xen network backend driver

netback is the host side counterpart to the frontend driver in
drivers/net/xen-netfront.c. The PV protocol is also implemented by
frontend drivers in other OSes too, such as the BSDs and even Windows.

The patch is based on the driver from the xen.git pvops kernel tree but
has been put through the checkpatch.pl wringer plus several manual
cleanup passes and review iterations. The driver has been moved from
drivers/xen/netback to drivers/net/xen-netback.

One major change from xen.git is that the guest transmit path (i.e. what
looks like receive to netback) has been significantly reworked to remove
the dependency on the out of tree PageForeign page flag (a core kernel
patch which enables a per page destructor callback on the final
put_page). This page flag was used in order to implement a grant map
based transmit path (where guest pages are mapped directly into SKB
frags). Instead this version of netback uses grant copy operations into
regular memory belonging to the backend domain. Reinstating the grant
map functionality is something which I would like to revisit in the
future.

Note that this driver depends on 2e820f58f7ad "xen/irq: implement
bind_interdomain_evtchn_to_irqhandler for backend drivers" which is in
linux next via the "xen-two" tree and is intended for the 2.6.39 merge
window:
        git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git stable/backends
this branch has only that single commit since 2.6.38-rc2 and is safe for
cross merging into the net branch.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 32 insertions, 6 deletions

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 46e1b1a28b80..797d68196728 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -2953,12 +2953,38 @@ config XEN_NETDEV_FRONTEND
         select XEN_XENBUS_FRONTEND
         default y
         help
-          The network device frontend driver allows the kernel to
-          access network devices exported exported by a virtual
-          machine containing a physical network device driver. The
-          frontend driver is intended for unprivileged guest domains;
-          if you are compiling a kernel for a Xen guest, you almost
-          certainly want to enable this.
+          This driver provides support for Xen paravirtual network
+          devices exported by a Xen network driver domain (often
+          domain 0).
+
+          The corresponding Linux backend driver is enabled by the
+          CONFIG_XEN_NETDEV_BACKEND option.
+
+          If you are compiling a kernel for use as Xen guest, you
+          should say Y here. To compile this driver as a module, chose
+          M here: the module will be called xen-netfront.
+
+config XEN_NETDEV_BACKEND
+        tristate "Xen backend network device"
+        depends on XEN_BACKEND
+        help
+          This driver allows the kernel to act as a Xen network driver
+          domain which exports paravirtual network devices to other
+          Xen domains. These devices can be accessed by any operating
+          system that implements a compatible front end.
+
+          The corresponding Linux frontend driver is enabled by the
+          CONFIG_XEN_NETDEV_FRONTEND configuration option.
+
+          The backend driver presents a standard network device
+          endpoint for each paravirtual network device to the driver
+          domain network stack. These can then be bridged or routed
+          etc in order to provide full network connectivity.
+
+          If you are compiling a kernel to run in a Xen network driver
+          domain (often this is domain 0) you should say Y here. To
+          compile this driver as a module, chose M here: the module
+          will be called xen-netback.
 
 config ISERIES_VETH
         tristate "iSeries Virtual Ethernet driver support"