1 .. SPDX-License-Identifier: GPL-2.0
2
3 ===========
4 Packet MMAP
5 ===========
6
7 Abstract
8 ========
9
10 This file documents the mmap() facility available with the PACKET
11 socket interface. This type of sockets is used for
12
13 i) capture network traffic with utilities like tcpdump,
14 ii) transmit network traffic, or any other that needs raw
15 access to network interface.
16
17 Howto can be found at:
18
19 https://sites.google.com/site/packetmmap/
20
21 Please send your comments to
22 - Ulisses Alonso Camaró <uaca@i.hate.spam.alumni.uv.es>
23 - Johann Baudy
24
25 Why use PACKET_MMAP
26 ===================
27
28 Non PACKET_MMAP capture process (plain AF_PACKET) is very
29 inefficient. It uses very limited buffers and requires one system call to
30 capture each packet, it requires two if you want to get packet's timestamp
31 (like libpcap always does).
32
33 On the other hand PACKET_MMAP is very efficient. PACKET_MMAP provides a size
34 configurable circular buffer mapped in user space that can be used to either
35 send or receive packets. This way reading packets just needs to wait for them,
36 most of the time there is no need to issue a single system call. Concerning
37 transmission, multiple packets can be sent through one system call to get the
38 highest bandwidth. By using a shared buffer between the kernel and the user
39 also has the benefit of minimizing packet copies.
40
41 It's fine to use PACKET_MMAP to improve the performance of the capture and
42 transmission process, but it isn't everything. At least, if you are capturing
43 at high speeds (this is relative to the cpu speed), you should check if the
44 device driver of your network interface card supports some sort of interrupt
45 load mitigation or (even better) if it supports NAPI, also make sure it is
46 enabled. For transmission, check the MTU (Maximum Transmission Unit) used and
47 supported by devices of your network. CPU IRQ pinning of your network interface
48 card can also be an advantage.
49
50 How to use mmap() to improve capture process
51 ============================================
52
53 From the user standpoint, you should use the higher level libpcap library, which
54 is a de facto standard, portable across nearly all operating systems
55 including Win32.
56
57 Packet MMAP support was integrated into libpcap around the time of version 1.3.0;
58 TPACKET_V3 support was added in version 1.5.0
59
60 How to use mmap() directly to improve capture process
61 =====================================================
62
63 From the system calls stand point, the use of PACKET_MMAP involves
64 the following process::
65
66
67 [setup] socket() -------> creation of the capture socket
68 setsockopt() ---> allocation of the circular buffer (ring)
69 option: PACKET_RX_RING
70 mmap() ---------> mapping of the allocated buffer to the
71 user process
72
73 [capture] poll() ---------> to wait for incoming packets
74
75 [shutdown] close() --------> destruction of the capture socket and
76 deallocation of all associated
77 resources.
78
79
80 socket creation and destruction is straight forward, and is done
81 the same way with or without PACKET_MMAP::
82
83 int fd = socket(PF_PACKET, mode, htons(ETH_P_ALL));
84
85 where mode is SOCK_RAW for the raw interface were link level
86 information can be captured or SOCK_DGRAM for the cooked
87 interface where link level information capture is not
88 supported and a link level pseudo-header is provided
89 by the kernel.
90
91 The destruction of the socket and all associated resources
92 is done by a simple call to close(fd).
93
94 Similarly as without PACKET_MMAP, it is possible to use one socket
95 for capture and transmission. This can be done by mapping the
96 allocated RX and TX buffer ring with a single mmap() call.
97 See "Mapping and use of the circular buffer (ring)".
98
99 Next I will describe PACKET_MMAP settings and its constraints,
100 also the mapping of the circular buffer in the user process and
101 the use of this buffer.
102
103 How to use mmap() directly to improve transmission process
104 ==========================================================
105 Transmission process is similar to capture as shown below::
106
107 [setup] socket() -------> creation of the transmission socket
108 setsockopt() ---> allocation of the circular buffer (ring)
109 option: PACKET_TX_RING
110 bind() ---------> bind transmission socket with a network interface
111 mmap() ---------> mapping of the allocated buffer to the
112 user process
113
114 [transmission] poll() ---------> wait for free packets (optional)
115 send() ---------> send all packets that are set as ready in
116 the ring
117 The flag MSG_DONTWAIT can be used to return
118 before end of transfer.
119
120 [shutdown] close() --------> destruction of the transmission socket and
121 deallocation of all associated resources.
122
123 Socket creation and destruction is also straight forward, and is done
124 the same way as in capturing described in the previous paragraph::
125
126 int fd = socket(PF_PACKET, mode, 0);
127
128 The protocol can optionally be 0 in case we only want to transmit
129 via this socket, which avoids an expensive call to packet_rcv().
130 In this case, you also need to bind(2) the TX_RING with sll_protocol = 0
131 set. Otherwise, htons(ETH_P_ALL) or any other protocol, for example.
132
133 Binding the socket to your network interface is mandatory (with zero copy) to
134 know the header size of frames used in the circular buffer.
135
136 As capture, each frame contains two parts::
137
138 --------------------
139 | struct tpacket_hdr | Header. It contains the status of
140 | | of this frame
141 |--------------------|
142 | data buffer |
143 . . Data that will be sent over the network interface.
