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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |STANDARDS |HISTORY |NOTES |EXAMPLES |SEE ALSO |COLOPHON | |
bpf(2) System Calls Manualbpf(2)bpf - perform a command on an extended BPF map or program
#include <linux/bpf.h>int bpf(intcmd, union bpf_attr *attr, unsigned intsize);
Thebpf() system call performs a range of operations related to extended Berkeley Packet Filters. Extended BPF (or eBPF) is similar to the original ("classic") BPF (cBPF) used to filter network packets. For both cBPF and eBPF programs, the kernel statically analyzes the programs before loading them, in order to ensure that they cannot harm the running system. eBPF extends cBPF in multiple ways, including the ability to call a fixed set of in-kernel helper functions (via theBPF_CALLopcode extension provided by eBPF) and access shared data structures such as eBPF maps.Extended BPF Design/Architecture eBPF maps are a generic data structure for storage of different data types. Data types are generally treated as binary blobs, so a user just specifies the size of the key and the size of the value at map-creation time. In other words, a key/value for a given map can have an arbitrary structure. A user process can create multiple maps (with key/value-pairs being opaque bytes of data) and access them via file descriptors. Different eBPF programs can access the same maps in parallel. It's up to the user process and eBPF program to decide what they store inside maps. There's one special map type, called a program array. This type of map stores file descriptors referring to other eBPF programs. When a lookup in the map is performed, the program flow is redirected in-place to the beginning of another eBPF program and does not return back to the calling program. The level of nesting has a fixed limit of 32, so that infinite loops cannot be crafted. At run time, the program file descriptors stored in the map can be modified, so program functionality can be altered based on specific requirements. All programs referred to in a program- array map must have been previously loaded into the kernel viabpf(). If a map lookup fails, the current program continues its execution. SeeBPF_MAP_TYPE_PROG_ARRAYbelow for further details. Generally, eBPF programs are loaded by the user process and automatically unloaded when the process exits. In some cases, for example,tc-bpf(8), the program will continue to stay alive inside the kernel even after the process that loaded the program exits. In that case, the tc subsystem holds a reference to the eBPF program after the file descriptor has been closed by the user- space program. Thus, whether a specific program continues to live inside the kernel depends on how it is further attached to a given kernel subsystem after it was loaded viabpf(). Each eBPF program is a set of instructions that is safe to run until its completion. An in-kernel verifier statically determines that the eBPF program terminates and is safe to execute. During verification, the kernel increments reference counts for each of the maps that the eBPF program uses, so that the attached maps can't be removed until the program is unloaded. eBPF programs can be attached to different events. These events can be the arrival of network packets, tracing events, classification events by network queueing disciplines (for eBPF programs attached to atc(8) classifier), and other types that may be added in the future. A new event triggers execution of the eBPF program, which may store information about the event in eBPF maps. Beyond storing data, eBPF programs may call a fixed set of in-kernel helper functions. The same eBPF program can be attached to multiple events and different eBPF programs can access the same map: tracing tracing tracing packet packet packet event A event B event C on eth0 on eth1 on eth2 | | | | | ^ | | | | v | --> tracing <-- tracing socket tc ingress tc egress prog_1 prog_2 prog_3 classifier action | | | | prog_4 prog_5 |--- -----| |------| map_3 | | map_1 map_2 --| map_4 |--Arguments The operation to be performed by thebpf() system call is determined by thecmd argument. Each operation takes an accompanying argument, provided viaattr, which is a pointer to a union of typebpf_attr (see below). The unused fields and padding must be zeroed out before the call. Thesize argument is the size of the union pointed to byattr. The value provided incmd is one of the following:BPF_MAP_CREATE Create a map and return a file descriptor that refers to the map. The close-on-exec file descriptor flag (seefcntl(2)) is automatically enabled for the new file