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[Xen-devel] [PATCH 4/4] [Net] Support accelerated network plugin modules

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH 4/4] [Net] Support accelerated network plugin modules
From: Kieran Mansley <kmansley@xxxxxxxxxxxxxx>
Date: Thu, 21 Jun 2007 14:17:27 +0100
Cc: netdev@xxxxxxxxxxxxxxx
Delivery-date: Thu, 21 Jun 2007 06:17:30 -0700
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Frontend net driver acceleration

Signed-off-by: Kieran Mansley <kmansley@xxxxxxxxxxxxxx> 

diff -r 82196b117a5b drivers/xen/netfront/Makefile
--- a/drivers/xen/netfront/Makefile     Wed Jun 20 17:01:02 2007 +0100
+++ b/drivers/xen/netfront/Makefile     Wed Jun 20 17:01:07 2007 +0100
@@ -1,4 +1,4 @@
 
 obj-$(CONFIG_XEN_NETDEV_FRONTEND)      := xennet.o
 
-xennet-objs := netfront.o
+xennet-objs := netfront.o accel.o
diff -r 82196b117a5b drivers/xen/netfront/accel.c
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/drivers/xen/netfront/accel.c      Thu Jun 21 13:47:33 2007 +0100
@@ -0,0 +1,773 @@
+/******************************************************************************
+ * Virtual network driver for conversing with remote driver backends.
+ *
+ * Copyright (C) 2007 Solarflare Communications, Inc.
+ *
+ * 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.
+ */
+
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/list.h>
+#include <linux/kref.h>
+
+#include <xen/xenbus.h>
+
+#include "netfront.h"
+
+#define DPRINTK(fmt, args...)                          \
+       pr_debug("netfront/accel (%s:%d) " fmt,         \
+                __FUNCTION__, __LINE__, ##args)
+#define IPRINTK(fmt, args...)                          \
+       printk(KERN_INFO "netfront/accel: " fmt, ##args)
+#define WPRINTK(fmt, args...)                          \
+       printk(KERN_WARNING "netfront/accel: " fmt, ##args)
+
+/*
+ * List of all netfront accelerator plugin modules available.  Each
+ * list entry is of type struct netfront_accelerator.
+ */ 
+static struct list_head accelerators_list;
+
+/*
+ * Lock to protect access to accelerators_list
+ */
+static spinlock_t accelerators_lock;
+
+/* Forward declaration of kref cleanup functions */
+static void accel_kref_release(struct kref *ref);
+static void vif_kref_release(struct kref *ref);
+
+
+void netif_init_accel(void)
+{
+       INIT_LIST_HEAD(&accelerators_list);
+       spin_lock_init(&accelerators_lock);
+}
+
+
+/* 
+ * Initialise the accel_vif_state field in the netfront state
+ */ 
+void init_accelerator_vif(struct netfront_info *np,
+                         struct xenbus_device *dev)
+{
+       np->accelerator = NULL;
+
+       /* It's assumed that these things don't change */
+       np->accel_vif_state.np = np;
+       np->accel_vif_state.dev = dev;
+
+       np->accel_vif_state.ready_for_probe = 1;
+       np->accel_vif_state.need_probe = NULL;
+}
+
+
+/*
+ * Compare a frontend description string against an accelerator to see
+ * if they match.  Would ultimately be nice to replace the string with
+ * a unique numeric identifier for each accelerator.
+ */
+static int match_accelerator(const char *frontend, 
+                            struct netfront_accelerator *accelerator)
+{
+       return strcmp(frontend, accelerator->frontend) == 0;
+}
+
+
+/* 
+ * Add a frontend vif to the list of vifs that is using a netfront
+ * accelerator plugin module.
+ */
+static void add_accelerator_vif(struct netfront_accelerator *accelerator,
+                               struct netfront_info *np)
+{
+       np->accelerator = accelerator;
+
+       list_add(&np->accel_vif_state.link, &accelerator->vif_states);
+}
+
+
+/*
+ * Initialise the state to track an accelerator plugin module.
+ */ 
+static int init_accelerator(const char *frontend, 
+                           struct netfront_accelerator **result)
+{
+       struct netfront_accelerator *accelerator = 
+               kmalloc(sizeof(struct netfront_accelerator), GFP_KERNEL);
+       int frontend_len;
+
+       if (!accelerator) {
+               DPRINTK("%s: no memory for accelerator", __FUNCTION__);
+               return -ENOMEM;
+       }
+
+       frontend_len = strlen(frontend) + 1;
+       accelerator->frontend = kmalloc(frontend_len, GFP_KERNEL);
+       if (!accelerator->frontend) {
+               DPRINTK("%s: no memory for accelerator", __FUNCTION__);
+               kfree(accelerator);
+               return -ENOMEM;
+       }
+       strlcpy(accelerator->frontend, frontend, frontend_len);
+       
+       INIT_LIST_HEAD(&accelerator->vif_states);
+       spin_lock_init(&accelerator->vif_states_lock);
+
+       accelerator->hooks = NULL;
+
+       accelerator->ready_for_probe = 1;
+       accelerator->need_probe = NULL;
+
+       list_add(&accelerator->link, &accelerators_list);
+
+       *result = accelerator;
+
+       return 0;
+}                                      
+
+
+/* 
+ * Modify the hooks stored in the per-vif state to match that in the
+ * netfront accelerator's state.
+ */
+static void 
+accelerator_set_vif_state_hooks(struct netfront_accel_vif_state *vif_state)
+{
+       /* This function must be called with the vif_state_lock held */
+
+       /*
+        * Take references to stop hooks disappearing.
+        * This persists until vif_kref gets to zero.
+        */
+       kref_get(&vif_state->np->accelerator->accel_kref);
+       /* This persists until vif_state->hooks are cleared */
+       kref_init(&vif_state->vif_kref);
+
+       /* Make sure there are no data path operations going on */
+       netif_poll_disable(vif_state->np->netdev);
+       netif_tx_lock_bh(vif_state->np->netdev);
+
+       vif_state->hooks = vif_state->np->accelerator->hooks;
+
+       netif_tx_unlock_bh(vif_state->np->netdev);
+       netif_poll_enable(vif_state->np->netdev);
+}
+
+
+static void accelerator_probe_new_vif(struct netfront_info *np,
+                                     struct xenbus_device *dev, 
+                                     struct netfront_accelerator *accelerator)
+{
+       struct netfront_accel_hooks *hooks;
+       unsigned flags;
+       
+       DPRINTK("%s\n", __FUNCTION__);
+
+       spin_lock_irqsave(&accelerator->vif_states_lock, flags);
+       
+       /*
+        * Include this frontend device on the accelerator's list
+        */
+       add_accelerator_vif(accelerator, np);
+       
+       hooks = accelerator->hooks;
+       
+       if (hooks) {
+               if (np->accel_vif_state.ready_for_probe) {
+                       np->accel_vif_state.ready_for_probe = 0;
+                       
+                       kref_get(&accelerator->accel_kref);
+                       
+                       spin_unlock_irqrestore(&accelerator->vif_states_lock,
+                                              flags);
+                       
+                       hooks->new_device(np->netdev, dev);
