[v2] VLAN, support ingress/egress priority map flushing

When sending packets via a vlan device we can manipulate the priority bits in the vlan header (PCP) via a mapping based on tc class value.
Similarly, when packets are received via a vlan device, the PCP value can be mapped onto a tc class value, which is available for iptables rules and tc queueing disciplines.

One can use the vconfig utility to set both ingress and egress mapping entries (set_ingress_map/set_egress_map) or any other application to call the vlan ioctl handler.

The resulting map can be printed via /proc/net/vlan/<ifname> , i.e. :
# cat /proc/net/vlan/vlan11
vlan11  VID: 11  REORDER_HDR: 1  dev->priv_flags: 1
          total frames received     52331849
           total bytes received  17451834908
       Broadcast/Multicast Rcvd      1525155

       total frames transmitted     98569270
        total bytes transmitted 144870211289
Device: eth_test
INGRESS priority mappings: 0:0  1:1  2:2  3:3  4:0  5:0  6:0 7:0
  EGRESS priority mappings: 0:7

The current API offers only GET and SET operations, and when actually using this functionality a flush is missing to reset all entries.
This patch adds a FLUSH operation for both ingress and egress map which can then be used by vconfig or other applications.

Signed-off-by: Thierry Du Tre <thierry@dtsystems.be>
---
Changes in v2:
   - Move new vlan cmd values to end of enum list.

  include/uapi/linux/if_vlan.h |  4 +++-
  net/8021q/vlan.c             | 16 ++++++++++++++++
  net/8021q/vlan.h             |  2 ++
  net/8021q/vlan_dev.c         | 23 +++++++++++++++++++++++
  4 files changed, 44 insertions(+), 1 deletion(-)

On Mon, 2017-03-13 at 15:36 +0100, Thierry Du Tre wrote:

> +void vlan_dev_flush_egress_priority(const struct net_device *dev)
> +{
> +	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
> +	struct vlan_priority_tci_mapping *mp;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(vlan->egress_priority_map); i++) {
> +		while ((mp = vlan->egress_priority_map[i]) != NULL) {
> +			vlan->egress_priority_map[i] = mp->next;
> +			kfree(mp);
> +		}
> +	}
> +	vlan->nr_egress_mappings = 0;
> +}


Are you doing this on a live device ?

Looks you'll need proper RCU support then.

Otherwise, crashes will happen, say in egress_priority_map()

smp_rmb() wont be enough if items can now be destroyed.

On 13-03-17 16:28, Eric Dumazet wrote:
> On Mon, 2017-03-13 at 15:36 +0100, Thierry Du Tre wrote:
>
>> +void vlan_dev_flush_egress_priority(const struct net_device *dev)
>> +{
>> +	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
>> +	struct vlan_priority_tci_mapping *mp;
>> +	int i;
>> +
>> +	for (i = 0; i < ARRAY_SIZE(vlan->egress_priority_map); i++) {
>> +		while ((mp = vlan->egress_priority_map[i]) != NULL) {
>> +			vlan->egress_priority_map[i] = mp->next;
>> +			kfree(mp);
>> +		}
>> +	}
>> +	vlan->nr_egress_mappings = 0;
>> +}
>
> Are you doing this on a live device ?
>
> Looks you'll need proper RCU support then.
>
> Otherwise, crashes will happen, say in egress_priority_map()
>
> smp_rmb() wont be enough if items can now be destroyed.
Yes, good point about the smp concurrency.
I wrongly assumed there was already some locking mechanism in place to 
protect these structures.

Let me take a look at this and I'll come back with a new proposal.

--
Thierry