batadv_mcas..._expand_head(9)

💅 batadv_mcas..._expand_head(9) 💅

okay so real talk, bestie, we're in the Kernel API Manual today and this little icon is called batadv_mcast_forw_expand_head — say that five times fast, i literally can't 😭. it's giving batman-adv multicast energy and honestly? we're obsessed.

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✨ NAME ✨

batadv_mcast_forw_expand_head — expand headroom for an mcast packet 🎀

like, it makes room at the front of your packet. that's the whole vibe.

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🌸 SYNOPSIS 🌸

int batadv_mcast_forw_expand_head (struct batadv_priv *bat_priv , struct
       sk_buff *skb );

two args, one int back, we love a tidy little signature bestie 🫶

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🦋 ARGUMENTS 🦋

• bat_priv — the bat priv with all the mesh interface information ✨ like, all of it. every little mesh interface detail lives in here, it's the main character.
• skb — the multicast packet to send 💌 the lil guy we're about to make room in.

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💜 DESCRIPTION 💜

okay so here's the tea: this function tries to expand an skb's headroom so that its head to tail is 1298 bytes large (that's minimum IPv6 MTU + vlan ethernet header size, no cap 📏).

⚠️ Warning warning warning ⚠️ — this function may reallocate the skb data buffer via skb_cow/skb_linearize/... and bestie, that means any pointer into the skb data (e.g. obtained from skb->data or eth_hdr) that you grabbed before this call must be considered invalid afterwards and has to be reacquired. like, do not be out here using a stale pointer, it's giving undefined chaos 💀🙈

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🔥 RETURN 🔥

• -EINVAL — if the given skb's length is too large 😤
• -ENOMEM — on memory allocation failure 😭
• zero — on success! 🎉 slay, we love a zero return

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🌈 SEE ALSO 🌈

the kernel file itself, first of all:

• Kernel file ./net/batman-adv/multicast_forw.c

and then the whole friend group, no one left out, periodt 👑:

• batadv_mcast_forw_skb_push(9), batadv_mcast_forw_push_padding(9), batadv_mcast_forw_push_est_padding(9), batadv_mcast_forw_orig_entry(9), batadv_mcast_forw_push_dest(9), batadv_mcast_forw_push_dests_list(9), batadv_mcast_forw_push_tt(9), batadv_mcast_forw_push_want_all(9), batadv_mcast_forw_push_want_rtr(9), batadv_mcast_forw_scrape(9), batadv_mcast_forw_push_scrape_padding(9), batadv_mcast_forw_push_insert_padding(9), batadv_mcast_forw_push_adjust_padding(9), batadv_mcast_forw_push_dests(9), batadv_mcast_forw_push_tracker(9), batadv_mcast_forw_push_tvlvs(9), batadv_mcast_forw_push_hdr(9), batadv_mcast_forw_scrub_dests(9), batadv_mcast_forw_shrink_fill(9), batadv_mcast_forw_shrink_pack_dests(9), batadv_mcast_forw_shrink_align_offset(9), batadv_mcast_forw_shrink_update_headers(9), batadv_mcast_forw_shrink_move_headers(9), batadv_mcast_forw_shrink_tracker(9), batadv_mcast_forw_packet(9), batadv_mcast_forw_tracker_tvlv_handler(9), batadv_mcast_forw_packet_hdrlen(9), batadv_mcast_forw_push(9), batadv_mcast_forw_mcsend(9)

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k bye bestie, go expand some headroom responsibly 💅✨

this page lives in ./net/batman-adv, it's dated October 2026, and it signs off as batadv_mcas..._expand_head(9) — mwah, see u in the group chat 🎀🦋💖