+                       
+                       kref_put(&accelerator->accel_kref,
+                                accel_kref_release);
+                       /* 
+                        * Hooks will get linked into vif_state by a
+                        * future call by the accelerator to
+                        * netfront_accelerator_ready()
+                        */
+                       return;
+               } else {
+                       if (np->accel_vif_state.need_probe != NULL)
+                               DPRINTK("Probe request on vif awaiting 
probe\n");
+                       np->accel_vif_state.need_probe = hooks;
+               }
+       }
+               
+       spin_unlock_irqrestore(&accelerator->vif_states_lock,
+                              flags);
+       return;
+}
+
+/*  
+ * Request that a particular netfront accelerator plugin is loaded.
+ * Usually called as a result of the vif configuration specifying
+ * which one to use.
+ */
+int netfront_load_accelerator(struct netfront_info *np, 
+                             struct xenbus_device *dev, 
+                             const char *frontend)
+{
+       struct netfront_accelerator *accelerator;
+       int rc;
+       unsigned flags;
+
+       DPRINTK("%s: %s\n", __FUNCTION__, frontend);
+
+       spin_lock_irqsave(&accelerators_lock, flags);
+
+       /* 
+        * Look at list of loaded accelerators to see if the requested
+        * one is already there 
+        */
+       list_for_each_entry(accelerator, &accelerators_list, link) {
+               if (match_accelerator(frontend, accelerator)) {
+                       spin_unlock_irqrestore(&accelerators_lock, flags);
+
+                       accelerator_probe_new_vif(np, dev, accelerator);
+
+                       return 0;
+               }
+       }
+
+       /* Couldn't find it, so create a new one and load the module */
+       if ((rc = init_accelerator(frontend, &accelerator)) < 0) {
+               spin_unlock_irqrestore(&accelerators_lock, flags);
+               return rc;
+       }
+
+       spin_unlock_irqrestore(&accelerators_lock, flags);
+
+       /* Include this frontend device on the accelerator's list */
+       spin_lock_irqsave(&accelerator->vif_states_lock, flags);
+       add_accelerator_vif(accelerator, np);
+       spin_unlock_irqrestore(&accelerator->vif_states_lock, flags);
+
+       DPRINTK("%s: loading module %s\n", __FUNCTION__, frontend);
+
+       /* load module */
+       request_module("%s", frontend);
+
+       /*
+        * Module should now call netfront_accelerator_loaded() once
+        * it's up and running, and we can continue from there 
+        */
+
+       return 0;
+}
+
+
+/*
+ * Go through all the netfront vifs and see if they have requested
+ * this accelerator.  Notify the accelerator plugin of the relevant
+ * device if so.  Called when an accelerator plugin module is first
+ * loaded and connects to netfront.
+ */
+static void 
+accelerator_probe_vifs(struct netfront_accelerator *accelerator,
+                      struct netfront_accel_hooks *hooks,
+                      unsigned lock_flags)
+{
+       struct netfront_accel_vif_state *vif_state, *tmp;
+
+       /* Calling function must have taken the vif_states_lock */
+
+       DPRINTK("%s: %p\n", __FUNCTION__, accelerator);
+
+       /* 
+        * kref_init() takes a single reference to the hooks that will
+        * persist until the accelerator hooks are removed (e.g. by
+        * accelerator module unload)
+        */
+       kref_init(&accelerator->accel_kref);
+
+       /* 
+        * Store the hooks for future calls to probe a new device, and
+        * to wire into the vif_state once the accelerator plugin is
+        * ready to accelerate each vif
+        */
+       BUG_ON(hooks == NULL);
+       accelerator->hooks = hooks;
+       
+       list_for_each_entry_safe(vif_state, tmp, &accelerator->vif_states,
+                                link) {
+               struct netfront_info *np = vif_state->np;
+
+               if (vif_state->ready_for_probe) {
+                       vif_state->ready_for_probe = 0;
+                       kref_get(&accelerator->accel_kref);
+
+                       /* 
+                        * drop lock before calling hook.  hooks are
+                        * protected by the kref
+                        */
+                       spin_unlock_irqrestore(&accelerator->vif_states_lock,
+                                              lock_flags);
+                       
+                       hooks->new_device(np->netdev, vif_state->dev);
+                       
+                       kref_put(&accelerator->accel_kref, accel_kref_release);
+
+                       /* Retake lock for next go round the loop */
+                       spin_lock_irqsave(&accelerator->vif_states_lock, 
lock_flags);
+                       
+                       /*
+                        * Hooks will get linked into vif_state by a call to
+                        * netfront_accelerator_ready() once accelerator
+                        * plugin is ready for action
+                        */
+               } else {
+                       if (vif_state->need_probe != NULL)
+                               DPRINTK("Probe request on vif awaiting 
probe\n");
+                       vif_state->need_probe = hooks;
+               }
+       }
+       
+       /* Return with vif_states_lock held, as on entry */
+}
+
+
+/* 
+ * Wrapper for accelerator_probe_vifs that checks now is a good time
+ * to do the probe, and postpones till previous state cleared up if
+ * necessary
+ */
+static void 
+accelerator_probe_vifs_on_load(struct netfront_accelerator *accelerator,
+                              struct netfront_accel_hooks *hooks)
+{
+       unsigned flags;
+
+       DPRINTK("%s\n", __FUNCTION__);
+
+       spin_lock_irqsave(&accelerator->vif_states_lock, flags);
+       
+       if (accelerator->ready_for_probe) {
+               accelerator->ready_for_probe = 0;
+               accelerator_probe_vifs(accelerator, hooks, flags);
+       } else {
+               if (accelerator->need_probe)
+                       DPRINTK("Probe request on accelerator awaiting 
probe\n");
+               accelerator->need_probe = hooks;
+       }
+
+       spin_unlock_irqrestore(&accelerator->vif_states_lock,
+                              flags);
+}
+
+
+/* 
+ * Called by the netfront accelerator plugin module when it has loaded 
+ */
+int netfront_accelerator_loaded(const char *frontend, 
+                               struct netfront_accel_hooks *hooks)
+{
+       struct netfront_accelerator *accelerator;
+       unsigned flags;
+
+       spin_lock_irqsave(&accelerators_lock, flags);
+
+       /* 
+        * Look through list of accelerators to see if it has already