descriptor.BPF_MAP_LOOKUP_ELEM Look up an element by key in a specified map and return its value.BPF_MAP_UPDATE_ELEM Create or update an element (key/value pair) in a specified map.BPF_MAP_DELETE_ELEM Look up and delete an element by key in a specified map.BPF_MAP_GET_NEXT_KEY Look up an element by key in a specified map and return the key of the next element.BPF_PROG_LOAD Verify and load an eBPF program, returning a new file descriptor associated with the program. The close-on-exec file descriptor flag (seefcntl(2)) is automatically enabled for the new file descriptor. Thebpf_attr union consists of various anonymous structures that are used by differentbpf() commands: union bpf_attr { struct { /* Used by BPF_MAP_CREATE */ __u32 map_type; __u32 key_size; /* size of key in bytes */ __u32 value_size; /* size of value in bytes */ __u32 max_entries; /* maximum number of entries in a map */ }; struct { /* Used by BPF_MAP_*_ELEM and BPF_MAP_GET_NEXT_KEY commands */ __u32 map_fd; __aligned_u64 key; union { __aligned_u64 value; __aligned_u64 next_key; }; __u64 flags; }; struct { /* Used by BPF_PROG_LOAD */ __u32 prog_type; __u32 insn_cnt; __aligned_u64 insns; /* 'const struct bpf_insn *' */ __aligned_u64 license; /* 'const char *' */ __u32 log_level; /* verbosity level of verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *' buffer */ __u32 kern_version; /* checked when prog_type=kprobe (since Linux 4.1) */ }; } __attribute__((aligned(8)));eBPF maps Maps are a generic data structure for storage of different types of data. They allow sharing of data between eBPF kernel programs, and also between kernel and user-space applications. Each map type has the following attributes: • type • maximum number of elements • key size in bytes • value size in bytes The following wrapper functions demonstrate how variousbpf() commands can be used to access the maps. The functions use thecmd argument to invoke different operations.BPF_MAP_CREATE TheBPF_MAP_CREATEcommand creates a new map, returning a new file descriptor that refers to the map. int bpf_create_map(enum bpf_map_type map_type, unsigned int key_size, unsigned int value_size, unsigned int max_entries) { union bpf_attr attr = { .map_type = map_type, .key_size = key_size, .value_size = value_size, .max_entries = max_entries }; return bpf(BPF_MAP_CREATE, &attr, sizeof(attr)); } The new map has the type specified bymap_type, and attributes as specified inkey_size,value_size, andmax_entries. On success, this operation returns a file descriptor. On error, -1 is returned anderrno is set toEINVAL,EPERM, orENOMEM. Thekey_size andvalue_size attributes will be used by the verifier during program loading to check that the program is callingbpf_map_*_elem() helper functions with a correctly initializedkey and to check that the program doesn't access the map elementvalue beyond the specifiedvalue_size. For example, when a map is created with akey_size of 8 and the eBPF program calls bpf_map_lookup_elem(map_fd, fp - 4) the program will be rejected, since the in-kernel helper function bpf_map_lookup_elem(map_fd, void *key) expects to read 8 bytes from the location pointed to bykey, but thefp - 4 (wherefp is the top of the stack) starting address will cause out-of-bounds stack access. Similarly, when a map is created with avalue_size of 1 and the eBPF program contains value = bpf_map_lookup_elem(...); *(u32 *) value = 1; the program will be rejected, since it accesses thevalue pointer beyond the specified 1 bytevalue_size limit. Currently, the following values are supported formap_type: enum bpf_map_type { BPF_MAP_TYPE_UNSPEC, /* Reserve 0 as invalid map type */ BPF_MAP_TYPE_HASH, BPF_MAP_TYPE_ARRAY, BPF_MAP_TYPE_PROG_ARRAY, BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_MAP_TYPE_PERCPU_HASH, BPF_MAP_TYPE_PERCPU_ARRAY, BPF_MAP_TYPE_STACK_TRACE, BPF_MAP_TYPE_CGROUP_ARRAY, BPF_MAP_TYPE_LRU_HASH, BPF_MAP_TYPE_LRU_PERCPU_HASH, BPF_MAP_TYPE_LPM_TRIE, BPF_MAP_TYPE_ARRAY_OF_MAPS, BPF_MAP_TYPE_HASH_OF_MAPS, BPF_MAP_TYPE_DEVMAP, BPF_MAP_TYPE_SOCKMAP, BPF_MAP_TYPE_CPUMAP, BPF_MAP_TYPE_XSKMAP, BPF_MAP_TYPE_SOCKHASH, BPF_MAP_TYPE_CGROUP_STORAGE, BPF_MAP_TYPE_REUSEPORT_SOCKARRAY, BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE, BPF_MAP_TYPE_QUEUE, BPF_MAP_TYPE_STACK, /* See /usr/include/linux/bpf.h for the full list. */ };map_type selects one of the available map implementations in the kernel. For all map types, eBPF programs access maps with the samebpf_map_lookup_elem() andbpf_map_update_elem() helper functions. Further details of the various map types are given below.BPF_MAP_LOOKUP_ELEM TheBPF_MAP_LOOKUP_ELEMcommand looks up an