On 11/10/2011 10:50 AM, Juan Quintela wrote:
Kevin Wolf<kwolf@xxxxxxxxxx> 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).
Reopening with iSCSI is strictly an issue with the in-kernel initiator, right?
libiscsi should be safe with a delayed open I would imagine.
Regards,
Anthony Liguori
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.
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