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net: create a dummy net_device allocator

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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>
This commit is contained in:
Breno Leitao 2024-04-22 05:38:56 -07:00 committed by David S. Miller
parent f8d05679fb
commit c661050f93
2 changed files with 41 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/netdevice.h
View File

@ -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,

56
net/core/dev.c
View File

@ -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
*