RDMA_POST_READ(3)

✨ NAME ✨

rdma_post_read — bestie, this is the one that posts an RDMA read work request. 🦋

It lives in the Librdmacm Programmer's Manual (section 3, so it's a library call, iykyk).

🌸 SYNOPSIS 🌸

#include <rdma/rdma_verbs.h>

int rdma_post_read (struct rdma_cm_id *id, void *context, void *addr,
size_t length, struct ibv_mr *mr, int flags, uint64_t remote_addr,
uint32_t rkey);

Like… that's the whole vibe. Eight args. She's high maintenance but she serves. 💅

🎀 ARGUMENTS 🎀

• id — a reference to a communication identifier where the request will be posted. It's giving "the address of the function" but for RDMA, periodt.
• context — user-defined context associated with the request. You pick it, you own it, it comes back to you later. 💖
• addr — the address of the local destination of the read request. So like, where the data lands. 🫶
• length — the length of the read operation. How many bytes we're moving, no cap.
• mr — registered memory region associated with the local buffer. Yes, registered. Do not skip this step, I'm literally begging. 😭
• flags — optional flags used to control the read operation. Optional bestie, but read the NOTES.
• remote_addr — the address of the remote registered memory to read from. That's the other side's memory. Over there. 👀
• rkey — the registered memory key associated with the remote address. It's the little permission slip that lets you touch their buffer. 🔑

💫 DESCRIPTION 💫

Okay so here's what actually happens: this posts a work request to the send queue of the queue pair associated with the rdma_cm_id. ✨

Then the contents of the remote memory region get read into the local data buffer. That's it. That's the whole plot. Remote memory → your buffer. Iconic behavior, honestly. 🔥

⭐ RETURN VALUE ⭐

Returns 0 on success, or -1 on error. 🙈

If an error occurs, errno will be set to indicate the failure reason. So like, check errno, bestie, she's literally telling you what went wrong.

🌈 NOTES 🌈

Read this part. I know you wanna skip it. Don't. 💀

• For a list of supported flags, see ibv_post_send. Go look. I'll wait. 🧚
• Both the remote and local data buffers must have been registered before the read is issued, and the buffers must remain registered until the read completes. Not before-completes. Until it completes. This is not a drill. 🚨
• Read operations may not be posted to an rdma_cm_id or the corresponding queue pair until it has been connected. No connection = no read. Periodt. 👑
• The user-defined context associated with the read request will be returned to you through the work completion wr_id, work request identifier, field. So that context you passed in? That's your little note-to-self coming back home. 💜

🌸 SEE ALSO 🌸

• rdma_cm(7)
• rdma_connect(3)
• rdma_accept(3)
• ibv_post_send(3)
• rdma_post_readv(3)
• rdma_reg_read(3)
• rdma_reg_msgs(3)

okay that's the whole page bestie, go post some reads 💅✨🦋

librdmacm · 2010-07-19 · mwah, xoxo, and remember: register your buffers before you ship it 🫶💖