+        * been requested
+        */
+       list_for_each_entry(accelerator, &accelerators_list, link) {
+               if (match_accelerator(frontend, accelerator)) {
+                       spin_unlock_irqrestore(&accelerators_lock, flags);
+
+                       accelerator_probe_vifs_on_load(accelerator, hooks);
+
+                       return 0;
+               }
+       }
+
+       /*
+        * If it wasn't in the list, add it now so that when it is
+        * requested the caller will find it
+        */
+       DPRINTK("%s: Couldn't find matching accelerator (%s)\n",
+               __FUNCTION__, frontend);
+
+       init_accelerator(frontend, &accelerator);
+
+       spin_unlock_irqrestore(&accelerators_lock, flags);
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(netfront_accelerator_loaded);
+
+
+/* 
+ * Called by the accelerator module after it has been probed with a
+ * network device to say that it is ready to start accelerating
+ * traffic on that device
+ */
+void netfront_accelerator_ready(const char *frontend,
+                               struct xenbus_device *dev)
+{
+       struct netfront_accelerator *accelerator;
+       struct netfront_accel_vif_state *accel_vif_state;
+       unsigned flags, flags1;
+
+       DPRINTK("%s: %s %p\n", __FUNCTION__, frontend, dev);
+
+       spin_lock_irqsave(&accelerators_lock, flags);
+
+       list_for_each_entry(accelerator, &accelerators_list, link) {
+               if (match_accelerator(frontend, accelerator)) {
+                       spin_lock_irqsave
+                               (&accelerator->vif_states_lock, flags1);
+
+                       list_for_each_entry(accel_vif_state,
+                                           &accelerator->vif_states, link) {
+                               if (accel_vif_state->dev == dev)
+                                       accelerator_set_vif_state_hooks
+                                               (accel_vif_state);
+                       }
+
+                       spin_unlock_irqrestore
+                               (&accelerator->vif_states_lock, flags1);
+                       goto done;
+               }
+       }
+
+ done:
+       spin_unlock_irqrestore(&accelerators_lock, flags);
+}
+EXPORT_SYMBOL_GPL(netfront_accelerator_ready);
+
+
+/* 
+ * Safely remove the accelerator function hooks from a netfront state.
+ */
+static void accelerator_remove_hooks(struct netfront_accelerator *accelerator)
+{
+       struct netfront_accel_vif_state *vif_state, *tmp;
+       unsigned flags;
+
+       spin_lock_irqsave(&accelerator->vif_states_lock, flags);
+
+       list_for_each_entry_safe(vif_state, tmp,
+                                &accelerator->vif_states,
+                                link) {
+               /* Make sure there are no data path operations going on */
+               netif_poll_disable(vif_state->np->netdev);
+               netif_tx_lock_bh(vif_state->np->netdev);
+
+               /* 
+                * Remove the hooks, but leave the vif_state on the
+                * accelerator's list as that signifies this vif is
+                * interested in using that accelerator if it becomes
+                * available again
+                */
+               vif_state->hooks = NULL;
+               
+               netif_tx_unlock_bh(vif_state->np->netdev);
+               netif_poll_enable(vif_state->np->netdev);
+
+               /* 
+                * Remove the reference taken when the vif_state hooks
+                * were set, must be called without lock held
+                */
+               spin_unlock_irqrestore(&accelerator->vif_states_lock, flags);
+               kref_put(&vif_state->vif_kref, vif_kref_release);
+               spin_lock_irqsave(&accelerator->vif_states_lock, flags);
+       }
+       
+       accelerator->hooks = NULL;
+
+       spin_unlock_irqrestore(&accelerator->vif_states_lock, flags);
+
+       /* Remove the reference taken when module loaded */ 
+       kref_put(&accelerator->accel_kref, accel_kref_release);
+}
+
+
+/* 
+ * Called by a netfront accelerator when it is unloaded.  This safely
+ * removes the hooks into the plugin and blocks until all devices have
+ * finished using it, so on return it is safe to unload.
+ */
+void netfront_accelerator_unloaded(const char *frontend)
+{
+       struct netfront_accelerator *accelerator;
+       unsigned flags;
+
+       spin_lock_irqsave(&accelerators_lock, flags);
+
+       list_for_each_entry(accelerator, &accelerators_list, link) {
+               if (match_accelerator(frontend, accelerator)) {
+                       spin_unlock_irqrestore(&accelerators_lock, flags);
+
+                       /* 
+                        * Use semaphore to ensure we know when all
+                        * uses of hooks are complete
+                        */
+                       sema_init(&accelerator->exit_semaphore, 0);
+
+                       accelerator_remove_hooks(accelerator);
+
+                       /* Wait for hooks to be unused, then return */
+                       down(&accelerator->exit_semaphore);
+                       
+                       return;
+               }
+       }
+       spin_unlock_irqrestore(&accelerators_lock, flags);
+}
+EXPORT_SYMBOL_GPL(netfront_accelerator_unloaded);
+
+
+int netfront_check_accelerator_queue_busy(struct net_device *dev,
+                                         struct netfront_info *np)
+{
+       struct netfront_accel_hooks *hooks;
+       int rc = 1;
+       unsigned flags;
+
+       /*
+        * Call the check busy accelerator hook. The use count for the
+        * accelerator's hooks is incremented for the duration of the
+        * call to prevent the accelerator being able to modify the
+        * hooks in the middle (by, for example, unloading)
+        */ 
+       if (np->accel_vif_state.hooks) {
+               spin_lock_irqsave(&np->accelerator->vif_states_lock, flags); 
+               hooks = np->accel_vif_state.hooks;
+               if (hooks) {
+                       kref_get(&np->accel_vif_state.vif_kref);
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+
+                       rc = np->accel_vif_state.hooks->check_busy(dev);
+                       
+                       kref_put(&np->accel_vif_state.vif_kref,
+                                vif_kref_release);
+               } else {
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+               }
+       }
+
+       return rc;
+}
+
+
+int netfront_accelerator_call_remove(struct netfront_info *np,
+                                    struct xenbus_device *dev)
+{
+       struct netfront_accel_hooks *hooks;
+       unsigned flags;
+       int rc = 0;
+
+       /* 
+        * Call the remove accelerator hook. The use count for the
+        * accelerator's hooks is incremented for the duration of the
