On Fri, Feb 19, 2010 at 12:22:20AM +0200, Michael S. Tsirkin wrote: > I took a stub at documenting CMD and FLUSH request types in virtio > block. Christoph, could you look over this please? > > I note that the interface seems full of warts to me, > this might be a first step to cleaning them.
The whole virtio-blk interface is full of warts. It has been extended rather ad-hoc, so that is rather expected. > One issue I struggled with especially is how type > field mixes bits and non-bit values. I ended up > simply defining all legal values, so that we have > CMD = 2, CMD_OUT = 3 and so on. It's basically a complete mess without much logic behind it. > +\change_unchanged > +the high bit > +\change_inserted 0 1266497301 > + (VIRTIO_BLK_T_BARRIER) > +\change_unchanged > + indicates that this request acts as a barrier and that all preceeding > requests > + must be complete before this one, and all following requests must not be > + started until this is complete. > + > +\change_inserted 0 1266504385 > + Note that a barrier does not flush caches in the underlying backend device > + in host, and thus does not serve as data consistency guarantee. > + Driver must use FLUSH request to flush the host cache. > +\change_unchanged I'm not sure it's even worth documenting it. I can't see any way to actually implement safe behaviour with the VIRTIO_BLK_T_BARRIER-style barriers. Btw, did I mention that .lyx is a a really horrible format to review diffs for? Plain latex would be a lot better.. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/virtualization
