Re: [PATCH net V3 2/2] net: core: explicitly select a txq before doing l2 forwarding

On 1/10/2014 12:18 AM, Jason Wang wrote:

Currently, the tx queue were selected implicitly in ndo_dfwd_start_xmit(). The
will cause several issues:

- NETIF_F_LLTX were removed for macvlan, so txq lock were done for macvlan
   instead of lower device which misses the necessary txq synchronization for
   lower device such as txq stopping or frozen required by dev watchdog or
   control path.
- dev_hard_start_xmit() was called with NULL txq which bypasses the net device
   watchdog.
- dev_hard_start_xmit() does not check txq everywhere which will lead a crash
   when tso is disabled for lower device.

Fix this by explicitly introducing a new param for .ndo_select_queue() for just
selecting queues in the case of l2 forwarding offload. netdev_pick_tx() was also
extended to accept this parameter and dev_queue_xmit_accel() was used to do l2
forwarding transmission.

With this fixes, NETIF_F_LLTX could be preserved for macvlan and there's no need
to check txq against NULL in dev_hard_start_xmit(). Also there's no need to keep
a dedicated ndo_dfwd_start_xmit() and we can just reuse the code of
dev_queue_xmit() to do the transmission.

In the future, it was also required for macvtap l2 forwarding support since it
provides a necessary synchronization method.

Cc: John Fastabend <redacted>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: e1000-devel@lists.sourceforge.net
Signed-off-by: Jason Wang <redacted>

---
Changes from V2:
- Reuse dev_queue_xmit() instead of re-inventing dfwd_direct_xmit()
- remove the unnecessary braces
Changes from V1:
- Adding a new parameter to ndo_select_queue instead of a new method to select
   queue for l2 forwarding.
- Remove the unnecessary ndo_dfwd_start_xmit() since txq was selected
   explicitly.
- Keep NETIF_F_LLTX when netdev feature is changed.
- Shape the commit log
---

Looks good to me thanks, I tested my macvlan use cases and everything
works as expected.

Acked-by: John Fastabend <redacted>