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docs: net: reformat driver.rst from a list to sections

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[ Upstream commit d2f5c68e3f7157e874a759e382a5eaffa775b869 ]

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>
Stable-dep-of: 95ecba62e2fd ("net: fix races in netdev_tx_sent_queue()/dev_watchdog()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jakub Kicinski
2023-04-06 18:25:30 -07:00
committed by Greg Kroah-Hartman
parent 9683804e36
commit 1af2abd342
1 changed files with 56 additions and 35 deletions
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91
Documentation/networking/driver.rst
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@@ -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 @@ Transmit path guidelines:
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
----------------------
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.
An ndo_start_xmit method must not modify the shared parts of a
cloned SKB.
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.
Timely completions
------------------
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.
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.
Probing guidelines:
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.
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()
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.
Close/stop guidelines:
Probing guidelines
==================
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.
Address validation
------------------
2) The ndo_stop routine will be called by unregister_netdevice
if device is still UP.
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
=====================
Quiescence
----------
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
----------
The ndo_stop routine will be called by unregister_netdevice
if device is still UP.