element with a givenkey in the map referred to by the file descriptorfd. int bpf_lookup_elem(int fd, const void *key, void *value) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), .value = ptr_to_u64(value), }; return bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr)); } If an element is found, the operation returns zero and stores the element's value intovalue, which must point to a buffer ofvalue_size bytes. If no element is found, the operation returns -1 and setserrno toENOENT.BPF_MAP_UPDATE_ELEM TheBPF_MAP_UPDATE_ELEMcommand creates or updates an element with a givenkey/value in the map referred to by the file descriptorfd. int bpf_update_elem(int fd, const void *key, const void *value, uint64_t flags) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), .value = ptr_to_u64(value), .flags = flags, }; return bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr)); } Theflags argument should be specified as one of the following:BPF_ANY Create a new element or update an existing element.BPF_NOEXIST Create a new element only if it did not exist.BPF_EXIST Update an existing element. On success, the operation returns zero. On error, -1 is returned anderrno is set toEINVAL,EPERM,ENOMEM, orE2BIG.E2BIGindicates that the number of elements in the map reached themax_entries limit specified at map creation time.EEXISTwill be returned ifflags specifiesBPF_NOEXISTand the element withkey already exists in the map.ENOENTwill be returned ifflags specifiesBPF_EXIST and the element withkey doesn't exist in the map.BPF_MAP_DELETE_ELEM TheBPF_MAP_DELETE_ELEMcommand deletes the element whose key iskey from the map referred to by the file descriptorfd. int bpf_delete_elem(int fd, const void *key) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), }; return bpf(BPF_MAP_DELETE_ELEM, &attr, sizeof(attr)); } On success, zero is returned. If the element is not found, -1 is returned anderrno is set toENOENT.BPF_MAP_GET_NEXT_KEY TheBPF_MAP_GET_NEXT_KEYcommand looks up an element bykey in the map referred to by the file descriptorfd and sets thenext_key pointer to the key of the next element. int bpf_get_next_key(int fd, const void *key, void *next_key) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), .next_key = ptr_to_u64(next_key), }; return bpf(BPF_MAP_GET_NEXT_KEY, &attr, sizeof(attr)); } Ifkey is found, the operation returns zero and sets thenext_key pointer to the key of the next element. Ifkey is not found, the operation returns zero and sets thenext_key pointer to the key of the first element. Ifkey is the last element, -1 is returned anderrno is set toENOENT. Other possibleerrno values areENOMEM,EFAULT,EPERM, andEINVAL. This method can be used to iterate over all elements in the map.close(map_fd) Delete the map referred to by the file descriptormap_fd. When the user-space program that created a map exits, all maps will be deleted automatically (but see NOTES).eBPF map types The following map types are supported:BPF_MAP_TYPE_HASH Hash-table maps have the following characteristics: • Maps are created and destroyed by user-space programs. Both user-space and eBPF programs can perform lookup, update, and delete operations. • The kernel takes care of allocating and freeing key/value pairs. • Themap_update_elem() helper will fail to insert new element when themax_entries limit is reached. (This ensures that eBPF programs cannot exhaust memory.) •map_update_elem() replaces existing elements atomically. Hash-table maps are optimized for speed of lookup.BPF_MAP_TYPE_ARRAY Array maps have the following characteristics: • Optimized for fastest possible lookup. In the future the verifier/JIT compiler may recognize lookup() operations that employ a constant key and optimize it into constant pointer. It is possible to optimize a non-constant key into direct pointer arithmetic as well, since pointers andvalue_size are constant for the life of the eBPF program. In other words,array_map_lookup_elem() may be 'inlined' by the verifier/JIT compiler while preserving concurrent access to this map from user space. • All array elements pre-allocated and zero initialized at init time • The key is an array index, and must be exactly four bytes. •map_delete_elem() fails with the errorEINVAL, since elements cannot be deleted. •map_update_elem() replaces elements in anonatomic fashion; for atomic updates, a hash-table map should be used instead. There is however one special case that can also be used with arrays: the atomic built-in__sync_fetch_and_add()can be used on 32 and 64 bit atomic counters. For example, it can be applied on the whole value itself if it represents a single