Under what circumstances does the new NFS client return EAGAIN?

[Garrett Wollman]

I'm testing out a new file server, and trying to rsync files from
a proprietary NAS to the box I'm testing.  It's running the new NFS
code and 9.0.  rsync frequently and repeatably errors out with
something like this:

rsync: read errors mapping "[source file name]": Resource temporarily unavailable (35)

cp(1), on the other hand, seems just fine with the same source files.

Any ideas what causes this?

-GAWollman