Commit c661050f authored by Breno Leitao's avatar Breno Leitao Committed by David S. Miller
Browse files

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: default avatarJakub Kicinski <kuba@kernel.org>
Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
Reviewed-by: default avatarIdo Schimmel <idosch@nvidia.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f8d05679

include/linux/netdevice.h

+3 −0
Original line number Diff line number Diff line
@@ -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,

net/core/dev.c

+38 −18
Original line number Diff line number Diff line
@@ -10420,25 +10420,12 @@ int register_netdevice(struct net_device *dev) 
}

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

 *