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Diffstat (limited to 'Documentation/networking/netdevices.rst')
-rw-r--r-- | Documentation/networking/netdevices.rst | 151 |
1 files changed, 135 insertions, 16 deletions
diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst index c2476917a6c3..7ebb6c36482d 100644 --- a/Documentation/networking/netdevices.rst +++ b/Documentation/networking/netdevices.rst @@ -8,7 +8,7 @@ Network Devices, the Kernel, and You! Introduction ============ The following is a random collection of documentation regarding -network devices. +network devices. It is intended for driver developers. struct net_device lifetime rules ================================ @@ -210,59 +210,65 @@ packets is preferred. struct net_device synchronization rules ======================================= ndo_open: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process ndo_stop: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process Note: netif_running() is guaranteed false ndo_do_ioctl: Synchronization: rtnl_lock() semaphore. - Context: process - This is only called by network subsystems internally, - not by user space calling ioctl as it was in before - linux-5.14. + This is only called by network subsystems internally, + not by user space calling ioctl as it was in before + linux-5.14. ndo_siocbond: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process - Used by the bonding driver for the SIOCBOND family of - ioctl commands. + Used by the bonding driver for the SIOCBOND family of + ioctl commands. ndo_siocwandev: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process Used by the drivers/net/wan framework to handle the SIOCWANDEV ioctl with the if_settings structure. ndo_siocdevprivate: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process This is used to implement SIOCDEVPRIVATE ioctl helpers. These should not be added to new drivers, so don't use. ndo_eth_ioctl: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process ndo_get_stats: - Synchronization: rtnl_lock() semaphore, or RCU. + Synchronization: RCU (can be called concurrently with the stats + update path). Context: atomic (can't sleep under RCU) ndo_start_xmit: Synchronization: __netif_tx_lock spinlock. - When the driver sets NETIF_F_LLTX in dev->features this will be + When the driver sets dev->lltx this will be called without holding netif_tx_lock. In this case the driver has to lock by itself when needed. The locking there should also properly protect against - set_rx_mode. WARNING: use of NETIF_F_LLTX is deprecated. + set_rx_mode. WARNING: use of dev->lltx is deprecated. Don't use it for new drivers. Context: Process with BHs disabled or BH (timer), @@ -284,6 +290,16 @@ ndo_set_rx_mode: Synchronization: netif_addr_lock spinlock. Context: BHs disabled +ndo_setup_tc: + ``TC_SETUP_BLOCK`` and ``TC_SETUP_FT`` are running under NFT locks + (i.e. no ``rtnl_lock`` and no device instance lock). The rest of + ``tc_setup_type`` types run under netdev instance lock if the driver + implements queue management or shaper API. + +Most ndo callbacks not specified in the list above are running +under ``rtnl_lock``. In addition, netdev instance lock is taken as well if +the driver implements queue management or shaper API. + struct napi_struct synchronization rules ======================================== napi->poll: @@ -297,3 +313,106 @@ napi->poll: Context: softirq will be called with interrupts disabled by netconsole. + +netdev instance lock +==================== + +Historically, all networking control operations were protected by a single +global lock known as ``rtnl_lock``. There is an ongoing effort to replace this +global lock with separate locks for each network namespace. Additionally, +properties of individual netdev are increasingly protected by per-netdev locks. + +For device drivers that implement shaping or queue management APIs, all control +operations will be performed under the netdev instance lock. +Drivers can also explicitly request instance lock to be held during ops +by setting ``request_ops_lock`` to true. Code comments and docs refer +to drivers which have ops called under the instance lock as "ops locked". +See also the documentation of the ``lock`` member of struct net_device. + +In the future, there will be an option for individual +drivers to opt out of using ``rtnl_lock`` and instead perform their control +operations directly under the netdev instance lock. + +Devices drivers are encouraged to rely on the instance lock where possible. + +For the (mostly software) drivers that need to interact with the core stack, +there are two sets of interfaces: ``dev_xxx``/``netdev_xxx`` and ``netif_xxx`` +(e.g., ``dev_set_mtu`` and ``netif_set_mtu``). The ``dev_xxx``/``netdev_xxx`` +functions handle acquiring the instance lock themselves, while the +``netif_xxx`` functions assume that the driver has already acquired +the instance lock. + +struct net_device_ops +--------------------- + +``ndos`` are called without holding the instance lock for most drivers. + +"Ops locked" drivers will have most of the ``ndos`` invoked under +the instance lock. + +struct ethtool_ops +------------------ + +Similarly to ``ndos`` the instance lock is only held for select drivers. +For "ops locked" drivers all ethtool ops without exceptions should +be called under the instance lock. + +struct netdev_stat_ops +---------------------- + +"qstat" ops are invoked under the instance lock for "ops locked" drivers, +and under rtnl_lock for all other drivers. + +struct net_shaper_ops +--------------------- + +All net shaper callbacks are invoked while holding the netdev instance +lock. ``rtnl_lock`` may or may not be held. + +Note that supporting net shapers automatically enables "ops locking". + +struct netdev_queue_mgmt_ops +---------------------------- + +All queue management callbacks are invoked while holding the netdev instance +lock. ``rtnl_lock`` may or may not be held. + +Note that supporting struct netdev_queue_mgmt_ops automatically enables +"ops locking". + +Notifiers and netdev instance lock +---------------------------------- + +For device drivers that implement shaping or queue management APIs, +some of the notifiers (``enum netdev_cmd``) are running under the netdev +instance lock. + +The following netdev notifiers are always run under the instance lock: +* ``NETDEV_XDP_FEAT_CHANGE`` + +For devices with locked ops, currently only the following notifiers are +running under the lock: +* ``NETDEV_CHANGE`` +* ``NETDEV_REGISTER`` +* ``NETDEV_UP`` + +The following notifiers are running without the lock: +* ``NETDEV_UNREGISTER`` + +There are no clear expectations for the remaining notifiers. Notifiers not on +the list may run with or without the instance lock, potentially even invoking +the same notifier type with and without the lock from different code paths. +The goal is to eventually ensure that all (or most, with a few documented +exceptions) notifiers run under the instance lock. Please extend this +documentation whenever you make explicit assumption about lock being held +from a notifier. + +NETDEV_INTERNAL symbol namespace +================================ + +Symbols exported as NETDEV_INTERNAL can only be used in networking +core and drivers which exclusively flow via the main networking list and trees. +Note that the inverse is not true, most symbols outside of NETDEV_INTERNAL +are not expected to be used by random code outside netdev either. +Symbols may lack the designation because they predate the namespaces, +or simply due to an oversight. |