| -------------------------------------------------------------------------------- |
| + ABSTRACT |
| -------------------------------------------------------------------------------- |
| |
| This file documents the mmap() facility available with the PACKET |
| socket interface on 2.4/2.6/3.x kernels. 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. |
| |
| You can find the latest version of this document at: |
| http://wiki.ipxwarzone.com/index.php5?title=Linux_packet_mmap |
| |
| Howto can be found at: |
| http://wiki.gnu-log.net (packet_mmap) |
| |
| Please send your comments to |
| Ulisses Alonso CamarĂ³ <uaca@i.hate.spam.alumni.uv.es> |
| Johann Baudy <johann.baudy@gnu-log.net> |
| |
| ------------------------------------------------------------------------------- |
| + Why use PACKET_MMAP |
| -------------------------------------------------------------------------------- |
| |
| In Linux 2.4/2.6/3.x if PACKET_MMAP is not enabled, the capture process 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). |
| |
| In 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. |
| |
| Said that, at time of this writing, official libpcap 0.8.1 is out and doesn't include |
| support for PACKET_MMAP, and also probably the libpcap included in your distribution. |
| |
| I'm aware of two implementations of PACKET_MMAP in libpcap: |
| |
| http://wiki.ipxwarzone.com/ (by Simon Patarin, based on libpcap 0.6.2) |
| http://public.lanl.gov/cpw/ (by Phil Wood, based on lastest libpcap) |
| |
| The rest of this document is intended for people who want to understand |
| the low level details or want to improve libpcap by including PACKET_MMAP |
| support. |
| |
| -------------------------------------------------------------------------------- |
| + 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). |
| |
| 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; |
| ... |
| |
| strncpy (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: http://wiki.gnu-log.net/ |
| |
| 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. For information on these kernel versions |
| see http://pusa.uv.es/~ulisses/packet_mmap/packet_mmap.pre-2.4.26_2.6.5.txt |
| |
| 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. |
| |
| 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 2 |
| #define TP_STATUS_LOSING 4 |
| #define TP_STATUS_CSUMNOTREADY 8 |
| |
| 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 than 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. |
| |
| 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: |
| 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 |
| - Currently only RX_RING available |
| |
| ------------------------------------------------------------------------------- |
| + 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 rxhash |
| - 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 |
| |
| 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.txt). |
| |
| PACKET_TIMESTAMP accepts the same integer bit field as |
| SO_TIMESTAMPING. However, only the SOF_TIMESTAMPING_SYS_HARDWARE |
| and SOF_TIMESTAMPING_RAW_HARDWARE values are recognized by |
| PACKET_TIMESTAMP. SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over |
| SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set. |
| |
| int req = 0; |
| req |= SOF_TIMESTAMPING_SYS_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 |'ed |
| with the following possible bits ... |
| |
| TP_STATUS_TS_SYS_HARDWARE |
| TP_STATUS_TS_RAW_HARDWARE |
| TP_STATUS_TS_SOFTWARE |
| |
| ... that are equivalent to its SOF_TIMESTAMPING_* counterparts. For the |
| RX_RING, if none of those 3 are set (i.e. PACKET_TIMESTAMP is not set), |
| then this means that 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 |
| 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.txt |
| |
| -------------------------------------------------------------------------------- |
| + THANKS |
| -------------------------------------------------------------------------------- |
| |
| Jesse Brandeburg, for fixing my grammathical/spelling errors |
| |