On 13.04.2016 11:41, Michael S. Tsirkin wrote:
On Wed, Apr 13, 2016 at 11:04:46AM +0200, Paolo Abeni wrote:
The current tun_net_xmit() implementation don't need any external
lock since it relay on rcu protection for the tun data structure
and on socket queue lock for skb queuing.
This patch set the NETIF_F_LLTX feature bit in the tun device, so
that on xmit, in absence of qdisc, no serialization lock is acquired
by the caller.
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
drivers/net/tun.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index faf9297..42992dc 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1796,7 +1796,7 @@ static int tun_set_iff(struct net *net, struct file
*file, struct ifreq *ifr)
dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
NETIF_F_HW_VLAN_STAG_TX;
- dev->features = dev->hw_features;
+ dev->features = dev->hw_features | NETIF_F_LLTX;
the documentation says:
NETIF_F_LLTX_BIT, /* LockLess TX - deprecated. Please */
/* do not use LLTX in new drivers */
In networking/netdev-features.txt
* LLTX driver (deprecated for hardware drivers)
NETIF_F_LLTX should be set in drivers that implement their own locking in
transmit path or don't need locking at all (e.g. software tunnels).
In ndo_start_xmit, it is recommended to use a try_lock and return
NETDEV_TX_LOCKED when the spin lock fails. The locking should also properly
protect against other callbacks (the rules you need to find out).
Don't use it for new drivers.
I think this is documentation is correct and it is only deprecated for
hardware drivers.
Bye,
Hannes
