&quot;a&quot; is sort of orthogonal to rump kernels, but yes, you can run at least file system drivers transparently as userspace servers (just give -o rump to mount(8)).  I&#x27;ve also run a USB modem driver as a userspace server, in the &quot;the kernel I&#x27;m running doesn&#x27;t contain support, but a future kernel revision has&quot; fashion.<p>For &quot;b&quot;, rump kernels don&#x27;t support &quot;compiling out&quot;.  Rather, the idea is to &quot;link in&quot; only what you need, as in &quot;don&#x27;t need file systems in that particular application?  well don&#x27;t link in VFS then&quot;.<p>I&#x27;m not sure if you&#x27;re right or wrong, but maybe the rump kernel FAQ at <a href="http:&#x2F;&#x2F;wiki.rumpkernel.org&#x2F;Info:-FAQ" rel="nofollow">http:&#x2F;&#x2F;wiki.rumpkernel.org&#x2F;Info:-FAQ</a> will straighten your thoughts.  In the regrettable case that it doesn&#x27;t, you can always suggestion additional questions.