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 2e820f5 "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 <[email protected]>
Reviewed-by: Ben Hutchings <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Ian Campbell

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"

drivers/net/Makefile

@@ -172,6 +172,7 @@ obj-$(CONFIG_SLIP) += slip.o
 obj-$(CONFIG_SLHC) += slhc.o
 
 obj-$(CONFIG_XEN_NETDEV_FRONTEND) += xen-netfront.o
+obj-$(CONFIG_XEN_NETDEV_BACKEND) += xen-netback/
 
 obj-$(CONFIG_DUMMY) += dummy.o
 obj-$(CONFIG_IFB) += ifb.o

drivers/net/xen-netback/Makefile

@@ -0,0 +1,3 @@
+obj-$(CONFIG_XEN_NETDEV_BACKEND) := xen-netback.o
+
+xen-netback-y := netback.o xenbus.o interface.o

drivers/net/xen-netback/common.h

@@ -0,0 +1,161 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#ifndef __XEN_NETBACK__COMMON_H__
+#define __XEN_NETBACK__COMMON_H__
+
+#define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
+
+#include <linux/module.h>
+#include <linux/interrupt.h>
+#include <linux/slab.h>
+#include <linux/ip.h>
+#include <linux/in.h>
+#include <linux/io.h>
+#include <linux/netdevice.h>
+#include <linux/etherdevice.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+
+#include <xen/interface/io/netif.h>
+#include <xen/interface/grant_table.h>
+#include <xen/grant_table.h>
+#include <xen/xenbus.h>
+
+struct xen_netbk;
+
+struct xenvif {
+	/* Unique identifier for this interface. */
+	domid_t          domid;
+	unsigned int     handle;
+
+	/* Reference to netback processing backend. */
+	struct xen_netbk *netbk;
+
+	u8               fe_dev_addr[6];
+
+	/* Physical parameters of the comms window. */
+	grant_handle_t   tx_shmem_handle;
+	grant_ref_t      tx_shmem_ref;
+	grant_handle_t   rx_shmem_handle;
+	grant_ref_t      rx_shmem_ref;
+	unsigned int     irq;
+
+	/* List of frontends to notify after a batch of frames sent. */
+	struct list_head notify_list;
+
+	/* The shared rings and indexes. */
+	struct xen_netif_tx_back_ring tx;
+	struct xen_netif_rx_back_ring rx;
+	struct vm_struct *tx_comms_area;
+	struct vm_struct *rx_comms_area;
+
+	/* Flags that must not be set in dev->features */
+	u32 features_disabled;
+
+	/* Frontend feature information. */
+	u8 can_sg:1;
+	u8 gso:1;
+	u8 gso_prefix:1;
+	u8 csum:1;
+
+	/* Internal feature information. */
+	u8 can_queue:1;	    /* can queue packets for receiver? */
+
+	/*
+	 * Allow xenvif_start_xmit() to peek ahead in the rx request
+	 * ring.  This is a prediction of what rx_req_cons will be
+	 * once all queued skbs are put on the ring.
+	 */
+	RING_IDX rx_req_cons_peek;
+
+	/* Transmit shaping: allow 'credit_bytes' every 'credit_usec'. */
+	unsigned long   credit_bytes;
+	unsigned long   credit_usec;
+	unsigned long   remaining_credit;
+	struct timer_list credit_timeout;
+
+	/* Statistics */
+	unsigned long rx_gso_checksum_fixup;
+
+	/* Miscellaneous private stuff. */
+	struct list_head schedule_list;
+	atomic_t         refcnt;
+	struct net_device *dev;
+
+	wait_queue_head_t waiting_to_free;
+};
+
+#define XEN_NETIF_TX_RING_SIZE __RING_SIZE((struct xen_netif_tx_sring *)0, PAGE_SIZE)
+#define XEN_NETIF_RX_RING_SIZE __RING_SIZE((struct xen_netif_rx_sring *)0, PAGE_SIZE)
+
+struct xenvif *xenvif_alloc(struct device *parent,
+			    domid_t domid,
+			    unsigned int handle);
+
+int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
+		   unsigned long rx_ring_ref, unsigned int evtchn);
+void xenvif_disconnect(struct xenvif *vif);
+
+void xenvif_get(struct xenvif *vif);
+void xenvif_put(struct xenvif *vif);
+
+int xenvif_xenbus_init(void);
+
+int xenvif_schedulable(struct xenvif *vif);
+
+int xen_netbk_rx_ring_full(struct xenvif *vif);
+
+int xen_netbk_must_stop_queue(struct xenvif *vif);
+
+/* (Un)Map communication rings. */
+void xen_netbk_unmap_frontend_rings(struct xenvif *vif);
+int xen_netbk_map_frontend_rings(struct xenvif *vif,
+				 grant_ref_t tx_ring_ref,
+				 grant_ref_t rx_ring_ref);
+
+/* (De)Register a xenvif with the netback backend. */
+void xen_netbk_add_xenvif(struct xenvif *vif);
+void xen_netbk_remove_xenvif(struct xenvif *vif);
+
+/* (De)Schedule backend processing for a xenvif */
+void xen_netbk_schedule_xenvif(struct xenvif *vif);
+void xen_netbk_deschedule_xenvif(struct xenvif *vif);
+
+/* Check for SKBs from frontend and schedule backend processing */
+void xen_netbk_check_rx_xenvif(struct xenvif *vif);
+/* Receive an SKB from the frontend */
+void xenvif_receive_skb(struct xenvif *vif, struct sk_buff *skb);
+
+/* Queue an SKB for transmission to the frontend */
+void xen_netbk_queue_tx_skb(struct xenvif *vif, struct sk_buff *skb);
+/* Notify xenvif that ring now has space to send an skb to the frontend */
+void xenvif_notify_tx_completion(struct xenvif *vif);
+
+/* Returns number of ring slots required to send an skb to the frontend */
+unsigned int xen_netbk_count_skb_slots(struct xenvif *vif, struct sk_buff *skb);
+
+#endif /* __XEN_NETBACK__COMMON_H__ */