+        * call to prevent the accelerator being able to modify the
+        * hooks in the middle (by, for example, unloading)
+        */ 
+       if (np->accel_vif_state.hooks) {
+               spin_lock_irqsave(&np->accelerator->vif_states_lock, flags); 
+               hooks = np->accel_vif_state.hooks;
+               if (hooks) {
+                       kref_get(&np->accel_vif_state.vif_kref);
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+
+                       rc = np->accel_vif_state.hooks->remove(dev);
+
+                       kref_put(&np->accel_vif_state.vif_kref,
+                                vif_kref_release);
+               } else {
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+               }
+       }
+       return rc;
+}
+
+
+int netfront_accelerator_call_resume(struct netfront_info *np,
+                                    struct xenbus_device *dev)
+{
+       struct netfront_accel_hooks *hooks;
+       unsigned flags;
+       int rc = 0;
+
+       /* 
+        *  Call the resume accelerator hook.  The use count for the
+        *  accelerator's hooks is incremented for the duration of
+        *  the call to prevent the accelerator being able to modify
+        *  the hooks in the middle (by, for example, unloading)
+        */
+       if (np->accel_vif_state.hooks) {
+               spin_lock_irqsave(&np->accelerator->vif_states_lock, flags); 
+               hooks = np->accel_vif_state.hooks;
+               if (hooks) {
+                       kref_get(&np->accel_vif_state.vif_kref);
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+
+                       rc = np->accel_vif_state.hooks->resume(dev);
+
+                       kref_put(&np->accel_vif_state.vif_kref,
+                                vif_kref_release);
+               } else {
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+               }
+       }
+       return rc;
+}
+
+
+void netfront_accelerator_call_backend_changed(struct netfront_info *np,
+                                              struct xenbus_device *dev,
+                                              enum xenbus_state backend_state)
+{
+       struct netfront_accel_hooks *hooks;
+       unsigned flags;
+
+       /* 
+        * Call the backend_changed accelerator hook. The use count
+        * for the accelerator's hooks is incremented for the duration
+        * of the call to prevent the accelerator being able to modify
+        * the hooks in the middle (by, for example, unloading)
+        */
+       if (np->accel_vif_state.hooks) {
+               spin_lock_irqsave(&np->accelerator->vif_states_lock, flags); 
+               hooks = np->accel_vif_state.hooks;
+               if (hooks) {
+                       kref_get(&np->accel_vif_state.vif_kref);
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+
+                       np->accel_vif_state.hooks->backend_changed
+                               (dev, backend_state);
+
+                       kref_put(&np->accel_vif_state.vif_kref,
+                                vif_kref_release);
+               } else {
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+               }
+       }
+}
+
+
+void netfront_accelerator_call_stop_napi_irq(struct netfront_info *np,
+                                            struct net_device *dev)
+{
+       struct netfront_accel_hooks *hooks;
+       unsigned flags;
+
+       /* 
+        * Call the stop_napi_interrupts accelerator hook.  The use
+        * count for the accelerator's hooks is incremented for the
+        * duration of the call to prevent the accelerator being able
+        * to modify the hooks in the middle (by, for example,
+        * unloading)
+        */
+
+       if (np->accel_vif_state.hooks) {
+               spin_lock_irqsave(&np->accelerator->vif_states_lock, flags); 
+               hooks = np->accel_vif_state.hooks;
+               if (hooks) {
+                       kref_get(&np->accel_vif_state.vif_kref);
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+
+                       np->accel_vif_state.hooks->stop_napi_irq(dev);
+               
+                       kref_put(&np->accel_vif_state.vif_kref,
+                                vif_kref_release);
+               } else {
+                       spin_unlock_irqrestore
+                               (&np->accelerator->vif_states_lock, flags);
+               }
+       }
+}
+
+
+/* 
+ * Once all users of hooks have kref_put()'d we can signal that it's
+ * safe to unload
+ */ 
+static void accel_kref_release(struct kref *ref)
+{
+       struct netfront_accelerator *accelerator =
+               container_of(ref, struct netfront_accelerator, accel_kref);
+       struct netfront_accel_hooks *hooks;
+       unsigned flags;
+
+       /* Signal that all users of hooks are done */
+       up(&accelerator->exit_semaphore);
+
+       spin_lock_irqsave(&accelerator->vif_states_lock, flags);
+       if (accelerator->need_probe) {
+               hooks = accelerator->need_probe;
+               accelerator->need_probe = NULL;
+               accelerator_probe_vifs(accelerator, hooks, flags);
+       } 
+       else
+               accelerator->ready_for_probe = 1;
+
+       spin_unlock_irqrestore(&accelerator->vif_states_lock, flags);
+}
+
+
+static void vif_kref_release(struct kref *ref)
+{
+       struct netfront_accel_vif_state *vif_state = 
+               container_of(ref, struct netfront_accel_vif_state, vif_kref);
+       struct netfront_accel_hooks *hooks;
+       unsigned flags;
+
+       /* 
+        * Now that this vif has finished using the hooks, it can
+        * decrement the accelerator's global copy ref count 
+        */
+       kref_put(&vif_state->np->accelerator->accel_kref, accel_kref_release);
+
+       spin_lock_irqsave(&vif_state->np->accelerator->vif_states_lock, flags);
+       if (vif_state->need_probe) {
+               hooks = vif_state->need_probe;
+               vif_state->need_probe = NULL;
+               spin_unlock_irqrestore
+                       (&vif_state->np->accelerator->vif_states_lock, flags);
+               hooks->new_device(vif_state->np->netdev, vif_state->dev);
+       } else {
+               vif_state->ready_for_probe = 1;
+               spin_unlock_irqrestore
+                       (&vif_state->np->accelerator->vif_states_lock, flags);
+       }
+}
+
diff -r 82196b117a5b drivers/xen/netfront/netfront.c
--- a/drivers/xen/netfront/netfront.c   Wed Jun 20 17:01:02 2007 +0100
+++ b/drivers/xen/netfront/netfront.c   Wed Jun 20 17:01:07 2007 +0100
@@ -3,6 +3,7 @@
  *
  * Copyright (c) 2002-2005, K A Fraser
  * Copyright (c) 2005, XenSource Ltd
+ * Copyright (C) 2007 Solarflare Communications, Inc.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version 2
@@ -74,6 +75,8 @@ struct netfront_cb {
 
