af-xdp

Name: af-xdp
Author: mohitmishra786

141stars19forks

How to install af-xdp?

mohitmishra786/low-level-dev-skills/af-xdp

$npx -y skills add mohitmishra786/low-level-dev-skills --skill af-xdp

Installs into the current project.

Summary

AF_XDP skill for high-performance XDP sockets. Use when creating AF_XDP sockets, configuring UMEM and XSK rings, XDP_REDIRECT programs, copy vs zero-copy mode, or comparing with DPDK. Activates on queries about AF_XDP, xsk_umem, XDP_REDIRECT, libbpf xsk, or zero-copy XDP.

Files · 1

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SKILL.md

1	# AF_XDP
2
3	## Purpose
4
5	Guide agents through AF_XDP sockets for high-performance packet I/O: socket creation, UMEM setup, fill/completion/RX/TX rings, XDP programs with `XDP_REDIRECT` to XSK, copy vs zero-copy modes, libbpf helpers, performance comparison with DPDK, and production use cases.
6
7	## When to Use
8
9	- Building a userspace packet processor with lower overhead than raw sockets
10	- Redirecting XDP-filtered traffic to userspace without DPDK complexity
11	- Implementing a custom load balancer or IDS dataplane
12	- Comparing zero-copy vs copy mode on your NIC/driver
13	- Integrating with existing libbpf/XDP infrastructure
14	- Need kernel cooperation (firewall rules) plus userspace processing
15
16	## Workflow
17
18	### 1. Architecture overview
19
20	```
21	NIC → XDP program (BPF) → XDP_REDIRECT → AF_XDP socket → userspace
22	↓
23	XDP_DROP/PASS/TX
24	```
25
26	Components:
27	- UMEM — shared memory region for frames
28	- Fill ring — userspace provides empty frame addresses to kernel
29	- Completion ring — kernel returns completed TX frames
30	- RX ring — kernel delivers received packets
31	- TX ring — userspace submits packets for transmission
32
33	### 2. UMEM and XSK socket creation
34
35	```c
36	#include <bpf/xsk.h>
37	#include <bpf/libbpf.h>
38	#include <xdp/xsk.h>
39
40	#define NUM_FRAMES 4096
41	#define FRAME_SIZE XSK_UMEM__DEFAULT_FRAME_SIZE
42	#define RX_BATCH_SIZE 64
43
44	struct xsk_umem_info {
45	struct xsk_ring_prod fill;
46	struct xsk_ring_cons comp;
47	struct xsk_umem *umem;
48	void *buffer;
49	};
50
51	struct xsk_socket_info {
52	struct xsk_ring_cons rx;
53	struct xsk_ring_prod tx;
54	struct xsk_socket *xsk;
55	};
56
57	int xsk_setup(struct xsk_umem_info *umem_info,
58	struct xsk_socket_info *xsk_info,
59	int ifindex, int queue_id, int xsk_flags)
60	{
61	umem_info->buffer = mmap(NULL, NUM_FRAMES * FRAME_SIZE,
62	PROT_READ \| PROT_WRITE, MAP_PRIVATE \| MAP_ANONYMOUS, -1, 0);
63
64	struct xsk_umem_config umem_cfg = {
65	.fill_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
66	.comp_size = XSK_RING_CONS__DEFAULT_NUM_DESCS,
67	.frame_size = FRAME_SIZE,
