net: create a dummy net_device allocator

It is impossible to use init_dummy_netdev together with alloc_netdev()
as the 'setup' argument.

This is because alloc_netdev() initializes some fields in the net_device
structure, and later init_dummy_netdev() memzero them all. This causes
some problems as reported here:

	https://lore.kernel.org/all/20240322082336.49f110cc@kernel.org/

Split the init_dummy_netdev() function in two. Create a new function called
init_dummy_netdev_core() that does not memzero the net_device structure.
Then have init_dummy_netdev() memzero-ing and calling
init_dummy_netdev_core(), keeping the old behaviour.

init_dummy_netdev_core() is the new function that could be called as an
argument for alloc_netdev().

Also, create a helper to allocate and initialize dummy net devices,
leveraging init_dummy_netdev_core() as the setup argument. This function
basically simplify the allocation of dummy devices, by allocating and
initializing it. Freeing the device continue to be done through
free_netdev()

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d45f330d083df11eeb0fbe49b9be22a1bb23182d..f849e7d110ed9618078c49b7871070118edc5a5c 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4519,6 +4519,9 @@ static inline void netif_addr_unlock_bh(struct net_device *dev)
 
 void ether_setup(struct net_device *dev);
 
+/* Allocate dummy net_device */
+struct net_device *alloc_netdev_dummy(int sizeof_priv);
+
 /* Support for loadable net-drivers */
 struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
                                    unsigned char name_assign_type,

diff --git a/net/core/dev.c b/net/core/dev.c
index 62b39d6b1d8f44f18923a2cb301fd4efbf1485c9..e09aa3785c159b4ab0fe7eb3546f9dd6797ebce2 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10420,25 +10420,12 @@ err_free_name:
 }
 EXPORT_SYMBOL(register_netdevice);
 
-/**
- *     init_dummy_netdev       - init a dummy network device for NAPI
- *     @dev: device to init
- *
- *     This takes a network device structure and initializes the minimum
- *     amount of fields so it can be used to schedule NAPI polls without
- *     registering a full blown interface. This is to be used by drivers
- *     that need to tie several hardware interfaces to a single NAPI
- *     poll scheduler due to HW limitations.
+/* Initialize the core of a dummy net device.
+ * This is useful if you are calling this function after alloc_netdev(),
+ * since it does not memset the net_device fields.
  */
-void init_dummy_netdev(struct net_device *dev)
+static void init_dummy_netdev_core(struct net_device *dev)
 {
-       /* Clear everything. Note we don't initialize spinlocks
-        * as they aren't supposed to be taken by any of the
-        * NAPI code and this dummy netdev is supposed to be
-        * only ever used for NAPI polls
-        */
-       memset(dev, 0, sizeof(struct net_device));
-
        /* make sure we BUG if trying to hit standard
         * register/unregister code path
         */
@@ -10459,8 +10446,28 @@ void init_dummy_netdev(struct net_device *dev)
         * its refcount.
         */
 }
-EXPORT_SYMBOL_GPL(init_dummy_netdev);
 
+/**
+ *     init_dummy_netdev       - init a dummy network device for NAPI
+ *     @dev: device to init
+ *
+ *     This takes a network device structure and initializes the minimum
+ *     amount of fields so it can be used to schedule NAPI polls without
+ *     registering a full blown interface. This is to be used by drivers
+ *     that need to tie several hardware interfaces to a single NAPI
+ *     poll scheduler due to HW limitations.
+ */
+void init_dummy_netdev(struct net_device *dev)
+{
+       /* Clear everything. Note we don't initialize spinlocks
+        * as they aren't supposed to be taken by any of the
+        * NAPI code and this dummy netdev is supposed to be
+        * only ever used for NAPI polls
+        */
+       memset(dev, 0, sizeof(struct net_device));
+       init_dummy_netdev_core(dev);
+}
+EXPORT_SYMBOL_GPL(init_dummy_netdev);
 
 /**
  *     register_netdev - register a network device
@@ -11080,6 +11087,19 @@ void free_netdev(struct net_device *dev)
 }
 EXPORT_SYMBOL(free_netdev);
 
+/**
+ * alloc_netdev_dummy - Allocate and initialize a dummy net device.
+ * @sizeof_priv: size of private data to allocate space for
+ *
+ * Return: the allocated net_device on success, NULL otherwise
+ */
+struct net_device *alloc_netdev_dummy(int sizeof_priv)
+{
+       return alloc_netdev(sizeof_priv, "dummy#", NET_NAME_UNKNOWN,
+                           init_dummy_netdev_core);
+}
+EXPORT_SYMBOL_GPL(alloc_netdev_dummy);
+
 /**
  *     synchronize_net -  Synchronize with packet receive processing
  *