text: // SPDX-License-Identifier: GPL-2.0-only
  /* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
   */
  
  /* Devmaps primary use is as a backend map for XDP BPF helper call
   * bpf_redirect_map(). Because XDP is mostly concerned with performance we
   * spent some effort to ensure the datapath with redirect maps does not use
   * any locking. This is a quick note on the details.
   *
   * We have three possible paths to get into the devmap control plane bpf
   * syscalls, bpf programs, and driver side xmit/flush operations. A bpf syscall
   * will invoke an update, delete, or lookup operation. To ensure updates and
   * deletes appear atomic from the datapath side xchg() is used to modify the
   * netdev_map array. Then because the datapath does a lookup into the netdev_map
   * array (read-only) from an RCU critical section we use call_rcu() to wait for
   * an rcu grace period before free'ing the old data structures. This ensures the
   * datapath always has a valid copy. However, the datapath does a "flush"
   * operation that pushes any pending packets in the driver outside the RCU
   * critical section. Each bpf_dtab_netdev tracks these pending operations using
   * a per-cpu flush list. The bpf_dtab_netdev object will not be destroyed  until
   * this list is empty, indicating outstanding flush operations have completed.
   *
   * BPF syscalls may race with BPF program calls on any of the update, delete
   * or lookup operations. As noted above the xchg() operation also keep the
   * netdev_map consistent in this case. From the devmap side BPF programs
   * calling into these operations are the same as multiple user space threads
   * making system calls.
   *
   * Finally, any of the above may race with a netdev_unregister notifier. The
   * unregister notifier must search for net devices in the map structure that
   * contain a reference to the net device and remove them. This is a two step
   * process (a) dereference the bpf_dtab_netdev object in netdev_map and (b)
   * check to see if the ifindex is the same as the net_device being removed.
   * When removing the dev a cmpxchg() is used to ensure the correct dev is
   * removed, in the case of a concurrent update or delete operation it is
   * possible that the initially referenced dev is no longer in the map. As the
   * notifier hook walks the map we know that new dev references can not be
   * added by the user because core infrastructure ensures dev_get_by_index()
   * calls will fail at this point.
   *
   * The devmap_hash type is a map type which interprets keys as ifindexes and
   * indexes these using a hashmap. This allows maps that use ifindex as key to be
   * densely packed instead of having holes in the lookup array for unused
   * ifindexes. The setup and packet enqueue/send code is shared between the two
   * types of devmap; only the lookup and insertion is different.
   */
  #include <linux/bpf.h>
  #include <net/xdp.h>
  #include <linux/filter.h>
  #include <trace/events/xdp.h>
  
  #define DEV_CREATE_FLAG_MASK \
  	(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
  
  #define DEV_MAP_BULK_SIZE 16
  struct bpf_dtab_netdev;
  
  struct xdp_bulk_queue {
  	struct xdp_frame *q[DEV_MAP_BULK_SIZE];
  	struct list_head flush_node;
  	struct net_device *dev_rx;
  	struct bpf_dtab_netdev *obj;
  	unsigned int count;
  };
  
  struct bpf_dtab_netdev {
  	struct net_device *dev; /* must be first member, due to tracepoint */
  	struct hlist_node index_hlist;
  	struct bpf_dtab *dtab;
  	struct xdp_bulk_queue __percpu *bulkq;
  	struct rcu_head rcu;
  	unsigned int idx; /* keep track of map index for tracepoint */
  };
  
  struct bpf_dtab {
  	struct bpf_map map;
  	struct bpf_dtab_netdev **netdev_map; /* DEVMAP type only */
  	struct list_head __percpu *flush_list;
  	struct list_head list;
  
