From: Jakub Kicinski Date: Wed, 6 Jan 2021 18:40:05 +0000 (-0800) Subject: docs: net: explain struct net_device lifetime X-Git-Tag: v5.15~1988^2~36^2~2 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=2b446e650b418f9a9e75f99852e2f2560cabfa17;p=mirror_ubuntu-kernels.git docs: net: explain struct net_device lifetime Explain the two basic flows of struct net_device's operation. Signed-off-by: Jakub Kicinski --- diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst index e65665c5ab50..17bdcb746dcf 100644 --- a/Documentation/networking/netdevices.rst +++ b/Documentation/networking/netdevices.rst @@ -10,18 +10,177 @@ Introduction The following is a random collection of documentation regarding network devices. -struct net_device allocation rules -================================== +struct net_device lifetime rules +================================ Network device structures need to persist even after module is unloaded and must be allocated with alloc_netdev_mqs() and friends. If device has registered successfully, it will be freed on last use -by free_netdev(). This is required to handle the pathologic case cleanly -(example: rmmod mydriver needs_free_netdev = true; + } + + static void my_destructor(struct net_device *dev) + { + some_obj_destroy(priv->obj); + some_uninit(priv); + } + + int create_link() + { + struct my_device_priv *priv; + int err; + + ASSERT_RTNL(); + + dev = alloc_netdev(sizeof(*priv), "net%d", NET_NAME_UNKNOWN, my_setup); + if (!dev) + return -ENOMEM; + priv = netdev_priv(dev); + + /* Implicit constructor */ + err = some_init(priv); + if (err) + goto err_free_dev; + + priv->obj = some_obj_create(); + if (!priv->obj) { + err = -ENOMEM; + goto err_some_uninit; + } + /* End of constructor, set the destructor: */ + dev->priv_destructor = my_destructor; + + err = register_netdevice(dev); + if (err) + /* register_netdevice() calls destructor on failure */ + goto err_free_dev; + + /* If anything fails now unregister_netdevice() (or unregister_netdev()) + * will take care of calling my_destructor and free_netdev(). + */ + + return 0; + + err_some_uninit: + some_uninit(priv); + err_free_dev: + free_netdev(dev); + return err; + } + +If struct net_device.priv_destructor is set it will be called by the core +some time after unregister_netdevice(), it will also be called if +register_netdevice() fails. The callback may be invoked with or without +``rtnl_lock`` held. + +There is no explicit constructor callback, driver "constructs" the private +netdev state after allocating it and before registration. + +Setting struct net_device.needs_free_netdev makes core call free_netdevice() +automatically after unregister_netdevice() when all references to the device +are gone. It only takes effect after a successful call to register_netdevice() +so if register_netdevice() fails driver is responsible for calling +free_netdev(). + +free_netdev() is safe to call on error paths right after unregister_netdevice() +or when register_netdevice() fails. Parts of netdev (de)registration process +happen after ``rtnl_lock`` is released, therefore in those cases free_netdev() +will defer some of the processing until ``rtnl_lock`` is released. + +Devices spawned from struct rtnl_link_ops should never free the +struct net_device directly. + +.ndo_init and .ndo_uninit +~~~~~~~~~~~~~~~~~~~~~~~~~ + +``.ndo_init`` and ``.ndo_uninit`` callbacks are called during net_device +registration and de-registration, under ``rtnl_lock``. Drivers can use +those e.g. when parts of their init process need to run under ``rtnl_lock``. + +``.ndo_init`` runs before device is visible in the system, ``.ndo_uninit`` +runs during de-registering after device is closed but other subsystems +may still have outstanding references to the netdevice. MTU === diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index bb0596c41b3e..79f514afb17d 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -3441,7 +3441,7 @@ replay: if (ops->newlink) { err = ops->newlink(link_net ? : net, dev, tb, data, extack); - /* Drivers should call free_netdev() in ->destructor + /* Drivers should set dev->needs_free_netdev * and unregister it on failure after registration * so that device could be finally freed in rtnl_unlock. */