 #define NETFRONT_SKB_CB(skb)   ((struct netfront_cb *)((skb)->cb))
 
+#include "netfront.h"
+
 /*
  * Mutually-exclusive module options to select receive data path:
  *  rx_copy : Packets are copied by network backend into local memory
@@ -144,57 +147,6 @@ static inline int netif_needs_gso(struct
 
 #define GRANT_INVALID_REF      0
 
-#define NET_TX_RING_SIZE __RING_SIZE((struct netif_tx_sring *)0, PAGE_SIZE)
-#define NET_RX_RING_SIZE __RING_SIZE((struct netif_rx_sring *)0, PAGE_SIZE)
-
-struct netfront_info {
-       struct list_head list;
-       struct net_device *netdev;
-
-       struct net_device_stats stats;
-
-       struct netif_tx_front_ring tx;
-       struct netif_rx_front_ring rx;
-
-       spinlock_t   tx_lock;
-       spinlock_t   rx_lock;
-
-       unsigned int irq;
-       unsigned int copying_receiver;
-       unsigned int carrier;
-
-       /* Receive-ring batched refills. */
-#define RX_MIN_TARGET 8
-#define RX_DFL_MIN_TARGET 64
-#define RX_MAX_TARGET min_t(int, NET_RX_RING_SIZE, 256)
-       unsigned rx_min_target, rx_max_target, rx_target;
-       struct sk_buff_head rx_batch;
-
-       struct timer_list rx_refill_timer;
-
-       /*
-        * {tx,rx}_skbs store outstanding skbuffs. The first entry in tx_skbs
-        * is an index into a chain of free entries.
-        */
-       struct sk_buff *tx_skbs[NET_TX_RING_SIZE+1];
-       struct sk_buff *rx_skbs[NET_RX_RING_SIZE];
-
-#define TX_MAX_TARGET min_t(int, NET_RX_RING_SIZE, 256)
-       grant_ref_t gref_tx_head;
-       grant_ref_t grant_tx_ref[NET_TX_RING_SIZE + 1];
-       grant_ref_t gref_rx_head;
-       grant_ref_t grant_rx_ref[NET_RX_RING_SIZE];
-
-       struct xenbus_device *xbdev;
-       int tx_ring_ref;
-       int rx_ring_ref;
-       u8 mac[ETH_ALEN];
-
-       unsigned long rx_pfn_array[NET_RX_RING_SIZE];
-       struct multicall_entry rx_mcl[NET_RX_RING_SIZE+1];
-       struct mmu_update rx_mmu[NET_RX_RING_SIZE];
-};
-
 struct netfront_rx_info {
        struct netif_rx_response rx;
        struct netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX - 1];
@@ -334,6 +286,8 @@ static int __devexit netfront_remove(str
 