  	/* these are only used for DEVMAP_HASH type maps */
  	struct hlist_head *dev_index_head;
  	spinlock_t index_lock;
  	unsigned int items;
  	u32 n_buckets;
  };
  
  static DEFINE_SPINLOCK(dev_map_lock);
  static LIST_HEAD(dev_map_list);
  
  static struct hlist_head *dev_map_create_hash(unsigned int entries,
  					      int numa_node)
  {
  	int i;
  	struct hlist_head *hash;
  
  	hash = bpf_map_area_alloc(entries * sizeof(*hash), numa_node);
  	if (hash != NULL)
  		for (i = 0; i < entries; i++)
  			INIT_HLIST_HEAD(&hash[i]);
  
  	return hash;
  }
  
  static inline struct hlist_head *dev_map_index_hash(struct bpf_dtab *dtab,
  						    int idx)
  {
  	return &dtab->dev_index_head[idx & (dtab->n_buckets - 1)];
  }
  
  static int dev_map_init_map(struct bpf_dtab *dtab, union bpf_attr *attr)
  {
  	int err, cpu;
  	u64 cost;
  
  	/* check sanity of attributes */
  	if (attr->max_entries == 0 || attr->key_size != 4 ||
  	    attr->value_size != 4 || attr->map_flags & ~DEV_CREATE_FLAG_MASK)
  		return -EINVAL;
  
  	/* Lookup returns a pointer straight to dev->ifindex, so make sure the
  	 * verifier prevents writes from the BPF side
  	 */
  	attr->map_flags |= BPF_F_RDONLY_PROG;
  
  
  	bpf_map_init_from_attr(&dtab->map, attr);
  
  	/* make sure page count doesn't overflow */
  	cost = (u64) sizeof(struct list_head) * num_possible_cpus();
  
  	if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
  		dtab->n_buckets = roundup_pow_of_two(dtab->map.max_entries);
  
  		if (!dtab->n_buckets) /* Overflow check */
  			return -EINVAL;
  		cost += (u64) sizeof(struct hlist_head) * dtab->n_buckets;
  	} else {
  		cost += (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
  	}
  
  	/* if map size is larger than memlock limit, reject it */
  	err = bpf_map_charge_init(&dtab->map.memory, cost);
  	if (err)
  		return -EINVAL;
  
  	dtab->flush_list = alloc_percpu(struct list_head);
  	if (!dtab->flush_list)
  		goto free_charge;
  
  	for_each_possible_cpu(cpu)
  		INIT_LIST_HEAD(per_cpu_ptr(dtab->flush_list, cpu));
  
  	if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
  		dtab->dev_index_head = dev_map_create_hash(dtab->n_buckets,
  							   dtab->map.numa_node);
  		if (!dtab->dev_index_head)
  			goto free_percpu;
  
  		spin_lock_init(&dtab->index_lock);
  	} else {
  		dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
  						      sizeof(struct bpf_dtab_netdev *),
  						      dtab->map.numa_node);
  		if (!dtab->netdev_map)
  			goto free_percpu;
  	}
  
  	return 0;
  
  free_percpu:
  	free_percpu(dtab->flush_list);
  free_charge:
  	bpf_map_charge_finish(&dtab->map.memory);
  	return -ENOMEM;
  }
  
  static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
  {
  	struct bpf_dtab *dtab;
  	int err;
  
  	if (!capable(CAP_NET_ADMIN))
  		return ERR_PTR(-EPERM);
  
  	dtab = kzalloc(sizeof(*dtab), GFP_USER);
  	if (!dtab)
  		return ERR_PTR(-ENOMEM);
  
  	err = dev_map_init_map(dtab, attr);
  	if (err) {
  		kfree(dtab);
  		return ERR_PTR(err);
  	}
  
  	spin_lock(&dev_map_lock);
  	list_add_tail_rcu(&dtab->list, &dev_map_list);
  	spin_unlock(&dev_map_lock);
  
  	return &dtab->map;
  }
  
  static void dev_map_free(struct bpf_map *map)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	int i, cpu;
  
  	/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
  	 * so the programs (can be more than one that used this map) were
  	 * disconnected from events. Wait for outstanding critical sections in
  	 * these programs to complete. The rcu critical section only guarantees
  	 * no further reads against netdev_map. It does __not__ ensure pending
  	 * flush operations (if any) are complete.
  	 */
  
  	spin_lock(&dev_map_lock);
  	list_del_rcu(&dtab->list);
  	spin_unlock(&dev_map_lock);
  
  	bpf_clear_redirect_map(map);
  	synchronize_rcu();
  
