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 Camar�� <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 (1 << 1) 444 #define TP_STATUS_LOSING (1 << 2) 445 #define TP_STATUS_CSUMNOTREADY (1 << 3) 446 #define TP_STATUS_CSUM_VALID (1 << 7) 447 448TP_STATUS_COPY : This flag indicates that the frame (and associated 449 meta information) has been truncated because it's 450 larger than tp_frame_size. This packet can be 451 read entirely with recvfrom(). 452 453 In order to make this work it must to be 454 enabled previously with setsockopt() and 455 the PACKET_COPY_THRESH option. 456 457 The number of frames that can be buffered to 458 be read with recvfrom is limited like a normal socket. 459 See the SO_RCVBUF option in the socket (7) man page. 460 461TP_STATUS_LOSING : indicates there were packet drops from last time 462 statistics where checked with getsockopt() and 463 the PACKET_STATISTICS option. 464 465TP_STATUS_CSUMNOTREADY: currently it's used for outgoing IP packets which 466 its checksum will be done in hardware. So while 467 reading the packet we should not try to check the 468 checksum. 469 470TP_STATUS_CSUM_VALID : This flag indicates that at least the transport 471 header checksum of the packet has been already 472 validated on the kernel side. If the flag is not set 473 then we are free to check the checksum by ourselves 474 provided that TP_STATUS_CSUMNOTREADY is also not set. 475 476for convenience there are also the following defines: 477 478 #define TP_STATUS_KERNEL 0 479 #define TP_STATUS_USER 1 480 481The kernel initializes all frames to TP_STATUS_KERNEL, when the kernel 482receives a packet it puts in the buffer and updates the status with 483at least the TP_STATUS_USER flag. Then the user can read the packet, 484once the packet is read the user must zero the status field, so the kernel 485can use again that frame buffer. 486 487The user can use poll (any other variant should apply too) to check if new 488packets 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 499It doesn't incur in a race condition to first check the status value and 500then poll for frames. 501 502++ Transmission process 503Those defines are also used for transmission: 504 505 #define TP_STATUS_AVAILABLE 0 // Frame is available 506 #define TP_STATUS_SEND_REQUEST 1 // Frame will be sent on next send() 507 #define TP_STATUS_SENDING 2 // Frame is currently in transmission 508 #define TP_STATUS_WRONG_FORMAT 4 // Frame format is not correct 509 510First, the kernel initializes all frames to TP_STATUS_AVAILABLE. To send a 511packet, the user fills a data buffer of an available frame, sets tp_len to 512current data buffer size and sets its status field to TP_STATUS_SEND_REQUEST. 513This can be done on multiple frames. Once the user is ready to transmit, it 514calls send(). Then all buffers with status equal to TP_STATUS_SEND_REQUEST are 515forwarded to the network device. The kernel updates each status of sent 516frames with TP_STATUS_SENDING until the end of transfer. 517At the end of each transfer, buffer status returns to TP_STATUS_AVAILABLE. 