STRUCT IB_USER_MAD_HDR_OLD(9)

💅 struct ib_user_mad_hdr_old(9)

okay so bestie, welcome to the Kernel API Manual 🎀 — yes we're in kernel land today, and yes it's iconic. This page is about struct ib_user_mad_hdr_old, which is literally just the old version of the MAD packet header, except it's missing pkey_index. that's the whole vibe. she's the prequel. the OG. the "before the glow-up" header 🦋

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✨ NAME ✨

struct ib_user_mad_hdr_old — the old version of the MAD packet header, aka the one without pkey_index 💅

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🌸 SYNOPSIS 🌸

struct ib_user_mad_hdr_old {
    __u32 id;
    __u32 status;
    __u32 timeout_ms;
    __u32 retries;
    __u32 length;
    __be32 qpn;
    __be32 qkey;
    __be16 lid;
    __u8 sl;
    __u8 path_bits;
    __u8 grh_present;
    __u8 gid_index;
    __u8 hop_limit;
    __u8 traffic_class;
    __u8 gid[16];
    __be32 flow_label;
};

like, look at her. so many little fields. so much main character energy 👑

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🌈 Members 🌈

here's the full rundown, no cap, every single one:

• id — the ID of the agent MAD was received with / is gonna be sent with 🔥
• status — 0 on a successful receive, or ETIMEDOUT if no response came back (in that case the transaction ID in data[] gets set to the TID of the original request) 💀 — and heads up, this one's ignored on send
• timeout_ms — how many milliseconds to wait for a response. it's unset on receive
• retries — number of automatic retries to attempt 🌀
• qpn — the remote QP number, received from / to be sent to
• qkey — remote Q_Key to be sent with. unset on receive
• lid — remote lid, received from / to be sent to
• sl — service level, received with / to be sent with
• path_bits — local path bits, received with / to be sent with
• grh_present — if set, the GRH was received / should be sent ✨
• gid_index — local GID index to send with. unset on receive
• hop_limit — hop limit in the GRH
• traffic_class — traffic class in the GRH 🚦
• gid — remote GID in the GRH
• flow_label — flow label in the GRH 🌊

ngl, length is sitting right there in the struct but the page doesn't give her a description. she's mysterious. we respect that 🫶

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👀 SEE ALSO 👀

• Kernel file ./include/uapi/rdma/ib_user_mad.h
• struct ib_user_mad_hdr(9)
• struct ib_user_mad(9)
• struct ib_user_mad_reg_req(9)
• struct ib_user_mad_reg_req2(9)

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and that's the whole page, bestie 💖 she lives at ./include/uapi/rdma, dated October 2026, and she's filed under struct ib_user_mad_hdr_old(9) — go read the newer ones, they ate 🍓✨