  	/* Make sure prior __dev_map_entry_free() have completed. */
  	rcu_barrier();
  
  	/* To ensure all pending flush operations have completed wait for flush
  	 * list to empty on _all_ cpus.
  	 * Because the above synchronize_rcu() ensures the map is disconnected
  	 * from the program we can assume no new items will be added.
  	 */
  	for_each_online_cpu(cpu) {
  		struct list_head *flush_list = per_cpu_ptr(dtab->flush_list, cpu);
  
  		while (!list_empty(flush_list))
  			cond_resched();
  	}
  
  	if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
  		for (i = 0; i < dtab->n_buckets; i++) {
  			struct bpf_dtab_netdev *dev;
  			struct hlist_head *head;
  			struct hlist_node *next;
  
  			head = dev_map_index_hash(dtab, i);
  
  			hlist_for_each_entry_safe(dev, next, head, index_hlist) {
  				hlist_del_rcu(&dev->index_hlist);
  				free_percpu(dev->bulkq);
  				dev_put(dev->dev);
  				kfree(dev);
  			}
  		}
  
  		bpf_map_area_free(dtab->dev_index_head);
  	} else {
  		for (i = 0; i < dtab->map.max_entries; i++) {
  			struct bpf_dtab_netdev *dev;
  
  			dev = dtab->netdev_map[i];
  			if (!dev)
  				continue;
  
  			free_percpu(dev->bulkq);
  			dev_put(dev->dev);
  			kfree(dev);
  		}
  
  		bpf_map_area_free(dtab->netdev_map);
  	}
  
  	free_percpu(dtab->flush_list);
  	kfree(dtab);
  }
  
  static int dev_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	u32 index = key ? *(u32 *)key : U32_MAX;
  	u32 *next = next_key;
  
  	if (index >= dtab->map.max_entries) {
  		*next = 0;
  		return 0;
  	}
  
  	if (index == dtab->map.max_entries - 1)
  		return -ENOENT;
  	*next = index + 1;
  	return 0;
  }
  
  struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	struct hlist_head *head = dev_map_index_hash(dtab, key);
  	struct bpf_dtab_netdev *dev;
  
  	hlist_for_each_entry_rcu(dev, head, index_hlist,
  				 lockdep_is_held(&dtab->index_lock))
  		if (dev->idx == key)
  			return dev;
  
  	return NULL;
  }
  
  static int dev_map_hash_get_next_key(struct bpf_map *map, void *key,
  				    void *next_key)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	u32 idx, *next = next_key;
  	struct bpf_dtab_netdev *dev, *next_dev;
  	struct hlist_head *head;
  	int i = 0;
  
  	if (!key)
  		goto find_first;
  
  	idx = *(u32 *)key;
  
  	dev = __dev_map_hash_lookup_elem(map, idx);
  	if (!dev)
  		goto find_first;
  
  	next_dev = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&dev->index_hlist)),
  				    struct bpf_dtab_netdev, index_hlist);
  
  	if (next_dev) {
  		*next = next_dev->idx;
  		return 0;
  	}
  
  	i = idx & (dtab->n_buckets - 1);
  	i++;
  
   find_first:
  	for (; i < dtab->n_buckets; i++) {
  		head = dev_map_index_hash(dtab, i);
  
  		next_dev = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
  					    struct bpf_dtab_netdev,
  					    index_hlist);
  		if (next_dev) {
  			*next = next_dev->idx;
  			return 0;
  		}
  	}
  
  	return -ENOENT;
  }
  
  static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags,
  		       bool in_napi_ctx)
  {
  	struct bpf_dtab_netdev *obj = bq->obj;
  	struct net_device *dev = obj->dev;
  	int sent = 0, drops = 0, err = 0;
  	int i;
  
