Virtio helper routines for a descriptor ringbuffer implementation

These helper routines supply most of the virtqueue_ops for hypervisors
which want to use a ring for virtio.  Unlike the previous lguest
implementation:

1) The rings are variable sized (2^n-1 elements).
2) They have an unfortunate limit of 65535 bytes per sg element.
3) The page numbers are always 64 bit (PAE anyone?)
4) They no longer place used[] on a separate page, just a separate
   cacheline.
5) We do a modulo on a variable.  We could be tricky if we cared.
6) Interrupts and notifies are suppressed using flags within the rings.

Users need only get the ring pages and provide a notify hook (KVM
wants the guest to allocate the rings, lguest does it sanely).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Dor Laor <dor.laor@qumranet.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/x86/lguest/Kconfig b/arch/x86/lguest/Kconfig
index 0fabf87db998..44dccfd845f8 100644
--- a/arch/x86/lguest/Kconfig
+++ b/arch/x86/lguest/Kconfig
@@ -2,6 +2,7 @@ config LGUEST_GUEST
         bool "Lguest guest support"
         select PARAVIRT
         depends on !X86_PAE
+        select VIRTIO_RING
         help
           Lguest is a tiny in-kernel hypervisor.  Selecting this will
           allow your kernel to boot under lguest.  This option will increase