IBV_ATTACH_MCAST(3)

💅 ibv_attach_mcast(3) — like, the libibverbs programmer's manual, but make it make sense

okay bestie, welcome to the ibv_attach_mcast page from the Libibverbs Programmer's Manual. yes you read that right, we're doing multicast group stuff today and honestly? it's giving networking royalty 👑

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✨ NAME ✨

ibv_attach_mcast, ibv_detach_mcast — attach and detach a queue pair (QPs) to/from a multicast group 🎀

(yes, the original really does say "a queue pair (QPs)" — we don't gatekeep, we report 💅)

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✨ SYNOPSIS ✨

#include <infiniband/verbs.h>

int ibv_attach_mcast(struct ibv_qp *qp, const union ibv_gid *gid, uint16_t lid);

int ibv_detach_mcast(struct ibv_qp *qp, const union ibv_gid *gid, uint16_t lid);

literally copy that header line exactly, bestie, no typos, #include <infiniband/verbs.h> and you're in 🦋

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✨ DESCRIPTION ✨

ibv_attach_mcast() — attaches the QP qp to the multicast group having MGID gid and MLID lid. that's the whole vibe: qp goes in, group gets a new member 🌸

ibv_detach_mcast() — detaches the QP qp to the multicast group having MGID gid and MLID lid. (and yes, the original says "detaches ... to" and not "from" — we're keeping it 100% as written, ngl 🫶)

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✨ RETURN VALUE ✨

both ibv_attach_mcast() and ibv_detach_mcast() return 0 on success 🔥 or, if things go sideways, the value of errno on failure — which is literally the universe telling you why it failed, so read it 😭

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✨ NOTES ✨

• only QPs of Transport Service Type IBV_QPT_UD may be attached to multicast groups. that's the dress code, no exceptions 🎀
• if a QP is attached to the same multicast group multiple times, the QP will still receive a single copy of a multicast message. not me spam-joining and still getting one message 💀 that's the rule.
• in order to receive multicast messages, a join request for the multicast group must be sent to the subnet administrator (SA), so that the fabric's multicast routing is configured to deliver messages to the local port. iykyk — no SA join, no messages, the fabric simply won't know where to send them 🧚

fr fr though: skipping the SA join request means the routing never gets set up, so don't come crying to me when nothing arrives 🙈

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✨ SEE ALSO ✨

• ibv_create_qp(3)

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✨ AUTHOR ✨

Dotan Barak <dotanba@gmail.com> 👑

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kisses, this page was brought to you by libibverbs, dated 2006-10-31 — and IBV_ATTACH_MCAST(3) says hi 💜💅