  	if (unlikely(!bq->count))
  		return 0;
  
  	for (i = 0; i < bq->count; i++) {
  		struct xdp_frame *xdpf = bq->q[i];
  
  		prefetch(xdpf);
  	}
  
  	sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q, flags);
  	if (sent < 0) {
  		err = sent;
  		sent = 0;
  		goto error;
  	}
  	drops = bq->count - sent;
  out:
  	bq->count = 0;
  
  	trace_xdp_devmap_xmit(&obj->dtab->map, obj->idx,
  			      sent, drops, bq->dev_rx, dev, err);
  	bq->dev_rx = NULL;
  	__list_del_clearprev(&bq->flush_node);
  	return 0;
  error:
  	/* If ndo_xdp_xmit fails with an errno, no frames have been
  	 * xmit'ed and it's our responsibility to them free all.
  	 */
  	for (i = 0; i < bq->count; i++) {
  		struct xdp_frame *xdpf = bq->q[i];
  
  		/* RX path under NAPI protection, can return frames faster */
  		if (likely(in_napi_ctx))
  			xdp_return_frame_rx_napi(xdpf);
  		else
  			xdp_return_frame(xdpf);
  		drops++;
  	}
  	goto out;
  }
  
  /* __dev_map_flush is called from xdp_do_flush_map() which _must_ be signaled
   * from the driver before returning from its napi->poll() routine. The poll()
   * routine is called either from busy_poll context or net_rx_action signaled
   * from NET_RX_SOFTIRQ. Either way the poll routine must complete before the
   * net device can be torn down. On devmap tear down we ensure the flush list
   * is empty before completing to ensure all flush operations have completed.
   */
  void __dev_map_flush(struct bpf_map *map)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	struct list_head *flush_list = this_cpu_ptr(dtab->flush_list);
  	struct xdp_bulk_queue *bq, *tmp;
  
  	rcu_read_lock();
  	list_for_each_entry_safe(bq, tmp, flush_list, flush_node)
  		bq_xmit_all(bq, XDP_XMIT_FLUSH, true);
  	rcu_read_unlock();
  }
  
  /* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
   * update happens in parallel here a dev_put wont happen until after reading the
   * ifindex.
   */
  struct bpf_dtab_netdev *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	struct bpf_dtab_netdev *obj;
  
  	if (key >= map->max_entries)
  		return NULL;
  
  	obj = READ_ONCE(dtab->netdev_map[key]);
  	return obj;
  }
  
  /* Runs under RCU-read-side, plus in softirq under NAPI protection.
   * Thus, safe percpu variable access.
   */
  static int bq_enqueue(struct bpf_dtab_netdev *obj, struct xdp_frame *xdpf,
  		      struct net_device *dev_rx)
  
  {
  	struct list_head *flush_list = this_cpu_ptr(obj->dtab->flush_list);
  	struct xdp_bulk_queue *bq = this_cpu_ptr(obj->bulkq);
  
  	if (unlikely(bq->count == DEV_MAP_BULK_SIZE))
  		bq_xmit_all(bq, 0, true);
  
  	/* Ingress dev_rx will be the same for all xdp_frame's in
  	 * bulk_queue, because bq stored per-CPU and must be flushed
  	 * from net_device drivers NAPI func end.
  	 */
  	if (!bq->dev_rx)
  		bq->dev_rx = dev_rx;
  
  	bq->q[bq->count++] = xdpf;
  
  	if (!bq->flush_node.prev)
  		list_add(&bq->flush_node, flush_list);
  
  	return 0;
  }
  
  int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
  		    struct net_device *dev_rx)
  {
  	struct net_device *dev = dst->dev;
  	struct xdp_frame *xdpf;
  	int err;
  
  	if (!dev->netdev_ops->ndo_xdp_xmit)
  		return -EOPNOTSUPP;
  
  	err = xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data);
  	if (unlikely(err))
  		return err;
  
  	xdpf = convert_to_xdp_frame(xdp);
  	if (unlikely(!xdpf))
  		return -EOVERFLOW;
  