counter, or in case of a structure containing multiple counters, it could be used on individual counters. This is quite often useful for aggregation and accounting of events. Among the uses for array maps are the following: • As "global" eBPF variables: an array of 1 element whose key is (index) 0 and where the value is a collection of 'global' variables which eBPF programs can use to keep state between events. • Aggregation of tracing events into a fixed set of buckets. • Accounting of networking events, for example, number of packets and packet sizes.BPF_MAP_TYPE_PROG_ARRAY(since Linux 4.2) A program array map is a special kind of array map whose map values contain only file descriptors referring to other eBPF programs. Thus, both thekey_size andvalue_size must be exactly four bytes. This map is used in conjunction with thebpf_tail_call() helper. This means that an eBPF program with a program array map attached to it can call from kernel side into void bpf_tail_call(void *context, void *prog_map, unsigned int index); and therefore replace its own program flow with the one from the program at the given program array slot, if present. This can be regarded as kind of a jump table to a different eBPF program. The invoked program will then reuse the same stack. When a jump into the new program has been performed, it won't return to the old program anymore. If no eBPF program is found at the given index of the program array (because the map slot doesn't contain a valid program file descriptor, the specified lookup index/key is out of bounds, or the limit of 32 nested calls has been exceed), execution continues with the current eBPF program. This can be used as a fall-through for default cases. A program array map is useful, for example, in tracing or networking, to handle individual system calls or protocols in their own subprograms and use their identifiers as an individual map index. This approach may result in performance benefits, and also makes it possible to overcome the maximum instruction limit of a single eBPF program. In dynamic environments, a user-space daemon might atomically replace individual subprograms at run-time with newer versions to alter overall program behavior, for instance, if global policies change.eBPF programs TheBPF_PROG_LOADcommand is used to load an eBPF program into the kernel. The return value for this command is a new file descriptor associated with this eBPF program. char bpf_log_buf[LOG_BUF_SIZE]; int bpf_prog_load(enum bpf_prog_type type, const struct bpf_insn *insns, int insn_cnt, const char *license) { union bpf_attr attr = { .prog_type = type, .insns = ptr_to_u64(insns), .insn_cnt = insn_cnt, .license = ptr_to_u64(license), .log_buf = ptr_to_u64(bpf_log_buf), .log_size = LOG_BUF_SIZE, .log_level = 1, }; return bpf(BPF_PROG_LOAD, &attr, sizeof(attr)); }prog_type is one of the available program types: enum bpf_prog_type { BPF_PROG_TYPE_UNSPEC, /* Reserve 0 as invalid program type */ BPF_PROG_TYPE_SOCKET_FILTER, BPF_PROG_TYPE_KPROBE, BPF_PROG_TYPE_SCHED_CLS, BPF_PROG_TYPE_SCHED_ACT, BPF_PROG_TYPE_TRACEPOINT, BPF_PROG_TYPE_XDP, BPF_PROG_TYPE_PERF_EVENT, BPF_PROG_TYPE_CGROUP_SKB, BPF_PROG_TYPE_CGROUP_SOCK, BPF_PROG_TYPE_LWT_IN, BPF_PROG_TYPE_LWT_OUT, BPF_PROG_TYPE_LWT_XMIT, BPF_PROG_TYPE_SOCK_OPS, BPF_PROG_TYPE_SK_SKB, BPF_PROG_TYPE_CGROUP_DEVICE, BPF_PROG_TYPE_SK_MSG, BPF_PROG_TYPE_RAW_TRACEPOINT, BPF_PROG_TYPE_CGROUP_SOCK_ADDR, BPF_PROG_TYPE_LWT_SEG6LOCAL, BPF_PROG_TYPE_LIRC_MODE2, BPF_PROG_TYPE_SK_REUSEPORT, BPF_PROG_TYPE_FLOW_DISSECTOR, /* See /usr/include/linux/bpf.h for the full list. */ }; For further details of eBPF program types, see below. The remaining fields ofbpf_attr are set as follows: •insns is an array ofstruct bpf_insn instructions. •insn_cnt is the number of instructions in the program referred to byinsns. •license is a license string, which must be GPL compatible to call helper functions markedgpl_only. (The licensing rules are the same as for kernel modules, so that also dual licenses, such as "Dual BSD/GPL", may be used.) •log_buf is a pointer to a caller-allocated buffer in which the in-kernel verifier can store the verification log. This log is a multi-line string that can be checked by the program author in order to understand how the verifier came to the conclusion that the eBPF program is unsafe. The format of the output can change at any time as the verifier evolves. •log_size size of the buffer pointed to bylog_buf. If the size of the buffer is not large enough to store all verifier messages, -1 is returned anderrno is set toENOSPC. •log_level verbosity level of the verifier. A value of zero means that