144 . .
145 --------------------
146
147 bind() associates the socket to your network interface thanks to
148 sll_ifindex parameter of struct sockaddr_ll.
149
150 Initialization example::
151
152 struct sockaddr_ll my_addr;
153 struct ifreq s_ifr;
154 ...
155
156 strscpy_pad (s_ifr.ifr_name, "eth0", sizeof(s_ifr.ifr_name));
157
158 /* get interface index of eth0 */
159 ioctl(this->socket, SIOCGIFINDEX, &s_ifr);
160
161 /* fill sockaddr_ll struct to prepare binding */
162 my_addr.sll_family = AF_PACKET;
163 my_addr.sll_protocol = htons(ETH_P_ALL);
164 my_addr.sll_ifindex = s_ifr.ifr_ifindex;
165
166 /* bind socket to eth0 */
167 bind(this->socket, (struct sockaddr *)&my_addr, sizeof(struct sockaddr_ll));
168
169 A complete tutorial is available at: https://sites.google.com/site/packetmmap/
170
171 By default, the user should put data at::
172
173 frame base + TPACKET_HDRLEN - sizeof(struct sockaddr_ll)
174
175 So, whatever you choose for the socket mode (SOCK_DGRAM or SOCK_RAW),
176 the beginning of the user data will be at::
177
178 frame base + TPACKET_ALIGN(sizeof(struct tpacket_hdr))
179
180 If you wish to put user data at a custom offset from the beginning of
181 the frame (for payload alignment with SOCK_RAW mode for instance) you
182 can set tp_net (with SOCK_DGRAM) or tp_mac (with SOCK_RAW). In order
183 to make this work it must be enabled previously with setsockopt()
184 and the PACKET_TX_HAS_OFF option.
185
186 PACKET_MMAP settings
187 ====================
188
189 To setup PACKET_MMAP from user level code is done with a call like
190
191 - Capture process::
192
193 setsockopt(fd, SOL_PACKET, PACKET_RX_RING, (void *) &req, sizeof(req))
194
195 - Transmission process::
196
197 setsockopt(fd, SOL_PACKET, PACKET_TX_RING, (void *) &req, sizeof(req))
198
199 The most significant argument in the previous call is the req parameter,
200 this parameter must to have the following structure::
201
202 struct tpacket_req
203 {
204 unsigned int tp_block_size; /* Minimal size of contiguous block */
205 unsigned int tp_block_nr; /* Number of blocks */
206 unsigned int tp_frame_size; /* Size of frame */
207 unsigned int tp_frame_nr; /* Total number of frames */
208 };
209
210 This structure is defined in /usr/include/linux/if_packet.h and establishes a
211 circular buffer (ring) of unswappable memory.
212 Being mapped in the capture process allows reading the captured frames and
213 related meta-information like timestamps without requiring a system call.
214
215 Frames are grouped in blocks. Each block is a physically contiguous
216 region of memory and holds tp_block_size/tp_frame_size frames. The total number
217 of blocks is tp_block_nr. Note that tp_frame_nr is a redundant parameter because::
218
219 frames_per_block = tp_block_size/tp_frame_size
220
221 indeed, packet_set_ring checks that the following condition is true::
222
223 frames_per_block * tp_block_nr == tp_frame_nr
224
225 Lets see an example, with the following values::
226
227 tp_block_size= 4096
228 tp_frame_size= 2048
229 tp_block_nr = 4
230 tp_frame_nr = 8
231
232 we will get the following buffer structure::
233
234 block #1 block #2
235 +---------+---------+ +---------+---------+
236 | frame 1 | frame 2 | | frame 3 | frame 4 |
237 +---------+---------+ +---------+---------+
238
239 block #3 block #4
240 +---------+---------+ +---------+---------+
241 | frame 5 | frame 6 | | frame 7 | frame 8 |
242 +---------+---------+ +---------+---------+
243
244 A frame can be of any size with the only condition it can fit in a block. A block
245 can only hold an integer number of frames, or in other words, a frame cannot
246 be spawned across two blocks, so there are some details you have to take into
247 account when choosing the frame_size. See "Mapping and use of the circular
248 buffer (ring)".
249
250 PACKET_MMAP setting constraints
251 ===============================
252
253 In kernel versions prior to 2.4.26 (for the 2.4 branch) and 2.6.5 (2.6 branch),
254 the PACKET_MMAP buffer could hold only 32768 frames in a 32 bit architecture or
255 16384 in a 64 bit architecture.
256
257 Block size limit
258 ----------------
259
260 As stated earlier, each block is a contiguous physical region of memory. These
261 memory regions are allocated with calls to the __get_free_pages() function. As
262 the name indicates, this function allocates pages of memory, and the second
263 argument is "order" or a power of two number of pages, that is
264 (for PAGE_SIZE == 4096) order=0 ==> 4096 bytes, order=1 ==> 8192 bytes,
265 order=2 ==> 16384 bytes, etc. The maximum size of a
266 region allocated by __get_free_pages is determined by the MAX_PAGE_ORDER macro.
267 More precisely the limit can be calculated as::
268
269 PAGE_SIZE << MAX_PAGE_ORDER
270
271 In a i386 architecture PAGE_SIZE is 4096 bytes
272 In a 2.4/i386 kernel MAX_PAGE_ORDER is 10
273 In a 2.6/i386 kernel MAX_PAGE_ORDER is 11
274
275 So get_free_pages can allocate as much as 4MB or 8MB in a 2.4/2.6 kernel
276 respectively, with an i386 architecture.
277
278 User space programs can include /usr/include/sys/user.h and
279 /usr/include/linux/mmzone.h to get PAGE_SIZE MAX_PAGE_ORDER declarations.
280
281 The pagesize can also be determined dynamically with the getpagesize (2)
282 system call.
283
284 Block number limit
285 ------------------
286
287 To understand the constraints of PACKET_MMAP, we have to see the structure
288 used to hold the pointers to each block.
289
290 Currently, this structure is a dynamically allocated vector with kmalloc
291 called pg_vec, its size limits the number of blocks that can be allocated::
292
293 +---+---+---+---+
294 | x | x | x | x |
295 +---+---+---+---+
296 | | | |
297 | | | v
298 | | v block #4
299 | v block #3
300 v block #2
301 block #1
302
303 kmalloc allocates any number of bytes of physically contiguous memory from
304 a pool of pre-determined sizes. This pool of memory is maintained by the slab
305 allocator which is at the end the responsible for doing the allocation and
306 hence which imposes the maximum memory that kmalloc can allocate.
307
308 In a 2.4/2.6 kernel and the i386 architecture, the limit is 131072 bytes. The
309 predetermined sizes that kmalloc uses can be checked in the "size-<bytes>"
310 entries of /proc/slabinfo
311
312 In a 32 bit architecture, pointers are 4 bytes long, so the total number of
313 pointers to blocks is::
314
315 131072/4 = 32768 blocks
316
317 PACKET_MMAP buffer size calculator
318 ==================================
319
320 Definitions:
321
322 ============== ================================================================
323 <size-max> is the maximum size of allocable with kmalloc
324 (see /proc/slabinfo)
325 <pointer size> depends on the architecture -- ``sizeof(void *)``
326 <page size> depends on the architecture -- PAGE_SIZE or getpagesize (2)
327 <max-order> is the value defined with MAX_PAGE_ORDER
328 <frame size> it's an upper bound of frame's capture size (more on this later)
329 ============== ================================================================
330
331 from these definitions we will derive::
332
333 <block number> = <size-max>/<pointer size>
334 <block size> = <pagesize> << <max-order>
335
336 so, the max buffer size is::
337
338 <block number> * <block size>
339
340 and, the number of frames be::
341
342 <block number> * <block size> / <frame size>
343
344 Suppose the following parameters, which apply for 2.6 kernel and an
345 i386 architecture::
346
347 <size-max> = 131072 bytes
348 <pointer size> = 4 bytes
349 <pagesize> = 4096 bytes
350 <max-order> = 11
351
352 and a value for <frame size> of 2048 bytes. These parameters will yield::
353
354 <block number> = 131072/4 = 32768 blocks
355 <block size> = 4096 << 11 = 8 MiB.
356
357 and hence the buffer will have a 262144 MiB size. So it can hold
358 262144 MiB / 2048 bytes = 134217728 frames
359
360 Actually, this buffer size is not possible with an i386 architecture.
361 Remember that the memory is allocated in kernel space, in the case of
362 an i386 kernel's memory size is limited to 1GiB.
363
364 All memory allocations are not freed until the socket is closed. The memory
365 allocations are done with GFP_KERNEL priority, this basically means that
366 the allocation can wait and swap other process' memory in order to allocate
367 the necessary memory, so normally limits can be reached.
368
369 Other constraints
370 -----------------
371
372 If you check the source code you will see that what I draw here as a frame
373 is not only the link level frame. At the beginning of each frame there is a
374 header called struct tpacket_hdr used in PACKET_MMAP to hold link level's frame
375 meta information like timestamp. So what we draw here a frame it's really
376 the following (from include/linux/if_packet.h)::
377
378 /*
379 Frame structure:
380
381 - Start. Frame must be aligned to TPACKET_ALIGNMENT=16
382 - struct tpacket_hdr
383 - pad to TPACKET_ALIGNMENT=16
384 - struct sockaddr_ll
385 - Gap, chosen so that packet data (Start+tp_net) aligns to
386 TPACKET_ALIGNMENT=16
387 - Start+tp_mac: [ Optional MAC header ]
388 - Start+tp_net: Packet data, aligned to TPACKET_ALIGNMENT=16.
389 - Pad to align to TPACKET_ALIGNMENT=16
390 */
391
392 The following are conditions that are checked in packet_set_ring
393
394 - tp_block_size must be a multiple of PAGE_SIZE (1)
395 - tp_frame_size must be greater than TPACKET_HDRLEN (obvious)
396 - tp_frame_size must be a multiple of TPACKET_ALIGNMENT
397 - tp_frame_nr must be exactly frames_per_block*tp_block_nr
398
399 Note that tp_block_size should be chosen to be a power of two or there will
400 be a waste of memory.
401
402 Mapping and use of the circular buffer (ring)
403 ---------------------------------------------
404
405 The mapping of the buffer in the user process is done with the conventional
406 mmap function. Even the circular buffer is compound of several physically
407 discontiguous blocks of memory, they are contiguous to the user space, hence
408 just one call to mmap is needed::
409
410 mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
411
412 If tp_frame_size is a divisor of tp_block_size frames will be
413 contiguously spaced by tp_frame_size bytes. If not, each
414 tp_block_size/tp_frame_size frames there will be a gap between
415 the frames. This is because a frame cannot be spawn across two
416 blocks.
417
418 To use one socket for capture and transmission, the mapping of both the
419 RX and TX buffer ring has to be done with one call to mmap::
420
421 ...
422 setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &foo, sizeof(foo));
423 setsockopt(fd, SOL_PACKET, PACKET_TX_RING, &bar, sizeof(bar));
424 ...
425 rx_ring = mmap(0, size * 2, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
426 tx_ring = rx_ring + size;
427
428 RX must be the first as the kernel maps the TX ring memory right
429 after the RX one.
430
431 At the beginning of each frame there is an status field (see
432 struct tpacket_hdr). If this field is 0 means that the frame is ready
433 to be used for the kernel, If not, there is a frame the user can read
434 and the following flags apply:
435
436 Capture process
437 ^^^^^^^^^^^^^^^
438
439 From include/linux/if_packet.h::
440
441 #define TP_STATUS_COPY (1 << 1)
442 #define TP_STATUS_LOSING (1 << 2)
443 #define TP_STATUS_CSUMNOTREADY (1 << 3)
444 #define TP_STATUS_CSUM_VALID (1 << 7)
445
446 ====================== =======================================================
447 TP_STATUS_COPY This flag indicates that the frame (and associated
448 meta information) has been truncated because it's
449 larger than tp_frame_size. This packet can be
450 read entirely with recvfrom().
451
452 In order to make this work it must to be
453 enabled previously with setsockopt() and
454 the PACKET_COPY_THRESH option.
455
456 The number of frames that can be buffered to
457 be read with recvfrom is limited like a normal socket.
458 See the SO_RCVBUF option in the socket (7) man page.
459
460 TP_STATUS_LOSING indicates there were packet drops from last time
461 statistics where checked with getsockopt() and
462 the PACKET_STATISTICS option.
463
464 TP_STATUS_CSUMNOTREADY currently it's used for outgoing IP packets which
465 its checksum will be done in hardware. So while
466 reading the packet we should not try to check the
467 checksum.
468
469 TP_STATUS_CSUM_VALID This flag indicates that at least the transport
470 header checksum of the packet has been already
471 validated on the kernel side. If the flag is not set
472 then we are free to check the checksum by ourselves
473 provided that TP_STATUS_CSUMNOTREADY is also not set.
474 ====================== =======================================================
475
476 for convenience there are also the following defines::
477
478 #define TP_STATUS_KERNEL 0
479 #define TP_STATUS_USER 1
480
481 The kernel initializes all frames to TP_STATUS_KERNEL, when the kernel
482 receives a packet it puts in the buffer and updates the status with
483 at least the TP_STATUS_USER flag. Then the user can read the packet,
484 once the packet is read the user must zero the status field, so the kernel
485 can use again that frame buffer.
486
487 The user can use poll (any other variant should apply too) to check if new
488 packets are in the ring::
489
490 struct pollfd pfd;
491
492 pfd.fd = fd;
493 pfd.revents = 0;
494 pfd.events = POLLIN|POLLRDNORM|POLLERR;
495
496 if (status == TP_STATUS_KERNEL)
497 retval = poll(&pfd, 1, timeout);
498
499 It doesn't incur in a race condition to first check the status value and
500 then poll for frames.
501
502 Transmission process
503 ^^^^^^^^^^^^^^^^^^^^
504
505 Those defines are also used for transmission::
506
507 #define TP_STATUS_AVAILABLE 0 // Frame is available
508 #define TP_STATUS_SEND_REQUEST 1 // Frame will be sent on next send()
509 #define TP_STATUS_SENDING 2 // Frame is currently in transmission
510 #define TP_STATUS_WRONG_FORMAT 4 // Frame format is not correct
511
512 First, the kernel initializes all frames to TP_STATUS_AVAILABLE. To send a
513 packet, the user fills a data buffer of an available frame, sets tp_len to
514 current data buffer size and sets its status field to TP_STATUS_SEND_REQUEST.
515 This can be done on multiple frames. Once the user is ready to transmit, it
516 calls send(). Then all buffers with status equal to TP_STATUS_SEND_REQUEST are
517 forwarded to the network device. The kernel updates each status of sent
518 frames with TP_STATUS_SENDING until the end of transfer.
519
520 At the end of each transfer, buffer status returns to TP_STATUS_AVAILABLE.
521
522 ::
523
524 header->tp_len = in_i_size;
525 header->tp_status = TP_STATUS_SEND_REQUEST;
526 retval = send(this->socket, NULL, 0, 0);
527
528 The user can also use poll() to check if a buffer is available:
529
530 (status == TP_STATUS_SENDING)
531
532 ::
533
534 struct pollfd pfd;
535 pfd.fd = fd;
536 pfd.revents = 0;
537 pfd.events = POLLOUT;
538 retval = poll(&pfd, 1, timeout);
539
540 What TPACKET versions are available and when to use them?
541 =========================================================
542
543 ::
544
545 int val = tpacket_version;
546 setsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val));
547 getsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val));
548
549 where 'tpacket_version' can be TPACKET_V1 (default), TPACKET_V2, TPACKET_V3.
550
551 TPACKET_V1:
552 - Default if not otherwise specified by setsockopt(2)
553 - RX_RING, TX_RING available
554
555 TPACKET_V1 --> TPACKET_V2:
556 - Made 64 bit clean due to unsigned long usage in TPACKET_V1
557 structures, thus this also works on 64 bit kernel with 32 bit
558 userspace and the like
559 - Timestamp resolution in nanoseconds instead of microseconds
560 - RX_RING, TX_RING available
561 - VLAN metadata information available for packets
562 (TP_STATUS_VLAN_VALID, TP_STATUS_VLAN_TPID_VALID),
563 in the tpacket2_hdr structure:
564
565 - TP_STATUS_VLAN_VALID bit being set into the tp_status field indicates
566 that the tp_vlan_tci field has valid VLAN TCI value
567 - TP_STATUS_VLAN_TPID_VALID bit being set into the tp_status field
568 indicates that the tp_vlan_tpid field has valid VLAN TPID value
569
570 - How to switch to TPACKET_V2:
571
572 1. Replace struct tpacket_hdr by struct tpacket2_hdr
573 2. Query header len and save
574 3. Set protocol version to 2, set up ring as usual
575 4. For getting the sockaddr_ll,
576 use ``(void *)hdr + TPACKET_ALIGN(hdrlen)`` instead of
577 ``(void *)hdr + TPACKET_ALIGN(sizeof(struct tpacket_hdr))``
578
579 TPACKET_V2 --> TPACKET_V3:
580 - Flexible buffer implementation for RX_RING:
581 1. Blocks can be configured with non-static frame-size
582 2. Read/poll is at a block-level (as opposed to packet-level)
583 3. Added poll timeout to avoid indefinite user-space wait
584 on idle links
585 4. Added user-configurable knobs:
586
587 4.1 block::timeout
588 4.2 tpkt_hdr::sk_rxhash
589
590 - RX Hash data available in user space
591 - TX_RING semantics are conceptually similar to TPACKET_V2;
592 use tpacket3_hdr instead of tpacket2_hdr, and TPACKET3_HDRLEN
593 instead of TPACKET2_HDRLEN. In the current implementation,
594 the tp_next_offset field in the tpacket3_hdr MUST be set to
595 zero, indicating that the ring does not hold variable sized frames.
596 Packets with non-zero values of tp_next_offset will be dropped.
597
598 AF_PACKET fanout mode
599 =====================
600
601 In the AF_PACKET fanout mode, packet reception can be load balanced among
602 processes. This also works in combination with mmap(2) on packet sockets.
603
604 Currently implemented fanout policies are:
605
606 - PACKET_FANOUT_HASH: schedule to socket by skb's packet hash
607 - PACKET_FANOUT_LB: schedule to socket by round-robin
608 - PACKET_FANOUT_CPU: schedule to socket by CPU packet arrives on
609 - PACKET_FANOUT_RND: schedule to socket by random selection
610 - PACKET_FANOUT_ROLLOVER: if one socket is full, rollover to another
611 - PACKET_FANOUT_QM: schedule to socket by skbs recorded queue_mapping
612
613 Minimal example code by David S. Miller (try things like "./test eth0 hash",
614 "./test eth0 lb", etc.)::
615
616 #include <stddef.h>
617 #include <stdlib.h>
618 #include <stdio.h>
619 #include <string.h>
620
621 #include <sys/types.h>
622 #include <sys/wait.h>
623 #include <sys/socket.h>
624 #include <sys/ioctl.h>
625
626 #include <unistd.h>
627
628 #include <linux/if_ether.h>
629 #include <linux/if_packet.h>
630
631 #include <net/if.h>
632
633 static const char *device_name;
634 static int fanout_type;
635 static int fanout_id;
636
637 #ifndef PACKET_FANOUT
638 # define PACKET_FANOUT 18
639 # define PACKET_FANOUT_HASH 0
640 # define PACKET_FANOUT_LB 1
641 #endif
642
643 static int setup_socket(void)
644 {
645 int err, fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP));
646 struct sockaddr_ll ll;
647 struct ifreq ifr;
648 int fanout_arg;
649
650 if (fd < 0) {
651 perror("socket");
652 return EXIT_FAILURE;
653 }
654
655 memset(&ifr, 0, sizeof(ifr));
656 strcpy(ifr.ifr_name, device_name);
657 err = ioctl(fd, SIOCGIFINDEX, &ifr);
658 if (err < 0) {
659 perror("SIOCGIFINDEX");
660 return EXIT_FAILURE;
661 }
662
663 memset(&ll, 0, sizeof(ll));
664 ll.sll_family = AF_PACKET;
665 ll.sll_ifindex = ifr.ifr_ifindex;
666 err = bind(fd, (struct sockaddr *) &ll, sizeof(ll));
667 if (err < 0) {
668 perror("bind");
669 return EXIT_FAILURE;
670 }
671
672 fanout_arg = (fanout_id | (fanout_type << 16));
673 err = setsockopt(fd, SOL_PACKET, PACKET_FANOUT,
674 &fanout_arg, sizeof(fanout_arg));
675 if (err) {
676 perror("setsockopt");
677 return EXIT_FAILURE;
678 }
679
680 return fd;
681 }
682
683 static void fanout_thread(void)
684 {
685 int fd = setup_socket();
686 int limit = 10000;
687
688 if (fd < 0)
689 exit(fd);
690
691 while (limit-- > 0) {
692 char buf[1600];
693 int err;
694
695 err = read(fd, buf, sizeof(buf));
696 if (err < 0) {
697 perror("read");
698 exit(EXIT_FAILURE);
699 }
700 if ((limit % 10) == 0)
701 fprintf(stdout, "(%d) \n", getpid());
702 }
703
704 fprintf(stdout, "%d: Received 10000 packets\n", getpid());
705
706 close(fd);
707 exit(0);
708 }
709
710 int main(int argc, char **argp)
711 {
712 int fd, err;
713 int i;
714
715 if (argc != 3) {
716 fprintf(stderr, "Usage: %s INTERFACE {hash|lb}\n", argp[0]);
717 return EXIT_FAILURE;
718 }
719
720 if (!strcmp(argp[2], "hash"))
721 fanout_type = PACKET_FANOUT_HASH;
722 else if (!strcmp(argp[2], "lb"))
723 fanout_type = PACKET_FANOUT_LB;
724 else {
725 fprintf(stderr, "Unknown fanout type [%s]\n", argp[2]);
726 exit(EXIT_FAILURE);
727 }
728
729 device_name = argp[1];
730 fanout_id = getpid() & 0xffff;
731
732 for (i = 0; i < 4; i++) {
733 pid_t pid = fork();
734
735 switch (pid) {
736 case 0:
737 fanout_thread();
738
739 case -1:
740 perror("fork");
741 exit(EXIT_FAILURE);
742 }
743 }
744
745 for (i = 0; i < 4; i++) {
746 int status;
747
748 wait(&status);
749 }
750
751 return 0;
752 }
753
754 AF_PACKET TPACKET_V3 example
755 ============================
756
757 AF_PACKET's TPACKET_V3 ring buffer can be configured to use non-static frame
758 sizes by doing its own memory management. It is based on blocks where polling
759 works on a per block basis instead of per ring as in TPACKET_V2 and predecessor.
760
761 It is said that TPACKET_V3 brings the following benefits:
762
763 * ~15% - 20% reduction in CPU-usage
764 * ~20% increase in packet capture rate
765 * ~2x increase in packet density
766 * Port aggregation analysis
767 * Non static frame size to capture entire packet payload
768
769 So it seems to be a good candidate to be used with packet fanout.
770
771 Minimal example code by Daniel Borkmann based on Chetan Loke's lolpcap (compile
772 it with gcc -Wall -O2 blob.c, and try things like "./a.out eth0", etc.)::
773
774 /* Written from scratch, but kernel-to-user space API usage
775 * dissected from lolpcap:
776 * Copyright 2011, Chetan Loke <loke.chetan@gmail.com>
777 * License: GPL, version 2.0
778 */
779
780 #include <stdio.h>
781 #include <stdlib.h>
782 #include <stdint.h>
783 #include <string.h>
784 #include <assert.h>
785 #include <net/if.h>
786 #include <arpa/inet.h>
787 #include <netdb.h>
788 #include <poll.h>
789 #include <unistd.h>
790 #include <signal.h>
791 #include <inttypes.h>
792 #include <sys/socket.h>
793 #include <sys/mman.h>
794 #include <linux/if_packet.h>
795 #include <linux/if_ether.h>
796 #include <linux/ip.h>
797
798 #ifndef likely
799 # define likely(x) __builtin_expect(!!(x), 1)
800 #endif
801 #ifndef unlikely
802 # define unlikely(x) __builtin_expect(!!(x), 0)
803 #endif
804
805 struct block_desc {
806 uint32_t version;
807 uint32_t offset_to_priv;
808 struct tpacket_hdr_v1 h1;
809 };
810
811 struct ring {
812 struct iovec *rd;
813 uint8_t *map;
814 struct tpacket_req3 req;
815 };
816
817 static unsigned long packets_total = 0, bytes_total = 0;
818 static sig_atomic_t sigint = 0;
819
820 static void sighandler(int num)
821 {
822 sigint = 1;
823 }
824
825 static int setup_socket(struct ring *ring, char *netdev)
826 {
827 int err, i, fd, v = TPACKET_V3;
828 struct sockaddr_ll ll;
829 unsigned int blocksiz = 1 << 22, framesiz = 1 << 11;
830 unsigned int blocknum = 64;
831
832 fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
833 if (fd < 0) {
834 perror("socket");
835 exit(1);
836 }
837
838 err = setsockopt(fd, SOL_PACKET, PACKET_VERSION, &v, sizeof(v));
839 if (err < 0) {
840 perror("setsockopt");
841 exit(1);
842 }
843
844 memset(&ring->req, 0, sizeof(ring->req));
845 ring->req.tp_block_size = blocksiz;
846 ring->req.tp_frame_size = framesiz;
847 ring->req.tp_block_nr = blocknum;
848 ring->req.tp_frame_nr = (blocksiz * blocknum) / framesiz;
849 ring->req.tp_retire_blk_tov = 60;
850 ring->req.tp_feature_req_word = TP_FT_REQ_FILL_RXHASH;
851
852 err = setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &ring->req,
853 sizeof(ring->req));
854 if (err < 0) {
855 perror("setsockopt");
856 exit(1);
857 }
858
859 ring->map = mmap(NULL, ring->req.tp_block_size * ring->req.tp_block_nr,
860 PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0);
861 if (ring->map == MAP_FAILED) {
862 perror("mmap");
863 exit(1);
864 }
865
866 ring->rd = malloc(ring->req.tp_block_nr * sizeof(*ring->rd));
867 assert(ring->rd);
868 for (i = 0; i < ring->req.tp_block_nr; ++i) {
869 ring->rd[i].iov_base = ring->map + (i * ring->req.tp_block_size);
870 ring->rd[i].iov_len = ring->req.tp_block_size;
871 }
872
873 memset(&ll, 0, sizeof(ll));
874 ll.sll_family = PF_PACKET;
875 ll.sll_protocol = htons(ETH_P_ALL);
876 ll.sll_ifindex = if_nametoindex(netdev);
877 ll.sll_hatype = 0;
878 ll.sll_pkttype = 0;
879 ll.sll_halen = 0;
880
881 err = bind(fd, (struct sockaddr *) &ll, sizeof(ll));
882 if (err < 0) {
883 perror("bind");
884 exit(1);
885 }
886
887 return fd;
888 }
889
890 static void display(struct tpacket3_hdr *ppd)
891 {
892 struct ethhdr *eth = (struct ethhdr *) ((uint8_t *) ppd + ppd->tp_mac);
893 struct iphdr *ip = (struct iphdr *) ((uint8_t *) eth + ETH_HLEN);
894
895 if (eth->h_proto == htons(ETH_P_IP)) {
896 struct sockaddr_in ss, sd;
897 char sbuff[NI_MAXHOST], dbuff[NI_MAXHOST];
898
899 memset(&ss, 0, sizeof(ss));
900 ss.sin_family = PF_INET;
901 ss.sin_addr.s_addr = ip->saddr;
902 getnameinfo((struct sockaddr *) &ss, sizeof(ss),
903 sbuff, sizeof(sbuff), NULL, 0, NI_NUMERICHOST);
904
905 memset(&sd, 0, sizeof(sd));
906 sd.sin_family = PF_INET;
907 sd.sin_addr.s_addr = ip->daddr;
908 getnameinfo((struct sockaddr *) &sd, sizeof(sd),
909 dbuff, sizeof(dbuff), NULL, 0, NI_NUMERICHOST);
910
911 printf("%s -> %s, ", sbuff, dbuff);
912 }
913
914 printf("rxhash: 0x%x\n", ppd->hv1.tp_rxhash);
915 }
916
917 static void walk_block(struct block_desc *pbd, const int block_num)
918 {
919 int num_pkts = pbd->h1.num_pkts, i;
920 unsigned long bytes = 0;
921 struct tpacket3_hdr *ppd;
922
923 ppd = (struct tpacket3_hdr *) ((uint8_t *) pbd +
924 pbd->h1.offset_to_first_pkt);
925 for (i = 0; i < num_pkts; ++i) {
926 bytes += ppd->tp_snaplen;
927 display(ppd);
928
929 ppd = (struct tpacket3_hdr *) ((uint8_t *) ppd +
930 ppd->tp_next_offset);
931 }
932
933 packets_total += num_pkts;
934 bytes_total += bytes;
935 }
936
937 static void flush_block(struct block_desc *pbd)
938 {
939 pbd->h1.block_status = TP_STATUS_KERNEL;
940 }
941
942 static void teardown_socket(struct ring *ring, int fd)
943 {
944 munmap(ring->map, ring->req.tp_block_size * ring->req.tp_block_nr);
945 free(ring->rd);
946 close(fd);
947 }
948
949 int main(int argc, char **argp)
950 {
951 int fd, err;
952 socklen_t len;
953 struct ring ring;
954 struct pollfd pfd;
955 unsigned int block_num = 0, blocks = 64;
956 struct block_desc *pbd;
957 struct tpacket_stats_v3 stats;
958
959 if (argc != 2) {
960 fprintf(stderr, "Usage: %s INTERFACE\n", argp[0]);
961 return EXIT_FAILURE;
962 }
963
964 signal(SIGINT, sighandler);
965
966 memset(&ring, 0, sizeof(ring));
967 fd = setup_socket(&ring, argp[argc - 1]);
968 assert(fd > 0);
969
970 memset(&pfd, 0, sizeof(pfd));
971 pfd.fd = fd;
972 pfd.events = POLLIN | POLLERR;
973 pfd.revents = 0;
974
975 while (likely(!sigint)) {
976 pbd = (struct block_desc *) ring.rd[block_num].iov_base;
977
978 if ((pbd->h1.block_status & TP_STATUS_USER) == 0) {
979 poll(&pfd, 1, -1);
980 continue;
981 }
982
983 walk_block(pbd, block_num);
984 flush_block(pbd);
985 block_num = (block_num + 1) % blocks;
986 }
987
988 len = sizeof(stats);
989 err = getsockopt(fd, SOL_PACKET, PACKET_STATISTICS, &stats, &len);
990 if (err < 0) {
991 perror("getsockopt");
992 exit(1);
993 }
994
995 fflush(stdout);
996 printf("\nReceived %u packets, %lu bytes, %u dropped, freeze_q_cnt: %u\n",
997 stats.tp_packets, bytes_total, stats.tp_drops,
998 stats.tp_freeze_q_cnt);
999
1000 teardown_socket(&ring, fd);
1001 return 0;
1002 }
1003
1004 PACKET_QDISC_BYPASS
1005 ===================
1006
1007 If there is a requirement to load the network with many packets in a similar
1008 fashion as pktgen does, you might set the following option after socket
1009 creation::
1010
1011 int one = 1;
1012 setsockopt(fd, SOL_PACKET, PACKET_QDISC_BYPASS, &one, sizeof(one));
1013
1014 This has the side-effect, that packets sent through PF_PACKET will bypass the
1015 kernel's qdisc layer and are forcedly pushed to the driver directly. Meaning,
1016 packet are not buffered, tc disciplines are ignored, increased loss can occur
1017 and such packets are also not visible to other PF_PACKET sockets anymore. So,
1018 you have been warned; generally, this can be useful for stress testing various
1019 components of a system.
1020
1021 On default, PACKET_QDISC_BYPASS is disabled and needs to be explicitly enabled
1022 on PF_PACKET sockets.
1023
1024 PACKET_TIMESTAMP
1025 ================
1026
1027 The PACKET_TIMESTAMP setting determines the source of the timestamp in
1028 the packet meta information for mmap(2)ed RX_RING and TX_RINGs. If your
1029 NIC is capable of timestamping packets in hardware, you can request those
1030 hardware timestamps to be used. Note: you may need to enable the generation
1031 of hardware timestamps with SIOCSHWTSTAMP (see related information from
1032 Documentation/networking/timestamping.rst).
1033
1034 PACKET_TIMESTAMP accepts the same integer bit field as SO_TIMESTAMPING::
1035
1036 int req = SOF_TIMESTAMPING_RAW_HARDWARE;
1037 setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req))
1038
1039 For the mmap(2)ed ring buffers, such timestamps are stored in the
1040 ``tpacket{,2,3}_hdr`` structure's tp_sec and ``tp_{n,u}sec`` members.
1041 To determine what kind of timestamp has been reported, the tp_status field
1042 is binary or'ed with the following possible bits ...
1043
1044 ::
1045
1046 TP_STATUS_TS_RAW_HARDWARE
1047 TP_STATUS_TS_SOFTWARE
1048
1049 ... that are equivalent to its ``SOF_TIMESTAMPING_*`` counterparts. For the
1050 RX_RING, if neither is set (i.e. PACKET_TIMESTAMP is not set), then a
1051 software fallback was invoked *within* PF_PACKET's processing code (less
1052 precise).
1053
1054 Getting timestamps for the TX_RING works as follows: i) fill the ring frames,
1055 ii) call sendto() e.g. in blocking mode, iii) wait for status of relevant
1056 frames to be updated resp. the frame handed over to the application, iv) walk
1057 through the frames to pick up the individual hw/sw timestamps.
1058
1059 Only (!) if transmit timestamping is enabled, then these bits are combined
1060 with binary | with TP_STATUS_AVAILABLE, so you must check for that in your
1061 application (e.g. !(tp_status & (TP_STATUS_SEND_REQUEST | TP_STATUS_SENDING))
1062 in a first step to see if the frame belongs to the application, and then
1063 one can extract the type of timestamp in a second step from tp_status)!
1064
1065 If you don't care about them, thus having it disabled, checking for
1066 TP_STATUS_AVAILABLE resp. TP_STATUS_WRONG_FORMAT is sufficient. If in the
1067 TX_RING part only TP_STATUS_AVAILABLE is set, then the tp_sec and tp_{n,u}sec
1068 members do not contain a valid value. For TX_RINGs, by default no timestamp
1069 is generated!
1070
1071 See include/linux/net_tstamp.h and Documentation/networking/timestamping.rst
1072 for more information on hardware timestamps.
1073
1074 Miscellaneous bits
1075 ==================
1076
1077 - Packet sockets work well together with Linux socket filters, thus you also
1078 might want to have a look at Documentation/networking/filter.rst
1079
1080 THANKS
1081 ======
1082
1083 Jesse Brandeburg, for fixing my grammathical/spelling errors
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.