68	.frame_headroom = XSK_UMEM__DEFAULT_FRAME_HEADROOM,
69	.flags = 0,
70	};
71
72	int ret = xsk_umem__create(&umem_info->umem, umem_info->buffer,
73	NUM_FRAMES * FRAME_SIZE, &umem_info->fill, &umem_info->comp,
74	&umem_cfg);
75	if (ret)
76	return ret;
77
78	struct xsk_socket_config xsk_cfg = {
79	.rx_size = XSK_RING_CONS__DEFAULT_NUM_DESCS,
80	.tx_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
81	.libbpf_flags = XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD,
82	.xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST,
83	.bind_flags = xsk_flags, // XDP_ZEROCOPY or XDP_COPY
84	};
85
86	return xsk_socket__create(&xsk_info->xsk, "eth0", queue_id,
87	umem_info->umem, &xsk_info->rx, &xsk_info->tx, &xsk_cfg);
88	}
89	```
90
91	### 3. Populate fill ring
92
93	```c
94	void populate_fill_ring(struct xsk_umem_info *umem) {
95	uint32_t idx;
96	uint32_t ret = xsk_ring_prod__reserve(&umem->fill, RX_BATCH_SIZE, &idx);
97	for (uint32_t i = 0; i < ret; i++)
98	xsk_ring_prod__fill_addr(&umem->fill, idx + i) = i FRAME_SIZE;
99	xsk_ring_prod__submit(&umem->fill, ret);
100	}
101	```
102
103	Must keep fill ring stocked — kernel drops packets if no buffers available.
104
105	### 4. XDP redirect program
106
107	```c
108	// xdp_redirect.c
109	#include <linux/bpf.h>
110	#include <bpf/bpf_helpers.h>
111
112	struct {
113	__uint(type, BPF_MAP_TYPE_XSKMAP);
114	__uint(max_entries, 64);
115	__type(key, int);
116	__type(value, int);
117	} xsks_map SEC(".maps");
118
119	SEC("xdp")
120	int xdp_redirect_prog(struct xdp_md *ctx)
121	{
122	int index = ctx->rx_queue_index;
123	return bpf_redirect_map(&xsks_map, index, 0);
124	}
125	```
126
127	```bash
128	# Load and attach
129	bpftool prog load xdp_redirect.o /sys/fs/bpf/xdp_redirect
130	ip link set dev eth0 xdp obj xdp_redirect.o sec xdp
131
132	# Pin xsks_map and update with socket fd
133	```
134
135	### 5. RX processing loop
136
137	```c
138	while (running) {
139	uint32_t idx_rx = 0, rcvd;
140	rcvd = xsk_ring_cons__peek(&xsk_info->rx, RX_BATCH_SIZE, &idx_rx);
141	if (!rcvd)
142	continue;
143
144	for (uint32_t i = 0; i < rcvd; i++) {
145	const struct xdp_desc *desc = xsk_ring_cons__rx_desc(&xsk_info->rx, idx_rx + i);
146	uint64_t addr = desc->addr;
147	uint32_t len = desc->len;
148	uint8_t pkt = (uint8_t )xsk_umem__get_data(umem_info->buffer, addr);
149	process_packet(pkt, len);
150	}
151	xsk_ring_cons__release(&xsk_info->rx, rcvd);
152
153	// Return frames to fill ring
154	refill_fill_ring(umem_info, rcvd);
155	}
156	```
157
158	### 6. Copy vs zero-copy
159
160	\| Mode \| Flag \| Requirements \|
161	\|------\|------\|--------------\|
162	\| Copy \| `XDP_COPY` (default) \| Any driver; kernel copies to UMEM \|
163	\| Zero-copy \| `XDP_ZEROCOPY` \| Driver support (i40e, ixgbe, mlx5,