518 519 header->tp_len = in_i_size; 520 header->tp_status = TP_STATUS_SEND_REQUEST; 521 retval = send(this->socket, NULL, 0, 0); 522 523The user can also use poll() to check if a buffer is available: 524(status == TP_STATUS_SENDING) 525 526 struct pollfd pfd; 527 pfd.fd = fd; 528 pfd.revents = 0; 529 pfd.events = POLLOUT; 530 retval = poll(&pfd, 1, timeout); 531 532------------------------------------------------------------------------------- 533+ What TPACKET versions are available and when to use them? 534------------------------------------------------------------------------------- 535 536 int val = tpacket_version; 537 setsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val)); 538 getsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val)); 539 540where 'tpacket_version' can be TPACKET_V1 (default), TPACKET_V2, TPACKET_V3. 541 542TPACKET_V1: 543 - Default if not otherwise specified by setsockopt(2) 544 - RX_RING, TX_RING available 545 546TPACKET_V1 --> TPACKET_V2: 547 - Made 64 bit clean due to unsigned long usage in TPACKET_V1 548 structures, thus this also works on 64 bit kernel with 32 bit 549 userspace and the like 550 - Timestamp resolution in nanoseconds instead of microseconds 551 - RX_RING, TX_RING available 552 - VLAN metadata information available for packets 553 (TP_STATUS_VLAN_VALID, TP_STATUS_VLAN_TPID_VALID), 554 in the tpacket2_hdr structure: 555 - TP_STATUS_VLAN_VALID bit being set into the tp_status field indicates 556 that the tp_vlan_tci field has valid VLAN TCI value 557 - TP_STATUS_VLAN_TPID_VALID bit being set into the tp_status field 558 indicates that the tp_vlan_tpid field has valid VLAN TPID value 559 - How to switch to TPACKET_V2: 560 1. Replace struct tpacket_hdr by struct tpacket2_hdr 561 2. Query header len and save 562 3. Set protocol version to 2, set up ring as usual 563 4. For getting the sockaddr_ll, 564 use (void *)hdr + TPACKET_ALIGN(hdrlen) instead of 565 (void *)hdr + TPACKET_ALIGN(sizeof(struct tpacket_hdr)) 566 567TPACKET_V2 --> TPACKET_V3: 568 - Flexible buffer implementation: 569 1. Blocks can be configured with non-static frame-size 570 2. Read/poll is at a block-level (as opposed to packet-level) 571 3. Added poll timeout to avoid indefinite user-space wait 572 on idle links 573 4. Added user-configurable knobs: 574 4.1 block::timeout 575 4.2 tpkt_hdr::sk_rxhash 576 - RX Hash data available in user space 577 - Currently only RX_RING available 578 579------------------------------------------------------------------------------- 580+ AF_PACKET fanout mode 581------------------------------------------------------------------------------- 582 583In the AF_PACKET fanout mode, packet reception can be load balanced among 584processes. This also works in combination with mmap(2) on packet sockets. 585 586Currently implemented fanout policies are: 587 588 - PACKET_FANOUT_HASH: schedule to socket by skb's packet hash 589 - PACKET_FANOUT_LB: schedule to socket by round-robin 590 - PACKET_FANOUT_CPU: schedule to socket by CPU packet arrives on 591 - PACKET_FANOUT_RND: schedule to socket by random selection 592 - PACKET_FANOUT_ROLLOVER: if one socket is full, rollover to another 593 - PACKET_FANOUT_QM: schedule to socket by skbs recorded queue_mapping 594 595Minimal example code by David S. Miller (try things like "./test eth0 hash", 596"./test eth0 lb", etc.): 597 598#include <stddef.h> 599#include <stdlib.h> 600#include <stdio.h> 601#include <string.h> 602 603#include <sys/types.h> 604#include <sys/wait.h> 605#include <sys/socket.h> 606#include <sys/ioctl.h> 607 608#include <unistd.h> 609 610#include <linux/if_ether.h> 611#include <linux/if_packet.h> 612 613#include <net/if.h> 614 615static const char *device_name; 616static int fanout_type; 617static int fanout_id; 618 619#ifndef PACKET_FANOUT 620# define PACKET_FANOUT 18 621# define PACKET_FANOUT_HASH 0 622# define PACKET_FANOUT_LB 1 623#endif 624 625static int setup_socket(void) 626{ 627 int err, fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP)); 628 struct sockaddr_ll ll; 629 struct ifreq ifr; 630 int fanout_arg; 631 632 if (fd < 0) { 633 perror("socket"); 634 return EXIT_FAILURE; 635 } 636 637 memset(&ifr, 0, sizeof(ifr)); 638 strcpy(ifr.ifr_name, device_name); 639 err = ioctl(fd, SIOCGIFINDEX, &ifr); 640 if (err < 0) { 641 perror("SIOCGIFINDEX"); 642 return EXIT_FAILURE; 643 } 644 645 memset(&ll, 0, sizeof(ll)); 646 ll.sll_family = AF_PACKET; 647 ll.sll_ifindex = ifr.ifr_ifindex; 648 err = bind(fd, (struct sockaddr *) &ll, sizeof(ll)); 649 if (err < 0) { 650 perror("bind"); 651 return EXIT_FAILURE; 652 } 653 654 fanout_arg = (fanout_id | (fanout_type << 16)); 655 err = setsockopt(fd, SOL_PACKET, PACKET_FANOUT, 656 &fanout_arg, sizeof(fanout_arg)); 657 if (err) { 658 perror("setsockopt"); 659 return EXIT_FAILURE; 660 } 661 662 return fd; 663} 664 665static void fanout_thread(void) 666{ 667 int fd = setup_socket(); 668 int limit = 10000; 669 670 if (fd < 0) 671 exit(fd); 672 673 while (limit-- > 0) { 674 char buf[1600]; 675 int err; 676 677 err = read(fd, buf, sizeof(buf)); 678 if (err < 0) { 679 perror("read"); 680 exit(EXIT_FAILURE); 681 } 682 if ((limit % 10) == 0) 683 fprintf(stdout, "(%d) \n", getpid()); 684 } 685 686 fprintf(stdout, "%d: Received 10000 packets\n", getpid()); 687 688 close(fd); 689 exit(0); 690} 691 692int main(int argc, char **argp) 693{ 694 int fd, err; 695 int i; 696 697 if (argc != 3) { 698 fprintf(stderr, "Usage: %s INTERFACE {hash|lb}\n", argp[0]); 699 return EXIT_FAILURE; 700 } 701 702 if (!strcmp(argp[2], "hash")) 703 fanout_type = PACKET_FANOUT_HASH; 704 else if (!strcmp(argp[2], "lb")) 705 fanout_type = PACKET_FANOUT_LB; 706 else { 707 fprintf(stderr, "Unknown fanout type [%s]\n", argp[2]); 708 exit(EXIT_FAILURE); 709 } 710 711 device_name = argp[1]; 712 fanout_id = getpid() & 0xffff; 713 714 for (i = 0; i < 4; i++) { 715 pid_t pid = fork(); 716 717 switch (pid) { 718 case 0: 719 fanout_thread(); 720 721 case -1: 722 perror("fork"); 723 exit(EXIT_FAILURE); 724 } 725 } 726 727 for (i = 0; i < 4; i++) { 728 int status; 729 730 wait(&status); 731 } 732 733 return 0; 734} 735 736------------------------------------------------------------------------------- 737+ AF_PACKET TPACKET_V3 example 738------------------------------------------------------------------------------- 739 740AF_PACKET's TPACKET_V3 ring buffer can be configured to use non-static frame 741sizes by doing it's own memory management. It is based on blocks where polling 742works on a per block basis instead of per ring as in TPACKET_V2 and predecessor. 743 744It is said that TPACKET_V3 brings the following benefits: 745 *) ~15 - 20% reduction in CPU-usage 746 *) ~20% increase in packet capture rate 747 *) ~2x increase in packet density 748 *) Port aggregation analysis 749 *) Non static frame size to capture entire packet payload 750 751So it seems to be a good candidate to be used with packet fanout. 752 753Minimal example code by Daniel Borkmann based on Chetan Loke's lolpcap (compile 754it with gcc -Wall -O2 blob.c, and try things like "./a.out eth0", etc.): 755 756/* Written from scratch, but kernel-to-user space API usage 757 * dissected from lolpcap: 758 * Copyright 2011, Chetan Loke <loke.chetan@gmail.com> 759 * License: GPL, version 2.0 760 */ 761 762#include <stdio.h> 763#include <stdlib.h> 764#include <stdint.h> 765#include <string.h> 766#include <assert.h> 767#include <net/if.h> 768#include <arpa/inet.h> 769#include <netdb.h> 770#include <poll.h> 771#include <unistd.h> 772#include <signal.h> 773#include <inttypes.h> 774#include <sys/socket.h> 775#include <sys/mman.h> 776#include <linux/if_packet.h> 777#include <linux/if_ether.h> 778#include <linux/ip.h> 779 780#ifndef likely 781# define likely(x) __builtin_expect(!!(x), 1) 782#endif 783#ifndef unlikely 784# define unlikely(x) __builtin_expect(!!(x), 0) 785#endif 786 787struct block_desc { 788 uint32_t version; 789 uint32_t offset_to_priv; 790 struct tpacket_hdr_v1 h1; 791}; 792 793struct ring { 794 struct iovec *rd; 795 uint8_t *map; 796 struct tpacket_req3 req; 797}; 798 799static unsigned long packets_total = 0, bytes_total = 0; 800static sig_atomic_t sigint = 0; 801 802static void sighandler(int num) 803{ 804 sigint = 1; 805} 806 807static int setup_socket(struct ring *ring, char *netdev) 808{ 809 int err, i, fd, v = TPACKET_V3; 810 struct sockaddr_ll ll; 811 unsigned int blocksiz = 1 << 22, framesiz = 1 << 11; 812 unsigned int blocknum = 64; 813 814 fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL)); 815 if (fd < 0) { 816 perror("socket"); 817 exit(1); 818 } 819 820 err = setsockopt(fd, SOL_PACKET, PACKET_VERSION, &v, sizeof(v)); 821 if (err < 0) { 822 perror("setsockopt"); 823 exit(1); 824 } 825 826 memset(&ring->req, 0, sizeof(ring->req)); 827 ring->req.tp_block_size = blocksiz; 828 ring->req.tp_frame_size = framesiz; 829 ring->req.tp_block_nr = blocknum; 830 ring->req.tp_frame_nr = (blocksiz * blocknum) / framesiz; 831 ring->req.tp_retire_blk_tov = 60; 832 ring->req.tp_feature_req_word = TP_FT_REQ_FILL_RXHASH; 833 834 err = setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &ring->req, 835 sizeof(ring->req)); 836 if (err < 0) { 837 perror("setsockopt"); 838 exit(1); 839 } 840 841 ring->map = mmap(NULL, ring->req.tp_block_size * ring->req.tp_block_nr, 842 PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0); 843 if (ring->map == MAP_FAILED) { 844 perror("mmap"); 845 exit(1); 846 } 847 848 ring->rd = malloc(ring->req.tp_block_nr * sizeof(*ring->rd)); 849 assert(ring->rd); 850 for (i = 0; i < ring->req.tp_block_nr; ++i) { 851 ring->rd[i].iov_base = ring->map + (i * ring->req.tp_block_size); 852 ring->rd[i].iov_len = ring->req.tp_block_size; 853 } 854 855 memset(&ll, 0, sizeof(ll)); 856 ll.sll_family = PF_PACKET; 857 ll.sll_protocol = htons(ETH_P_ALL); 858 ll.sll_ifindex = if_nametoindex(netdev); 859 ll.sll_hatype = 0; 860 ll.sll_pkttype = 0; 861 ll.sll_halen = 0; 862 863 err = bind(fd, (struct sockaddr *) &ll, sizeof(ll)); 864 if (err < 0) { 865 perror("bind"); 866 exit(1); 867 } 868 869 return fd; 870} 871 872static void display(struct tpacket3_hdr *ppd) 873{ 874 struct ethhdr *eth = (struct ethhdr *) ((uint8_t *) ppd + ppd->tp_mac); 875 struct iphdr *ip = (struct iphdr *) ((uint8_t *) eth + ETH_HLEN); 876 877 if (eth->h_proto == htons(ETH_P_IP)) { 878 struct sockaddr_in ss, sd; 879 char sbuff[NI_MAXHOST], dbuff[NI_MAXHOST]; 880 881 memset(&ss, 0, sizeof(ss)); 882 ss.sin_family = PF_INET; 883 ss.sin_addr.s_addr = ip->saddr; 884 getnameinfo((struct sockaddr *) &ss, sizeof(ss), 885 sbuff, sizeof(sbuff), NULL, 0, NI_NUMERICHOST); 886 887 memset(&sd, 0, sizeof(sd)); 888 sd.sin_family = PF_INET; 889 sd.sin_addr.s_addr = ip->daddr; 890 getnameinfo((struct sockaddr *) &sd, sizeof(sd), 891 dbuff, sizeof(dbuff), NULL, 0, NI_NUMERICHOST); 892 893 printf("%s -> %s, ", sbuff, dbuff); 894 } 895 896 printf("rxhash: 0x%x\n", ppd->hv1.tp_rxhash); 897} 898 899static void walk_block(struct block_desc *pbd, const int block_num) 900{ 901 int num_pkts = pbd->h1.num_pkts, i; 902 unsigned long bytes = 0; 903 struct tpacket3_hdr *ppd; 904 905 ppd = (struct tpacket3_hdr *) ((uint8_t *) pbd + 906 pbd->h1.offset_to_first_pkt); 907 for (i = 0; i < num_pkts; ++i) { 908 bytes += ppd->tp_snaplen; 909 display(ppd); 910 911 ppd = (struct tpacket3_hdr *) ((uint8_t *) ppd + 912 ppd->tp_next_offset); 913 } 914 915 packets_total += num_pkts; 916 bytes_total += bytes; 917} 918 919static void flush_block(struct block_desc *pbd) 920{ 921 pbd->h1.block_status = TP_STATUS_KERNEL; 922} 923 924static void teardown_socket(struct ring *ring, int fd) 925{ 926 munmap(ring->map, ring->req.tp_block_size * ring->req.tp_block_nr); 927 free(ring->rd); 928 close(fd); 929} 930 931int main(int argc, char **argp) 932{ 933 int fd, err; 934 socklen_t len; 935 struct ring ring; 936 struct pollfd pfd; 937 unsigned int block_num = 0, blocks = 64; 938 struct block_desc *pbd; 939 struct tpacket_stats_v3 stats; 940 941 if (argc != 2) { 942 fprintf(stderr, "Usage: %s INTERFACE\n", argp[0]); 943 return EXIT_FAILURE; 944 } 945 946 signal(SIGINT, sighandler); 947 948 memset(&ring, 0, sizeof(ring)); 949 fd = setup_socket(&ring, argp[argc - 1]); 950 assert(fd > 0); 951 952 memset(&pfd, 0, sizeof(pfd)); 953 pfd.fd = fd; 954 pfd.events = POLLIN | POLLERR; 955 pfd.revents = 0; 956 957 while (likely(!sigint)) { 958 pbd = (struct block_desc *) ring.rd[block_num].iov_base; 959 960 if ((pbd->h1.block_status & TP_STATUS_USER) == 0) { 961 poll(&pfd, 1, -1); 962 continue; 963 } 964 965 walk_block(pbd, block_num); 966 flush_block(pbd); 967 block_num = (block_num + 1) % blocks; 968 } 969 970 len = sizeof(stats); 971 err = getsockopt(fd, SOL_PACKET, PACKET_STATISTICS, &stats, &len); 972 if (err < 0) { 973 perror("getsockopt"); 974 exit(1); 975 } 976 977 fflush(stdout); 978 printf("\nReceived %u packets, %lu bytes, %u dropped, freeze_q_cnt: %u\n", 979 stats.tp_packets, bytes_total, stats.tp_drops, 980 stats.tp_freeze_q_cnt); 981 982 teardown_socket(&ring, fd); 983 return 0; 984} 985 986------------------------------------------------------------------------------- 987+ PACKET_QDISC_BYPASS 988------------------------------------------------------------------------------- 989 990If there is a requirement to load the network with many packets in a similar 991fashion as pktgen does, you might set the following option after socket 992creation: 993 994 int one = 1; 995 setsockopt(fd, SOL_PACKET, PACKET_QDISC_BYPASS, &one, sizeof(one)); 996 997This has the side-effect, that packets sent through PF_PACKET will bypass the 998kernel's qdisc layer and are forcedly pushed to the driver directly. Meaning, 999packet are not buffered, tc disciplines are ignored, increased loss can occur 1000and such packets are also not visible to other PF_PACKET sockets anymore. So, 1001you have been warned; generally, this can be useful for stress testing various 1002components of a system. 