Originally Posted by zander
Please note that although doing so is unsupported, 100.14.11 can be built against RHEL5's Xen kernels without patches if the IGNORE_XEN_PRESENCE environment variable is set to a non-zero value (you may also need to create an include2 directory in the top-level directory of the kernel development files and place an asm symlink to /usr/src/kernels/2.6.18-8.el5-xen-i686/include/asm-i386 in it). Mileage with other Xen kernels will vary.
It works for gentoo with a little bit of symlink magic. Great feature, took me less than 10 minutes to get the driver running with xen-3.1.