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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
10You can find the latest version of this document at:
11 http://wiki.ipxwarzone.com/index.php5?title=Linux_packet_mmap
12
13Howto can be found at:
14 http://wiki.gnu-log.net (packet_mmap)
15
16Please send your comments to
17 Ulisses Alonso Camaró <uaca@i.hate.spam.alumni.uv.es>
18 Johann Baudy <johann.baudy@gnu-log.net>
19
20-------------------------------------------------------------------------------
21+ Why use PACKET_MMAP
22--------------------------------------------------------------------------------
23
24In Linux 2.4/2.6/3.x if PACKET_MMAP is not enabled, the capture process is very
25inefficient. It uses very limited buffers and requires one system call to
26capture each packet, it requires two if you want to get packet's timestamp
27(like libpcap always does).
28
29In the other hand PACKET_MMAP is very efficient. PACKET_MMAP provides a size
30configurable circular buffer mapped in user space that can be used to either
31send or receive packets. This way reading packets just needs to wait for them,
32most of the time there is no need to issue a single system call. Concerning
33transmission, multiple packets can be sent through one system call to get the
34highest bandwidth. By using a shared buffer between the kernel and the user
35also has the benefit of minimizing packet copies.
36
37It's fine to use PACKET_MMAP to improve the performance of the capture and
38transmission process, but it isn't everything. At least, if you are capturing
39at high speeds (this is relative to the cpu speed), you should check if the
40device driver of your network interface card supports some sort of interrupt
41load mitigation or (even better) if it supports NAPI, also make sure it is
42enabled. For transmission, check the MTU (Maximum Transmission Unit) used and
43supported by devices of your network. CPU IRQ pinning of your network interface
44card can also be an advantage.
45
46--------------------------------------------------------------------------------
47+ How to use mmap() to improve capture process
48--------------------------------------------------------------------------------
49
50From the user standpoint, you should use the higher level libpcap library, which
51is a de facto standard, portable across nearly all operating systems
52including Win32.
53
54Said that, at time of this writing, official libpcap 0.8.1 is out and doesn't include
55support for PACKET_MMAP, and also probably the libpcap included in your distribution.
56
57I'm aware of two implementations of PACKET_MMAP in libpcap:
58
59 http://wiki.ipxwarzone.com/ (by Simon Patarin, based on libpcap 0.6.2)
60 http://public.lanl.gov/cpw/ (by Phil Wood, based on lastest libpcap)
61
62The rest of this document is intended for people who want to understand
63the low level details or want to improve libpcap by including PACKET_MMAP
64support.
65
66--------------------------------------------------------------------------------
67+ How to use mmap() directly to improve capture process
68--------------------------------------------------------------------------------
69
70From the system calls stand point, the use of PACKET_MMAP involves
71the following process:
72
73
74[setup] socket() -------> creation of the capture socket
75 setsockopt() ---> allocation of the circular buffer (ring)
76 option: PACKET_RX_RING
77 mmap() ---------> mapping of the allocated buffer to the
78 user process
79
80[capture] poll() ---------> to wait for incoming packets
81
82[shutdown] close() --------> destruction of the capture socket and
83 deallocation of all associated
84 resources.
85
86
87socket creation and destruction is straight forward, and is done
88the same way with or without PACKET_MMAP:
89
90 int fd = socket(PF_PACKET, mode, htons(ETH_P_ALL));
91
92where mode is SOCK_RAW for the raw interface were link level
93information can be captured or SOCK_DGRAM for the cooked
94interface where link level information capture is not
95supported and a link level pseudo-header is provided
96by the kernel.
97
98The destruction of the socket and all associated resources
99is done by a simple call to close(fd).
100
101Similarly as without PACKET_MMAP, it is possible to use one socket
102for capture and transmission. This can be done by mapping the
103allocated RX and TX buffer ring with a single mmap() call.
104See "Mapping and use of the circular buffer (ring)".
105
106Next I will describe PACKET_MMAP settings and its constraints,
107also the mapping of the circular buffer in the user process and
108the use of this buffer.
109
110--------------------------------------------------------------------------------
111+ How to use mmap() directly to improve transmission process
112--------------------------------------------------------------------------------
113Transmission process is similar to capture as shown below.
