qeth_add_hw_header(9)

💖 qeth_add_hw_header(9) 💖

okay so this one lives in the Kernel API Manual and it's literally the function that gives your skb a little HW header glow-up ✨ stick around, bestie, it's short but it ate.

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🌸 NAME 🌸

qeth_add_hw_header — add a HW header to an skb. that's it, that's the whole vibe 💅

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✨ SYNOPSIS ✨

int qeth_add_hw_header (struct qeth_qdio_out_q *queue , struct sk_buff
*skb , struct qeth_hdr **hdr , unsigned int hdr_len , unsigned int
proto_len , unsigned int *elements );

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🎀 ARGUMENTS 🎀

• queue — the TX queue that the skb is gonna be placed on. like, which line is it queuing in 🫶
• skb — the skb that the HW header should be added to. this is the main character fr.
• hdr — a double pointer to a qeth_hdr. and listen: when it returns with >= 0, it contains a valid pointer to a qeth_hdr. so on the way out it's actually pointing at something real 👑
• hdr_len — length of the HW header. just the header, no extras.
• proto_len — length of protocol headers that need to be in the same page as the HW header. they gotta be page-mates, no cap 🧚
• elements — returns the required number of buffer elements for this skb. it's an out-param, so it's giving information on the way out energy 💫

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💜 DESCRIPTION 💜

Returns the pushed length. that's the happy path, slay 💅

But if the header can't be pushed on (eg. because it would cross a page boundary — rude of it honestly), then it is allocated from the cache instead and 0 is returned. not a fail, just a different route, iykyk.

The number of needed buffer elements is returned in elements.

And an error to create the hdr is indicated by returning with < 0. so if you see a negative number, that's your ✨ signal ✨ that the header did not happen.

real talk: >= 0 means hdr has a valid pointer, < 0 means error. don't mix those up, bestie 😭

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🦋 SEE ALSO 🦋

Kernel file ./drivers/s390/net/qeth_core_main.c 💖 and also these iconic functions:

• qeth_irq(9)
• qeth_send_control_data(9)
• qeth_prep_flush_pack_buffer(9)
• qeth_get_elements_for_frags(9)
• qeth_count_elements(9)
• qeth_fill_buffer(9)
• qeth_vm_request_mac(9)
• qeth_enable_hw_features(9)

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that's the whole page, babe 🎀 this one came from ./drivers/s390/net, dated October 2026, and it's filed under qeth_add_hw_header(9) in the Kernel API Manual — go read the source, it's giving main character energy 🌈⭐