skb_cow(9)

✨ NAME ✨

okay so welcome to the Kernel API Manual, bestie — this is skb_cow(9): copy header of skb when it is required. that's the whole vibe. no cap. 💅

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🎀 SYNOPSIS 🎀

int skb_cow (struct sk_buff *skb , unsigned int headroom );

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🫶 ARGUMENTS 🫶

• skb — the buffer to cow. yes, that's literally the note. 🐄
• headroom — the needed headroom. keep that number safe.

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🌸 DESCRIPTION 🌸

so here's the tea: if the skb you passed in doesn't have enough headroom, or if its data part is shared, the data gets reallocated. that's the move. ✨

if that reallocation fails, you get an error back, and the original skb is not changed — no sneaky edits, no broken vibes. 🙈

what you end up with is an skb whose writable area is skb->head...skb->tail, with at least headroom of space at the head. iconique. 👑

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🦋 SEE ALSO 🦋

bestie, the whole skb cinematic universe is here — zero skips, because we do not gatekeep the kernel docs:

• Kernel file ./include/linux/skbuff.h skb checksums(9)
• skb_frag_size(9)
• skb_frag_size_set(9)
• skb_frag_size_add(9)
• skb_frag_size_sub(9)
• skb_frag_must_loop(9)
• skb_frag_foreach_page(9)
• struct skb_shared_hwtstamps(9)
• dataref and headerless skbs(9)
• Basic sk_buff geometry(9)
• struct sk_buff(9)
• skb_pfmemalloc(9)
• skb_dst(9)
• skb_dstref_steal(9)
• skb_dstref_restore(9)
• skb_dst_set(9)
• skb_dst_set_noref(9)
• skb_dst_is_noref(9)
• skb_napi_id(9)
• skb_unref(9)
• kfree_skb(9)
• alloc_skb(9)
• skb_fclone_busy(9)
• alloc_skb_fclone(9)
• skb_pad(9)
• skb_queue_empty(9)
• skb_queue_empty_lockless(9)
• skb_queue_is_last(9)
• skb_queue_is_first(9)
• skb_queue_next(9)
• skb_queue_prev(9)
• skb_get(9)
• skb_cloned(9)
• skb_header_cloned(9)
• __skb_header_release(9)
• skb_shared(9)
• skb_share_check(9)
• skb_unshare(9)
• skb_peek(9)
• __skb_peek(9)
• skb_peek_next(9)
• skb_peek_tail(9)
• skb_queue_len(9)
• skb_queue_len_lockless(9)
• __skb_queue_head_init(9)
• skb_queue_splice(9)
• skb_queue_splice_init(9)
• skb_queue_splice_tail(9)
• skb_queue_splice_tail_init(9)
• __skb_queue_after(9)
• __skb_queue_head(9)
• __skb_queue_tail(9)
• __skb_dequeue(9)
• __skb_dequeue_tail(9)
• skb_len_add(9)
• __skb_fill_netmem_desc(9)
• skb_fill_page_desc(9)
• skb_fill_page_desc_noacc(9)
• skb_headroom(9)
• skb_tailroom(9)
• skb_availroom(9)
• skb_reserve(9)
• skb_tailroom_reserve(9)
• skb_reset_transport_header_careful(9)
• skb_set_transport_header_careful(9)
• pskb_trim_unique(9)
• skb_orphan(9)
• skb_orphan_frags(9)
• __skb_queue_purge_reason(9)
• netdev_alloc_frag(9)
• netdev_alloc_skb(9)
• __dev_alloc_pages(9)
• __dev_alloc_page(9)
• dev_page_is_reusable(9)
• skb_propagate_pfmemalloc(9)
• skb_frag_off(9)
• skb_frag_off_add(9)
• skb_frag_off_set(9)
• skb_frag_off_copy(9)
• skb_frag_net_iov(9)
• skb_frag_page(9)
• skb_frag_netmem(9)
• skb_frag_address(9)
• skb_frag_address_safe(9)
• skb_frag_phys(9)
• skb_frag_page_copy(9)
• __skb_frag_dma_map(9)
• skb_clone_writable(9)
• skb_cow_head(9)
• skb_padto(9)
• __skb_put_padto(9)
• skb_put_padto(9)
• skb_linearize(9)
• skb_has_shared_frag(9)
• skb_linearize_cow(9)
• skb_postpull_rcsum(9)
• skb_postpush_rcsum(9)
• skb_push_rcsum(9)
• pskb_trim_rcsum(9)
• skb_needs_linearize(9)
• skb_get_timestamp(9)
• skb_data_move(9)
• skb_postpull_data_move(9)
• skb_postpush_data_move(9)
• skb_complete_tx_timestamp(9)
• skb_tstamp_tx(9)
• skb_tx_timestamp(9)
• skb_complete_wifi_ack(9)
• skb_checksum_complete(9)
• struct skb_ext(9)
• skb_checksum_none_assert(9)
• skb_head_is_locked(9)

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source/version check: this page is from ./include/linux, dated October 2026 — bye bestie, go make that header writable 💅✨