114
115[setup] socket() -------> creation of the transmission socket
116 setsockopt() ---> allocation of the circular buffer (ring)
117 option: PACKET_TX_RING
118 bind() ---------> bind transmission socket with a network interface
119 mmap() ---------> mapping of the allocated buffer to the
120 user process
121
122[transmission] poll() ---------> wait for free packets (optional)
123 send() ---------> send all packets that are set as ready in
124 the ring
125 The flag MSG_DONTWAIT can be used to return
126 before end of transfer.
127
128[shutdown] close() --------> destruction of the transmission socket and
129 deallocation of all associated resources.
130
131Socket creation and destruction is also straight forward, and is done
132the same way as in capturing described in the previous paragraph:
133
134 int fd = socket(PF_PACKET, mode, 0);
135
136The protocol can optionally be 0 in case we only want to transmit
137via this socket, which avoids an expensive call to packet_rcv().
138In this case, you also need to bind(2) the TX_RING with sll_protocol = 0
139set. Otherwise, htons(ETH_P_ALL) or any other protocol, for example.
140
141Binding the socket to your network interface is mandatory (with zero copy) to
142know the header size of frames used in the circular buffer.
143
144As capture, each frame contains two parts:
145
146 --------------------
147| struct tpacket_hdr | Header. It contains the status of
148| | of this frame
149|--------------------|
150| data buffer |
151. . Data that will be sent over the network interface.
152. .
153 --------------------
154
155 bind() associates the socket to your network interface thanks to
156 sll_ifindex parameter of struct sockaddr_ll.
157
158 Initialization example:
159
160 struct sockaddr_ll my_addr;
161 struct ifreq s_ifr;
162 ...
163
164 strncpy (s_ifr.ifr_name, "eth0", sizeof(s_ifr.ifr_name));
165
166 /* get interface index of eth0 */
167 ioctl(this->socket, SIOCGIFINDEX, &s_ifr);
168
169 /* fill sockaddr_ll struct to prepare binding */
170 my_addr.sll_family = AF_PACKET;
171 my_addr.sll_protocol = htons(ETH_P_ALL);
172 my_addr.sll_ifindex = s_ifr.ifr_ifindex;
173
174 /* bind socket to eth0 */
175 bind(this->socket, (struct sockaddr *)&my_addr, sizeof(struct sockaddr_ll));
176
177 A complete tutorial is available at: http://wiki.gnu-log.net/
178
179By default, the user should put data at :
180 frame base + TPACKET_HDRLEN - sizeof(struct sockaddr_ll)
181
182So, whatever you choose for the socket mode (SOCK_DGRAM or SOCK_RAW),
183the beginning of the user data will be at :
184 frame base + TPACKET_ALIGN(sizeof(struct tpacket_hdr))
185
186If you wish to put user data at a custom offset from the beginning of
187the frame (for payload alignment with SOCK_RAW mode for instance) you
188can set tp_net (with SOCK_DGRAM) or tp_mac (with SOCK_RAW). In order
189to make this work it must be enabled previously with setsockopt()
190and the PACKET_TX_HAS_OFF option.
191
192--------------------------------------------------------------------------------
193+ PACKET_MMAP settings
194--------------------------------------------------------------------------------
195
196To setup PACKET_MMAP from user level code is done with a call like
197
198 - Capture process
199 setsockopt(fd, SOL_PACKET, PACKET_RX_RING, (void *) &req, sizeof(req))
200 - Transmission process
201 setsockopt(fd, SOL_PACKET, PACKET_TX_RING, (void *) &req, sizeof(req))
202
203The most significant argument in the previous call is the req parameter,
204this parameter must to have the following structure:
205
206 struct tpacket_req
207 {
208 unsigned int tp_block_size; /* Minimal size of contiguous block */
209 unsigned int tp_block_nr; /* Number of blocks */
210 unsigned int tp_frame_size; /* Size of frame */
211 unsigned int tp_frame_nr; /* Total number of frames */
212 };
213
214This structure is defined in /usr/include/linux/if_packet.h and establishes a
215circular buffer (ring) of unswappable memory.
216Being mapped in the capture process allows reading the captured frames and
217related meta-information like timestamps without requiring a system call.
218
219Frames are grouped in blocks. Each block is a physically contiguous
220region of memory and holds tp_block_size/tp_frame_size frames. The total number
221of blocks is tp_block_nr. Note that tp_frame_nr is a redundant parameter because
222
223 frames_per_block = tp_block_size/tp_frame_size
224
225indeed, packet_set_ring checks that the following condition is true
226
227 frames_per_block * tp_block_nr == tp_frame_nr
228
229Lets see an example, with the following values:
230
231 tp_block_size= 4096
232 tp_frame_size= 2048
233 tp_block_nr = 4
234 tp_frame_nr = 8
235
236we will get the following buffer structure:
237
238 block #1 block #2
239+---------+---------+ +---------+---------+
240| frame 1 | frame 2 | | frame 3 | frame 4 |
241+---------+---------+ +---------+---------+
242
243 block #3 block #4
244+---------+---------+ +---------+---------+
245| frame 5 | frame 6 | | frame 7 | frame 8 |
246+---------+---------+ +---------+---------+
247
248A frame can be of any size with the only condition it can fit in a block. A block
249can only hold an integer number of frames, or in other words, a frame cannot
250be spawned across two blocks, so there are some details you have to take into
251account when choosing the frame_size. See "Mapping and use of the circular
252buffer (ring)".
253
254--------------------------------------------------------------------------------
255+ PACKET_MMAP setting constraints
256--------------------------------------------------------------------------------
257
258In kernel versions prior to 2.4.26 (for the 2.4 branch) and 2.6.5 (2.6 branch),
259the PACKET_MMAP buffer could hold only 32768 frames in a 32 bit architecture or
26016384 in a 64 bit architecture. For information on these kernel versions
261see http://pusa.uv.es/~ulisses/packet_mmap/packet_mmap.pre-2.4.26_2.6.5.txt
262
263 Block size limit
264------------------
265
266As stated earlier, each block is a contiguous physical region of memory. These
267memory regions are allocated with calls to the __get_free_pages() function. As
268the name indicates, this function allocates pages of memory, and the second
269argument is "order" or a power of two number of pages, that is
270(for PAGE_SIZE == 4096) order=0 ==> 4096 bytes, order=1 ==> 8192 bytes,
271order=2 ==> 16384 bytes, etc. The maximum size of a
272region allocated by __get_free_pages is determined by the MAX_ORDER macro. More
273precisely the limit can be calculated as:
274
275 PAGE_SIZE << MAX_ORDER
276
277 In a i386 architecture PAGE_SIZE is 4096 bytes
278 In a 2.4/i386 kernel MAX_ORDER is 10
279 In a 2.6/i386 kernel MAX_ORDER is 11
280
281So get_free_pages can allocate as much as 4MB or 8MB in a 2.4/2.6 kernel
282respectively, with an i386 architecture.
283
284User space programs can include /usr/include/sys/user.h and
285/usr/include/linux/mmzone.h to get PAGE_SIZE MAX_ORDER declarations.
286
287The pagesize can also be determined dynamically with the getpagesize (2)
288system call.
289
290 Block number limit
291--------------------
292
293To understand the constraints of PACKET_MMAP, we have to see the structure
294used to hold the pointers to each block.
295
296Currently, this structure is a dynamically allocated vector with kmalloc
297called pg_vec, its size limits the number of blocks that can be allocated.
298
299 +---+---+---+---+
300 | x | x | x | x |
301 +---+---+---+---+
302 | | | |
303 | | | v
304 | | v block #4
305 | v block #3
306 v block #2
307 block #1
308
309kmalloc allocates any number of bytes of physically contiguous memory from
310a pool of pre-determined sizes. This pool of memory is maintained by the slab
311allocator which is at the end the responsible for doing the allocation and
312hence which imposes the maximum memory that kmalloc can allocate.
313
314In a 2.4/2.6 kernel and the i386 architecture, the limit is 131072 bytes. The
315predetermined sizes that kmalloc uses can be checked in the "size-<bytes>"
316entries of /proc/slabinfo
317
318In a 32 bit architecture, pointers are 4 bytes long, so the total number of
319pointers to blocks is
320
321 131072/4 = 32768 blocks
322
323 PACKET_MMAP buffer size calculator
324------------------------------------
325
326Definitions:
327
328<size-max> : is the maximum size of allocable with kmalloc (see /proc/slabinfo)
329<pointer size>: depends on the architecture -- sizeof(void *)
330<page size> : depends on the architecture -- PAGE_SIZE or getpagesize (2)
331<max-order> : is the value defined with MAX_ORDER
332<frame size> : it's an upper bound of frame's capture size (more on this later)
333
334from these definitions we will derive
335
336 <block number> = <size-max>/<pointer size>
337 <block size> = <pagesize> << <max-order>
338
339so, the max buffer size is
340
341 <block number> * <block size>
342
343and, the number of frames be
344
345 <block number> * <block size> / <frame size>
346
347Suppose the following parameters, which apply for 2.6 kernel and an
348i386 architecture:
349
350 <size-max> = 131072 bytes
351 <pointer size> = 4 bytes
352 <pagesize> = 4096 bytes
353 <max-order> = 11
354
355and a value for <frame size> of 2048 bytes. These parameters will yield
356
357 <block number> = 131072/4 = 32768 blocks
358 <block size> = 4096 << 11 = 8 MiB.
359
360and hence the buffer will have a 262144 MiB size. So it can hold
361262144 MiB / 2048 bytes = 134217728 frames
362
363Actually, this buffer size is not possible with an i386 architecture.
364Remember that the memory is allocated in kernel space, in the case of
365an i386 kernel's memory size is limited to 1GiB.
366
367All memory allocations are not freed until the socket is closed. The memory
368allocations are done with GFP_KERNEL priority, this basically means that
369the allocation can wait and swap other process' memory in order to allocate
370the necessary memory, so normally limits can be reached.
371
372 Other constraints
373-------------------
374
375If you check the source code you will see that what I draw here as a frame
376is not only the link level frame. At the beginning of each frame there is a
377header called struct tpacket_hdr used in PACKET_MMAP to hold link level's frame
378meta information like timestamp. So what we draw here a frame it's really
379the following (from include/linux/if_packet.h):
380
381/*
382 Frame structure:
383
384 - Start. Frame must be aligned to TPACKET_ALIGNMENT=16
385 - struct tpacket_hdr
386 - pad to TPACKET_ALIGNMENT=16
387 - struct sockaddr_ll
388 - Gap, chosen so that packet data (Start+tp_net) aligns to
389 TPACKET_ALIGNMENT=16
390 - Start+tp_mac: [ Optional MAC header ]
391 - Start+tp_net: Packet data, aligned to TPACKET_ALIGNMENT=16.
392 - Pad to align to TPACKET_ALIGNMENT=16
393 */
394
395 The following are conditions that are checked in packet_set_ring
396
397 tp_block_size must be a multiple of PAGE_SIZE (1)
398 tp_frame_size must be greater than TPACKET_HDRLEN (obvious)
399 tp_frame_size must be a multiple of TPACKET_ALIGNMENT
400 tp_frame_nr must be exactly frames_per_block*tp_block_nr
401
402Note that tp_block_size should be chosen to be a power of two or there will
403be a waste of memory.
404
405--------------------------------------------------------------------------------
406+ Mapping and use of the circular buffer (ring)
407--------------------------------------------------------------------------------
408
409The mapping of the buffer in the user process is done with the conventional
410mmap function. Even the circular buffer is compound of several physically
411discontiguous blocks of memory, they are contiguous to the user space, hence
412just one call to mmap is needed:
413
414 mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
415
416If tp_frame_size is a divisor of tp_block_size frames will be
417contiguously spaced by tp_frame_size bytes. If not, each
418tp_block_size/tp_frame_size frames there will be a gap between
419the frames. This is because a frame cannot be spawn across two
420blocks.
421
422To use one socket for capture and transmission, the mapping of both the
423RX and TX buffer ring has to be done with one call to mmap:
424
425 ...
426 setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &foo, sizeof(foo));
427 setsockopt(fd, SOL_PACKET, PACKET_TX_RING, &bar, sizeof(bar));
428 ...
429 rx_ring = mmap(0, size * 2, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
430 tx_ring = rx_ring + size;
431
432RX must be the first as the kernel maps the TX ring memory right
433after the RX one.
434
435At the beginning of each frame there is an status field (see
436struct tpacket_hdr). If this field is 0 means that the frame is ready
437to be used for the kernel, If not, there is a frame the user can read
438and the following flags apply:
439
440+++ Capture process:
441 from include/linux/if_packet.h
442
443 #define TP_STATUS_COPY 2
444 #define TP_STATUS_LOSING 4
445 #define TP_STATUS_CSUMNOTREADY 8
446
447TP_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
460TP_STATUS_LOSING : indicates there were packet drops from last time
461 statistics where checked with getsockopt() and
462 the PACKET_STATISTICS option.
463
464TP_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
469for convenience there are also the following defines:
470
471 #define TP_STATUS_KERNEL 0
472 #define TP_STATUS_USER 1
473
474The kernel initializes all frames to TP_STATUS_KERNEL, when the kernel
475receives a packet it puts in the buffer and updates the status with
476at least the TP_STATUS_USER flag. Then the user can read the packet,
477once the packet is read the user must zero the status field, so the kernel
478can use again that frame buffer.
479
480The user can use poll (any other variant should apply too) to check if new
481packets are in the ring:
482
483 struct pollfd pfd;
484
485 pfd.fd = fd;
486 pfd.revents = 0;
487 pfd.events = POLLIN|POLLRDNORM|POLLERR;
488
489 if (status == TP_STATUS_KERNEL)
490 retval = poll(&pfd, 1, timeout);
491
492It doesn't incur in a race condition to first check the status value and
493then poll for frames.
494
495++ Transmission process
496Those defines are also used for transmission:
497
498 #define TP_STATUS_AVAILABLE 0 // Frame is available
499 #define TP_STATUS_SEND_REQUEST 1 // Frame will be sent on next send()
500 #define TP_STATUS_SENDING 2 // Frame is currently in transmission
501 #define TP_STATUS_WRONG_FORMAT 4 // Frame format is not correct
502
503First, the kernel initializes all frames to TP_STATUS_AVAILABLE. To send a
504packet, the user fills a data buffer of an available frame, sets tp_len to
505current data buffer size and sets its status field to TP_STATUS_SEND_REQUEST.
506This can be done on multiple frames. Once the user is ready to transmit, it
507calls send(). Then all buffers with status equal to TP_STATUS_SEND_REQUEST are
508forwarded to the network device. The kernel updates each status of sent
509frames with TP_STATUS_SENDING until the end of transfer.
510At the end of each transfer, buffer status returns to TP_STATUS_AVAILABLE.
511
512 header->tp_len = in_i_size;
513 header->tp_status = TP_STATUS_SEND_REQUEST;
514 retval = send(this->socket, NULL, 0, 0);
515
516The user can also use poll() to check if a buffer is available:
517(status == TP_STATUS_SENDING)
518
519 struct pollfd pfd;
520 pfd.fd = fd;
521 pfd.revents = 0;
522 pfd.events = POLLOUT;
523 retval = poll(&pfd, 1, timeout);
524
525-------------------------------------------------------------------------------
526+ What TPACKET versions are available and when to use them?
527-------------------------------------------------------------------------------
528
529 int val = tpacket_version;
530 setsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val));
531 getsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val));
532
533where 'tpacket_version' can be TPACKET_V1 (default), TPACKET_V2, TPACKET_V3.