  	return bq_enqueue(dst, xdpf, dev_rx);
  }
  
  int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
  			     struct bpf_prog *xdp_prog)
  {
  	int err;
  
  	err = xdp_ok_fwd_dev(dst->dev, skb->len);
  	if (unlikely(err))
  		return err;
  	skb->dev = dst->dev;
  	generic_xdp_tx(skb, xdp_prog);
  
  	return 0;
  }
  
  static void *dev_map_lookup_elem(struct bpf_map *map, void *key)
  {
  	struct bpf_dtab_netdev *obj = __dev_map_lookup_elem(map, *(u32 *)key);
  	struct net_device *dev = obj ? obj->dev : NULL;
  
  	return dev ? &dev->ifindex : NULL;
  }
  
  static void *dev_map_hash_lookup_elem(struct bpf_map *map, void *key)
  {
  	struct bpf_dtab_netdev *obj = __dev_map_hash_lookup_elem(map,
  								*(u32 *)key);
  	struct net_device *dev = obj ? obj->dev : NULL;
  
  	return dev ? &dev->ifindex : NULL;
  }
  
  static void dev_map_flush_old(struct bpf_dtab_netdev *dev)
  {
  	if (dev->dev->netdev_ops->ndo_xdp_xmit) {
  		struct xdp_bulk_queue *bq;
  		int cpu;
  
  		rcu_read_lock();
  		for_each_online_cpu(cpu) {
  			bq = per_cpu_ptr(dev->bulkq, cpu);
  			bq_xmit_all(bq, XDP_XMIT_FLUSH, false);
  		}
  		rcu_read_unlock();
  	}
  }
  
  static void __dev_map_entry_free(struct rcu_head *rcu)
  {
  	struct bpf_dtab_netdev *dev;
  
  	dev = container_of(rcu, struct bpf_dtab_netdev, rcu);
  	dev_map_flush_old(dev);
  	free_percpu(dev->bulkq);
  	dev_put(dev->dev);
  	kfree(dev);
  }
  
  static int dev_map_delete_elem(struct bpf_map *map, void *key)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	struct bpf_dtab_netdev *old_dev;
  	int k = *(u32 *)key;
  
  	if (k >= map->max_entries)
  		return -EINVAL;
  
  	/* Use call_rcu() here to ensure any rcu critical sections have
  	 * completed, but this does not guarantee a flush has happened
  	 * yet. Because driver side rcu_read_lock/unlock only protects the
  	 * running XDP program. However, for pending flush operations the
  	 * dev and ctx are stored in another per cpu map. And additionally,
  	 * the driver tear down ensures all soft irqs are complete before
  	 * removing the net device in the case of dev_put equals zero.
  	 */
  	old_dev = xchg(&dtab->netdev_map[k], NULL);
  	if (old_dev)
  		call_rcu(&old_dev->rcu, __dev_map_entry_free);
  	return 0;
  }
  
  static int dev_map_hash_delete_elem(struct bpf_map *map, void *key)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	struct bpf_dtab_netdev *old_dev;
  	int k = *(u32 *)key;
  	unsigned long flags;
  	int ret = -ENOENT;
  
  	spin_lock_irqsave(&dtab->index_lock, flags);
  
  	old_dev = __dev_map_hash_lookup_elem(map, k);
  	if (old_dev) {
  		dtab->items--;
  		hlist_del_init_rcu(&old_dev->index_hlist);
  		call_rcu(&old_dev->rcu, __dev_map_entry_free);
  		ret = 0;
  	}
  	spin_unlock_irqrestore(&dtab->index_lock, flags);
  
  	return ret;
  }
  
  static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net,
  						    struct bpf_dtab *dtab,
  						    u32 ifindex,
  						    unsigned int idx)
  {
  	gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN;
  	struct bpf_dtab_netdev *dev;
  	struct xdp_bulk_queue *bq;
  	int cpu;
  
