diff options
Diffstat (limited to 'Documentation/networking/packet_mmap.rst')
| -rw-r--r-- | Documentation/networking/packet_mmap.rst | 1083 |
1 files changed, 1083 insertions, 0 deletions
diff --git a/Documentation/networking/packet_mmap.rst b/Documentation/networking/packet_mmap.rst new file mode 100644 index 000000000..c5da1a5d9 --- /dev/null +++ b/Documentation/networking/packet_mmap.rst @@ -0,0 +1,1083 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=========== +Packet MMAP +=========== + +Abstract +======== + +This file documents the mmap() facility available with the PACKET +socket interface. This type of sockets is used for + +i) capture network traffic with utilities like tcpdump, +ii) transmit network traffic, or any other that needs raw + access to network interface. + +Howto can be found at: + + https://sites.google.com/site/packetmmap/ + +Please send your comments to + - Ulisses Alonso Camaró <uaca@i.hate.spam.alumni.uv.es> + - Johann Baudy + +Why use PACKET_MMAP +=================== + +Non PACKET_MMAP capture process (plain AF_PACKET) is very +inefficient. It uses very limited buffers and requires one system call to +capture each packet, it requires two if you want to get packet's timestamp +(like libpcap always does). + +On the other hand PACKET_MMAP is very efficient. PACKET_MMAP provides a size +configurable circular buffer mapped in user space that can be used to either +send or receive packets. This way reading packets just needs to wait for them, +most of the time there is no need to issue a single system call. Concerning +transmission, multiple packets can be sent through one system call to get the +highest bandwidth. By using a shared buffer between the kernel and the user +also has the benefit of minimizing packet copies. + +It's fine to use PACKET_MMAP to improve the performance of the capture and +transmission process, but it isn't everything. At least, if you are capturing +at high speeds (this is relative to the cpu speed), you should check if the +device driver of your network interface card supports some sort of interrupt +load mitigation or (even better) if it supports NAPI, also make sure it is +enabled. For transmission, check the MTU (Maximum Transmission Unit) used and +supported by devices of your network. CPU IRQ pinning of your network interface +card can also be an advantage. + +How to use mmap() to improve capture process +============================================ + +From the user standpoint, you should use the higher level libpcap library, which +is a de facto standard, portable across nearly all operating systems +including Win32. + +Packet MMAP support was integrated into libpcap around the time of version 1.3.0; +TPACKET_V3 support was added in version 1.5.0 + +How to use mmap() directly to improve capture process +===================================================== + +From the system calls stand point, the use of PACKET_MMAP involves +the following process:: + + + [setup] socket() -------> creation of the capture socket + setsockopt() ---> allocation of the circular buffer (ring) + option: PACKET_RX_RING + mmap() ---------> mapping of the allocated buffer to the + user process + + [capture] poll() ---------> to wait for incoming packets + + [shutdown] close() --------> destruction of the capture socket and + deallocation of all associated + resources. + + +socket creation and destruction is straight forward, and is done +the same way with or without PACKET_MMAP:: + + int fd = socket(PF_PACKET, mode, htons(ETH_P_ALL)); + +where mode is SOCK_RAW for the raw interface were link level +information can be captured or SOCK_DGRAM for the cooked +interface where link level information capture is not +supported and a link level pseudo-header is provided +by the kernel. + +The destruction of the socket and all associated resources +is done by a simple call to close(fd). + +Similarly as without PACKET_MMAP, it is possible to use one socket +for capture and transmission. This can be done by mapping the +allocated RX and TX buffer ring with a single mmap() call. +See "Mapping and use of the circular buffer (ring)". + +Next I will describe PACKET_MMAP settings and its constraints, +also the mapping of the circular buffer in the user process and +the use of this buffer. + +How to use mmap() directly to improve transmission process +========================================================== +Transmission