the verifier will not provide a log; in this case,log_buf must be a null pointer, andlog_size must be zero. Applyingclose(2) to the file descriptor returned byBPF_PROG_LOAD will unload the eBPF program (but see NOTES). Maps are accessible from eBPF programs and are used to exchange data between eBPF programs and between eBPF programs and user- space programs. For example, eBPF programs can process various events (like kprobe, packets) and store their data into a map, and user-space programs can then fetch data from the map. Conversely, user-space programs can use a map as a configuration mechanism, populating the map with values checked by the eBPF program, which then modifies its behavior on the fly according to those values.eBPF program types The eBPF program type (prog_type) determines the subset of kernel helper functions that the program may call. The program type also determines the program input (context)—the format ofstructbpf_context (which is the data blob passed into the eBPF program as the first argument). For example, a tracing program does not have the exact same subset of helper functions as a socket filter program (though they may have some helpers in common). Similarly, the input (context) for a tracing program is a set of register values, while for a socket filter it is a network packet. The set of functions available to eBPF programs of a given type may increase in the future. The following program types are supported:BPF_PROG_TYPE_SOCKET_FILTER(since Linux 3.19) Currently, the set of functions forBPF_PROG_TYPE_SOCKET_FILTERis: bpf_map_lookup_elem(map_fd, void *key) /* look up key in a map_fd */ bpf_map_update_elem(map_fd, void *key, void *value) /* update key/value */ bpf_map_delete_elem(map_fd, void *key) /* delete key in a map_fd */ Thebpf_context argument is a pointer to astruct__sk_buff.BPF_PROG_TYPE_KPROBE(since Linux 4.1) [To be documented]BPF_PROG_TYPE_SCHED_CLS(since Linux 4.1) [To be documented]BPF_PROG_TYPE_SCHED_ACT(since Linux 4.1) [To be documented]Events Once a program is loaded, it can be attached to an event. Various kernel subsystems have different ways to do so. Since Linux 3.19, the following call will attach the programprog_fd to the socketsockfd, which was created by an earlier call tosocket(2): setsockopt(sockfd, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd, sizeof(prog_fd)); Since Linux 4.1, the following call may be used to attach the eBPF program referred to by the file descriptorprog_fd to a perf event file descriptor,event_fd, that was created by a previous call toperf_event_open(2): ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);For a successful call, the return value depends on the operation:BPF_MAP_CREATE The new file descriptor associated with the eBPF map.BPF_PROG_LOAD The new file descriptor associated with the eBPF program. All other commands Zero. On error, -1 is returned, anderrno is set to indicate the error.
E2BIGThe eBPF program is too large or a map reached themax_entries limit (maximum number of elements).EACCESForBPF_PROG_LOAD, even though all program instructions are valid, the program has been rejected because it was deemed unsafe. This may be because it may have accessed a disallowed memory region or an uninitialized stack/register or because the function constraints don't match the actual types or because there was a misaligned memory access. In this case, it is recommended to callbpf() again withlog_level = 1 and examinelog_buf for the specific reason provided by the verifier.EAGAINForBPF_PROG_LOAD, indicates that needed resources are blocked. This happens when the verifier detects pending signals while it is checking the validity of the bpf program. In this case, just callbpf() again with the same parameters.EBADFfd is not an open file descriptor.EFAULTOne of the pointers (key orvalue orlog_buf orinsns) is outside the accessible address space.EINVALThe value specified incmd is not recognized by this kernel.EINVALForBPF_MAP_CREATE, eithermap_type or attributes are invalid.EINVALForBPF_MAP_*_ELEMcommands, some of the fields ofunionbpf_attr that are not used by this command are not set to zero.EINVALForBPF_PROG_LOAD, indicates an attempt to load an invalid program. eBPF programs can be deemed invalid due to unrecognized instructions, the use of reserved fields, jumps out of range, infinite loops or calls of unknown functions.ENOENTForBPF_MAP_LOOKUP_ELEMorBPF_MAP_DELETE_ELEM, indicates that the element with the givenkey was not found.ENOMEMCannot allocate sufficient memory.EPERMThe call was made without sufficient privilege (without theCAP_SYS_ADMINcapability).
Linux.
Linux 3.18.