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Type

af-xdp

141stars19forks

View on GitHub

How to install af-xdp?

mohitmishra786/low-level-dev-skills/af-xdp

$npx -y skills add mohitmishra786/low-level-dev-skills --skill af-xdp

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# AF_XDP
2
3	## Purpose
4
5	Guide agents through AF_XDP sockets for high-performance packet I/O: socket creation, UMEM setup, fill/completion/RX/TX rings, XDP programs with `XDP_REDIRECT` to XSK, copy vs zero-copy modes, libbpf helpers, performance comparison with DPDK, and production use cases.
6
7	## When to Use
8
9	- Building a userspace packet processor with lower overhead than raw sockets
10	- Redirecting XDP-filtered traffic to userspace without DPDK complexity
11	- Implementing a custom load balancer or IDS dataplane
12	- Comparing zero-copy vs copy mode on your NIC/driver
13	- Integrating with existing libbpf/XDP infrastructure
14	- Need kernel cooperation (firewall rules) plus userspace processing
15
16	## Workflow
17
18	### 1. Architecture overview
19
20	```
21	NIC → XDP program (BPF) → XDP_REDIRECT → AF_XDP socket → userspace
22	↓
23	XDP_DROP/PASS/TX
24	```
25
26	Components:
27	- UMEM — shared memory region for frames
28	- Fill ring — userspace provides empty frame addresses to kernel
29	- Completion ring — kernel returns completed TX frames
30	- RX ring — kernel delivers received packets
31	- TX ring — userspace submits packets for transmission
32
33	### 2. UMEM and XSK socket creation
34
35	```c
36	#include <bpf/xsk.h>
37	#include <bpf/libbpf.h>
38	#include <xdp/xsk.h>
39
40	#define NUM_FRAMES 4096
41	#define FRAME_SIZE XSK_UMEM__DEFAULT_FRAME_SIZE
42	#define RX_BATCH_SIZE 64
43
44	struct xsk_umem_info {
45	struct xsk_ring_prod fill;
46	struct xsk_ring_cons comp;
47	struct xsk_umem *umem;
48	void *buffer;
49	};
50
51	struct xsk_socket_info {
52	struct xsk_ring_cons rx;
53	struct xsk_ring_prod tx;
54	struct xsk_socket *xsk;
55	};
56
57	int xsk_setup(struct xsk_umem_info *umem_info,
58	struct xsk_socket_info *xsk_info,
59	int ifindex, int queue_id, int xsk_flags)
60	{
61	umem_info->buffer = mmap(NULL, NUM_FRAMES * FRAME_SIZE,
62	PROT_READ \| PROT_WRITE, MAP_PRIVATE \| MAP_ANONYMOUS, -1, 0);
63
64	struct xsk_umem_config umem_cfg = {
65	.fill_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
66	.comp_size = XSK_RING_CONS__DEFAULT_NUM_DESCS,
67	.frame_size = FRAME_SIZE,
68	.frame_headroom = XSK_UMEM__DEFAULT_FRAME_HEADROOM,
69	.flags = 0,
70	};
71
72	int ret = xsk_umem__create(&umem_info->umem, umem_info->buffer,
73	NUM_FRAMES * FRAME_SIZE, &umem_info->fill, &umem_info->comp,
74	&umem_cfg);
75	if (ret)
76	return ret;
77
78	struct xsk_socket_config xsk_cfg = {
79	.rx_size = XSK_RING_CONS__DEFAULT_NUM_DESCS,
80	.tx_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
81	.libbpf_flags = XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD,
82	.xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST,
83	.bind_flags = xsk_flags, // XDP_ZEROCOPY or XDP_COPY
84	};
85
86	return xsk_socket__create(&xsk_info->xsk, "eth0", queue_id,
87	umem_info->umem, &xsk_info->rx, &xsk_info->tx, &xsk_cfg);
88	}
89	```
90
91	### 3. Populate fill ring
92
93	```c
94	void populate_fill_ring(struct xsk_umem_info *umem) {
95	uint32_t idx;
96	uint32_t ret = xsk_ring_prod__reserve(&umem->fill, RX_BATCH_SIZE, &idx);
97	for (uint32_t i = 0; i < ret; i++)
98	xsk_ring_prod__fill_addr(&umem->fill, idx + i) = i FRAME_SIZE;
99	xsk_ring_prod__submit(&umem->fill, ret);
100	}
101	```
102
103	Must keep fill ring stocked — kernel drops packets if no buffers available.
104
105	### 4. XDP redirect program
106
107	```c
108	// xdp_redirect.c
109	#include <linux/bpf.h>
110	#include <bpf/bpf_helpers.h>
111
112	struct {
113	__uint(type, BPF_MAP_TYPE_XSKMAP);
114	__uint(max_entries, 64);
115	__type(key, int);
116	__type(value, int);
117	} xsks_map SEC(".maps");
118
119	SEC("xdp")
120	int xdp_redirect_prog(struct xdp_md *ctx)
121	{
122	int index = ctx->rx_queue_index;
123	return bpf_redirect_map(&xsks_map, index, 0);
124	}
125	```
126
127	```bash
128	# Load and attach
129	bpftool prog load xdp_redirect.o /sys/fs/bpf/xdp_redirect
130	ip link set dev eth0 xdp obj xdp_redirect.o sec xdp
131
132	# Pin xsks_map and update with socket fd
133	```
134
135	### 5. RX processing loop
136
137	```c
138	while (running) {
139	uint32_t idx_rx = 0, rcvd;
140	rcvd = xsk_ring_cons__peek(&xsk_info->rx, RX_BATCH_SIZE, &idx_rx);
141	if (!rcvd)
142	continue;
143
144	for (uint32_t i = 0; i < rcvd; i++) {
145	const struct xdp_desc *desc = xsk_ring_cons__rx_desc(&xsk_info->rx, idx_rx + i);
146	uint64_t addr = desc->addr;
147	uint32_t len = desc->len;
148	uint8_t pkt = (uint8_t )xsk_umem__get_data(umem_info->buffer, addr);
149	process_packet(pkt, len);
150	}
151	xsk_ring_cons__release(&xsk_info->rx, rcvd);
152
153	// Return frames to fill ring
154	refill_fill_ring(umem_info, rcvd);
155	}
156	```
157
158	### 6. Copy vs zero-copy
159
160	\| Mode \| Flag \| Requirements \|
161	\|------\|------\|--------------\|
162	\| Copy \| `XDP_COPY` (default) \| Any driver; kernel copies to UMEM \|
163	\| Zero-copy \| `XDP_ZEROCOPY` \| Driver support (i40e, ixgbe, mlx5,

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