nfs + msdosfs = crashes & panics

[Chris Pressey <cpressey@xxxxxxxxxxxxxxx>]

Hi,

I'm having problems using a NFS-mounted MS-DOS (FAT) partition.  This
may well be because this combination isn't supported, but in case it
is supposed to be, here are some gory details.

I have an NFS server running DragonFly.  It shares the directory /c to
the NFS client, which is also running DragonFly.  (both are the same
version, fairly current as of a couple of days ago.)

The NFS server is dual-boot; ad0 has Windows installed, DragonFly
resides on ad1.  The /c directory, in DragonFly, is a mount of the
MS-DOS partition on ad0s1.  For local usage this is rock-solid.

Over NFS it does appear to work, at least initially.  I can list the
directories of /c on the client.  I can read files under normal usage. 
However, if I try to read a lot of files in quick succession, or really
big files, the NFS server just locks up.  The message on the client is:

	nfs server catbus:/c: not responding

And on the server, I can see via top that the nfsd process is stuck in
the state 'nfsd'.  I can kill nfsd, but trying to do anything else on
the client after this point is pretty much impossible; it requires a
power cycle.

Also, if I try to write a file to the /c share from the client, the
server's kernel panics.  This in general leads me to believe that the
combination is just not supported (much like write-through unionfs et al
aren't supported...) but if other people can normally get this to work
(under other BSD's...?) I'll happily post a backtrace.

-Chris