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

From: Jiri Pirko <[email-masked]>
Date: Thu, 28 Jun 2018 17:37:52 +0200

Thu, Jun 28, 2018 at 05:10:45PM CEST, [email-masked] wrote:
>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.

But why? The same restriction would be in all drivers. I believe it is
better to have in in tc in single place. Drivers can then depend on it.
Do you have a usecase where you need to remove template for non-empty
chain?