Subject: Re: [patch net-next v2 0/9] net: sched: introduce chain templates support with offloading to mlxsw

From: David Ahern <[email-masked]>
Date: Thu, 28 Jun 2018 09:10:45 -0600

On 6/28/18 8:29 AM, Jiri Pirko wrote:
> Thu, Jun 28, 2018 at 04:18:47PM CEST, [email-masked] wrote:
>> On 6/28/18 7:08 AM, Jiri Pirko wrote:
>>> Create dummy device with clsact first:
>>> # ip link add type dummy
>>> # tc qdisc add dev dummy0 clsact
>>>
>>> There is no template assigned by default:
>>> # tc chaintemplate show dev dummy0 ingress
>>>
>>> Add a template of type flower allowing to insert rules matching on last
>>> 2 bytes of destination mac address:
>>> # tc chaintemplate add dev dummy0 ingress proto ip flower dst_mac 00:00:00:00:00:00/00:00:00:00:FF:FF
>>>
>>> The template is now showed in the list:
>>> # tc chaintemplate show dev dummy0 ingress
>>> chaintemplate flower chain 0 
>>>   dst_mac 00:00:00:00:00:00/00:00:00:00:ff:ff
>>>   eth_type ipv4
>>>
>>> Add another template, this time for chain number 22:
>>> # tc chaintemplate add dev dummy0 ingress proto ip chain 22 flower dst_ip 0.0.0.0/16
>>> # tc chaintemplate show dev dummy0 ingress
>>> chaintemplate flower chain 0 
>>>   dst_mac 00:00:00:00:00:00/00:00:00:00:ff:ff
>>>   eth_type ipv4
>>> chaintemplate flower chain 22 
>>>   eth_type ipv4
>>>   dst_ip 0.0.0.0/16
>>>
>>> Add a filter that fits the template:
>>> # tc filter add dev dummy0 ingress proto ip flower dst_mac aa:bb:cc:dd:ee:ff/00:00:00:00:00:0F action drop
>>>
>>> Addition of filters that does not fit the template would fail:
>>> # tc filter add dev dummy0 ingress proto ip flower dst_mac aa:11:22:33:44:55/00:00:00:FF:00:00 action drop
>>> Error: Mask does not fit the template.
>>> We have an error talking to the kernel, -1
>>> # tc filter add dev dummy0 ingress proto ip flower dst_ip 10.0.0.1 action drop
>>> Error: Mask does not fit the template.
>>> We have an error talking to the kernel, -1
>>>
>>> Additions of filters to chain 22:
>>> # tc filter add dev dummy0 ingress proto ip chain 22 flower dst_ip 10.0.0.1/8 action drop
>>> # tc filter add dev dummy0 ingress proto ip chain 22 flower dst_ip 10.0.0.1 action drop
>>> Error: Mask does not fit the template.
>>> We have an error talking to the kernel, -1
>>> # tc filter add dev dummy0 ingress proto ip chain 22 flower dst_ip 10.0.0.1/24 action drop
>>> Error: Mask does not fit the template.
>>> We have an error talking to the kernel, -1
>>>
>>> Removal of a template from non-empty chain would fail:
>>> # tc chaintemplate del dev dummy0 ingress
>>> Error: The chain is not empty, unable to delete template.
>>> We have an error talking to the kernel, -1
>>
>> Why this restriction? It's a template, so why can't it be removed
>> regardless of whether there are filters?
> 
> That means you could start to insert filters that does not match the
> original template. I wanted to avoid it. The chain is utilized in hw for
> the original template, the filter insertion would have to be sanitized
> in driver. With this restriction, drivers can depend on filters always
> be fitting.
> 

Then the hardware driver should have that restriction not the core tc code.