process is similar to capture as shown below:: + + [setup] socket() -------> creation of the transmission socket + setsockopt() ---> allocation of the circular buffer (ring) + option: PACKET_TX_RING + bind() ---------> bind transmission socket with a network interface + mmap() ---------> mapping of the allocated buffer to the + user process + + [transmission] poll() ---------> wait for free packets (optional) + send() ---------> send all packets that are set as ready in + the ring + The flag MSG_DONTWAIT can be used to return + before end of transfer. + + [shutdown] close() --------> destruction of the transmission socket and + deallocation of all associated resources. + +Socket creation and destruction is also straight forward, and is done +the same way as in capturing described in the previous paragraph:: + + int fd = socket(PF_PACKET, mode, 0); + +The protocol can optionally be 0 in case we only want to transmit +via this socket, which avoids an expensive call to packet_rcv(). +In this case, you also need to bind(2) the TX_RING with sll_protocol = 0 +set. Otherwise, htons(ETH_P_ALL) or any other protocol, for example. + +Binding the socket to your network interface is mandatory (with zero copy) to +know the header size of frames used in the circular buffer. + +As capture, each frame contains two parts:: + + -------------------- + | struct tpacket_hdr | Header. It contains the status of + | | of this frame + |--------------------| + | data buffer | + . . Data that will be sent over the network interface. + . . + -------------------- + + bind() associates the socket to your network interface thanks to + sll_ifindex parameter of struct sockaddr_ll. + + Initialization example:: + + struct sockaddr_ll my_addr; + struct ifreq s_ifr; + ... + + strscpy_pad (s_ifr.ifr_name, "eth0", sizeof(s_ifr.ifr_name)); + + /* get interface index of eth0 */ + ioctl(this->socket, SIOCGIFINDEX, &s_ifr); + + /* fill sockaddr_ll struct to prepare binding */ + my_addr.sll_family = AF_PACKET; + my_addr.sll_protocol = htons(ETH_P_ALL); + my_addr.sll_ifindex = s_ifr.ifr_ifindex; + + /* bind socket to eth0 */ + bind(this->socket, (struct sockaddr *)&my_addr, sizeof(struct sockaddr_ll)); + + A complete tutorial is available at: https://sites.google.com/site/packetmmap/ + +By default, the user should put data at:: + + frame base + TPACKET_HDRLEN - sizeof(struct sockaddr_ll) + +So, whatever you choose for the socket mode (SOCK_DGRAM or SOCK_RAW), +the beginning of the user data will be at:: + + frame base + TPACKET_ALIGN(sizeof(struct tpacket_hdr)) + +If you wish to put user data at a custom offset from the beginning of +the frame (for payload alignment with SOCK_RAW mode for instance) you +can set tp_net (with SOCK_DGRAM) or tp_mac (with SOCK_RAW). In order +to make this work it must be enabled previously with setsockopt() +and the PACKET_TX_HAS_OFF option. + +PACKET_MMAP settings +==================== + +To setup PACKET_MMAP from user level code is done with a call like + + - Capture process:: + + setsockopt(fd, SOL_PACKET, PACKET_RX_RING, (void *) &req, sizeof(req)) + + - Transmission process:: + + setsockopt(fd, SOL_PACKET, PACKET_TX_RING, (void *) &req, sizeof(req)) + +The most significant argument in the previous call is the req parameter, +this parameter must to have the following structure:: + + struct tpacket_req + { + unsigned int tp_block_size; /* Minimal size of contiguous block */ + unsigned int tp_block_nr; /* Number of blocks */ + unsigned int tp_frame_size; /* Size of frame */ + unsigned int tp_frame_nr; /* Total number of frames */ + }; + +This structure is defined in /usr/include/linux/if_packet.h and establishes a +circular buffer (ring) of unswappable memory. +Being mapped in the capture process allows reading the captured frames and +related meta-information like timestamps without requiring a system call. + +Frames are grouped in blocks. Each block is a physically contiguous +region of memory and holds tp_block_size/tp_frame_size frames. The total number +of blocks is tp_block_nr. Note that tp_frame_nr is a redundant parameter because:: + + frames_per_block = tp_block_size/tp_frame_size + +indeed, packet_set_ring checks that the following condition is true:: + + frames_per_block * tp_block_nr == tp_frame_nr + +Lets see an example, with the following values:: + + tp_block_size= 4096 + tp_frame_size= 2048 + tp_block_nr = 4 + tp_frame_nr = 8 + +we will get the following buffer structure:: + + block #1 block #2 + +---------+---------+ +---------+---------+ + | frame 1 | frame 2 | | frame 3 | frame 4 | + +---------+---------+ +---------+---------+ + + block #3 block #4 + +---------+---------+ +---------+---------+ + | frame 5 | frame 6 | | frame 7 | frame 8 | + +---------+---------+ +---------+---------+ + +A frame can be of any size with the only condition it can fit in a block. A block +can only hold an integer number of frames, or in other words, a frame cannot +be spawned across two blocks, so there are some details you have to take into +account when choosing the frame_size. See "Mapping and use of the circular +buffer (ring)". + +PACKET_MMAP setting constraints +=============================== + +In kernel versions prior to 2.4.26 (for the 2.4 branch) and 2.6.5 (2.6 branch), +the PACKET_MMAP buffer could hold only 32768 frames in a 32 bit architecture or +16384 in a 64 bit architecture. + +Block size limit +---------------- + +As stated earlier, each block is a contiguous physical region of memory. These +memory regions are allocated with calls to the __get_free_pages() function. As +the name indicates, this function allocates pages of memory, and the second +argument is "order" or a power of two number of pages, that is +(for PAGE_SIZE == 4096) order=0 ==> 4096 bytes, order=1 ==> 8192 bytes, +order=2 ==> 16384 bytes, etc. The maximum size of a +region allocated by __get_free_pages is determined by the MAX_ORDER macro. More +precisely the limit can be calculated as:: + + PAGE_SIZE << MAX_ORDER + + In a i386 architecture PAGE_SIZE is 4096 bytes + In a 2.4/i386 kernel MAX_ORDER is 10 + In a 2.6/i386 kernel MAX_ORDER is 11 + +So get_free_pages can allocate as much as 4MB or 8MB in a 2.4/2.6 kernel +respectively, with an i386 architecture. + +User space programs can include /usr/include/sys/user.h and +/usr/include/linux/mmzone.h to get PAGE_SIZE MAX_ORDER declarations. + +The pagesize can also be determined dynamically with the getpagesize (2) +system call. + +Block number limit +------------------ + +To understand the constraints of PACKET_MMAP, we have to see the structure +used to hold the pointers to each block. + +Currently, this structure is a dynamically allocated vector with kmalloc +called pg_vec, its size limits the number of blocks that can be allocated:: + + +---+---+---+---+ + | x | x | x | x | + +---+---+---+---+ + | | | | + | | | v + | | v block #4 + | v block #3 + v block #2 + block #1 + +kmalloc allocates any number of bytes of physically contiguous memory from +a pool of pre-determined sizes. This pool of memory is maintained by the slab +allocator which is at the end the responsible for doing the allocation and +hence which imposes the maximum memory that kmalloc can allocate. + +In a 2.4/2.6 kernel and the i386 architecture, the limit is 131072 bytes. The +predetermined sizes that kmalloc uses can be checked in the "size-<bytes>" +entries of /proc/slabinfo + +In a 32 bit architecture, pointers are 4 bytes long, so the total number of +pointers to blocks is:: + + 131072/4 = 32768 blocks + +PACKET_MMAP buffer size calculator +================================== + +Definitions: + +============== ================================================================ +<size-max> is the maximum size of allocable with kmalloc + (see /proc/slabinfo) +<pointer size> depends on the architecture -- ``sizeof(void *)`` +<page size> depends on the architecture -- PAGE_SIZE or getpagesize (2) +<max-order> is the value defined with MAX_ORDER +<frame size> it's an upper bound of frame's capture size (more on this later) +============== ================================================================ + +from these definitions we will derive:: + + <block number> = <size-max>/<pointer size> + <block size> = <pagesize> << <max-order> + +so, the max buffer size is:: + + <block number> * <block size> + +and, the number of frames be:: + + <block number> * <block size> / <frame size> + +Suppose the following parameters, which apply for 2.6 kernel and an +i386 architecture:: + + <size-max> = 131072 bytes + <pointer size> = 4 bytes + <pagesize> = 4096 bytes + <max-order> = 11 + +and a value for <frame size> of 2048 bytes. These parameters will yield:: + + <block number> = 131072/4 = 32768 blocks + <block size> = 4096 << 11 = 8 MiB. + +and hence the buffer will have a 262144 MiB size. So it can hold +262144 MiB / 2048 bytes = 134217728 frames + +Actually, this buffer size is not possible with an i386 architecture. +Remember that the memory is allocated in kernel space, in the case of +an i386 kernel's memory size is limited to 1GiB. + +All memory allocations are not freed until the socket is closed. The memory +allocations are done with GFP_KERNEL priority, this basically means that +the allocation can wait and swap other process' memory in order to allocate +the necessary memory, so normally limits can be reached. + +Other constraints +----------------- + +If you check the source code you will see that what I draw here as a frame +is not only the link level frame. At the beginning of each frame there is a +header called struct tpacket_hdr used in PACKET_MMAP to hold link level's frame +meta information like timestamp. So what we draw here a frame it's really +the following (from include/linux/if_packet.h):: + + /* + Frame structure: + + - Start. Frame must be aligned to TPACKET_ALIGNMENT=16 + - struct tpacket_hdr + - pad to TPACKET_ALIGNMENT=16 + - struct sockaddr_ll + - Gap, chosen so that packet data (Start+tp_net) aligns to + TPACKET_ALIGNMENT=16 + - Start+tp_mac: [ Optional MAC header ] + - Start+tp_net: Packet data, aligned to TPACKET_ALIGNMENT=16. + - Pad to align to TPACKET_ALIGNMENT=16 + */ + +The following are conditions that are checked in packet_set_ring + + - tp_block_size must be a multiple of PAGE_SIZE (1) + - tp_frame_size must be greater than TPACKET_HDRLEN (obvious) + - tp_frame_size must be a multiple of TPACKET_ALIGNMENT + - tp_frame_nr must be exactly frames_per_block*tp_block_nr + +Note that tp_block_size should be chosen to be a power of two or there will +be a waste of memory. + +Mapping and use of the circular buffer (ring) +--------------------------------------------- + +The mapping of the buffer in the user process is done with the conventional +mmap function. Even the circular buffer is compound of several physically +discontiguous blocks of memory, they are contiguous to the user space, hence +just one call to mmap is needed:: + + mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); + +If tp_frame_size is a divisor of tp_block_size frames will be +contiguously spaced by tp_frame_size bytes. If not, each +tp_block_size/tp_frame_size frames there will be a gap between +the frames. This is because a frame cannot be spawn across two +blocks. + +To use one socket for capture and transmission, the mapping of both the +RX and TX buffer ring has to be done with one call to mmap:: + + ... + setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &foo, sizeof(foo)); + setsockopt(fd, SOL_PACKET, PACKET_TX_RING, &bar, sizeof(bar)); + ... + rx_ring = mmap(0, size * 2, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); + tx_ring = rx_ring + size; + +RX must be the first as the kernel maps the TX ring memory right +after the RX one. + +At the beginning of each frame there is an status field (see +struct tpacket_hdr). If this field is 0 means that the frame is ready +to be used for the kernel, If not, there is a frame the user can read +and the following flags apply: + +Capture process +^^^^^^^^^^^^^^^ + +From include/linux/if_packet.h:: + + #define TP_STATUS_COPY (1 << 1) + #define TP_STATUS_LOSING (1 << 2) + #define TP_STATUS_CSUMNOTREADY (1 << 3) + #define TP_STATUS_CSUM_VALID (1 << 7) + +====================== ======================================================= +TP_STATUS_COPY This flag indicates that the frame (and associated + meta information) has been truncated because it's + larger than tp_frame_size. This packet can be + read entirely with recvfrom(). + + In order to make this work it must to be + enabled previously with setsockopt() and + the PACKET_COPY_THRESH option. + + The number of frames that can be buffered to + be read with recvfrom is limited like a normal socket. + See the SO_RCVBUF option in the socket (7) man page. + +TP_STATUS_LOSING indicates there were packet drops from last time + statistics where checked with getsockopt() and + the PACKET_STATISTICS option. + +TP_STATUS_CSUMNOTREADY currently it's used for outgoing IP packets which + its checksum will be done in hardware. So while + reading the packet we should not try to check the + checksum. + +TP_STATUS_CSUM_VALID This flag indicates that at least the transport + header checksum of the packet has been already + validated on the kernel side. If the flag is not set + then we are free to check the checksum by ourselves + provided that TP_STATUS_CSUMNOTREADY is also not set. +====================== ======================================================= + +for convenience there are also the following defines:: + + #define TP_STATUS_KERNEL 0 + #define TP_STATUS_USER 1 + +The kernel initializes all frames to TP_STATUS_KERNEL, when the kernel +receives a packet it puts in the buffer and updates the status with +at least the TP_STATUS_USER flag. Then the user can read the packet, +once the packet is read the user must zero the status field, so the kernel +can use again that frame buffer. + +The user can use poll (any other variant should apply too) to check if new +packets are in the ring:: + + struct pollfd pfd; + + pfd.fd = fd; + pfd.revents = 0; + pfd.events = POLLIN|POLLRDNORM|POLLERR; + + if (status == TP_STATUS_KERNEL) + retval = poll(&pfd, 1, timeout); + +It doesn't incur in a race condition to first check the status value and +then poll for frames. + +Transmission process +^^^^^^^^^^^^^^^^^^^^ + +Those defines are also used for transmission:: + + #define TP_STATUS_AVAILABLE 0 // Frame is available + #define TP_STATUS_SEND_REQUEST 1 // Frame will be sent on next send() + #define TP_STATUS_SENDING 2 // Frame is currently in transmission + #define TP_STATUS_WRONG_FORMAT 4 // Frame format is not correct + +First, the kernel initializes all frames to TP_STATUS_AVAILABLE. To send a +packet, the user fills a data buffer of an available frame, sets tp_len to +current data buffer size and sets its status field to TP_STATUS_SEND_REQUEST. +This can be done on multiple frames. Once the user is ready to transmit, it +calls send(). Then all buffers with status equal to TP_STATUS_SEND_REQUEST are +forwarded to the network device. The kernel updates each status of sent +frames with TP_STATUS_SENDING until the end of transfer. + +At the end of each transfer, buffer status returns to TP_STATUS_AVAILABLE. + +:: + + header->tp_len = in_i_size; + header->tp_status = TP_STATUS_SEND_REQUEST; + retval = send(this->socket, NULL, 0, 0); + +The user can also use poll() to check if a buffer is available: + +(status == TP_STATUS_SENDING) + +:: + + struct pollfd pfd; + pfd.fd = fd; + pfd.revents = 0; + pfd.events = POLLOUT; + retval = poll(&pfd, 1, timeout); + +What TPACKET versions are available and when to use them? +========================================================= + +:: + + int val = tpacket_version; + setsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val)); + getsockopt(fd, SOL_PACKET, PACKET_VERSION, &val, sizeof(val)); + +where 'tpacket_version' can be TPACKET_V1 (default), TPACKET_V2, TPACKET_V3. + +TPACKET_V1: + - Default if not otherwise specified by setsockopt(2) + - RX_RING, TX_RING available + +TPACKET_V1 --> TPACKET_V2: + - Made 64 bit clean due to unsigned long usage in TPACKET_V1 + structures, thus this also works on 64 bit kernel with 32 bit + userspace and the like + - Timestamp resolution in nanoseconds instead of microseconds + - RX_RING, TX_RING available + - VLAN metadata information available for packets + (TP_STATUS_VLAN_VALID, TP_STATUS_VLAN_TPID_VALID), + in the tpacket2_hdr structure: + + - TP_STATUS_VLAN_VALID bit being set into the tp_status field indicates + that the tp_vlan_tci field has valid VLAN TCI value + - TP_STATUS_VLAN_TPID_VALID bit being set into the tp_status field + indicates that the tp_vlan_tpid field has valid VLAN TPID value + + - How to switch to TPACKET_V2: + + 1. Replace struct tpacket_hdr by struct tpacket2_hdr + 2. Query header len and save + 3. Set protocol version to 2, set up ring as usual + 4. For getting the sockaddr_ll, + use ``(void *)hdr + TPACKET_ALIGN(hdrlen)`` instead of + ``(void *)hdr + TPACKET_ALIGN(sizeof(struct tpacket_hdr))`` + +TPACKET_V2 --> TPACKET_V3: + - Flexible buffer implementation for RX_RING: + 1. Blocks can be configured with non-static frame-size + 2. Read/poll is at a block-level (as opposed to packet-level) + 3. Added poll timeout to avoid indefinite user-space wait + on idle links + 4. Added user-configurable knobs: + + 4.1 block::timeout + 4.2 tpkt_hdr::sk_rxhash + + - RX Hash data available in user space + - TX_RING semantics are conceptually similar to TPACKET_V2; + use tpacket3_hdr instead of tpacket2_hdr, and TPACKET3_HDRLEN + instead of TPACKET2_HDRLEN. In the current implementation, + the tp_next_offset field in the tpacket3_hdr MUST be set to + zero, indicating that the ring does not hold variable sized frames. + Packets with non-zero values of tp_next_offset will be dropped. + +AF_PACKET fanout mode +===================== + +In the AF_PACKET fanout mode, packet reception can be load balanced among +processes. This also works in combination with mmap(2) on packet sockets. + +Currently implemented fanout policies are: + + - PACKET_FANOUT_HASH: schedule to socket by skb's packet hash + - PACKET_FANOUT_LB: schedule to socket by round-robin + - PACKET_FANOUT_CPU: schedule to socket by CPU packet arrives on + - PACKET_FANOUT_RND: schedule to socket by random selection + - PACKET_FANOUT_ROLLOVER: if one socket is full, rollover to another + - PACKET_FANOUT_QM: schedule to socket by skbs recorded queue_mapping + +Minimal example code by David S. Miller (try things like "./test eth0 hash", +"./test eth0 lb", etc.):: + + #include <stddef.h> + #include <stdlib.h> + #include <stdio.h> + #include <string.h> + + #include <sys/types.h> + #include <sys/wait.h> + #include <sys/socket.h> + #include <sys/ioctl.h> + + #include <unistd.h> + + #include <linux/if_ether.h> + #include <linux/if_packet.h> + + #include <net/if.h> + + static const char *device_name; + static int fanout_type; + static int fanout_id; + + #ifndef PACKET_FANOUT + # define PACKET_FANOUT 18 + # define PACKET_FANOUT_HASH 0 + # define PACKET_FANOUT_LB 1 + #endif + + static int setup_socket(void) + { + int err, fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP)); + struct sockaddr_ll ll; + struct ifreq ifr; + int fanout_arg; + + if (fd < 0) { + perror("socket"); + return EXIT_FAILURE; + } + + memset(&ifr, 0, sizeof(ifr)); + strcpy(ifr.ifr_name, device_name); + err = ioctl(fd, SIOCGIFINDEX, &ifr); + if (err < 0) { + perror("SIOCGIFINDEX"); + return EXIT_FAILURE; + } + + memset(&ll, 0, sizeof(ll)); + ll.sll_family = AF_PACKET; + ll.sll_ifindex = ifr.ifr_ifindex; + err = bind(fd, (struct sockaddr *) &ll, sizeof(ll)); + if (err < 0) { + perror("bind"); + return EXIT_FAILURE; + } + + fanout_arg = (fanout_id | (fanout_type << 16)); + err = setsockopt(fd, SOL_PACKET, PACKET_FANOUT, + &fanout_arg, sizeof(fanout_arg)); + if (err) { + perror("setsockopt"); + return EXIT_FAILURE; + } + + return fd; + } + + static void fanout_thread(void) + { + int fd = setup_socket(); + int limit = 10000; + + if (fd < 0) + exit(fd); + + while (limit-- > 0) { + char buf[1600]; + int err; + + err = read(fd, buf, sizeof(buf)); + if (err < 0) { + perror("read"); + exit(EXIT_FAILURE); + } + if ((limit % 10) == 0) + fprintf(stdout, "(%d) \n", getpid()); + } + + fprintf(stdout, "%d: Received 10000 packets\n", getpid()); + + close(fd); + exit(0); + } + + int main(int argc, char **argp) + { + int fd, err; + int i; + + if (argc != 3) { + fprintf(stderr, "Usage: %s INTERFACE {hash|lb}\n", argp[0]); + return EXIT_FAILURE; + } + + if (!strcmp(argp[2], "hash")) + fanout_type = PACKET_FANOUT_HASH; + else if (!strcmp(argp[2], "lb")) + fanout_type = PACKET_FANOUT_LB; + else { + fprintf(stderr, "Unknown fanout type [%s]\n", argp[2]); + exit(EXIT_FAILURE); + } + + device_name = argp[1]; + fanout_id = getpid() & 0xffff; + + for (i = 0; i < 4; i++) { + pid_t pid = fork(); + + switch (pid) { + case 0: + fanout_thread(); + + case -1: + perror("fork"); + exit(EXIT_FAILURE); + } + } + + for (i = 0; i < 4; i++) { + int status; + + wait(&status); + } + + return 0; + } + +AF_PACKET TPACKET_V3 example +============================ + +AF_PACKET's TPACKET_V3 ring buffer can be configured to use non-static frame +sizes by doing it's own memory management. It is based on blocks where polling +works on a per block basis instead of per ring as in TPACKET_V2 and predecessor. + +It is said that TPACKET_V3 brings the following benefits: + + * ~15% - 20% reduction in CPU-usage + * ~20% increase in packet capture rate + * ~2x increase in packet density + * Port aggregation analysis + * Non static frame size to capture entire packet payload + +So it seems to be a good candidate to be used with packet fanout. + +Minimal example code by Daniel Borkmann based on Chetan Loke's lolpcap (compile +it with gcc -Wall -O2 blob.c, and try things like "./a.out eth0", etc.):: + + /* Written from scratch, but kernel-to-user space API usage + * dissected from lolpcap: + * Copyright 2011, Chetan Loke <loke.chetan@gmail.com> + * License: GPL, version 2.0 + */ + + #include <stdio.h> + #include <stdlib.h> + #include <stdint.h> + #include <string.h> + #include <assert.h> + #include <net/if.h> + #include <arpa/inet.h> + #include <netdb.h> + #include <poll.h> + #include <unistd.h> + #include <signal.h> + #include <inttypes.h> + #include <sys/socket.h> + #include <sys/mman.h> + #include <linux/if_packet.h> + #include <linux/if_ether.h> + #include <linux/ip.h> + + #ifndef likely + # define likely(x) __builtin_expect(!!(x), 1) + #endif + #ifndef unlikely + # define unlikely(x) __builtin_expect(!!(x), 0) + #endif + + struct block_desc { + uint32_t version; + uint32_t offset_to_priv; + struct tpacket_hdr_v1 h1; + }; + + struct ring { + struct iovec *rd; + uint8_t *map; + struct tpacket_req3 req; + }; + + static unsigned long packets_total = 0, bytes_total = 0; + static sig_atomic_t sigint = 0; + + static void sighandler(int num) + { + sigint = 1; + } + + static int setup_socket(struct ring *ring, char *netdev) + { + int err, i, fd, v = TPACKET_V3; + struct sockaddr_ll ll; + unsigned int blocksiz = 1 << 22, framesiz = 1 << 11; + unsigned int blocknum = 64; + + fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL)); + if (fd < 0) { + perror("socket"); + exit(1); + } + + err = setsockopt(fd, SOL_PACKET, PACKET_VERSION, &v, sizeof(v)); + if (err < 0) { + perror("setsockopt"); + exit(1); + } + + memset(&ring->req, 0, sizeof(ring->req)); + ring->req.tp_block_size = blocksiz; + ring->req.tp_frame_size = framesiz; + ring->req.tp_block_nr = blocknum; + ring->req.tp_frame_nr = (blocksiz * blocknum) / framesiz; + ring->req.tp_retire_blk_tov = 60; + ring->req.tp_feature_req_word = TP_FT_REQ_FILL_RXHASH; + + err = setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &ring->req, + sizeof(ring->req)); + if (err < 0) { + perror("setsockopt"); + exit(1); + } + + ring->map = mmap(NULL, ring->req.tp_block_size * ring->req.tp_block_nr, + PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0); + if (ring->map == MAP_FAILED) { + perror("mmap"); + exit(1); + } + + ring->rd = malloc(ring->req.tp_block_nr * sizeof(*ring->rd)); + assert(ring->rd); + for (i = 0; i < ring->req.tp_block_nr; ++i) { + ring->rd[i].iov_base = ring->map + (i * ring->req.tp_block_size); + ring->rd[i].iov_len = ring->req.tp_block_size; + } + + memset(&ll, 0, sizeof(ll)); + ll.sll_family = PF_PACKET; + ll.sll_protocol = htons(ETH_P_ALL); + ll.sll_ifindex = if_nametoindex(netdev); + ll.sll_hatype = 0; + ll.sll_pkttype = 0; + ll.sll_halen = 0; + + err = bind(fd, (struct sockaddr *) &ll, sizeof(ll)); + if (err < 0) { + perror("bind"); + exit(1); + } + + return fd; + } + + static void display(struct tpacket3_hdr *ppd) + { + struct ethhdr *eth = (struct ethhdr *) ((uint8_t *) ppd + ppd->tp_mac); + struct iphdr *ip = (struct iphdr *) ((uint8_t *) eth + ETH_HLEN); + + if (eth->h_proto == htons(ETH_P_IP)) { + struct sockaddr_in ss, sd; + char sbuff[NI_MAXHOST], dbuff[NI_MAXHOST]; + + memset(&ss, 0, sizeof(ss)); + ss.sin_family = PF_INET; + ss.sin_addr.s_addr = ip->saddr; + getnameinfo((struct sockaddr *) &ss, sizeof(ss), + sbuff, sizeof(sbuff), NULL, 0, NI_NUMERICHOST); + + memset(&sd, 0, sizeof(sd)); + sd.sin_family = PF_INET; + sd.sin_addr.s_addr = ip->daddr; + getnameinfo((struct sockaddr *) &sd, sizeof(sd), + dbuff, sizeof(dbuff), NULL, 0, NI_NUMERICHOST); + + printf("%s -> %s, ", sbuff, dbuff); + } + + printf("rxhash: 0x%x\n", ppd->hv1.tp_rxhash); + } + + static void walk_block(struct block_desc *pbd, const int block_num) + { + int num_pkts = pbd->h1.num_pkts, i; + unsigned long bytes = 0; + struct tpacket3_hdr *ppd; + + ppd = (struct tpacket3_hdr *) ((uint8_t *) pbd + + pbd->h1.offset_to_first_pkt); + for (i = 0; i < num_pkts; ++i) { + bytes += ppd->tp_snaplen; + display(ppd); + + ppd = (struct tpacket3_hdr *) ((uint8_t *) ppd + + ppd->tp_next_offset); + } + + packets_total += num_pkts; + bytes_total += bytes; + } + + static void flush_block(struct block_desc *pbd) + { + pbd->h1.block_status = TP_STATUS_KERNEL; + } + + static void teardown_socket(struct ring *ring, int fd) + { + munmap(ring->map, ring->req.tp_block_size * ring->req.tp_block_nr); + free(ring->rd); + close(fd); + } + + int main(int argc, char **argp) + { + int fd, err; + socklen_t len; + struct ring ring; + struct pollfd pfd; + unsigned int block_num = 0, blocks = 64; + struct block_desc *pbd; + struct tpacket_stats_v3 stats; + + if (argc != 2) { + fprintf(stderr, "Usage: %s INTERFACE\n", argp[0]); + return EXIT_FAILURE; + } + + signal(SIGINT, sighandler); + + memset(&ring, 0, sizeof(ring)); + fd = setup_socket(&ring, argp[argc - 1]); + assert(fd > 0); + + memset(&pfd, 0, sizeof(pfd)); + pfd.fd = fd; + pfd.events = POLLIN | POLLERR; + pfd.revents = 0; + + while (likely(!sigint)) { + pbd = (struct block_desc *) ring.rd[block_num].iov_base; + + if ((pbd->h1.block_status & TP_STATUS_USER) == 0) { + poll(&pfd, 1, -1); + continue; + } + + walk_block(pbd, block_num); + flush_block(pbd); + block_num = (block_num + 1) % blocks; + } + + len = sizeof(stats); + err = getsockopt(fd, SOL_PACKET, PACKET_STATISTICS, &stats, &len); + if (err < 0) { + perror("getsockopt"); + exit(1); + } + + fflush(stdout); + printf("\nReceived %u packets, %lu bytes, %u dropped, freeze_q_cnt: %u\n", + stats.tp_packets, bytes_total, stats.tp_drops, + stats.tp_freeze_q_cnt); + + teardown_socket(&ring, fd); + return 0; + } + +PACKET_QDISC_BYPASS +=================== + +If there is a requirement to load the network with many packets in a similar +fashion as pktgen does, you might set the following option after socket +creation:: + + int one = 1; + setsockopt(fd, SOL_PACKET, PACKET_QDISC_BYPASS, &one, sizeof(one)); + +This has the side-effect, that packets sent through PF_PACKET will bypass the +kernel's qdisc layer and are forcedly pushed to the driver directly. Meaning, +packet are not buffered, tc disciplines are ignored, increased loss can occur +and such packets are also not visible to other PF_PACKET sockets anymore. So, +you have been warned; generally, this can be useful for stress testing various +components of a system. + +On default, PACKET_QDISC_BYPASS is disabled and needs to be explicitly enabled +on PF_PACKET sockets. + +PACKET_TIMESTAMP +================ + +The PACKET_TIMESTAMP setting determines the source of the timestamp in +the packet meta information for mmap(2)ed RX_RING and TX_RINGs. If your +NIC is capable of timestamping packets in hardware, you can request those +hardware timestamps to be used. Note: you may need to enable the generation +of hardware timestamps with SIOCSHWTSTAMP (see related information from +Documentation/networking/timestamping.rst). + +PACKET_TIMESTAMP accepts the same integer bit field as SO_TIMESTAMPING:: + + int req = SOF_TIMESTAMPING_RAW_HARDWARE; + setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req)) + +For the mmap(2)ed ring buffers, such timestamps are stored in the +``tpacket{,2,3}_hdr`` structure's tp_sec and ``tp_{n,u}sec`` members. +To determine what kind of timestamp has been reported, the tp_status field +is binary or'ed with the following possible bits ... + +:: + + TP_STATUS_TS_RAW_HARDWARE + TP_STATUS_TS_SOFTWARE + +... that are equivalent to its ``SOF_TIMESTAMPING_*`` counterparts. For the +RX_RING, if neither is set (i.e. PACKET_TIMESTAMP is not set), then a +software fallback was invoked *within* PF_PACKET's processing code (less +precise). + +Getting timestamps for the TX_RING works as follows: i) fill the ring frames, +ii) call sendto() e.g. in blocking mode, iii) wait for status of relevant +frames to be updated resp. the frame handed over to the application, iv) walk +through the frames to pick up the individual hw/sw timestamps. + +Only (!) if transmit timestamping is enabled, then these bits are combined +with binary | with TP_STATUS_AVAILABLE, so you must check for that in your +application (e.g. !(tp_status & (TP_STATUS_SEND_REQUEST | TP_STATUS_SENDING)) +in a first step to see if the frame belongs to the application, and then +one can extract the type of timestamp in a second step from tp_status)! + +If you don't care about them, thus having it disabled, checking for +TP_STATUS_AVAILABLE resp. TP_STATUS_WRONG_FORMAT is sufficient. If in the +TX_RING part only TP_STATUS_AVAILABLE is set, then the tp_sec and tp_{n,u}sec +members do not contain a valid value. For TX_RINGs, by default no timestamp +is generated! + +See include/linux/net_tstamp.h and Documentation/networking/timestamping.rst +for more information on hardware timestamps. + +Miscellaneous bits +================== + +- Packet sockets work well together with Linux socket filters, thus you also + might want to have a look at Documentation/networking/filter.rst + +THANKS +====== + + Jesse Brandeburg, for fixing my grammathical/spelling errors |