Re: [PATCH] bonding: reset queue mapping prior to transmission to physical device (v4)

Le vendredi 03 juin 2011 à 15:57 -0400, Neil Horman a écrit :

On Fri, Jun 03, 2011 at 09:48:51PM +0200, Eric Dumazet wrote:

quoted

Le vendredi 03 juin 2011 à 15:24 -0400, Neil Horman a écrit :

quoted

The bonding driver is multiqueue enabled, in which each queue represents a slave
to enable optional steering of output frames to given slaves against the default
output policy.  However, it needs to reset the skb->queue_mapping prior to
queuing to the physical device or the physical slave (if it is multiqueue) could
wind up transmitting on an unintended tx queue

Change Notes:
v2) Based on first pass review, updated the patch to restore the origional queue
mapping that was found in bond_select_queue, rather than simply resetting to
zero.  This preserves the value of queue_mapping when it was set on receive in
the forwarding case which is desireable.

v3) Fixed spelling an casting error in skb->cb

v4) fixed to store raw queue_mapping to avoid double decrement

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Jay Vosburgh <redacted>
CC: Andy Gospodarek <andy@greyhouse.net>
CC: "David S. Miller" <davem@davemloft.net>
---
 drivers/net/bonding/bond_main.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 17b4dd9..76adf27 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c

@@ -400,6 +400,9 @@ int bond_dev_queue_xmit(struct bonding *bond, struct sk_buff *skb,
 {
 	skb->dev = slave_dev;
 	skb->priority = 1;
+
+	skb->queue_mapping = ((u16 *)skb->cb)[0];

Please dont do that. Use a helper.

Why?  It seems to be reasonably common practice for drivers to access
queue_mapping directly.

Examples can be found in:
ixgbe_xmit_frame
mlx4_en_xmit
qlge_send
igb_xmit_frame_adv
gfar_start_xmit

among others.

Not saying its correct to do so necessecarily, but it seems a helper doesn't buy
us much here, particularly a per-driver helper.  If a helper really should be
used, why not just consistently use skb_get_queue_mapping?
Neil

I was speaking of skb->cb access, of course, sorry if you missed my
point ;)

Please take a look at various files using helpers for this.

For example : net/ipv4/igmp.c

#define igmp_skb_size(skb) (*(unsigned int *)((skb)->cb))