1003 1004On default, PACKET_QDISC_BYPASS is disabled and needs to be explicitly enabled 1005on PF_PACKET sockets. 1006 1007------------------------------------------------------------------------------- 1008+ PACKET_TIMESTAMP 1009------------------------------------------------------------------------------- 1010 1011The PACKET_TIMESTAMP setting determines the source of the timestamp in 1012the packet meta information for mmap(2)ed RX_RING and TX_RINGs. If your 1013NIC is capable of timestamping packets in hardware, you can request those 1014hardware timestamps to be used. Note: you may need to enable the generation 1015of hardware timestamps with SIOCSHWTSTAMP (see related information from 1016Documentation/networking/timestamping.txt). 1017 1018PACKET_TIMESTAMP accepts the same integer bit field as SO_TIMESTAMPING: 1019 1020 int req = SOF_TIMESTAMPING_RAW_HARDWARE; 1021 setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req)) 1022 1023For the mmap(2)ed ring buffers, such timestamps are stored in the 1024tpacket{,2,3}_hdr structure's tp_sec and tp_{n,u}sec members. To determine 1025what kind of timestamp has been reported, the tp_status field is binary |'ed 1026with the following possible bits ... 1027 1028 TP_STATUS_TS_RAW_HARDWARE 1029 TP_STATUS_TS_SOFTWARE 1030 1031... that are equivalent to its SOF_TIMESTAMPING_* counterparts. For the 1032RX_RING, if neither is set (i.e. PACKET_TIMESTAMP is not set), then a 1033software fallback was invoked *within* PF_PACKET's processing code (less 1034precise). 1035 1036Getting timestamps for the TX_RING works as follows: i) fill the ring frames, 1037ii) call sendto() e.g. in blocking mode, iii) wait for status of relevant 1038frames to be updated resp. the frame handed over to the application, iv) walk 1039through the frames to pick up the individual hw/sw timestamps. 1040 1041Only (!) if transmit timestamping is enabled, then these bits are combined 1042with binary | with TP_STATUS_AVAILABLE, so you must check for that in your 1043application (e.g. !(tp_status & (TP_STATUS_SEND_REQUEST | TP_STATUS_SENDING)) 1044in a first step to see if the frame belongs to the application, and then 1045one can extract the type of timestamp in a second step from tp_status)! 1046 1047If you don't care about them, thus having it disabled, checking for 1048TP_STATUS_AVAILABLE resp. TP_STATUS_WRONG_FORMAT is sufficient. If in the 1049TX_RING part only TP_STATUS_AVAILABLE is set, then the tp_sec and tp_{n,u}sec 1050members do not contain a valid value. For TX_RINGs, by default no timestamp 1051is generated! 1052 1053See include/linux/net_tstamp.h and Documentation/networking/timestamping 1054for more information on hardware timestamps. 1055 1056------------------------------------------------------------------------------- 1057+ Miscellaneous bits 1058------------------------------------------------------------------------------- 1059 1060- Packet sockets work well together with Linux socket filters, thus you also 1061 might want to have a look at Documentation/networking/filter.txt 1062 1063-------------------------------------------------------------------------------- 1064+ THANKS 1065-------------------------------------------------------------------------------- 1066 1067 Jesse Brandeburg, for fixing my grammathical/spelling errors 1068 1069