| Message ID | 20240404114854.2498663-2-leitao@debian.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | allocate dummy device dynamically | expand |
From: Breno Leitao <leitao@debian.org> Date: Thu, 4 Apr 2024 04:48:41 -0700 > 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() [...] > @@ -11063,6 +11070,17 @@ 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 > + */ > +struct net_device *alloc_netdev_dummy(int sizeof_priv) Repeating my question from the previous thread: I see that in your series you always pass 0 as @sizeof_priv, does it make sense to have this argument or we can just pass 0 here to alloc_netdev() unconditionally? Drivers that have &net_device embedded can't have any private data there anyway. > +{ > + 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 > * Thanks, Olek
Hello Alexander, On Thu, Apr 04, 2024 at 06:40:33PM +0200, Alexander Lobakin wrote: > > @@ -11063,6 +11070,17 @@ 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 > > + */ > > +struct net_device *alloc_netdev_dummy(int sizeof_priv) > > Repeating my question from the previous thread: I see that in your > series you always pass 0 as @sizeof_priv, does it make sense to have > this argument or we can just pass 0 here to alloc_netdev() unconditionally? > Drivers that have &net_device embedded can't have any private data there > anyway. Sorry, I answered you this question in the previous thread, and gave you an example why we need the @sizeof_priv. https://lore.kernel.org/all/ZgWrcvKyAzDvl%2Fjn@gmail.com/ I didn't see any reply from you, so, I suppose you were OK with it, but maybe you missed it?! Anyway, let me paste what I've sent there here, so, we can continue the discussion in this thread, which might make the reviewing process here. This is what I wrote in the thread/message above: We need to have this private size for cases where we need to get the pointer to their private structure given the dummy device. In the embedded case you can use container_of(), but, with a pointer to net_device, that is not the case anymore, and we should use the dummy private data pointer back to the private data. For instance, see the example of iwlwifi: https://lore.kernel.org/all/20240307174843.1719130-1-leitao@debian.org/
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 0c198620ac93..544767d218c0 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -4517,6 +4517,9 @@ 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 818699dea9d7..4d0109f2fe80 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -10412,25 +10412,12 @@ 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 initialize 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 - * are 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 */ @@ -10451,8 +10438,28 @@ 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 initialize 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 + * are 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 @@ -11063,6 +11070,17 @@ 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 + */ +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 *
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> --- include/linux/netdevice.h | 3 +++ net/core/dev.c | 54 ++++++++++++++++++++++++++------------- 2 files changed, 39 insertions(+), 18 deletions(-)