        DPRINTK("%s\n", dev->nodename);
 
+       netfront_accelerator_call_remove(info, dev);
+
        netif_disconnect_backend(info);
 
        del_timer_sync(&info->rx_refill_timer);
@@ -358,6 +312,8 @@ static int netfront_resume(struct xenbus
        struct netfront_info *info = dev->dev.driver_data;
 
        DPRINTK("%s\n", dev->nodename);
+
+       netfront_accelerator_call_resume(info, dev);
 
        netif_disconnect_backend(info);
        return 0;
@@ -577,6 +533,8 @@ static void backend_changed(struct xenbu
                xenbus_frontend_closed(dev);
                break;
        }
+
+       netfront_accelerator_call_backend_changed(np, dev, backend_state);
 }
 
 /** Send a packet on a net device to encourage switches to learn the
@@ -613,15 +571,29 @@ static inline int netfront_tx_slot_avail
                (TX_MAX_TARGET - MAX_SKB_FRAGS - 2));
 }
 
+
 static inline void network_maybe_wake_tx(struct net_device *dev)
 {
        struct netfront_info *np = netdev_priv(dev);
 
        if (unlikely(netif_queue_stopped(dev)) &&
            netfront_tx_slot_available(np) &&
-           likely(netif_running(dev)))
+           likely(netif_running(dev)) &&
+           netfront_check_accelerator_queue_busy(dev, np))
                netif_wake_queue(dev);
 }
+
+
+int netfront_check_queue_busy(struct net_device *dev)
+{
+       struct netfront_info *np = netdev_priv(dev);
+
+       return unlikely(netif_queue_stopped(dev)) &&
+               netfront_tx_slot_available(np) &&
+               likely(netif_running(dev));
+}
+EXPORT_SYMBOL(netfront_check_queue_busy);
+
 
 static int network_open(struct net_device *dev)
 {
@@ -633,8 +605,11 @@ static int network_open(struct net_devic
        if (netfront_carrier_ok(np)) {
                network_alloc_rx_buffers(dev);
                np->rx.sring->rsp_event = np->rx.rsp_cons + 1;
-               if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
+               if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx)){
+                       netfront_accelerator_call_stop_napi_irq(np, dev);
+
                        netif_rx_schedule(dev);
+               }
        }
        spin_unlock_bh(&np->rx_lock);
 
@@ -702,6 +677,10 @@ static void rx_refill_timeout(unsigned l
 static void rx_refill_timeout(unsigned long data)
 {
        struct net_device *dev = (struct net_device *)data;
+       struct netfront_info *np = netdev_priv(dev);
+
+       netfront_accelerator_call_stop_napi_irq(np, dev);
+
        netif_rx_schedule(dev);
 }
 
@@ -941,6 +920,13 @@ static int network_start_xmit(struct sk_
        unsigned int offset = offset_in_page(data);
        unsigned int len = skb_headlen(skb);
 
+       /* Check the fast path, if hooks are available */
+       if (np->accel_vif_state.hooks &&
+           np->accel_vif_state.hooks->start_xmit(skb, dev)) {
+               /* Fast path has sent this packet */
+               return 0;
+       }
+
        frags += (offset + len + PAGE_SIZE - 1) / PAGE_SIZE;
        if (unlikely(frags > MAX_SKB_FRAGS + 1)) {
                printk(KERN_ALERT "xennet: skb rides the rocket: %d frags\n",
@@ -1044,8 +1030,11 @@ static irqreturn_t netif_int(int irq, vo
        if (likely(netfront_carrier_ok(np))) {
                network_tx_buf_gc(dev);
                /* Under tx_lock: protects access to rx shared-ring indexes. */
-               if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
+               if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx)) {
+                       netfront_accelerator_call_stop_napi_irq(np, dev);
+
                        netif_rx_schedule(dev);
+               }
        }
 
        spin_unlock_irqrestore(&np->tx_lock, flags);
@@ -1305,7 +1294,7 @@ static int netif_poll(struct net_device 
        struct netif_extra_info *extras = rinfo.extras;
        RING_IDX i, rp;
        struct multicall_entry *mcl;
-       int work_done, budget, more_to_do = 1;
+       int work_done, budget, more_to_do = 1, accel_more_to_do = 1;
        struct sk_buff_head rxq;
        struct sk_buff_head errq;
        struct sk_buff_head tmpq;
@@ -1472,6 +1461,20 @@ err:
 
        network_alloc_rx_buffers(dev);
 
+       if (work_done < budget) {
+               /* there's some spare capacity, try the accelerated path */
+               int accel_budget = budget - work_done;
+               int accel_budget_start = accel_budget;
+
+               if (np->accel_vif_state.hooks) {
+                       accel_more_to_do = 
+                               np->accel_vif_state.hooks->netdev_poll
+                               (dev, &accel_budget);
+                       work_done += (accel_budget_start - accel_budget);
+               } else 
+                       accel_more_to_do = 0;
+       }
+
        *pbudget   -= work_done;
        dev->quota -= work_done;
 
@@ -1479,15 +1482,26 @@ err:
                local_irq_save(flags);
 
