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BPF(2)                     Linux Programmer's ManualBPF(2)NAME       bpf - perform a command on an extended BPF map or programSYNOPSIS       #include <linux/bpf.h>       int bpf(int cmd, union bpf_attr *attr, unsigned int size);DESCRIPTION       The  bpf()  system  call  performs a range of operations related to ex-       tended 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 the BPF_CALL opcode exten-       sion 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 via bpf().  If a map lookup fails, the current program continues       its execution.  See BPF_MAP_TYPE_PROG_ARRAY below for further details.       Generally, eBPF programs are loaded by the user process  and  automati-       cally 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 descrip-       tor  has  been  closed by the user-space program.  Thus, whether a spe-       cific program continues to live inside the kernel depends on how it  is       further  attached  to  a given kernel subsystem after it was loaded via       bpf().       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 informa-       tion 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 the bpf() system call is determined by       the  cmd argument.  Each operation takes an accompanying argument, pro-       vided via attr, which is a pointer to a union of type bpf_attr (see be-       low).  The size argument is the size of the union pointed to by attr.       The value provided in cmd 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.              The bpf_attr union consists of various anonymous structures that              are used by different bpf() 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 various bpf() commands       can be used to access the maps.  The functions use the cmd argument  to       invoke different operations.       BPF_MAP_CREATE              The  BPF_MAP_CREATE  command  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 by map_type,  and  attributes              as  specified in key_size, value_size, and max_entries.  On suc-              cess, this operation returns a file descriptor.  On error, -1 is              returned and errno is set to EINVAL, EPERM, or ENOMEM.              The key_size and value_size attributes will be used by the veri-              fier during program loading to check that the program is calling              bpf_map_*_elem()  helper  functions with a correctly initialized              key and to check that the program doesn't access the map element              value  beyond the specified value_size.  For example, when a map              is created with a key_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  func-              tion                  bpf_map_lookup_elem(map_fd, void *key)              expects to read 8 bytes from the location pointed to by key, but              the fp - 4 (where fp is the top of the stack)  starting  address              will cause out-of-bounds stack access.              Similarly,  when a map is created with a value_size of 1 and the              eBPF program contains                  value = bpf_map_lookup_elem(...);                  *(u32 *) value = 1;              the program will  be  rejected,  since  it  accesses  the  value              pointer beyond the specified 1 byte value_size limit.              Currently, the following values are supported for map_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,                  };              map_type selects one of the available map implementations in the              kernel.  For all map types, eBPF programs access maps  with  the              same   bpf_map_lookup_elem()  and  bpf_map_update_elem()  helper              functions.  Further details of the various map types  are  given              below.       BPF_MAP_LOOKUP_ELEM              The BPF_MAP_LOOKUP_ELEM command looks up an element with a given              key in the map referred to by the file descriptor fd.                  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 into value, which must point to a buffer of              value_size bytes.              If no element is found, the operation returns -1 and sets  errno              to ENOENT.       BPF_MAP_UPDATE_ELEM              The  BPF_MAP_UPDATE_ELEM  command  creates or updates an element              with a given key/value in the map referred to by  the  file  de-              scriptor fd.                  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));                  }              The flags 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 re-              turned and errno is set to  EINVAL,  EPERM,  ENOMEM,  or  E2BIG.              E2BIG  indicates  that the number of elements in the map reached              the max_entries limit specified at map  creation  time.   EEXIST              will  be returned if flags specifies BPF_NOEXIST and the element              with key already exists in the map.  ENOENT will be returned  if              flags specifies BPF_EXIST and the element with key doesn't exist              in the map.       BPF_MAP_DELETE_ELEM              The BPF_MAP_DELETE_ELEM command deletes the element whose key is              key from the map referred to by the file descriptor fd.                  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 and errno is set to ENOENT.       BPF_MAP_GET_NEXT_KEY              The BPF_MAP_GET_NEXT_KEY command looks up an element by  key  in              the  map  referred  to  by  the  file descriptor fd and sets the              next_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));                  }              If key is  found,  the  operation  returns  zero  and  sets  the              next_key  pointer to the key of the next element.  If key is not              found, the operation returns zero and sets the next_key  pointer              to the key of the first element.  If key is the last element, -1              is returned and errno is set to ENOENT.   Other  possible  errno              values  are  ENOMEM, EFAULT, EPERM, and EINVAL.  This method can              be used to iterate over all elements in the map.       close(map_fd)              Delete the map referred to by the file descriptor map_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.              *  The  map_update_elem() helper will fail to insert new element                 when the max_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 and value_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 error EINVAL, since elements                 cannot be deleted.              *  map_update_elem()  replaces  elements in a nonatomic 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  sin-                 gle  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 pack-                 ets 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  the key_size and value_size must be ex-              actly four bytes.  This map is  used  in  conjunction  with  the              bpf_tail_call() helper.              