RDMA_JOIN_MULTICAST(3)

💖 RDMA_JOIN_MULTICAST 💖

okay bestie, so this is a page from the Librdmacm Programmer's Manual and it's literally about rdma_join_multicast, which does exactly what it says on the tin: it joins a multicast group. no cap. 🦋

✨ NAME ✨

rdma_join_multicast — joins a multicast group. that's it, that's the whole vibe. 👑

🎀 SYNOPSIS 🎀

#include <rdma/rdma_cma.h>

int rdma_join_multicast (struct rdma_cm_id *id, struct sockaddr *addr,
void *context);

three args, one int back. she's lowkey simple but highkey important. 💅

🌸 ARGUMENTS 🌸

• id — the communication identifier that's associated with this request. like, who's asking? this girl.
• addr — the multicast address that identifies the group you're trying to join. this is the group chat, fr fr.
• context — your own user-defined context that gets attached to the join request. put whatever you want in there, it's your little emotional support pointer. 🫶

💜 DESCRIPTION 💜

Joins a multicast group and attaches an associated QP to the group. the way that this function just does the thing. iconic behavior. ✨

⭐ RETURN VALUE ⭐

Returns 0 on success, or -1 on error. and if an error happens, errno will be set to indicate the failure reason — so like, always check it, bestie, don't just assume. 😭

🌈 NOTES 🌈

okay this is the part you actually need to read, so lock in. 🙈

Before joining a multicast group, the rdma_cm_id must be bound to an RDMA device by calling rdma_bind_addr or rdma_resolve_addr. no shortcuts, she needs a home first.

Use of rdma_resolve_addr requires the local routing tables to resolve the multicast address to an RDMA device, unless a specific source address is provided. iykyk.

The user must call rdma_leave_multicast to leave the multicast group and release any multicast resources. it's giving "you can check out any time you like" — please actually leave, the resources are not infinite. 💀

After the join operation completes, if a QP is associated with the rdma_cm_id, it is automatically attached to the multicast group when the multicast event is retrieved by the user. Otherwise, the user is responsible for calling ibv_attach_mcast to bind the QP to the multicast group. so either the system handles it or you do — there is no third option. 👑

The join context is returned to the user through the private_data field in the rdma_cm_event. that's where your context pointer comes back to you, like a little boomerang of friendship. 🪃💖

🔥 SEE ALSO 🔥

• rdma_leave_multicast(3)
• rdma_bind_addr(3)
• rdma_resolve_addr(3)
• rdma_create_qp(3)
• rdma_get_cm_event(3)

and that's the whole page, periodt. 💅 this little gem is from librdmacm, dated 2008-01-02 — she's been serving accurate multicast knowledge since way before you were on the internet, and she still ate. 🌟 bye bestie, go join your group! 🎀🦋💖