  	dev = kmalloc_node(sizeof(*dev), gfp, dtab->map.numa_node);
  	if (!dev)
  		return ERR_PTR(-ENOMEM);
  
  	dev->bulkq = __alloc_percpu_gfp(sizeof(*dev->bulkq),
  					sizeof(void *), gfp);
  	if (!dev->bulkq) {
  		kfree(dev);
  		return ERR_PTR(-ENOMEM);
  	}
  
  	for_each_possible_cpu(cpu) {
  		bq = per_cpu_ptr(dev->bulkq, cpu);
  		bq->obj = dev;
  	}
  
  	dev->dev = dev_get_by_index(net, ifindex);
  	if (!dev->dev) {
  		free_percpu(dev->bulkq);
  		kfree(dev);
  		return ERR_PTR(-EINVAL);
  	}
  
  	dev->idx = idx;
  	dev->dtab = dtab;
  
  	return dev;
  }
  
  static int __dev_map_update_elem(struct net *net, struct bpf_map *map,
  				 void *key, void *value, u64 map_flags)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	struct bpf_dtab_netdev *dev, *old_dev;
  	u32 ifindex = *(u32 *)value;
  	u32 i = *(u32 *)key;
  
  	if (unlikely(map_flags > BPF_EXIST))
  		return -EINVAL;
  	if (unlikely(i >= dtab->map.max_entries))
  		return -E2BIG;
  	if (unlikely(map_flags == BPF_NOEXIST))
  		return -EEXIST;
  
  	if (!ifindex) {
  		dev = NULL;
  	} else {
  		dev = __dev_map_alloc_node(net, dtab, ifindex, i);
  		if (IS_ERR(dev))
  			return PTR_ERR(dev);
  	}
  
  	/* Use call_rcu() here to ensure rcu critical sections have completed
  	 * Remembering the driver side flush operation will happen before the
  	 * net device is removed.
  	 */
  	old_dev = xchg(&dtab->netdev_map[i], dev);
  	if (old_dev)
  		call_rcu(&old_dev->rcu, __dev_map_entry_free);
  
  	return 0;
  }
  
  static int dev_map_update_elem(struct bpf_map *map, void *key, void *value,
  			       u64 map_flags)
  {
  	return __dev_map_update_elem(current->nsproxy->net_ns,
  				     map, key, value, map_flags);
  }
  
  static int __dev_map_hash_update_elem(struct net *net, struct bpf_map *map,
  				     void *key, void *value, u64 map_flags)
  {
  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
  	struct bpf_dtab_netdev *dev, *old_dev;
  	u32 ifindex = *(u32 *)value;
  	u32 idx = *(u32 *)key;
  	unsigned long flags;
  	int err = -EEXIST;
  
  	if (unlikely(map_flags > BPF_EXIST || !ifindex))
  		return -EINVAL;
  
  	spin_lock_irqsave(&dtab->index_lock, flags);
  
  	old_dev = __dev_map_hash_lookup_elem(map, idx);
  	if (old_dev && (map_flags & BPF_NOEXIST))
  		goto out_err;
  
  	dev = __dev_map_alloc_node(net, dtab, ifindex, idx);
  	if (IS_ERR(dev)) {
  		err = PTR_ERR(dev);
  		goto out_err;
  	}
  
  	if (old_dev) {
  		hlist_del_rcu(&old_dev->index_hlist);
  	} else {
  		if (dtab->items >= dtab->map.max_entries) {
  			spin_unlock_irqrestore(&dtab->index_lock, flags);
  			call_rcu(&dev->rcu, __dev_map_entry_free);
  			return -E2BIG;
  		}
  		dtab->items++;
  	}
  
  	hlist_add_head_rcu(&dev->index_hlist,
  			   dev_map_index_hash(dtab, idx));
  	spin_unlock_irqrestore(&dtab->index_lock, flags);
  
  	if (old_dev)
  		call_rcu(&old_dev->rcu, __dev_map_entry_free);
  
  	return 0;
  
