ibvpostsend

ibv_post_send is a function in the Infiniband Verbs API that posts one or more send work requests to the send queue of a queue pair (QP). It is used to initiate data transfers over RDMA by placing work requests into the QP’s send ring for asynchronous completion.

Signature and behavior: int ibv_post_send(struct ibv_qp *qp, const struct ibv_send_wr *wr, struct ibv_send_wr **bad_wr); The wr argument points to the first work request in a linked list of ibv_send_wr structures; each work request includes details such as the operation (for example SEND, SEND_WITH_IMM, or ATOMIC), scatter/gather elements, immediate data, and a next pointer to chain additional requests. The chain ends when wr->next is NULL. The operation is asynchronous, and completion is reported via a completion queue (CQ). A successful call returns 0; on error, -1 is returned and errno is set to indicate the failure. If bad_wr is non-NULL, it is set to point to the first faulty work request in the list, enabling the caller to diagnose and fix the issue.

Usage considerations: The QP must be in a valid ready state (typically RTS) for the post to succeed. Resources in the send queue and the protection domain must be sufficient; exhaustion may yield errors such as EAGAIN or ENOMEM. Errors can also arise from invalid inputs (EINVAL, EFAULT). The caller is responsible for ensuring that memory regions referenced by the work requests remain valid until completion, and for handling completions to reuse or recycle buffers.

Related concepts: ibv_post_recv is used for receive work requests, and both functions interact with a CQ to notify completion. Proper synchronization and error handling are essential in high-performance RDMA applications.