undefined reference to xenpci_alloc_space

Hi List,

is it intended that kernel does not build if

device         xenpci

is omitted in the kernel config? I get the following error:

linking kernel
gnttab.o: In function `gnttab_resume':
/usr/src/sys/xen/gnttab.c:(.text+0xe47): undefined reference to 
`xenpci_alloc_space'

Thanks,
   Michael