Re: [PATCH RFC v3 2/9] virtio_net: Add functions for hashing

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Akihiko Odaki wrote:
> They are useful to implement VIRTIO_NET_F_RSS and
> VIRTIO_NET_F_HASH_REPORT.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  include/linux/virtio_net.h | 198 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 198 insertions(+)
> 
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index 6c395a2600e8..7ee2e2f2625a 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -9,6 +9,183 @@
>  #include <uapi/linux/tcp.h>
>  #include <uapi/linux/virtio_net.h>
>  
> +struct virtio_net_hash {
> +	u32 value;
> +	u16 report;
> +};
> +
> +struct virtio_net_toeplitz_state {
> +	u32 hash;
> +	u32 key_buffer;
> +	const __be32 *key;
> +};
> +
> +#define VIRTIO_NET_SUPPORTED_HASH_TYPES (VIRTIO_NET_RSS_HASH_TYPE_IPv4 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_TCPv4 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_IPv6 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_TCPv6 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_UDPv6)
> +
> +#define VIRTIO_NET_RSS_MAX_KEY_SIZE 40
> +
> +static inline void virtio_net_toeplitz(struct virtio_net_toeplitz_state *state,
> +				       const __be32 *input, size_t len)
> +{
> +	u32 key;
> +
> +	while (len) {
> +		state->key++;
> +		key = be32_to_cpu(*state->key);
> +
> +		for (u32 bit = BIT(31); bit; bit >>= 1) {
> +			if (be32_to_cpu(*input) & bit)
> +				state->hash ^= state->key_buffer;
> +
> +			state->key_buffer =
> +				(state->key_buffer << 1) | !!(key & bit);
> +		}
> +
> +		input++;
> +		len--;
> +	}
> +}
> +
> +static inline u8 virtio_net_hash_key_length(u32 types)
> +{
> +	size_t len = 0;
> +
> +	if (types & VIRTIO_NET_HASH_REPORT_IPv4)
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv4_addrs));
> +
> +	if (types &
> +	    (VIRTIO_NET_HASH_REPORT_TCPv4 | VIRTIO_NET_HASH_REPORT_UDPv4))
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv4_addrs) +
> +			  sizeof(struct flow_dissector_key_ports));
> +
> +	if (types & VIRTIO_NET_HASH_REPORT_IPv6)
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv6_addrs));
> +
> +	if (types &
> +	    (VIRTIO_NET_HASH_REPORT_TCPv6 | VIRTIO_NET_HASH_REPORT_UDPv6))
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv6_addrs) +
> +			  sizeof(struct flow_dissector_key_ports));
> +
> +	return 4 + len;

Avoid raw constants like this 4. What field does it capture?

Instead of working from shortest to longest and using max, how about
the inverse and return as soon as a match is found.

> +}
> +
> +static inline u32 virtio_net_hash_report(u32 types,
> +					 struct flow_dissector_key_basic key)
> +{
> +	switch (key.n_proto) {
> +	case htons(ETH_P_IP):
> +		if (key.ip_proto == IPPROTO_TCP &&
> +		    (types & VIRTIO_NET_RSS_HASH_TYPE_TCPv4))
> +			return VIRTIO_NET_HASH_REPORT_TCPv4;
> +
> +		if (key.ip_proto == IPPROTO_UDP &&
> +		    (types & VIRTIO_NET_RSS_HASH_TYPE_UDPv4))
> +			return VIRTIO_NET_HASH_REPORT_UDPv4;
> +
> +		if (types & VIRTIO_NET_RSS_HASH_TYPE_IPv4)
> +			return VIRTIO_NET_HASH_REPORT_IPv4;
> +
> +		return VIRTIO_NET_HASH_REPORT_NONE;
> +
> +	case htons(ETH_P_IPV6):
> +		if (key.ip_proto == IPPROTO_TCP &&
> +		    (types & VIRTIO_NET_RSS_HASH_TYPE_TCPv6))
> +			return VIRTIO_NET_HASH_REPORT_TCPv6;
> +
> +		if (key.ip_proto == IPPROTO_UDP &&
> +		    (types & VIRTIO_NET_RSS_HASH_TYPE_UDPv6))
> +			return VIRTIO_NET_HASH_REPORT_UDPv6;
> +
> +		if (types & VIRTIO_NET_RSS_HASH_TYPE_IPv6)
> +			return VIRTIO_NET_HASH_REPORT_IPv6;
> +
> +		return VIRTIO_NET_HASH_REPORT_NONE;
> +
> +	default:
> +		return VIRTIO_NET_HASH_REPORT_NONE;
> +	}
> +}
> +
> +static inline bool virtio_net_hash_rss(const struct sk_buff *skb,
> +				       u32 types, const __be32 *key,
> +				       struct virtio_net_hash *hash)
> +{
> +	u16 report;

nit: move below the struct declarations.

