RDMA_POST_RECV(3)

💌 RDMA_POST_RECV(3) — the librdmacm programmer's manual, but make it cute

okay so bestie, welcome to the glow-up of rdma_post_recv from the librdmacm Programmer's Manual. this is the one where you tell the network "hey, i'm ready to receive, send me stuff" 🫶

✨ NAME ✨

rdma_post_recv — post a work request to receive an incoming message. literally just "inbox open, bestie" 💖

🌸 SYNOPSIS 🌸

#include <rdma/rdma_verbs.h>

int rdma_post_recv (struct rdma_cm_id *id, void *context, void *addr,
size_t length, struct ibv_mr *mr);

no cap, that's the whole signature. five little arguments and you're posting 🎀

🦋 ARGUMENTS 🦋

• id — a reference to a communication identifier where the message buffer will be posted. this is your main character, the rdma_cm_id everything hangs off of ✨
• context — user-defined context associated with the request. put whatever you want in here, it's your little emotional support pointer 💅
• addr — the address of the memory buffer to post. the actual spot where the incoming data is gonna land 📍
• length — the length of the memory buffer. how much room you're giving it, be generous 🍓
• mr — a registered memory region associated with the posted buffer. registered, bestie, don't forget 🧚

💜 DESCRIPTION 💜

Posts a work request to the receive queue of the queue pair associated with the rdma_cm_id. the posted buffer will be queued to receive an incoming message sent by the remote peer.

that's it. that's the vibe. you drop a buffer into the receive queue, and it sits there patiently waiting like a girl who texted first and is now refreshing 🥲

👑 RETURN VALUE 👑

Returns 0 on success, or -1 on error. and if it's an error? errno will be set to indicate the failure reason. so check it, don't just assume, okay? 💀

🔥 NOTES 🔥

okay this part actually matters so listen up bestie:

• the user is responsible for ensuring that a receive buffer is posted and large enough to contain all sent data before the peer posts the corresponding send message. if you're late, that's on you 😭
• the message buffer must have been registered before being posted, with the mr parameter referencing the registration.
• the buffer must remain registered until the receive completes. do not un-register it early, i am begging 🙈
• messages may be posted to an rdma_cm_id only after a queue pair has been associated with it. a queue pair is bound to an rdma_cm_id after calling rdma_create_ep or rdma_create_qp, if the rdma_cm_id is allocated using rdma_create_id.
• the user-defined context associated with the receive request will be returned to the user through the work completion wr_id, work request identifier, field. so that context you passed in? it comes back to you. it's giving boomerang 🪃

ngl the ordering rules here are not a suggestion, they're the whole plot. post the buffer first, keep it registered, and only post after the qp is associated. periodt. 💅

🌈 SEE ALSO 🌈

• rdma_cm(7)
• rdma_create_id(3)
• rdma_create_ep(3)
• rdma_create_qp(3)
• rdma_reg_read(3)
• ibv_reg_mr(3)
• ibv_dereg_mr(3)
• rdma_post_recvv(3)
• rdma_post_send(3)

librdmacm · 2010-07-19 — and that's the whole page, bestie. go forth and receive, you absolute icon 👑💖✨