                RING_FINAL_CHECK_FOR_RESPONSES(&np->rx, more_to_do);
-               if (!more_to_do)
+
+               if (!more_to_do && !accel_more_to_do && 
+                   np->accel_vif_state.hooks) {
+                       /* 
+                        *  Slow path has nothing more to do, see if
+                        *  fast path is likewise
+                        */
+                       accel_more_to_do = 
+                               np->accel_vif_state.hooks->start_napi_irq(dev);
+               }
+
+               if (!more_to_do && !accel_more_to_do)
                        __netif_rx_complete(dev);
 
                local_irq_restore(flags);
        }
 
        spin_unlock(&np->rx_lock);
-
-       return more_to_do;
+       
+       return more_to_do | accel_more_to_do;
 }
 
 static void netif_release_tx_bufs(struct netfront_info *np)
@@ -1687,7 +1701,9 @@ static int network_connect(struct net_de
        struct sk_buff *skb;
        grant_ref_t ref;
        netif_rx_request_t *req;
-       unsigned int feature_rx_copy, feature_rx_flip;
+       unsigned int feature_rx_copy, feature_rx_flip, feature_accel;
+       char *accel_frontend;
+       int accel_len;
 
        err = xenbus_scanf(XBT_NIL, np->xbdev->otherend,
                           "feature-rx-copy", "%u", &feature_rx_copy);
@@ -1698,6 +1714,12 @@ static int network_connect(struct net_de
        if (err != 1)
                feature_rx_flip = 1;
 
+       feature_accel = 1;
+       accel_frontend = xenbus_read(XBT_NIL, np->xbdev->otherend, 
+                                    "accel", &accel_len);
+       if (IS_ERR(accel_frontend)) 
+               feature_accel = 0;
+
        /*
         * Copy packets on receive path if:
         *  (a) This was requested by user, and the backend supports it; or
@@ -1709,6 +1731,11 @@ static int network_connect(struct net_de
        err = talk_to_backend(np->xbdev, np);
        if (err)
                return err;
+
+       if (feature_accel) {
+               netfront_load_accelerator(np, np->xbdev, accel_frontend);
+               kfree(accel_frontend);
+       }
 
        xennet_set_features(dev);
 
@@ -1956,6 +1983,8 @@ static struct net_device * __devinit cre
        spin_lock_init(&np->tx_lock);
        spin_lock_init(&np->rx_lock);
 
+       init_accelerator_vif(np, dev);
+
        skb_queue_head_init(&np->rx_batch);
        np->rx_target     = RX_DFL_MIN_TARGET;
        np->rx_min_target = RX_DFL_MIN_TARGET;
@@ -2110,6 +2139,8 @@ static int __init netif_init(void)
        if (is_initial_xendomain())
                return 0;
 
+       netif_init_accel();
+
        IPRINTK("Initialising virtual ethernet driver.\n");
 