> +	struct virtio_net_toeplitz_state toeplitz_state = {
> +		.key_buffer = be32_to_cpu(*key),
> +		.key = key
> +	};
> +	struct flow_keys flow;
> +
> +	if (!skb_flow_dissect_flow_keys(skb, &flow, 0))
> +		return false;
> +
> +	report = virtio_net_hash_report(types, flow.basic);
> +
> +	switch (report) {
> +	case VIRTIO_NET_HASH_REPORT_IPv4:
> +		virtio_net_toeplitz(&toeplitz_state,
> +				    (__be32 *)&flow.addrs.v4addrs,
> +				    sizeof(flow.addrs.v4addrs) / 4);
> +		break;
> +
> +	case VIRTIO_NET_HASH_REPORT_TCPv4:
> +		virtio_net_toeplitz(&toeplitz_state,
> +				    (__be32 *)&flow.addrs.v4addrs,
> +				    sizeof(flow.addrs.v4addrs) / 4);
> +		virtio_net_toeplitz(&toeplitz_state, &flow.ports.ports,
> +				    1);
> +		break;
> +
> +	case VIRTIO_NET_HASH_REPORT_UDPv4:
> +		virtio_net_toeplitz(&toeplitz_state,
> +				    (__be32 *)&flow.addrs.v4addrs,
> +				    sizeof(flow.addrs.v4addrs) / 4);
> +		virtio_net_toeplitz(&toeplitz_state, &flow.ports.ports,
> +				    1);
> +		break;
> +
> +	case VIRTIO_NET_HASH_REPORT_IPv6:
> +		virtio_net_toeplitz(&toeplitz_state,
> +				    (__be32 *)&flow.addrs.v6addrs,
> +				    sizeof(flow.addrs.v6addrs) / 4);
> +		break;
> +
> +	case VIRTIO_NET_HASH_REPORT_TCPv6:
> +		virtio_net_toeplitz(&toeplitz_state,
> +				    (__be32 *)&flow.addrs.v6addrs,
> +				    sizeof(flow.addrs.v6addrs) / 4);
> +		virtio_net_toeplitz(&toeplitz_state, &flow.ports.ports,
> +				    1);
> +		break;
> +
> +	case VIRTIO_NET_HASH_REPORT_UDPv6:
> +		virtio_net_toeplitz(&toeplitz_state,
> +				    (__be32 *)&flow.addrs.v6addrs,
> +				    sizeof(flow.addrs.v6addrs) / 4);
> +		virtio_net_toeplitz(&toeplitz_state, &flow.ports.ports,
> +				    1);
> +		break;
> +
> +	default:
> +		return false;
> +	}
> +
> +	hash->value = toeplitz_state.hash;
> +	hash->report = report;
> +
> +	return true;
> +}
> +
>  static inline bool virtio_net_hdr_match_proto(__be16 protocol, __u8 gso_type)
>  {
>  	switch (gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
> @@ -239,4 +416,25 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
>  	return 0;
>  }
>  
> +static inline int virtio_net_hdr_v1_hash_from_skb(const struct sk_buff *skb,
> +						  struct virtio_net_hdr_v1_hash *hdr,
> +						  bool has_data_valid,
> +						  int vlan_hlen,
> +						  const struct virtio_net_hash *hash)
> +{
> +	int ret;
> +
> +	memset(hdr, 0, sizeof(*hdr));
> +
> +	ret = virtio_net_hdr_from_skb(skb, (struct virtio_net_hdr *)hdr,
> +				      true, has_data_valid, vlan_hlen);
> +	if (!ret) {
> +		hdr->hdr.num_buffers = cpu_to_le16(1);
> +		hdr->hash_value = cpu_to_le32(hash->value);
> +		hdr->hash_report = cpu_to_le16(hash->report);
> +	}
> +
> +	return ret;
> +}
> +

I don't think that this helper is very helpful, as all the information
it sets are first passed in. Just set the hdr fields directy in the
caller. It is easier to follow the control flow.