Messages in this thread | | | Date | Thu, 28 Mar 2024 16:02:12 +0100 | Subject | Re: [PATCH net-next] net: create a dummy net_device allocator | From | Alexander Lobakin <> |
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From: Breno Leitao <leitao@debian.org> Date: Wed, 27 Mar 2024 13:08:04 -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() > > Suggested-by: Jakub Kicinski <kuba@kernel.org> > Signed-off-by: Breno Leitao <leitao@debian.org> > --- > include/linux/netdevice.h | 3 +++ > net/core/dev.c | 55 ++++++++++++++++++++++++++------------- > 2 files changed, 40 insertions(+), 18 deletions(-) > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > index c6f6ac779b34..f4226a99a146 100644 > --- a/include/linux/netdevice.h > +++ b/include/linux/netdevice.h > @@ -4545,6 +4545,9 @@ 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, const char *name); > + > /* 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 0766a245816b..df2484bbc041 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -10340,25 +10340,12 @@ 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 > */ > @@ -10379,8 +10366,28 @@ 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 > @@ -10991,6 +10998,18 @@ 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 > + * @name: device name format string > + */ > +struct net_device *alloc_netdev_dummy(int sizeof_priv, const char *name)
Since the users of init_dummy_netdev embed &net_device into their private structures, do we need sizeof_priv here at all? Or maybe we could unconditionally pass 0?
> +{ > + return alloc_netdev(sizeof_priv, name, NET_NAME_UNKNOWN, > + init_dummy_netdev_core); > +} > +EXPORT_SYMBOL_GPL(alloc_netdev_dummy); > + > /** > * synchronize_net - Synchronize with packet receive processing > *
As Jakub mentioned, you need to introduce consumers of the functionality you add within the same series. Personally, I'd like to see a series with agressive conversion of all the affected drivers from init_dummy_netdev() to alloc_dummy_netdev() and final removal of init_dummy_netdev() :D
(and then a followup which converts &net_device to proper flex arrays)
Thanks, Olek
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