  out_err:
  	spin_unlock_irqrestore(&dtab->index_lock, flags);
  	return err;
  }
  
  static int dev_map_hash_update_elem(struct bpf_map *map, void *key, void *value,
  				   u64 map_flags)
  {
  	return __dev_map_hash_update_elem(current->nsproxy->net_ns,
  					 map, key, value, map_flags);
  }
  
  const struct bpf_map_ops dev_map_ops = {
  	.map_alloc = dev_map_alloc,
  	.map_free = dev_map_free,
  	.map_get_next_key = dev_map_get_next_key,
  	.map_lookup_elem = dev_map_lookup_elem,
  	.map_update_elem = dev_map_update_elem,
  	.map_delete_elem = dev_map_delete_elem,
  	.map_check_btf = map_check_no_btf,
  };
  
  const struct bpf_map_ops dev_map_hash_ops = {
  	.map_alloc = dev_map_alloc,
  	.map_free = dev_map_free,
  	.map_get_next_key = dev_map_hash_get_next_key,
  	.map_lookup_elem = dev_map_hash_lookup_elem,
  	.map_update_elem = dev_map_hash_update_elem,
  	.map_delete_elem = dev_map_hash_delete_elem,
  	.map_check_btf = map_check_no_btf,
  };
  
  static void dev_map_hash_remove_netdev(struct bpf_dtab *dtab,
  				       struct net_device *netdev)
  {
  	unsigned long flags;
  	u32 i;
  
  	spin_lock_irqsave(&dtab->index_lock, flags);
  	for (i = 0; i < dtab->n_buckets; i++) {
  		struct bpf_dtab_netdev *dev;
  		struct hlist_head *head;
  		struct hlist_node *next;
  
  		head = dev_map_index_hash(dtab, i);
  
  		hlist_for_each_entry_safe(dev, next, head, index_hlist) {
  			if (netdev != dev->dev)
  				continue;
  
  			dtab->items--;
  			hlist_del_rcu(&dev->index_hlist);
  			call_rcu(&dev->rcu, __dev_map_entry_free);
  		}
  	}
  	spin_unlock_irqrestore(&dtab->index_lock, flags);
  }
  
  static int dev_map_notification(struct notifier_block *notifier,
  				ulong event, void *ptr)
  {
  	struct net_device *netdev = netdev_notifier_info_to_dev(ptr);
  	struct bpf_dtab *dtab;
  	int i;
  
  	switch (event) {
  	case NETDEV_UNREGISTER:
  		/* This rcu_read_lock/unlock pair is needed because
  		 * dev_map_list is an RCU list AND to ensure a delete
  		 * operation does not free a netdev_map entry while we
  		 * are comparing it against the netdev being unregistered.
  		 */
  		rcu_read_lock();
  		list_for_each_entry_rcu(dtab, &dev_map_list, list) {
  			if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
  				dev_map_hash_remove_netdev(dtab, netdev);
  				continue;
  			}
  
  			for (i = 0; i < dtab->map.max_entries; i++) {
  				struct bpf_dtab_netdev *dev, *odev;
  
  				dev = READ_ONCE(dtab->netdev_map[i]);
  				if (!dev || netdev != dev->dev)
  					continue;
  				odev = cmpxchg(&dtab->netdev_map[i], dev, NULL);
  				if (dev == odev)
  					call_rcu(&dev->rcu,
  						 __dev_map_entry_free);
  			}
  		}
  		rcu_read_unlock();
  		break;
  	default:
  		break;
  	}
  	return NOTIFY_OK;
  }
  
  static struct notifier_block dev_map_notifier = {
  	.notifier_call = dev_map_notification,
  };
  
  static int __init dev_map_init(void)
  {
  	/* Assure tracepoint shadow struct _bpf_dtab_netdev is in sync */
  	BUILD_BUG_ON(offsetof(struct bpf_dtab_netdev, dev) !=
  		     offsetof(struct _bpf_dtab_netdev, dev));
  	register_netdevice_notifier(&dev_map_notifier);
  	return 0;
  }
  
  subsys_initcall(dev_map_init);
  