would be good for Kevin to comment here though because I might >> have >> misunderstood his feedback. > > Your approach was to delay reads, but still keep the image open. I think > I worried that we might have additional reads somewhere that we don't > know about, and this is why I proposed delaying the open as well, so > that any read would always fail. > > I believe just reopening the image is (almost?) as good and it's way > easier to do, so I would be inclined to do that for 1.0. > > I'm not 100% sure about cases like iscsi, where reopening doesn't help. > I think delaying the open doesn't help there either if you migrate from > A to B and then back from B to A, you could still get old data. So for > iscsi probably cache=none remains the only safe choice, whatever we do.
iSCSI and NFS only works with cache=none. Even on NFS with close+open, we have troubles if anything else has the file opened (think libvirt, guestfs, whatever). I really think that anynthing different of cache=none from iSCSI or NFS is just betting (and yes, it took a while for Christoph to convince me, I was trying to a "poor man" distributed lock manager, and as everybody knows, it is a _difficult_ problem to solve.). Later, Juan.
