Re: [PATCH net] net: ethtool: Allow matching on vlan CFI bit

[Jakub Kicinski <jakub.kicinski@netronome.com>]

On Tue, 11 Jun 2019 17:54:56 +0200, Maxime Chevallier wrote:
> Using ethtool, users can specify a classification action matching on the
> full vlan tag, which includes the CFI bit.
> 
> However, when converting the ethool_flow_spec to a flow_rule, we use
> dissector keys to represent the matching patterns.
> 
> Since the vlan dissector key doesn't include the CFI bit, this
> information was silently discarded when translating the ethtool
> flow spec in to a flow_rule.
> 
> This commit adds the CFI bit into the vlan dissector key, and allows
> propagating the information to the driver when parsing the ethtool flow
> spec.
> 
> Fixes: eca4205f9ec3 ("ethtool: add ethtool_rx_flow_spec to flow_rule structure translator")
> Reported-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> ---
> Hi all,
> 
> Although this prevents information to be silently discarded when parsing
> an ethtool_flow_spec, this information doesn't seem to be used by any
> driver that converts an ethtool_flow_spec to a flow_rule, hence I'm not
> sure this is suitable for -net.
> 
> Thanks,
> 
> Maxime
> 
>  include/net/flow_dissector.h | 1 +
>  net/core/ethtool.c           | 5 +++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
> index 7c5a8d9a8d2a..9d2e395c6568 100644
> --- a/include/net/flow_dissector.h
> +++ b/include/net/flow_dissector.h
> @@ -46,6 +46,7 @@ struct flow_dissector_key_tags {
>  
>  struct flow_dissector_key_vlan {
>  	u16	vlan_id:12,
> +		vlan_cfi:1,
>  		vlan_priority:3;
>  	__be16	vlan_tpid;
>  };
> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> index d08b1e19ce9c..43df34c1ebe1 100644
> --- a/net/core/ethtool.c
> +++ b/net/core/ethtool.c
> @@ -3020,6 +3020,11 @@ ethtool_rx_flow_rule_create(const struct ethtool_rx_flow_spec_input *input)
>  			match->mask.vlan.vlan_id =
>  				ntohs(ext_m_spec->vlan_tci) & 0x0fff;
>  
> +			match->key.vlan.vlan_cfi =
> +				!!(ntohs(ext_h_spec->vlan_tci) & 0x1000);
> +			match->mask.vlan.vlan_cfi =
> +				!!(ntohs(ext_m_spec->vlan_tci) & 0x1000);

nit: since you're only using the output as a boolean, you can apply the
     byteswap to the constant and have it performed at build time.
     Another option is be16_get_bits() from linux/bitfield.h.

>  			match->key.vlan.vlan_priority =
>  				(ntohs(ext_h_spec->vlan_tci) & 0xe000) >> 13;
>  			match->mask.vlan.vlan_priority =