534
535TPACKET_V1:
536 - Default if not otherwise specified by setsockopt(2)
537 - RX_RING, TX_RING available
538
539TPACKET_V1 --> TPACKET_V2:
540 - Made 64 bit clean due to unsigned long usage in TPACKET_V1
541 structures, thus this also works on 64 bit kernel with 32 bit
542 userspace and the like
543 - Timestamp resolution in nanoseconds instead of microseconds
544 - RX_RING, TX_RING available
545 - VLAN metadata information available for packets
546 (TP_STATUS_VLAN_VALID, TP_STATUS_VLAN_TPID_VALID),
547 in the tpacket2_hdr structure:
548 - TP_STATUS_VLAN_VALID bit being set into the tp_status field indicates
549 that the tp_vlan_tci field has valid VLAN TCI value
550 - TP_STATUS_VLAN_TPID_VALID bit being set into the tp_status field
551 indicates that the tp_vlan_tpid field has valid VLAN TPID value
552 - How to switch to TPACKET_V2:
553 1. Replace struct tpacket_hdr by struct tpacket2_hdr
554 2. Query header len and save
555 3. Set protocol version to 2, set up ring as usual
556 4. For getting the sockaddr_ll,
557 use (void *)hdr + TPACKET_ALIGN(hdrlen) instead of
558 (void *)hdr + TPACKET_ALIGN(sizeof(struct tpacket_hdr))
559
560TPACKET_V2 --> TPACKET_V3:
561 - Flexible buffer implementation:
562 1. Blocks can be configured with non-static frame-size
563 2. Read/poll is at a block-level (as opposed to packet-level)
564 3. Added poll timeout to avoid indefinite user-space wait
565 on idle links
566 4. Added user-configurable knobs:
567 4.1 block::timeout
568 4.2 tpkt_hdr::sk_rxhash
569 - RX Hash data available in user space
570 - Currently only RX_RING available
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
1012SO_TIMESTAMPING. However, only the SOF_TIMESTAMPING_SYS_HARDWARE
1013and SOF_TIMESTAMPING_RAW_HARDWARE values are recognized by
1014PACKET_TIMESTAMP. SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over
1015SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set.
1016
1017 int req = 0;
1018 req |= SOF_TIMESTAMPING_SYS_HARDWARE;
1019 setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req))
1020
1021For the mmap(2)ed ring buffers, such timestamps are stored in the
1022tpacket{,2,3}_hdr structure's tp_sec and tp_{n,u}sec members. To determine
1023what kind of timestamp has been reported, the tp_status field is binary |'ed
1024with the following possible bits ...
1025
1026 TP_STATUS_TS_SYS_HARDWARE
1027 TP_STATUS_TS_RAW_HARDWARE
1028 TP_STATUS_TS_SOFTWARE
1029
1030... that are equivalent to its SOF_TIMESTAMPING_* counterparts. For the
1031RX_RING, if none of those 3 are set (i.e. PACKET_TIMESTAMP is not set),
1032then this means that a software fallback was invoked *within* PF_PACKET's
1033processing code (less precise).
1034
1035Getting timestamps for the TX_RING works as follows: i) fill the ring frames,
1036ii) call sendto() e.g. in blocking mode, iii) wait for status of relevant
1037frames to be updated resp. the frame handed over to the application, iv) walk
1038through the frames to pick up the individual hw/sw timestamps.
1039
1040Only (!) if transmit timestamping is enabled, then these bits are combined
1041with binary | with TP_STATUS_AVAILABLE, so you must check for that in your
1042application (e.g. !(tp_status & (TP_STATUS_SEND_REQUEST | TP_STATUS_SENDING))
1043in a first step to see if the frame belongs to the application, and then
1044one can extract the type of timestamp in a second step from tp_status)!
1045
1046If you don't care about them, thus having it disabled, checking for
1047TP_STATUS_AVAILABLE resp. TP_STATUS_WRONG_FORMAT is sufficient. If in the
1048TX_RING part only TP_STATUS_AVAILABLE is set, then the tp_sec and tp_{n,u}sec
1049members do not contain a valid value. For TX_RINGs, by default no timestamp
1050is generated!
1051
1052See include/linux/net_tstamp.h and Documentation/networking/timestamping
1053for more information on hardware timestamps.
1054
1055-------------------------------------------------------------------------------
1056+ Miscellaneous bits
1057-------------------------------------------------------------------------------
1058
1059- Packet sockets work well together with Linux socket filters, thus you also
1060 might want to have a look at Documentation/networking/filter.txt
1061
1062--------------------------------------------------------------------------------
1063+ THANKS
1064--------------------------------------------------------------------------------
1065
1066 Jesse Brandeburg, for fixing my grammathical/spelling errors
1067