        (void)register_inetaddr_notifier(&notifier_inetdev);
diff -r 82196b117a5b drivers/xen/netfront/netfront.h
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/drivers/xen/netfront/netfront.h   Wed Jun 20 17:01:07 2007 +0100
@@ -0,0 +1,287 @@
+/******************************************************************************
+ * Virtual network driver for conversing with remote driver backends.
+ *
+ * Copyright (c) 2002-2005, K A Fraser
+ * Copyright (c) 2005, XenSource Ltd
+ * Copyright (C) 2007 Solarflare Communications, Inc.
+ *
+ * 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 NETFRONT_H
+#define NETFRONT_H
+
+#include <xen/interface/io/netif.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/list.h>
+#include <linux/kref.h>
+
+#define NET_TX_RING_SIZE __RING_SIZE((struct netif_tx_sring *)0, PAGE_SIZE)
+#define NET_RX_RING_SIZE __RING_SIZE((struct netif_rx_sring *)0, PAGE_SIZE)
+
+#include <xen/xenbus.h>
+
+/* 
+ * Function pointer table for hooks into a network acceleration
+ * plugin.  These are called at appropriate points from the netfront
+ * driver 
+ */
+struct netfront_accel_hooks {
+       /* 
+        * new_device: Accelerator hook to ask the plugin to support a
+        * new network interface
+        */
+       int (*new_device)(struct net_device *net_dev, struct xenbus_device 
*dev);
+       /*
+        * suspend, resume, remove: Equivalent to the normal xenbus_*
+        * callbacks 
+        */
+       int (*suspend)(struct xenbus_device *dev);
+       int (*resume)(struct xenbus_device *dev);
+       int (*remove)(struct xenbus_device *dev);
+       /* 
+        * backend_changed: Callback from watch based on backend's
+        * xenbus state changing
+        */
+       void (*backend_changed)(struct xenbus_device *dev,
+                               enum xenbus_state backend_state);
+       /*
+        * The net_device is being polled, check the accelerated
+        * hardware for any pending packets
+        */
+       int (*netdev_poll)(struct net_device *dev, int *pbudget);
+       /*
+        * start_xmit: Used to give the accelerated plugin the option
+        * of sending a packet.  Returns non-zero if has done so, or
+        * zero to decline and force the packet onto normal send
+        * path
+        */
+       int (*start_xmit)(struct sk_buff *skb, struct net_device *dev);
+       /* 
+        * start/stop_napi_interrupts Used by netfront to indicate
+        * when napi interrupts should be enabled or disabled 
+        */
+       int (*start_napi_irq)(struct net_device *dev);
+       void (*stop_napi_irq)(struct net_device *dev);
+       /* 
+        * Called before re-enabling the TX queue to check the fast
+        * path has slots too
+        */
+       int (*check_busy)(struct net_device *dev);
+};
+
+/* 
+ * Per-netfront device state for the accelerator.  This is used to
+ * allow efficient per-netfront device access to the accelerator
+ * hooks 
+ */
+struct netfront_accel_vif_state {
+       struct list_head link;
+
+       struct xenbus_device *dev;
+       struct netfront_info *np;
+       struct netfront_accel_hooks *hooks;
+
+       /* 
+        * Protect against removal of hooks while in use.  
+        */
+       struct kref vif_kref;
+
+       unsigned ready_for_probe;
+       struct netfront_accel_hooks *need_probe;
+}; 
+
+/* 
+ * Per-accelerator state stored in netfront.  These form a list that
+ * is used to track which devices are accelerated by which plugins,
+ * and what plugins are available/have been requested 
+ */
+struct netfront_accelerator {
+       /* Used to make a list */
+       struct list_head link;
+       /* ID of the accelerator */
+       int id;
+       /*
+        * String describing the accelerator.  Currently this is the
+        * name of the accelerator module.  This is provided by the
+        * backend accelerator through xenstore 
+        */
+       char *frontend;
+       /* The hooks into the accelerator plugin module */
+       struct netfront_accel_hooks *hooks;
+       /* 
+        * Protect against removal of hooks while in use.  
+        */
+       struct kref accel_kref;
+       /* 
+        * List of per-netfront device state (struct
+        * netfront_accel_vif_state) for each netfront device that is
+        * using this accelerator
+        */
+       struct list_head vif_states;
+       spinlock_t vif_states_lock;
+       /* 
+        * Semaphore to signal that all users of this accelerator have
+        * finished using it before module is unloaded
+        */
+       struct semaphore exit_semaphore; 
+
+       unsigned ready_for_probe;
+       struct netfront_accel_hooks *need_probe;
+};
+
+struct netfront_info {
+       struct list_head list;
+       struct net_device *netdev;
+
+       struct net_device_stats stats;
+
+       struct netif_tx_front_ring tx;
+       struct netif_rx_front_ring rx;
+
+       spinlock_t   tx_lock;
+       spinlock_t   rx_lock;
+
+       unsigned int irq;
+       unsigned int copying_receiver;
+       unsigned int carrier;
+
+       /* Receive-ring batched refills. */
+#define RX_MIN_TARGET 8
+#define RX_DFL_MIN_TARGET 64
+#define RX_MAX_TARGET min_t(int, NET_RX_RING_SIZE, 256)
+       unsigned rx_min_target, rx_max_target, rx_target;
+       struct sk_buff_head rx_batch;
+
+       struct timer_list rx_refill_timer;
+
+       /*
+        * {tx,rx}_skbs store outstanding skbuffs. The first entry in tx_skbs
+        * is an index into a chain of free entries.
+        */
+       struct sk_buff *tx_skbs[NET_TX_RING_SIZE+1];
+       struct sk_buff *rx_skbs[NET_RX_RING_SIZE];
+
+#define TX_MAX_TARGET min_t(int, NET_RX_RING_SIZE, 256)
+       grant_ref_t gref_tx_head;
+       grant_ref_t grant_tx_ref[NET_TX_RING_SIZE + 1];
+       grant_ref_t gref_rx_head;
+       grant_ref_t grant_rx_ref[NET_RX_RING_SIZE];
+
+       struct xenbus_device *xbdev;
+       int tx_ring_ref;
+       int rx_ring_ref;
+       u8 mac[ETH_ALEN];
+
+       unsigned long rx_pfn_array[NET_RX_RING_SIZE];
+       struct multicall_entry rx_mcl[NET_RX_RING_SIZE+1];
+       struct mmu_update rx_mmu[NET_RX_RING_SIZE];
+
+       /* Private pointer to state internal to accelerator module */
+       void *accel_priv;
+       /* The accelerator used by this netfront device */
+       struct netfront_accelerator *accelerator;
+       /* The accelerator state for this netfront device */
+       struct netfront_accel_vif_state accel_vif_state;
+};
+
+
+/* Exported Functions */
+
+/*
+ * Called by an accelerator plugin module when it has loaded.
+ *
+ * frontend: the string describing the accelerator, currently the module name 
+ * hooks: the hooks for netfront to use to call into the accelerator
+ */
+extern int netfront_accelerator_loaded(const char *frontend, 
+                                      struct netfront_accel_hooks *hooks);
+
+/* 
+ * Called when an accelerator plugin is ready to accelerate a device *
+ * that has been passed to it from netfront using the "new_device"
+ * hook.
+ *
+ * frontend: the string describing the accelerator. Must match the
+ * one passed to netfront_accelerator_loaded()
+ * dev: the xenbus device the plugin was asked to accelerate
+ */
+extern void netfront_accelerator_ready(const char *frontend,
+                                      struct xenbus_device *dev);
+
+/* 
+ * Called by an accelerator plugin module when it is about to unload.
+ *
+ * frontend: the string describing the accelerator.  Must match the
+ * one passed to netfront_accelerator_loaded()
+ */ 
+extern void netfront_accelerator_unloaded(const char *frontend);
+
+/* 
+ * Called by an accelerator before waking the net device's TX queue to
+ * ensure the slow path has available slots.  Returns true if OK to
+ * wake, false if still busy 
+ */
+extern int netfront_check_queue_busy(struct net_device *net_dev);
+
+
+
+/* Internal-to-netfront Functions */
+
+/* 
+ * Call into accelerator and check to see if it has tx space before we
+ * wake the net device's TX queue.  Returns true if OK to wake, false
+ * if still busy
+ */ 
+extern 
+int netfront_check_accelerator_queue_busy(struct net_device *dev,
+                                         struct netfront_info *np);
+extern
+int netfront_accelerator_call_remove(struct netfront_info *np,
+                                    struct xenbus_device *dev);
+extern
+int netfront_accelerator_call_resume(struct netfront_info *np,
+                                    struct xenbus_device *dev);
+extern
+void netfront_accelerator_call_backend_changed(struct netfront_info *np,
+                                              struct xenbus_device *dev,
+                                              enum xenbus_state backend_state);
+extern
+void netfront_accelerator_call_stop_napi_irq(struct netfront_info *np,
+                                            struct net_device *dev);
+
+extern
+int netfront_load_accelerator(struct netfront_info *np, 
+                             struct xenbus_device *dev, 
+                             const char *frontend);
+
+extern
+void netif_init_accel(void);
+
+extern
+void init_accelerator_vif(struct netfront_info *np,
+                         struct xenbus_device *dev);
+#endif /* NETFRONT_H */

Attachment: frontend_accel
Description: Text document

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