svn commit: r216406 - stable/8/sys/amd64/conf

Robert N. M. Watson rwatson at
Mon Dec 13 20:04:57 UTC 2010

On 13 Dec 2010, at 18:28, Ion-Mihai Tetcu <itetcu at> wrote:

> I see. Thanks for the time you took to explain things, I'm very new to
> XEN.
> Do we have any docs somewhere (well, except the sources) about our XEN
> support and various options / optimizations? I only know about
> AdrianChadd's wiki pags and (which
> are nice, if you happen to know about XEN already and especially if you
> want to work towards a FreebSD as XEN host).
> I guess there are more interested people taht want just to run FreeBSD
> as guest OS (my case).

The current state of our Xen documentation is ... minimalist. Having basically come to it for the first time last week, when we decided we needed to deploy FreeBSD on one of our Xen server pools, it's proven pretty hard-going. I have some more technical problems to resolve but high on my todo list for the next couple of days is documenting what has worked for me on the Wiki (with the intent of migrating that to the Handbook once I've confirmed my instructions are reproducible!). I also want to drop in at least some stub man pages for our PV drivers.

However, more fundamentally, we appear to have some serious functional gaps:

- No ability to use PV drivers under HVM on i386.
- No ability to use a full PV kernel for amd64 (I don't consider this a problem for my use though -- HVM on amd64 appears to work well).
- No (obvious) port of Xen guest command line tools to steer ballooning, etc.
- Likely under-testing in certain PV drivers, such as the balloon driver.
- A possible issue with VM migration on PV i386 (we saw panics in local testing, but now wonder I it was an unrelated issue relating to different CPU types -- more investigation due).
- No event mechanism for blkfront to propagate block device expansion up the geom stack, in support of live file system resizing. Right now a destructive orphan/retaste is required.
- No live file system resizing support in UFS (does work in ZFS).
- No reference "appliance" images for VM starting points (really requires live file system resizing to be useful). This was a top request o our admin folks.

All this said, and after quite a lot of head-scratching, FreeBSD/amd64 seems to work well on Xen here a Cambridge, both with and without Xen PV drivers compiled in. We need a lot of sanding and polishing but the foundations have been usefully laid. And I would agree that documentation is key.


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