Re: [PATCH net-next 01/10] docs: net: netdevices: small fixes and clarifications
From: Stanislav Fomichev <hidden>
Date: 2026-05-26 22:12:26
Also in:
linux-doc
On 05/26, Jakub Kicinski wrote:
quoted hunk ↗ jump to hunk
A handful of unrelated nits: - free_netdevice() does not exist; replace two stray references with free_netdev(). - The simple-driver probe example fell through into err_undo after register_netdev() success; add return 0 for clarity. - Clarify the netdev_priv() paragraph: "(netdev_priv())" was easy to misread as the thing that needs explicit freeing; spell out that it refers to extra pointers stored in the device private struct. - ndo_setup_tc synchronization note: TC_SETUP_BLOCK / TC_SETUP_FT actually run under block->cb_lock, not "NFT locks", and rtnl_lock may or may not be held depending on path. - ->lltx guidance reads as very outdated, it's not really deprecated. I suspect people may have been trying to use it for HW drivers in the past but I can't think of such a case in the last decade. Signed-off-by: Jakub Kicinski <kuba@kernel.org> --- Documentation/networking/netdevices.rst | 31 ++++++++++++++----------- 1 file changed, 17 insertions(+), 14 deletions(-)diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst index 93e06e8d51a9..60492d4df2ee 100644 --- a/Documentation/networking/netdevices.rst +++ b/Documentation/networking/netdevices.rst@@ -21,13 +21,14 @@ by free_netdev(). This is required to handle the pathological case cleanly alloc_netdev_mqs() / alloc_netdev() reserve extra space for driver private data which gets freed when the network device is freed. If separately allocated data is attached to the network device -(netdev_priv()) then it is up to the module exit handler to free that. +(extra pointers stored in the device private struct) then it is up +to the module exit handler to free that. There are two groups of APIs for registering struct net_device. First group can be used in normal contexts where ``rtnl_lock`` is not already held: register_netdev(), unregister_netdev(). Second group can be used when ``rtnl_lock`` is already held: -register_netdevice(), unregister_netdevice(), free_netdevice(). +register_netdevice(), unregister_netdevice(), free_netdev(). Simple drivers --------------@@ -58,6 +59,7 @@ In that case the struct net_device registration is done using goto err_undo; /* net_device is visible to the user! */ + return 0; err_undo: /* ... undo the device setup ... */@@ -73,7 +75,7 @@ In that case the struct net_device registration is done using Note that after calling register_netdev() the device is visible in the system. Users can open it and start sending / receiving traffic immediately, -or run any other callback, so all initialization must be done prior to +or run any other callback, so all initialization must be **complete** prior to registration. unregister_netdev() closes the device and waits for all users to be done@@ -157,7 +159,7 @@ register_netdevice() fails. The callback may be invoked with or without 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() +Setting struct net_device.needs_free_netdev makes core call free_netdev() 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@@ -256,7 +258,7 @@ struct net_device synchronization rules lock if the driver implements queue management or shaper API. Context: process -ndo_get_stats: +ndo_get_stats / ndo_get_stats64: Synchronization: RCU (can be called concurrently with the stats update path). Context: atomic (can't sleep under RCU)@@ -264,12 +266,9 @@ struct net_device synchronization rules ndo_start_xmit: Synchronization: __netif_tx_lock spinlock. - 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 dev->lltx is deprecated. - Don't use it for new drivers. + When the driver sets dev->lltx this will be called without holding + netif_tx_lock. dev->lltx is meant for software drivers only, since + they often have no per-queue state. Context: Process with BHs disabled or BH (timer), will be called with interrupts disabled by netconsole.@@ -304,11 +303,15 @@ struct net_device synchronization rules lock if the driver implements queue management or shaper API.
[..]
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 + Locking depends on ``tc_setup_type``. For most types the callback + is invoked under ``rtnl_lock`` and netdev instance lock if the driver implements queue management or shaper API. + For ``TC_SETUP_BLOCK`` and ``TC_SETUP_FT`` ``rtnl_lock`` may or + may not be held, and the netdev instance lock is not held. + ``TC_SETUP_BLOCK`` runs under ``block->cb_lock`` and ``TC_SETUP_FT`` + runs under ``flowtable->flow_block_lock``. + 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.
LGTM! Acked-by: Stanislav Fomichev <sdf@fomichev.me>