[Xen-devel] What are the semantics of BLKIF_OP_WRITE_BARRIER?

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

What does BLKIF_OP_WRITE_BARRIER mean precisely?  Presumably it prevents
writes from being reordered past it.  But does it also imply a flush, in
that all previous writes are on stable storage?  If not, is there
another operation which does guarantee that?  If the backend doesn't
support barriers, is there any other way for a guest to force writes to
stable storage?

How does blktap(2) deal with devices with volatile write caches?  Does
it generate its own barriers/flushes/FUA requests to push things out to
stable storage?

Thanks,
    J

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel