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1--------------------------------------------------------------------------------
2+ ABSTRACT
3--------------------------------------------------------------------------------
4
5This file documents the mmap() facility available with the PACKET
6socket interface on 2.4/2.6/3.x kernels. This type of sockets is used for
7i) capture network traffic with utilities like tcpdump, ii) transmit network
8traffic, or any other that needs raw access to network interface.
9
10Howto can be found at:
11 https://sites.google.com/site/packetmmap/
12
13Please send your comments to
14 Ulisses Alonso Camaró <uaca@i.hate.spam.alumni.uv.es>
15 Johann Baudy
16
17-------------------------------------------------------------------------------
18+ Why use PACKET_MMAP
19--------------------------------------------------------------------------------
20
21In Linux 2.4/2.6/3.x if PACKET_MMAP is not enabled, the capture process is very
22inefficient. It uses very limited buffers and requires one system call to
23capture each packet, it requires two if you want to get packet's timestamp
24(like libpcap always does).
25
26In the other hand PACKET_MMAP is very efficient. PACKET_MMAP provides a size
27configurable circular buffer mapped in user space that can be used to either
28send or receive packets. This way reading packets just needs to wait for them,
29most of the time there is no need to issue a single system call. Concerning
30transmission, multiple packets can be sent through one system call to get the
31highest bandwidth. By using a shared buffer between the kernel and the user
32also has the benefit of minimizing packet copies.
33
34It's fine to use PACKET_MMAP to improve the performance of the capture and
35transmission process, but it isn't everything. At least, if you are capturing
36at high speeds (this is relative to the cpu speed), you should check if the
37device driver of your network interface card supports some sort of interrupt
38load mitigation or (even better) if it supports NAPI, also make sure it is
39enabled. For transmission, check the MTU (Maximum Transmission Unit) used and
40supported by devices of your network. CPU IRQ pinning of your network interface
41card can also be an advantage.
42
43--------------------------------------------------------------------------------
44+ How to use mmap() to improve capture process
45--------------------------------------------------------------------------------
46
47From the user standpoint, you should use the higher level libpcap library, which
48is a de facto standard, portable across nearly all operating systems
49including Win32.
50
51Packet MMAP support was integrated into libpcap around the time of version 1.3.0;
52TPACKET_V3 support was added in version 1.5.0
53
54--------------------------------------------------------------------------------
55+ How to use mmap() directly to improve capture process
56--------------------------------------------------------------------------------
57
58From the system calls stand point, the use of PACKET_MMAP involves
59the following process:
60
61
62[setup] socket() -------> creation of the capture socket
63 setsockopt() ---> allocation of the circular buffer (ring)
64 option: PACKET_RX_RING
65 mmap() ---------> mapping of the allocated buffer to the
66 user process
67
68[capture] poll() ---------> to wait for incoming packets
69
70[shutdown] close() --------> destruction of the capture socket and
71 deallocation of all associated
72 resources.
73
74
75socket creation and destruction is straight forward, and is done
76the same way with or without PACKET_MMAP:
77
78 int fd = socket(PF_PACKET, mode, htons(ETH_P_ALL));
79
80where mode is SOCK_RAW for the raw interface were link level
81information can be captured or SOCK_DGRAM for the cooked
82interface where link level information capture is not
83supported and a link level pseudo-header is provided
84by the kernel.
85
86The destruction of the socket and all associated resources
87is done by a simple call to close(fd).
88
89Similarly as without PACKET_MMAP, it is possible to use one socket
90for capture and transmission. This can be done by mapping the
91allocated RX and TX buffer ring with a single mmap() call.
92See "Mapping and use of the circular buffer (ring)".
93
94Next I will describe PACKET_MMAP settings and its constraints,
95also the mapping of the circular buffer in the user process and
96the use of this buffer.
97
98--------------------------------------------------------------------------------
99+ How to use mmap() directly to improve transmission process
100--------------------------------------------------------------------------------
101Transmission process is similar to capture as shown below.
102
103[setup] socket() -------> creation of the transmission socket
104 setsockopt() ---> allocation of the circular buffer (ring)
105 option: PACKET_TX_RING
106 bind() ---------> bind transmission socket with a network interface
107 mmap() ---------> mapping of the allocated buffer to the
108 user process
109
110[transmission] poll() ---------> wait for free packets (optional)
111 send() ---------> send all packets that are set as ready in
112 the ring
113 The flag MSG_DONTWAIT can be used to return
114 before end of transfer.
115
116[shutdown] close() --------> destruction of the transmission socket and
117 deallocation of all associated resources.
118
119Socket creation and destruction is also straight forward, and is done
120the same way as in capturing described in the previous paragraph:
121
122 int fd = socket(PF_PACKET, mode, 0);
123
124The protocol can optionally be 0 in case we only want to transmit
125via this socket, which avoids an expensive call to packet_rcv().
126In this case, you also need to bind(2) the TX_RING with sll_protocol = 0
127set. Otherwise, htons(ETH_P_ALL) or any other protocol, for example.
128
129Binding the socket to your network interface is mandatory (with zero copy) to
130know the header size of frames used in the circular buffer.
131
132As capture, each frame contains two parts:
133
134 --------------------
135| struct tpacket_hdr | Header. It contains the status of
136| | of this frame
137|--------------------|
138| data buffer |
139. . Data that will be sent over the network interface.
140. .
141 --------------------
142
143 bind() associates the socket to your network interface thanks to
144 sll_ifindex parameter of struct sockaddr_ll.
145
146 Initialization example:
147
148 struct sockaddr_ll my_addr;
149 struct ifreq s_ifr;
150 ...
151
152 strncpy (s_ifr.ifr_name, "eth0", sizeof(s_ifr.ifr_name));
153
154 /* get interface index of eth0 */
155 ioctl(this->socket, SIOCGIFINDEX, &s_ifr);
156
157 /* fill sockaddr_ll struct to prepare binding */
158 my_addr.sll_family = AF_PACKET;
159 my_addr.sll_protocol = htons(ETH_P_ALL);
160 my_addr.sll_ifindex = s_ifr.ifr_ifindex;
161
162 /* bind socket to eth0 */
163 bind(this->socket, (struct sockaddr *)&my_addr, sizeof(struct sockaddr_ll));
164
165 A complete tutorial is available at: https://sites.google.com/site/packetmmap/
166
167By default, the user should put data at :
168 frame base + TPACKET_HDRLEN - sizeof(struct sockaddr_ll)
169
170So, whatever you choose for the socket mode (SOCK_DGRAM or SOCK_RAW),
171the beginning of the user data will be at :
172 frame base + TPACKET_ALIGN(sizeof(struct tpacket_hdr))
173
174If you wish to put user data at a custom offset from the beginning of
175the frame (for payload alignment with SOCK_RAW mode for instance) you
176can set tp_net (with SOCK_DGRAM) or tp_mac (with SOCK_RAW). In order
177to make this work it must be enabled previously with setsockopt()
178and the PACKET_TX_HAS_OFF option.
179
180--------------------------------------------------------------------------------
181+ PACKET_MMAP settings
182--------------------------------------------------------------------------------
183
184To setup PACKET_MMAP from user level code is done with a call like
185
186 - Capture process
187 setsockopt(fd, SOL_PACKET, PACKET_RX_RING, (void *) &req, sizeof(req))
188 - Transmission process
189 setsockopt(fd, SOL_PACKET, PACKET_TX_RING, (void *) &req, sizeof(req))
190
191The most significant argument in the previous call is the req parameter,
192this parameter must to have the following structure:
193
194 struct tpacket_req
195 {
196 unsigned int tp_block_size; /* Minimal size of contiguous block */
197 unsigned int tp_block_nr; /* Number of blocks */
198 unsigned int tp_frame_size; /* Size of frame */
199 unsigned int tp_frame_nr; /* Total number of frames */
200 };
201
202This structure is defined in /usr/include/linux/if_packet.h and establishes a
203circular buffer (ring) of unswappable memory.
204Being mapped in the capture process allows reading the captured frames and
205related meta-information like timestamps without requiring a system call.
206
207Frames are grouped in blocks. Each block is a physically contiguous
208region of memory and holds tp_block_size/tp_frame_size frames. The total number
209of blocks is tp_block_nr. Note that tp_frame_nr is a redundant parameter because
210
211 frames_per_block = tp_block_size/tp_frame_size
212
213indeed, packet_set_ring checks that the following condition is true
214
215 frames_per_block * tp_block_nr == tp_frame_nr
216
217Lets see an example, with the following values:
218
219 tp_block_size= 4096
220 tp_frame_size= 2048
221 tp_block_nr = 4
222 tp_frame_nr = 8
223
224we will get the following buffer structure:
225
226 block #1 block #2
227+---------+---------+ +---------+---------+
228| frame 1 | frame 2 | | frame 3 | frame 4 |
229+---------+---------+ +---------+---------+
230
231 block #3 block #4
232+---------+---------+ +---------+---------+
233| frame 5 | frame 6 | | frame 7 | frame 8 |
234+---------+---------+ +---------+---------+
235
236A frame can be of any size with the only condition it can fit in a block. A block
237can only hold an integer number of frames, or in other words, a frame cannot
238be spawned across two blocks, so there are some details you have to take into
239account when choosing the frame_size. See "Mapping and use of the circular
240buffer (ring)".
241
242--------------------------------------------------------------------------------
243+ PACKET_MMAP setting constraints
244--------------------------------------------------------------------------------
245
246In kernel versions prior to 2.4.26 (for the 2.4 branch) and 2.6.5 (2.6 branch),
247the PACKET_MMAP buffer could hold only 32768 frames in a 32 bit architecture or
24816384 in a 64 bit architecture. For information on these kernel versions
249see http://pusa.uv.es/~ulisses/packet_mmap/packet_mmap.pre-2.4.26_2.6.5.txt
250
251 Block size limit
252------------------
253
254As stated earlier, each block is a contiguous physical region of memory. These
255memory regions are allocated with calls to the __get_free_pages() function. As
256the name indicates, this function allocates pages of memory, and the second
257argument is "order" or a power of two number of pages, that is
258(for PAGE_SIZE == 4096) order=0 ==> 4096 bytes, order=1 ==> 8192 bytes,
259order=2 ==> 16384 bytes, etc. The maximum size of a
260region allocated by __get_free_pages is determined by the MAX_ORDER macro. More
261precisely the limit can be calculated as:
262
263 PAGE_SIZE << MAX_ORDER
264
265 In a i386 architecture PAGE_SIZE is 4096 bytes
266 In a 2.4/i386 kernel MAX_ORDER is 10
267 In a 2.6/i386 kernel MAX_ORDER is 11
268
269So get_free_pages can allocate as much as 4MB or 8MB in a 2.4/2.6 kernel
270respectively, with an i386 architecture.
271
272User space programs can include /usr/include/sys/user.h and
273/usr/include/linux/mmzone.h to get PAGE_SIZE MAX_ORDER declarations.
274
275The pagesize can also be determined dynamically with the getpagesize (2)
276system call.
277
278 Block number limit
279--------------------
280
281To understand the constraints of PACKET_MMAP, we have to see the structure
282used to hold the pointers to each block.
283
284Currently, this structure is a dynamically allocated vector with kmalloc
285called pg_vec, its size limits the number of blocks that can be allocated.
286
287 +---+---+---+---+
288 | x | x | x | x |
289 +---+---+---+---+
290 | | | |
291 | | | v
292 | | v block #4
293 | v block #3
294 v block #2
295 block #1
296
297kmalloc allocates any number of bytes of physically contiguous memory from
298a pool of pre-determined sizes. This pool of memory is maintained by the slab
299allocator which is at the end the responsible for doing the allocation and
300hence which imposes the maximum memory that kmalloc can allocate.
301
302In a 2.4/2.6 kernel and the i386 architecture, the limit is 131072 bytes. The
303predetermined sizes that kmalloc uses can be checked in the "size-<bytes>"
304entries of /proc/slabinfo
305
306In a 32 bit architecture, pointers are 4 bytes long, so the total number of
307pointers to blocks is
308
309 131072/4 = 32768 blocks
310
311 PACKET_MMAP buffer size calculator
312------------------------------------
313
314Definitions:
315
316<size-max> : is the maximum size of allocable with kmalloc (see /proc/slabinfo)
317<pointer size>: depends on the architecture -- sizeof(void *)
318<page size> : depends on the architecture -- PAGE_SIZE or getpagesize (2)
319<max-order> : is the value defined with MAX_ORDER
320<frame size> : it's an upper bound of frame's capture size (more on this later)
321
322from these definitions we will derive
323
324 <block number> = <size-max>/<pointer size>
325 <block size> = <pagesize> << <max-order>
326
327so, the max buffer size is
328
329 <block number> * <block size>
330
331and, the number of frames be
332
333 <block number> * <block size> / <frame size>
334
335Suppose the following parameters, which apply for 2.6 kernel and an
336i386 architecture:
337
338 <size-max> = 131072 bytes
339 <pointer size> = 4 bytes
340 <pagesize> = 4096 bytes
341 <max-order> = 11
342
343and a value for <frame size> of 2048 bytes. These parameters will yield
344
345 <block number> = 131072/4 = 32768 blocks
346 <block size> = 4096 << 11 = 8 MiB.
347
348and hence the buffer will have a 262144 MiB size. So it can hold
349262144 MiB / 2048 bytes = 134217728 frames
350
351Actually, this buffer size is not possible with an i386 architecture.
352Remember that the memory is allocated in kernel space, in the case of
353an i386 kernel's memory size is limited to 1GiB.
354
355All memory allocations are not freed until the socket is closed. The memory
356allocations are done with GFP_KERNEL priority, this basically means that
357the allocation can wait and swap other process' memory in order to allocate
358the necessary memory, so normally limits can be reached.
359
360 Other constraints
361-------------------
362
363If you check the source code you will see that what I draw here as a frame
364is not only the link level frame. At the beginning of each frame there is a
365header called struct tpacket_hdr used in PACKET_MMAP to hold link level's frame
366meta information like timestamp. So what we draw here a frame it's really
367the following (from include/linux/if_packet.h):
368
369/*
370 Frame structure:
371
372 - Start. Frame must be aligned to TPACKET_ALIGNMENT=16
373 - struct tpacket_hdr
374 - pad to TPACKET_ALIGNMENT=16
375 - struct sockaddr_ll
376 - Gap, chosen so that packet data (Start+tp_net) aligns to
377 TPACKET_ALIGNMENT=16
378 - Start+tp_mac: [ Optional MAC header ]
379 - Start+tp_net: Packet data, aligned to TPACKET_ALIGNMENT=16.
380 - Pad to align to TPACKET_ALIGNMENT=16
381 */
382
383 The following are conditions that are checked in packet_set_ring
384
385 tp_block_size must be a multiple of PAGE_SIZE (1)
386 tp_frame_size must be greater than TPACKET_HDRLEN (obvious)
387 tp_frame_size must be a multiple of TPACKET_ALIGNMENT
388 tp_frame_nr must be exactly frames_per_block*tp_block_nr
389
390Note that tp_block_size should be chosen to be a power of two or there will
391be a waste of memory.
392
393--------------------------------------------------------------------------------
394+ Mapping and use of the circular buffer (ring)
395--------------------------------------------------------------------------------
396
397The mapping of the buffer in the user process is done with the conventional
398mmap function. Even the circular buffer is compound of several physically
399discontiguous blocks of memory, they are contiguous to the user space, hence
400just one call to mmap is needed:
401
402 mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
403
404If tp_frame_size is a divisor of tp_block_size frames will be
405contiguously spaced by tp_frame_size bytes. If not, each
406tp_block_size/tp_frame_size frames there will be a gap between
407the frames. This is because a frame cannot be spawn across two
408blocks.
409
410To use one socket for capture and transmission, the mapping of both the
411RX and TX buffer ring has to be done with one call to mmap:
412
413 ...
414 setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &foo, sizeof(foo));
415 setsockopt(fd, SOL_PACKET, PACKET_TX_RING, &bar, sizeof(bar));
416 ...
417 rx_ring = mmap(0, size * 2, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
418 tx_ring = rx_ring + size;
419
420RX must be the first as the kernel maps the TX ring memory right
421after the RX one.
422
423At the beginning of each frame there is an status field (see
424struct tpacket_hdr). If this field is 0 means that the frame is ready
425to be used for the kernel, If not, there is a frame the user can read
426and the following flags apply:
427
428+++ Capture process:
429 from include/linux/if_packet.h
430
431 #define TP_STATUS_COPY (1 << 1)
432 #define TP_STATUS_LOSING (1 << 2)
433 #define TP_STATUS_CSUMNOTREADY (1 << 3)
434 #define TP_STATUS_CSUM_VALID (1 << 7)
435
436TP_STATUS_COPY : This flag indicates that the frame (and associated
437 meta information) has been truncated because it's
438 larger than tp_frame_size. This packet can be
439 read entirely with recvfrom().
440
441 In order to make this work it must to be
442 enabled previously with setsockopt() and
443 the PACKET_COPY_THRESH option.
444
445 The number of frames that can be buffered to
446 be read with recvfrom is limited like a normal socket.
447 See the SO_RCVBUF option in the socket (7) man page.
448
449TP_STATUS_LOSING : indicates there were packet drops from last time
450 statistics where checked with getsockopt() and
451 the PACKET_STATISTICS option.
452
453TP_STATUS_CSUMNOTREADY: currently it's used for outgoing IP packets which
454 its checksum will be done in hardware. So while
455 reading the packet we should not try to check the
456 checksum.
457
458TP_STATUS_CSUM_VALID : This flag indicates that at least the transport
459 header checksum of the packet has been already
460 validated on the kernel side. If the flag is not set
461 then we are free to check the checksum by ourselves
462 provided that TP_STATUS_CSUMNOTREADY is also not set.
463
464for convenience there are also the following defines:
465
466 #define TP_STATUS_KERNEL 0
467 #define TP_STATUS_USER 1
468
469The kernel initializes all frames to TP_STATUS_KERNEL, when the kernel
470receives a packet it puts in the buffer and updates the status with
471at least the TP_STATUS_USER flag. Then the user can read the packet,
472once the packet is read the user must zero the status field, so the kernel
473can use again that frame buffer.
474
475The user can use poll (any other variant should apply too) to check if new
476packets are in the ring:
477
478 struct pollfd pfd;
479
480 pfd.fd = fd;
481 pfd.revents = 0;
482 pfd.events = POLLIN|POLLRDNORM|POLLERR;
483
484 if (status == TP_STATUS_KERNEL)
485 retval = poll(&pfd, 1, timeout);
486
487It doesn't incur in a race condition to first check the status value and
488then poll for frames.
489
490++ Transmission process
491Those defines are also used for transmission:
492
493 #define TP_STATUS_AVAILABLE 0 // Frame is available
494 #define TP_STATUS_SEND_REQUEST 1 // Frame will be sent on next send()
495 #define TP_STATUS_SENDING 2 // Frame is currently in transmission
496 #define TP_STATUS_WRONG_FORMAT 4 // Frame format is not correct
497
498First, the kernel initializes all frames to TP_STATUS_AVAILABLE. To send a
499packet, the user fills a data buffer of an available frame, sets tp_len to
500current data buffer size and sets its status field to TP_STATUS_SEND_REQUEST.
501This can be done on multiple frames. Once the user is ready to transmit, it
502calls send(). Then all buffers with status equal to TP_STATUS_SEND_REQUEST are
503forwarded to the network device. The kernel updates each status of sent
504frames with TP_STATUS_SENDING until the end of transfer.
505At the end of each transfer, buffer status returns to TP_STATUS_AVAILABLE.
506
507 header->tp_len = in_i_size;
508 header->tp_status = TP_STATUS_SEND_REQUEST;
509 retval = send(this->socket, NULL, 0, 0);
510
511The user can also use poll() to check if a buffer is available:
512(status == TP_STATUS_SENDING)
513
514 struct pollfd pfd;
515 pfd.fd = fd;
516 pfd.revents = 0;
517 pfd.events = POLLOUT;
518 retval = poll(&pfd, 1, timeout);
519
520-------------------------------------------------------------------------------
521+ What TPACKET versions are available and when to use them?
522-------------------------------------------------------------------------------
523
524 int val = tpacket_version;
525 setsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val));
526 getsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val));
527
528where 'tpacket_version' can be TPACKET_V1 (default), TPACKET_V2, TPACKET_V3.
529
530TPACKET_V1:
531 - Default if not otherwise specified by setsockopt(2)
532 - RX_RING, TX_RING available
533
534TPACKET_V1 --> TPACKET_V2:
535 - Made 64 bit clean due to unsigned long usage in TPACKET_V1
536 structures, thus this also works on 64 bit kernel with 32 bit
537 userspace and the like
538 - Timestamp resolution in nanoseconds instead of microseconds
539 - RX_RING, TX_RING available
540 - VLAN metadata information available for packets
541 (TP_STATUS_VLAN_VALID, TP_STATUS_VLAN_TPID_VALID),
542 in the tpacket2_hdr structure:
543 - TP_STATUS_VLAN_VALID bit being set into the tp_status field indicates
544 that the tp_vlan_tci field has valid VLAN TCI value
545 - TP_STATUS_VLAN_TPID_VALID bit being set into the tp_status field
546 indicates that the tp_vlan_tpid field has valid VLAN TPID value
547 - How to switch to TPACKET_V2:
548 1. Replace struct tpacket_hdr by struct tpacket2_hdr
549 2. Query header len and save
550 3. Set protocol version to 2, set up ring as usual
551 4. For getting the sockaddr_ll,
552 use (void *)hdr + TPACKET_ALIGN(hdrlen) instead of
553 (void *)hdr + TPACKET_ALIGN(sizeof(struct tpacket_hdr))
554
555TPACKET_V2 --> TPACKET_V3:
556 - Flexible buffer implementation for RX_RING:
557 1. Blocks can be configured with non-static frame-size
558 2. Read/poll is at a block-level (as opposed to packet-level)
559 3. Added poll timeout to avoid indefinite user-space wait
560 on idle links
561 4. Added user-configurable knobs:
562 4.1 block::timeout
563 4.2 tpkt_hdr::sk_rxhash
564 - RX Hash data available in user space
565 - TX_RING semantics are conceptually similar to TPACKET_V2;
566 use tpacket3_hdr instead of tpacket2_hdr, and TPACKET3_HDRLEN
567 instead of TPACKET2_HDRLEN. In the current implementation,
568 the tp_next_offset field in the tpacket3_hdr MUST be set to
569 zero, indicating that the ring does not hold variable sized frames.
570 Packets with non-zero values of tp_next_offset will be dropped.
571
572-------------------------------------------------------------------------------
573+ AF_PACKET fanout mode
574-------------------------------------------------------------------------------
575
576In the AF_PACKET fanout mode, packet reception can be load balanced among
577processes. This also works in combination with mmap(2) on packet sockets.
578
579Currently implemented fanout policies are:
580
581 - PACKET_FANOUT_HASH: schedule to socket by skb's packet hash
582 - PACKET_FANOUT_LB: schedule to socket by round-robin
583 - PACKET_FANOUT_CPU: schedule to socket by CPU packet arrives on
584 - PACKET_FANOUT_RND: schedule to socket by random selection
585 - PACKET_FANOUT_ROLLOVER: if one socket is full, rollover to another
586 - PACKET_FANOUT_QM: schedule to socket by skbs recorded queue_mapping
587
588Minimal example code by David S. Miller (try things like "./test eth0 hash",
589"./test eth0 lb", etc.):
590
591#include <stddef.h>
592#include <stdlib.h>
593#include <stdio.h>
594#include <string.h>
595
596#include <sys/types.h>
597#include <sys/wait.h>
598#include <sys/socket.h>
599#include <sys/ioctl.h>
600
601#include <unistd.h>
602
603#include <linux/if_ether.h>
604#include <linux/if_packet.h>
605
606#include <net/if.h>
607
608static const char *device_name;
609static int fanout_type;
610static int fanout_id;
611
612#ifndef PACKET_FANOUT
613# define PACKET_FANOUT 18
614# define PACKET_FANOUT_HASH 0
615# define PACKET_FANOUT_LB 1
616#endif
617
618static int setup_socket(void)
619{
620 int err, fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP));
621 struct sockaddr_ll ll;
622 struct ifreq ifr;
623 int fanout_arg;
624
625 if (fd < 0) {
626 perror("socket");
627 return EXIT_FAILURE;
628 }
629
630 memset(&ifr, 0, sizeof(ifr));
631 strcpy(ifr.ifr_name, device_name);
632 err = ioctl(fd, SIOCGIFINDEX, &ifr);
633 if (err < 0) {
634 perror("SIOCGIFINDEX");
635 return EXIT_FAILURE;
636 }
637
638 memset(&ll, 0, sizeof(ll));
639 ll.sll_family = AF_PACKET;
640 ll.sll_ifindex = ifr.ifr_ifindex;
641 err = bind(fd, (struct sockaddr *) &ll, sizeof(ll));
642 if (err < 0) {
643 perror("bind");
644 return EXIT_FAILURE;
645 }
646
647 fanout_arg = (fanout_id | (fanout_type << 16));
648 err = setsockopt(fd, SOL_PACKET, PACKET_FANOUT,
649 &fanout_arg, sizeof(fanout_arg));
650 if (err) {
651 perror("setsockopt");
652 return EXIT_FAILURE;
653 }
654
655 return fd;
656}
657
658static void fanout_thread(void)
659{
660 int fd = setup_socket();
661 int limit = 10000;
662
663 if (fd < 0)
664 exit(fd);
665
666 while (limit-- > 0) {
667 char buf[1600];
668 int err;
669
670 err = read(fd, buf, sizeof(buf));
671 if (err < 0) {
672 perror("read");
673 exit(EXIT_FAILURE);
674 }
675 if ((limit % 10) == 0)
676 fprintf(stdout, "(%d) \n", getpid());
677 }
678
679 fprintf(stdout, "%d: Received 10000 packets\n", getpid());
680
681 close(fd);
682 exit(0);
683}
684
685int main(int argc, char **argp)
686{
687 int fd, err;
688 int i;
689
690 if (argc != 3) {
691 fprintf(stderr, "Usage: %s INTERFACE {hash|lb}\n", argp[0]);
692 return EXIT_FAILURE;
693 }
694
695 if (!strcmp(argp[2], "hash"))
696 fanout_type = PACKET_FANOUT_HASH;
697 else if (!strcmp(argp[2], "lb"))
698 fanout_type = PACKET_FANOUT_LB;
699 else {
700 fprintf(stderr, "Unknown fanout type [%s]\n", argp[2]);
701 exit(EXIT_FAILURE);
702 }
703
704 device_name = argp[1];
705 fanout_id = getpid() & 0xffff;
706
707 for (i = 0; i < 4; i++) {
708 pid_t pid = fork();
709
710 switch (pid) {
711 case 0:
712 fanout_thread();
713
714 case -1:
715 perror("fork");
716 exit(EXIT_FAILURE);
717 }
718 }
719
720 for (i = 0; i < 4; i++) {
721 int status;
722
723 wait(&status);
724 }
725
726 return 0;
727}
728
729-------------------------------------------------------------------------------
730+ AF_PACKET TPACKET_V3 example
731-------------------------------------------------------------------------------
732
733AF_PACKET's TPACKET_V3 ring buffer can be configured to use non-static frame
734sizes by doing it's own memory management. It is based on blocks where polling
735works on a per block basis instead of per ring as in TPACKET_V2 and predecessor.
736
737It is said that TPACKET_V3 brings the following benefits:
738 *) ~15 - 20% reduction in CPU-usage
739 *) ~20% increase in packet capture rate
740 *) ~2x increase in packet density
741 *) Port aggregation analysis
742 *) Non static frame size to capture entire packet payload
743
744So it seems to be a good candidate to be used with packet fanout.
745
746Minimal example code by Daniel Borkmann based on Chetan Loke's lolpcap (compile
747it with gcc -Wall -O2 blob.c, and try things like "./a.out eth0", etc.):
748
749/* Written from scratch, but kernel-to-user space API usage
750 * dissected from lolpcap:
751 * Copyright 2011, Chetan Loke <loke.chetan@gmail.com>
752 * License: GPL, version 2.0
753 */
754
755#include <stdio.h>
756#include <stdlib.h>
757#include <stdint.h>
758#include <string.h>
759#include <assert.h>
760#include <net/if.h>
761#include <arpa/inet.h>
762#include <netdb.h>
763#include <poll.h>
764#include <unistd.h>
765#include <signal.h>
766#include <inttypes.h>
767#include <sys/socket.h>
768#include <sys/mman.h>
769#include <linux/if_packet.h>
770#include <linux/if_ether.h>
771#include <linux/ip.h>
772
773#ifndef likely
774# define likely(x) __builtin_expect(!!(x), 1)
775#endif
776#ifndef unlikely
777# define unlikely(x) __builtin_expect(!!(x), 0)
778#endif
779
780struct block_desc {
781 uint32_t version;
782 uint32_t offset_to_priv;
783 struct tpacket_hdr_v1 h1;
784};
785
786struct ring {
787 struct iovec *rd;
788 uint8_t *map;
789 struct tpacket_req3 req;
790};
791
792static unsigned long packets_total = 0, bytes_total = 0;
793static sig_atomic_t sigint = 0;
794
795static void sighandler(int num)
796{
797 sigint = 1;
798}
799
800static int setup_socket(struct ring *ring, char *netdev)
801{
802 int err, i, fd, v = TPACKET_V3;
803 struct sockaddr_ll ll;
804 unsigned int blocksiz = 1 << 22, framesiz = 1 << 11;
805 unsigned int blocknum = 64;
806
807 fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
808 if (fd < 0) {
809 perror("socket");
810 exit(1);
811 }
812
813 err = setsockopt(fd, SOL_PACKET, PACKET_VERSION, &v, sizeof(v));
814 if (err < 0) {
815 perror("setsockopt");
816 exit(1);
817 }
818
819 memset(&ring->req, 0, sizeof(ring->req));
820 ring->req.tp_block_size = blocksiz;
821 ring->req.tp_frame_size = framesiz;
822 ring->req.tp_block_nr = blocknum;
823 ring->req.tp_frame_nr = (blocksiz * blocknum) / framesiz;
824 ring->req.tp_retire_blk_tov = 60;
825 ring->req.tp_feature_req_word = TP_FT_REQ_FILL_RXHASH;
826
827 err = setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &ring->req,
828 sizeof(ring->req));
829 if (err < 0) {
830 perror("setsockopt");
831 exit(1);
832 }
833
834 ring->map = mmap(NULL, ring->req.tp_block_size * ring->req.tp_block_nr,
835 PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0);
836 if (ring->map == MAP_FAILED) {
837 perror("mmap");
838 exit(1);
839 }
840
841 ring->rd = malloc(ring->req.tp_block_nr * sizeof(*ring->rd));
842 assert(ring->rd);
843 for (i = 0; i < ring->req.tp_block_nr; ++i) {
844 ring->rd[i].iov_base = ring->map + (i * ring->req.tp_block_size);
845 ring->rd[i].iov_len = ring->req.tp_block_size;
846 }
847
848 memset(&ll, 0, sizeof(ll));
849 ll.sll_family = PF_PACKET;
850 ll.sll_protocol = htons(ETH_P_ALL);
851 ll.sll_ifindex = if_nametoindex(netdev);
852 ll.sll_hatype = 0;
853 ll.sll_pkttype = 0;
854 ll.sll_halen = 0;
855
856 err = bind(fd, (struct sockaddr *) &ll, sizeof(ll));
857 if (err < 0) {
858 perror("bind");
859 exit(1);
860 }
861
862 return fd;
863}
864
865static void display(struct tpacket3_hdr *ppd)
866{
867 struct ethhdr *eth = (struct ethhdr *) ((uint8_t *) ppd + ppd->tp_mac);
868 struct iphdr *ip = (struct iphdr *) ((uint8_t *) eth + ETH_HLEN);
869
870 if (eth->h_proto == htons(ETH_P_IP)) {
871 struct sockaddr_in ss, sd;
872 char sbuff[NI_MAXHOST], dbuff[NI_MAXHOST];
873
874 memset(&ss, 0, sizeof(ss));
875 ss.sin_family = PF_INET;
876 ss.sin_addr.s_addr = ip->saddr;
877 getnameinfo((struct sockaddr *) &ss, sizeof(ss),
878 sbuff, sizeof(sbuff), NULL, 0, NI_NUMERICHOST);
879
880 memset(&sd, 0, sizeof(sd));
881 sd.sin_family = PF_INET;
882 sd.sin_addr.s_addr = ip->daddr;
883 getnameinfo((struct sockaddr *) &sd, sizeof(sd),
884 dbuff, sizeof(dbuff), NULL, 0, NI_NUMERICHOST);
885
886 printf("%s -> %s, ", sbuff, dbuff);
887 }
888
889 printf("rxhash: 0x%x\n", ppd->hv1.tp_rxhash);
890}
891
892static void walk_block(struct block_desc *pbd, const int block_num)
893{
894 int num_pkts = pbd->h1.num_pkts, i;
895 unsigned long bytes = 0;
896 struct tpacket3_hdr *ppd;
897
898 ppd = (struct tpacket3_hdr *) ((uint8_t *) pbd +
899 pbd->h1.offset_to_first_pkt);
900 for (i = 0; i < num_pkts; ++i) {
901 bytes += ppd->tp_snaplen;
902 display(ppd);
903
904 ppd = (struct tpacket3_hdr *) ((uint8_t *) ppd +
905 ppd->tp_next_offset);
906 }
907
908 packets_total += num_pkts;
909 bytes_total += bytes;
910}
911
912static void flush_block(struct block_desc *pbd)
913{
914 pbd->h1.block_status = TP_STATUS_KERNEL;
915}
916
917static void teardown_socket(struct ring *ring, int fd)
918{
919 munmap(ring->map, ring->req.tp_block_size * ring->req.tp_block_nr);
920 free(ring->rd);
921 close(fd);
922}
923
924int main(int argc, char **argp)
925{
926 int fd, err;
927 socklen_t len;
928 struct ring ring;
929 struct pollfd pfd;
930 unsigned int block_num = 0, blocks = 64;
931 struct block_desc *pbd;
932 struct tpacket_stats_v3 stats;
933
934 if (argc != 2) {
935 fprintf(stderr, "Usage: %s INTERFACE\n", argp[0]);
936 return EXIT_FAILURE;
937 }
938
939 signal(SIGINT, sighandler);
940
941 memset(&ring, 0, sizeof(ring));
942 fd = setup_socket(&ring, argp[argc - 1]);
943 assert(fd > 0);
944
945 memset(&pfd, 0, sizeof(pfd));
946 pfd.fd = fd;
947 pfd.events = POLLIN | POLLERR;
948 pfd.revents = 0;
949
950 while (likely(!sigint)) {
951 pbd = (struct block_desc *) ring.rd[block_num].iov_base;
952
953 if ((pbd->h1.block_status & TP_STATUS_USER) == 0) {
954 poll(&pfd, 1, -1);
955 continue;
956 }
957
958 walk_block(pbd, block_num);
959 flush_block(pbd);
960 block_num = (block_num + 1) % blocks;
961 }
962
963 len = sizeof(stats);
964 err = getsockopt(fd, SOL_PACKET, PACKET_STATISTICS, &stats, &len);
965 if (err < 0) {
966 perror("getsockopt");
967 exit(1);
968 }
969
970 fflush(stdout);
971 printf("\nReceived %u packets, %lu bytes, %u dropped, freeze_q_cnt: %u\n",
972 stats.tp_packets, bytes_total, stats.tp_drops,
973 stats.tp_freeze_q_cnt);
974
975 teardown_socket(&ring, fd);
976 return 0;
977}
978
979-------------------------------------------------------------------------------
980+ PACKET_QDISC_BYPASS
981-------------------------------------------------------------------------------
982
983If there is a requirement to load the network with many packets in a similar
984fashion as pktgen does, you might set the following option after socket
985creation:
986
987 int one = 1;
988 setsockopt(fd, SOL_PACKET, PACKET_QDISC_BYPASS, &one, sizeof(one));
989
990This has the side-effect, that packets sent through PF_PACKET will bypass the
991kernel's qdisc layer and are forcedly pushed to the driver directly. Meaning,
992packet are not buffered, tc disciplines are ignored, increased loss can occur
993and such packets are also not visible to other PF_PACKET sockets anymore. So,
994you have been warned; generally, this can be useful for stress testing various
995components of a system.
996
997On default, PACKET_QDISC_BYPASS is disabled and needs to be explicitly enabled
998on PF_PACKET sockets.
999
1000-------------------------------------------------------------------------------
1001+ PACKET_TIMESTAMP
1002-------------------------------------------------------------------------------
1003
1004The PACKET_TIMESTAMP setting determines the source of the timestamp in
1005the packet meta information for mmap(2)ed RX_RING and TX_RINGs. If your
1006NIC is capable of timestamping packets in hardware, you can request those
1007hardware timestamps to be used. Note: you may need to enable the generation
1008of hardware timestamps with SIOCSHWTSTAMP (see related information from
1009Documentation/networking/timestamping.txt).
1010
1011PACKET_TIMESTAMP accepts the same integer bit field as SO_TIMESTAMPING:
1012
1013 int req = SOF_TIMESTAMPING_RAW_HARDWARE;
1014 setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req))
1015
1016For the mmap(2)ed ring buffers, such timestamps are stored in the
1017tpacket{,2,3}_hdr structure's tp_sec and tp_{n,u}sec members. To determine
1018what kind of timestamp has been reported, the tp_status field is binary |'ed
1019with the following possible bits ...
1020
1021 TP_STATUS_TS_RAW_HARDWARE
1022 TP_STATUS_TS_SOFTWARE
1023
1024... that are equivalent to its SOF_TIMESTAMPING_* counterparts. For the
1025RX_RING, if neither is set (i.e. PACKET_TIMESTAMP is not set), then a
1026software fallback was invoked *within* PF_PACKET's processing code (less
1027precise).
1028
1029Getting timestamps for the TX_RING works as follows: i) fill the ring frames,
1030ii) call sendto() e.g. in blocking mode, iii) wait for status of relevant
1031frames to be updated resp. the frame handed over to the application, iv) walk
1032through the frames to pick up the individual hw/sw timestamps.
1033
1034Only (!) if transmit timestamping is enabled, then these bits are combined
1035with binary | with TP_STATUS_AVAILABLE, so you must check for that in your
1036application (e.g. !(tp_status & (TP_STATUS_SEND_REQUEST | TP_STATUS_SENDING))
1037in a first step to see if the frame belongs to the application, and then
1038one can extract the type of timestamp in a second step from tp_status)!
1039
1040If you don't care about them, thus having it disabled, checking for
1041TP_STATUS_AVAILABLE resp. TP_STATUS_WRONG_FORMAT is sufficient. If in the
1042TX_RING part only TP_STATUS_AVAILABLE is set, then the tp_sec and tp_{n,u}sec
1043members do not contain a valid value. For TX_RINGs, by default no timestamp
1044is generated!
1045
1046See include/linux/net_tstamp.h and Documentation/networking/timestamping.txt
1047for more information on hardware timestamps.
1048
1049-------------------------------------------------------------------------------
1050+ Miscellaneous bits
1051-------------------------------------------------------------------------------
1052
1053- Packet sockets work well together with Linux socket filters, thus you also
1054 might want to have a look at Documentation/networking/filter.txt
1055
1056--------------------------------------------------------------------------------
1057+ THANKS
1058--------------------------------------------------------------------------------
1059
1060 Jesse Brandeburg, for fixing my grammathical/spelling errors
1061