This  means  that  an  eBPF program with a program array map at-              tached 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 contin-              ues  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  net-              working, 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       The BPF_PROG_LOAD command is used to load an eBPF program into the ker-       nel.   The return value for this command is a new file descriptor asso-       ciated 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,                  };       For further details of eBPF program types, see below.       The remaining fields of bpf_attr are set as follows:       *  insns is an array of struct bpf_insn instructions.       *  insn_cnt is the number of instructions in the program referred to by          insns.       *  license  is  a  license string, which must be GPL compatible to call          helper functions marked gpl_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 by log_buf.  If the size of          the buffer is not large enough to store all verifier messages, -1 is          returned and errno is set to ENOSPC.       *  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, and log_size must be zero.       Applyingclose(2) to the file descriptor returned by BPF_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 pro-       grams.  For example, eBPF programs can  process  various  events  (like       kprobe,  packets)  and store their data into a map, and user-space pro-       grams can then fetch data from the map.   Conversely,  user-space  pro-       grams  can  use  a map as a configuration mechanism, populating the map       with values checked by the eBPF program, which then modifies its behav-       ior 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  de-       termines  the program input (context)--the format of struct bpf_context       (which is the data blob passed into the eBPF program as the first argu-       ment).       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 pro-       gram 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 in-       crease in the future.       The following program types are supported:       BPF_PROG_TYPE_SOCKET_FILTER (since Linux 3.19)              Currently, the set of functions for  BPF_PROG_TYPE_SOCKET_FILTER              is:                  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 */              The bpf_context argument is a pointer to a struct __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 ker-       nel subsystems have different ways to do so.       Since Linux 3.19, the following call will attach the program prog_fd to       the socket sockfd, 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 pro-       gram referred to by the file descriptor prog_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);EXAMPLES       /* 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 the samples/bpf directory in       the kernel source tree.RETURN VALUE       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, and errno is set appropriately.ERRORS       E2BIG  The  eBPF  program is too large or a map reached the max_entries              limit (maximum number of elements).       EACCES For BPF_PROG_LOAD, even  though  all  program  instructions  are              valid,  the  program has been rejected because it was deemed un-              safe.  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 rec-              ommended to call bpf() again with  log_level  =  1  and  examine              log_buf for the specific reason provided by the verifier.       EBADF  fd is not an open file descriptor.       EFAULT One  of  the pointers (key or value or log_buf or insns) is out-              side the accessible address space.       EINVAL The value specified in cmd is not recognized by this kernel.       EINVAL For BPF_MAP_CREATE, either map_type or attributes are invalid.       EINVAL For  BPF_MAP_*_ELEM  commands,  some  of  the  fields  of  union              bpf_attr that are not used by this command are not set to zero.       EINVAL For  BPF_PROG_LOAD, indicates an attempt to load an invalid pro-              gram.  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.       ENOENT For BPF_MAP_LOOKUP_ELEM or BPF_MAP_DELETE_ELEM,  indicates  that              the element with the given key was not found.       ENOMEM Cannot allocate sufficient memory.       EPERM  The  call  was  made  without  sufficient privilege (without the              CAP_SYS_ADMIN capability).VERSIONS       The bpf() system call first appeared in Linux 3.18.CONFORMING TO       The bpf() system call is Linux-specific.NOTES       In the current implementation, all bpf() commands require the caller to       have the CAP_SYS_ADMIN capability.       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  de-       scriptors referring to eBPF objects can be duplicated in the usual way,       usingdup(2) and similar calls.  An eBPF object is deallocated only af-       ter all file descriptors referring to the object have been closed.       eBPF  programs can be written in a restricted C that is compiled (using       the clang compiler) into eBPF bytecode.  Various features  are  omitted       from this restricted C, such as loops, global variables, variadic func-       tions, floating-point numbers, and passing structures as function argu-       ments.  Some examples can be found in the samples/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.  In kernels       before Linux 4.15, the JIT compiler is disabled by default, but its op-       eration  can  be  controlled  by  writing  one of the following integer       strings to the file /proc/sys/net/core/bpf_jit_enable:       0  Disable JIT compilation (default).       1  Normal compilation.       2  Debugging mode.  The generated opcodes  are  dumped  in  hexadecimal          into  the  kernel log.  These opcodes can then be disassembled using          the program tools/net/bpf_jit_disasm.c provided in the kernel source          tree.       Since Linux 4.15, the kernel may configured with the CONFIG_BPF_JIT_AL-       WAYS_ON option.  In this case, the JIT compiler is always enabled,  and       the  bpf_jit_enable is initialized to 1 and is immutable.  (This kernel       configuration option was provided as a mitigation for one of the  Spec-       tre attacks against the BPF interpreter.)       The  JIT compiler for eBPF is currently available for the following ar-       chitectures:       *  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).SEE ALSOseccomp(2),bpf-helpers(7),socket(7),tc(8),tc-bpf(8)       Both classic and extended BPF are explained in the kernel  source  file       Documentation/networking/filter.txt.COLOPHON       This  page  is  part of release 5.05 of the Linux man-pages project.  A       description of the project, information about reporting bugs,  and  the       latest     version     of     this    page,    can    be    found    at       https://www.kernel.org/doc/man-pages/.Linux                             2019-08-02BPF(2)