Prior to Linux 4.4, allbpf() commands require the caller to have theCAP_SYS_ADMINcapability. From Linux 4.4 onwards, an unprivileged user may create limited programs of typeBPF_PROG_TYPE_SOCKET_FILTERand associated maps. However they may not store kernel pointers within the maps and are presently limited to the following helper functions: • get_random • get_smp_processor_id • tail_call • ktime_get_ns Unprivileged access may be blocked by writing the value 1 to the file/proc/sys/kernel/unprivileged_bpf_disabled. eBPF objects (maps and programs) can be shared between processes. For example, afterfork(2), the child inherits file descriptors referring to the same eBPF objects. In addition, file descriptors referring to eBPF objects can be transferred over UNIX domain sockets. File descriptors referring to eBPF objects can be duplicated in the usual way, usingdup(2) and similar calls. An eBPF object is deallocated only after all file descriptors referring to the object have been closed. eBPF programs can be written in a restricted C that is compiled (using theclangcompiler) into eBPF bytecode. Various features are omitted from this restricted C, such as loops, global variables, variadic functions, floating-point numbers, and passing structures as function arguments. Some examples can be found in thesamples/bpf/*_kern.c files in the kernel source tree. The kernel contains a just-in-time (JIT) compiler that translates eBPF bytecode into native machine code for better performance. Before Linux 4.15, the JIT compiler is disabled by default, but its operation can be controlled by writing one of the following integer strings to the file/proc/sys/net/core/bpf_jit_enable:0Disable JIT compilation (default).1Normal compilation.2Debugging mode. The generated opcodes are dumped in hexadecimal into the kernel log. These opcodes can then be disassembled using the programtools/net/bpf_jit_disasm.c provided in the kernel source tree. Since Linux 4.15, the kernel may be configured with theCONFIG_BPF_JIT_ALWAYS_ONoption. In this case, the JIT compiler is always enabled, and thebpf_jit_enable is initialized to 1 and is immutable. (This kernel configuration option was provided as a mitigation for one of the Spectre attacks against the BPF interpreter.) The JIT compiler for eBPF is currently available for the following architectures: • x86-64 (since Linux 3.18; cBPF since Linux 3.0); • ARM32 (since Linux 3.18; cBPF since Linux 3.4); • SPARC 32 (since Linux 3.18; cBPF since Linux 3.5); • ARM-64 (since Linux 3.18); • s390 (since Linux 4.1; cBPF since Linux 3.7); • PowerPC 64 (since Linux 4.8; cBPF since Linux 3.1); • SPARC 64 (since Linux 4.12); • x86-32 (since Linux 4.18); • MIPS 64 (since Linux 4.18; cBPF since Linux 3.16); • riscv (since Linux 5.1).
/* bpf+sockets example: * 1. create array map of 256 elements * 2. load program that counts number of packets received * r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)] * map[r0]++ * 3. attach prog_fd to raw socket via setsockopt() * 4. print number of received TCP/UDP packets every second */ int main(int argc, char *argv[]) { int sock, map_fd, prog_fd, key; long long value = 0, tcp_cnt, udp_cnt; map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key), sizeof(value), 256); if (map_fd < 0) { printf("failed to create map '%s'\n", strerror(errno)); /* likely not run as root */ return 1; } struct bpf_insn prog[] = { BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), /* r6 = r1 */ BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol)), /* r0 = ip->proto */ BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *) (fp - 4) = r0 */ BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), /* r2 = fp */ BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = r2 - 4 */ BPF_LD_MAP_FD(BPF_REG_1, map_fd), /* r1 = map_fd */ BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), /* r0 = map_lookup(r1, r2) */ BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2), /* if (r0 == 0) goto pc+2 */ BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */ BPF_XADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* lock *(u64 *) r0 += r1 */ BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */ BPF_EXIT_INSN(), /* return r0 */ }; prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog, sizeof(prog) / sizeof(prog[0]), "GPL"); sock = open_raw_sock("lo"); assert(setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd, sizeof(prog_fd)) == 0); for (;;) { key = IPPROTO_TCP; assert(bpf_lookup_elem(map_fd, &key, &tcp_cnt) == 0); key = IPPROTO_UDP; assert(bpf_lookup_elem(map_fd, &key, &udp_cnt) == 0); printf("TCP %lld UDP %lld packets\n", tcp_cnt, udp_cnt); sleep(1); } return 0; } Some complete working code can be found in thesamples/bpf directory in the kernel source tree.seccomp(2),bpf-helpers(7),socket(7),tc(8),tc-bpf(8) Both classic and extended BPF are explained in the kernel source fileDocumentation/networking/filter.txt.
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17bpf(2)Pages that refer to this page:perf_event_open(2), seccomp(2), syscalls(2), lirc(4), proc_pid_fd(5), proc_sys_net(5), bpf-helpers(7), capabilities(7), socket(7), tc-bpf(8)
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