rdma_calc_flow_label(9)

💅 rdma_calc_flow_label(9) — the Kernel API Manual glow-up ✨

✨ NAME ✨

okay bestie, the name entry is: rdma_calc_flow_label — generate a RDMA symmetric flow label value based on local and remote qpn values. periodt. 💖

🫶 SYNOPSIS 🫶

the signature, served fresh:

u32 rdma_calc_flow_label (u32 lqpn , u32 rqpn );

💅 ARGUMENTS 💅

the OG page is literally giving us -- undescribed -- for both, so we keep it 100 and don't invent lore:

• lqpn — -- undescribed -- 🙈
• rqpn — -- undescribed -- 🙈

🌈 DESCRIPTION 🌈

okay so this function folds the multiplication results of two qpn fields — 24 bit each — and converts it to a 20 bit result. math girlie behavior, honestly. ✨

it creates a symmetric flow_label value based on the local and remote qpn values. the slay here is that both the requester and responder can calculate the same flow_label for a given connection. 🫶

this helper should be used by the driver in case the upper layer provides a zero flow_label value. why? to improve entropy of RDMA traffic in the network. entropy queen 🌸

👑 SEE ALSO 👑

the original page points at Kernel file ./include/rdma/ib_verbs.h, and then it name-drops this entire iconic guest list — every single one, no skips:

• struct rdma_stat_desc(9)
• struct rdma_hw_stats(9)
• ib_rate_to_mult(9)
• ib_rate_to_mbps(9)
• ib_port_attr_to_speed_info(9)
• enum ib_mr_type(9)
• struct ib_mr_status(9)
• mult_to_ib_rate(9)
• struct ib_udata(9)
• struct rdma_netdev(9)
• struct ib_device_ops(9)
• ib_get_client_data(9)
• ib_modify_qp_is_ok(9)
• rdma_cap_ib_switch(9)
• rdma_start_port(9)
• rdma_for_each_port(9)
• rdma_end_port(9)
• rdma_cap_ib_mad(9)
• rdma_cap_opa_mad(9)
• rdma_cap_ib_smi(9)
• rdma_cap_ib_cm(9)
• rdma_cap_iw_cm(9)
• rdma_cap_ib_sa(9)
• rdma_cap_ib_mcast(9)
• rdma_cap_af_ib(9)
• rdma_cap_eth_ah(9)
• rdma_cap_opa_ah(9)
• rdma_max_mad_size(9)
• rdma_cap_roce_gid_table(9)
• rdma_core_cap_opa_port(9)
• rdma_mtu_enum_to_int(9)
• rdma_mtu_from_attr(9)
• ib_alloc_pd(9)
• ib_dealloc_pd(9)
• rdma_create_ah(9)
• rdma_create_user_ah(9)
• ib_get_gids_from_rdma_hdr(9)
• ib_get_rdma_header_version(9)
• ib_init_ah_attr_from_wc(9)
• ib_create_ah_from_wc(9)
• rdma_modify_ah(9)
• rdma_query_ah(9)
• rdma_destroy_ah_user(9)
• rdma_destroy_ah(9)
• ib_modify_srq(9)
• ib_query_srq(9)
• ib_destroy_srq_user(9)
• ib_destroy_srq(9)
• ib_post_srq_recv(9)
• ib_create_qp(9)
• ib_modify_qp_with_udata(9)
• ib_modify_qp(9)
• ib_query_qp(9)
• ib_destroy_qp(9)
• ib_open_qp(9)
• ib_close_qp(9)
• ib_post_send(9)
• ib_post_recv(9)
• ib_alloc_cq_any(9)
• rdma_set_cq_moderation(9)
• ib_destroy_cq_user(9)
• ib_destroy_cq(9)
• ib_poll_cq(9)
• ib_req_notify_cq(9)
• ib_virt_dma_to_ptr(9)
• ib_virt_dma_to_page(9)
• ib_dma_mapping_error(9)
• ib_dma_map_single(9)
• ib_dma_unmap_single(9)
• ib_dma_map_page(9)
• ib_dma_unmap_page(9)
• ib_dma_map_bvec(9)
• ib_dma_unmap_bvec(9)
• ib_dma_map_sgtable_attrs(9)
• ib_dma_map_sg(9)
• ib_dma_unmap_sg(9)
• ib_dma_max_seg_size(9)
• ib_dma_sync_single_for_cpu(9)
• ib_dma_sync_single_for_device(9)
• ib_dereg_mr_user(9)
• ib_dereg_mr(9)
• ib_update_fast_reg_key(9)
• ib_inc_rkey(9)
• ib_attach_mcast(9)
• ib_detach_mcast(9)
• ib_check_mr_status(9)
• ib_device_try_get(9)
• rdma_ah_find_type(9)
• ib_lid_cpu16(9)
• ib_lid_be16(9)
• rdma_roce_rescan_device(9)
• rdma_device_to_ibdev(9)
• ibdev_to_node(9)
• rdma_device_to_drv_device(9)
• rdma_flow_label_to_udp_sport(9)
• rdma_get_udp_sport(9)

that's the page, bestie 🫶 — source/version is ./include/rdma, dated October 2026, and the star is rdma_calc_flow_label(9). periodt. 💅