@@ -4,15 +4,19 @@
Softnet Driver Issues
=====================
-Transmit path guidelines:
+Transmit path guidelines
+========================
-1) The ndo_start_xmit method must not return NETDEV_TX_BUSY under
- any normal circumstances. It is considered a hard error unless
- there is no way your device can tell ahead of time when its
- transmit function will become busy.
+Stop queues in advance
+----------------------
- Instead it must maintain the queue properly. For example,
- for a driver implementing scatter-gather this means::
+The ndo_start_xmit method must not return NETDEV_TX_BUSY under
+any normal circumstances. It is considered a hard error unless
+there is no way your device can tell ahead of time when its
+transmit function will become busy.
+
+Instead it must maintain the queue properly. For example,
+for a driver implementing scatter-gather this means::
static netdev_tx_t drv_hard_start_xmit(struct sk_buff *skb,
struct net_device *dev)
@@ -42,56 +46,73 @@ Softnet Driver Issues
return NETDEV_TX_OK;
}
- And then at the end of your TX reclamation event handling::
+And then at the end of your TX reclamation event handling::
if (netif_queue_stopped(dp->dev) &&
TX_BUFFS_AVAIL(dp) > (MAX_SKB_FRAGS + 1))
netif_wake_queue(dp->dev);
- For a non-scatter-gather supporting card, the three tests simply become::
+For a non-scatter-gather supporting card, the three tests simply become::
/* This is a hard error log it. */
if (TX_BUFFS_AVAIL(dp) <= 0)
- and::
+and::
if (TX_BUFFS_AVAIL(dp) == 0)
- and::
+and::
if (netif_queue_stopped(dp->dev) &&
TX_BUFFS_AVAIL(dp) > 0)
netif_wake_queue(dp->dev);
-2) An ndo_start_xmit method must not modify the shared parts of a
- cloned SKB.
+No exclusive ownership
+----------------------
+
+An ndo_start_xmit method must not modify the shared parts of a
+cloned SKB.
+
+Timely completions
+------------------
+
+Do not forget that once you return NETDEV_TX_OK from your
+ndo_start_xmit method, it is your driver's responsibility to free
+up the SKB and in some finite amount of time.
-3) Do not forget that once you return NETDEV_TX_OK from your
- ndo_start_xmit method, it is your driver's responsibility to free
- up the SKB and in some finite amount of time.
+For example, this means that it is not allowed for your TX
+mitigation scheme to let TX packets "hang out" in the TX
+ring unreclaimed forever if no new TX packets are sent.
+This error can deadlock sockets waiting for send buffer room
+to be freed up.
- For example, this means that it is not allowed for your TX
- mitigation scheme to let TX packets "hang out" in the TX
- ring unreclaimed forever if no new TX packets are sent.
- This error can deadlock sockets waiting for send buffer room
- to be freed up.
+If you return NETDEV_TX_BUSY from the ndo_start_xmit method, you
+must not keep any reference to that SKB and you must not attempt
+to free it up.
- If you return NETDEV_TX_BUSY from the ndo_start_xmit method, you
- must not keep any reference to that SKB and you must not attempt
- to free it up.
+Probing guidelines
+==================
-Probing guidelines:
+Address validation
+------------------
+
+Any hardware layer address you obtain for your device should
+be verified. For example, for ethernet check it with
+linux/etherdevice.h:is_valid_ether_addr()
+
+Close/stop guidelines
+=====================
-1) Any hardware layer address you obtain for your device should
- be verified. For example, for ethernet check it with
- linux/etherdevice.h:is_valid_ether_addr()
+Quiescence
+----------
-Close/stop guidelines:
+After the ndo_stop routine has been called, the hardware must
+not receive or transmit any data. All in flight packets must
+be aborted. If necessary, poll or wait for completion of
+any reset commands.
-1) After the ndo_stop routine has been called, the hardware must
- not receive or transmit any data. All in flight packets must
- be aborted. If necessary, poll or wait for completion of
- any reset commands.
+Auto-close
+----------
-2) The ndo_stop routine will be called by unregister_netdevice
- if device is still UP.
+The ndo_stop routine will be called by unregister_netdevice
+if device is still UP.
driver.rst had a historical form of list of common problems. In the age os Sphinx and rendered documentation it's better to use the more usual title + text format. This will allow us to render kdoc into the output more naturally. No changes to the actual text. Signed-off-by: Jakub Kicinski <kuba@kernel.org> --- Documentation/networking/driver.rst | 91 ++++++++++++++++++----------- 1 file changed, 56 insertions(+), 35 deletions(-)