Hi, Julian. > I had some time to try it out today, but I'm still having issues:
I've just made experiment alike to your with making bhyve to work on top of GEOM device instead of preferable "dev" mode of ZVOL. And I indeed reproduced the problem. But the problem that I see is not related to the block size. The block size is reported to the guest correctly as 4K, and as I can see it works as such at least in FreeBSD guest. The problem is in the way how bhyve inter-operates with block/GEOM devices. bhyve sends requests to the kernel with preadv()/pwritev() calls, specifying scatter/gather lists of buffer addresses provided by the guest. But GEOM code can not handle scatter/gather lists, only sequential buffer, and so single request is split into several. The problem is that splitting happens according to scatter/gather elements, and those elements in general case may not be multiple to the block size, that is fatal for GEOM and any block device. I am not yet sure how to fix this problem. The most straightforward way is to copy the data at some point to collect elements of scatter/gather list into something sequential to pass to GEOM, but that requires additional memory allocation, and the copying is not free. May be some cases could be optimized to work without copying but with some clever page mapping, but that seems absolutely not trivial. -- Alexander Motin _______________________________________________ firstname.lastname@example.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-virtualization To unsubscribe, send any mail to "freebsd-virtualization-unsubscr...@freebsd.org"