skb_checksum_maybe_trim(9)

💅 skb_checksum_maybe_trim — the kernel API manual page, bestie edition 💅

okay so picture this: you're deep in net/core/skbuff.c territory, poking at sk_buff structs like the main character you are, and you stumble on skb_checksum_maybe_trim. bestie. this one maybe trims the given skb. that's the whole vibe. the "maybe" is doing SO much work and honestly? iconic. 🎀

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✨ NAME ✨

skb_checksum_maybe_trim — maybe trims the given skb 🫶

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🌸 SYNOPSIS 🌸

struct sk_buff * skb_checksum_maybe_trim (struct sk_buff *skb , unsigned
       int transport_len );

like, that's it. that's the whole signature. she's compact, she's clean, she takes an skb and a transport_len and hands you back a struct sk_buff *. slay. ✨

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💖 ARGUMENTS 💖

• skb — the skb to check 🔍 (yes, "to check". that's literally the whole job description. vibe check: passed)
• transport_len — the data length beyond the network header 📏 so like, everything past the network header, that's the number we're working with

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🦋 DESCRIPTION 🦋

okay so here's the tea ☕ — this function checks whether the given skb has data beyond the given transport length. like, is there extra stuff hanging out past where the transport layer says it should end? 🙈

• if there is extra data: she returns a cloned skb trimmed to this transport length. freshly cloned, freshly trimmed, new hair, new outfit. 💅
• if there isn't: she just returns the provided skb. no notes. unchanged. lowkey the same girl.
• on error: returns NULL 😭 — and yes, error cases are real, like when transport_len exceeds the skb length, or you hit out-of-memory. no cap, both of those are in the original and both of those can absolutely ruin your day.

⚠️ bestie, listen to me, this part is important: the caller needs to set the skb transport header, and the caller needs to free any returned skb if it differs from the provided skb. if you skip that second bit you're gonna have a memory leak and the leak is gonna be your fault. periodt. 🫶

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🌈 SEE ALSO 🌈

the kernel file ./net/core/skbuff.c (and, like, honestly the entire skb cinematic universe):

drop_reasons_register_subsys(9), drop_reasons_unregister_subsys(9), skb_panic(9), napi_skb_cache_get_bulk(9), __build_skb(9), build_skb_around(9), __napi_build_skb(9), napi_build_skb(9), __alloc_skb(9), __netdev_alloc_skb(9), napi_alloc_skb(9), skb_pp_cow_data(9), skb_pp_frag_ref(9), __kfree_skb(9), sk_skb_reason_drop(9), skb_tx_error(9), consume_skb(9), __consume_stateless_skb(9), napi_consume_skb(9), alloc_skb_for_msg(9), skb_morph(9), skb_copy_ubufs(9), skb_clone(9), skb_copy(9), __pskb_copy_fclone(9), pskb_expand_head(9), skb_expand_head(9), skb_copy_expand(9), __skb_pad(9), pskb_put(9), skb_put(9), skb_push(9), skb_pull(9), skb_pull_data(9), skb_trim(9), __pskb_pull_tail(9), skb_copy_bits(9), skb_store_bits(9), skb_zerocopy(9), skb_dequeue(9), skb_dequeue_tail(9), skb_queue_purge_reason(9), skb_rbtree_purge(9), skb_queue_head(9), skb_queue_tail(9), skb_unlink(9), skb_append(9), skb_split(9), skb_shift(9), skb_prepare_seq_read(9), skb_seq_read(9), skb_abort_seq_read(9), skb_copy_seq_read(9), skb_find_text(9), skb_pull_rcsum(9), skb_segment(9), skb_to_sgvec(9), skb_cow_data(9), skb_clone_sk(9), skb_partial_csum_set(9), skb_checksum_setup(9), skb_checksum_trimmed(9), skb_try_coalesce(9), skb_scrub_packet(9), skb_eth_pop(9), skb_eth_push(9), skb_mpls_push(9), skb_mpls_pop(9), skb_mpls_update_lse(9), skb_mpls_dec_ttl(9), alloc_skb_with_frags(9), skb_condense(9), __skb_ext_alloc(9), __skb_ext_set(9), skb_ext_add(9), skb_attempt_defer_free(9), skb_splice_from_iter(9)

like I said. the whole skb cinematic universe. iykyk. 👑

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🧚 sign-off 🧚

this chapter of the Kernel API Manual lives at ./net/core, dated October 2026, and yes, the manual page's own name is skb_checksum_maybe_trim(9) — she named the page after herself, main character energy fr fr. go trim something (maybe). don't leak. love u, bye! 💜⭐🦋