Subject: Re: [PATCH net-next] vxlan: Provide means for obtaining port information

From: Alexander Duyck <[email-masked]>
Date: Wed, 27 Mar 2013 14:48:25 -0700

On 03/27/2013 02:38 PM, Stephen Hemminger wrote:
> On Wed, 27 Mar 2013 14:33:11 -0700
> Alexander Duyck <[email-masked]> wrote:
>
>> This patch provides a very simple means for device drivers to obtain access to
>> the VXLAN destination port number configuration.  This information is needed
>> in order to provide devices with a means of determining if a given UDP flow is
>> a VXLAN flow or if it is a standard flow for offload purposes.
>>
>> The main disadvantage with this approach is that loading a driver that calls
>> this interface will mean that it will also load the vxlan module and any other
>> modules it depends on.  To that end I really hope at some point the value
>> becomes static as we could then avoid this extra overhead.  The alternative to
>> this though is significantly more complicated as it would likely require
>> registering notifiers to capture when the vxlan module is loaded and then
>> updating the value.
>>
>> This patch adds a new header, if_vxlan.h which I suspect will slowly be
>> populated with more details such as the header layout as more devices end up
>> needing to figure out how to parse VXLAN for various offloads.
>>
>> Signed-off-by: Alexander Duyck <[email-masked]>
>> ---
>>
>>  drivers/net/vxlan.c      |    7 +++++++
>>  include/linux/if_vxlan.h |   28 ++++++++++++++++++++++++++++
>>  2 files changed, 35 insertions(+), 0 deletions(-)
>>  create mode 100644 include/linux/if_vxlan.h
>>
>> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
>> index 62a4438..5b3bb9a 100644
>> --- a/drivers/net/vxlan.c
>> +++ b/drivers/net/vxlan.c
>> @@ -898,6 +898,13 @@ static u16 vxlan_src_port(const struct vxlan_dev *vxlan, struct sk_buff *skb)
>>  	return (((u64) hash * range) >> 32) + vxlan->port_min;
>>  }
>>  
>> +/* simple accessor function for getting VXLAN destination port number */
>> +int vxlan_dst_port(void)
>> +{
>> +	return vxlan_port;
>> +}
>> +EXPORT_SYMBOL_GPL(vxlan_dst_port);
>> +
>>  static int handle_offloads(struct sk_buff *skb)
>>  {
>>  	if (skb_is_gso(skb)) {
>> diff --git a/include/linux/if_vxlan.h b/include/linux/if_vxlan.h
>> new file mode 100644
>> index 0000000..b997eac
>> --- /dev/null
>> +++ b/include/linux/if_vxlan.h
>> @@ -0,0 +1,28 @@
>> +/*
>> + * VXLAN: Virtual eXtensible Local Area Network
>> + *
>> + * Copyright (c) 2013, Intel Corporation.
>> + *
>> + * This program is free software; you can redistribute it and/or modify it
>> + * under the terms and conditions of the GNU General Public License,
>> + * version 2, as published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope it will be useful, but WITHOUT
>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
>> + * more details.
>> + *
>> + * You should have received a copy of the GNU General Public License along with
>> + * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
>> + * Place - Suite 330, Boston, MA 02111-1307 USA.
>> + *
>> + */
>> +
>> +#if IS_ENABLED(CONFIG_VXLAN)
>> +extern int vxlan_dst_port(void);
>> +#else
>> +static inline int vxlan_dst_port(void)
>> +{
>> +	return 0;
>> +}
>> +#endif
> Won't this all break if we what Dave wants and allow listening on multiple ports.
> The port should be a property of the vxlan device not global.

Yes this will break if we ended up supporting a different port per
VXLAN.  The problem is a port per VXLAN is going to be much more
difficult to support for any sort of hardware offload as well.  What we
end up having to do is add a significant number of filters just to
identify all of the possible ports that may be used.  In addition it
will mean having to add some sort of notifier as I mentioned in the
patch description since we will have VXLANs going into and out of
existence, each one with their own port number..

This was essentially a "good enough for now" fix to address the fact
that I needed the port number for offload testing, but I will sit back
and wait for the port per VXLAN stuff to be pushed in before I take any
steps to try to sort that out.

Thanks,

Alex