key_extract(9)

💅 key_extract 💅

okay bestie, welcome to the Kernel API Manual page for key_extract — the function that pulls a flow key out of an Ethernet frame. it's giving “extract the key, set the headers, no cap” 🫶

💖 NAME 💖

key_extract — extracts a flow key from an Ethernet frame. periodt. ✨

🎀 SYNOPSIS 🎀

int key_extract (struct sk_buff *skb , struct sw_flow_key *key );

🌸 ARGUMENTS 🌸

• skb — the sk_buff that contains the frame, with skb->data pointing to the Ethernet header. that's the main character input, fr fr. 👑
• key — the output flow key. this is where the key gets written out, bestie. 💖

🦋 DESCRIPTION 🦋

so this function initializes skb header fields like this:

• skb->mac_header — the L2 header. iconic. ✨
• skb->network_header — just past the L2 header, or just past the VLAN header, to the first byte of the L2 payload. slay. 🌈
• skb->transport_header — If key->eth.type is ETH_P_IP or ETH_P_IPV6 on output, then just past the IP header, if one is present and of a correct length, otherwise the same as skb->network_header. For other key->eth.type values it is left untouched. no cap, that's the whole rule. 🧚
• skb->protocol — the type of the data starting at skb->network_header. Equals to key->eth.type. literally matching, adorable. 💜

💜 RETURN 💜

0 if successful, otherwise a negative errno value. bestie, if it's negative, that's your signal something went sideways. 😭

🔥 SEE ALSO 🔥

Kernel file ./net/openvswitch/flow.c and the besties get_ipv6_ext_hdrs(9), parse_vlan_tag(9), key_extract_l3l4(9). iykyk 💅

mwah 💋 — source ./net/openvswitch, October 2026, page key_extract(9).