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BPF(2)			   Linux Programmer's Manual			BPF(2)

       bpf - perform a command on an extended BPF map or program

       #include <linux/bpf.h>

       int bpf(int cmd, union bpf_attr *attr, unsigned int size);

       The  bpf()  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 the BPF_CALL opcode exten-
       sion provided by eBPF) and access shared data structures such  as  eBPF

   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 runtime, 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

       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 a tc(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 |--

       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
       below).	The size argument is the size of the union pointed to by attr.

       The value provided in cmd is one of the following:

	      Create  a	 map  and  return a file descriptor that refers to the
	      map.  The close-on-exec file descriptor flag (see	 fcntl(2))  is
	      automatically enabled for the new file descriptor.

	      Look  up	an  element  by	 key in a specified map and return its

	      Create or update an element (key/value pair) in a specified map.

	      Look up and delete an element by key in a specified map.

	      Look up an element by key in a specified map and return the  key
	      of the next element.

	      Verify and load an eBPF program, returning a new file descriptor
	      associated with the program.  The close-on-exec file  descriptor
	      flag  (see  fcntl(2))  is automatically enabled for the new file

       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.

	      The  BPF_MAP_CREATE  command  creates a new map, returning a new
	      file descriptor that refers to the map.

		  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-

		  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 */

	      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

	      The BPF_MAP_LOOKUP_ELEM command looks up an element with a given
	      key in the map referred to by the file descriptor fd.

		  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.

	      The  BPF_MAP_UPDATE_ELEM	command	 creates or updates an element
	      with a given key/value in	 the  map  referred  to	 by  the  file
	      descriptor fd.

		  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:

		     Create a new element or update an existing element.

		     Create a new element only if it did not exist.

		     Update an existing element.

	      On  success,  the	 operation  returns  zero.   On	 error,	 -1 is
	      returned 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.

	      The BPF_MAP_DELETE_ELEM command deleted the element whose key is
	      key from the map referred to by the file descriptor fd.

		  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.

	      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.

		  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.

	      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:

	      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

	      *	 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.

	      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

	      *	 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

	      *	 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
	      exactly 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
	      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 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];

	   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 */

       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

       *  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_bug.	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.

       Applying close(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
       determines  the	program input (context)--the format of struct bpf_con-
       text (which is the data blob passed into the eBPF program as the	 first

       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
       increase 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

		  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]

       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 to socket(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  to

	   ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);

       /* 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
       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 */
				       /* 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), "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 packets0, tcp_cnt, udp_cnt);

	   return 0;

       Some complete working code can be found in the samples/bpf directory in
       the kernel source tree.

       For a successful call, the return value depends on the operation:

	      The new file descriptor associated with the eBPF map.

	      The new file descriptor associated with the eBPF program.

       All other commands

       On error, -1 is returned, and errno is set appropriately.

       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
	      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 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).

       The bpf() system call first appeared in Linux 3.18.

       The bpf() system call is Linux-specific.

       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, after fork(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, using dup(2) and similar calls.  An	 eBPF  object  is  deallocated
       only  after  all	 file  descriptors  referring  to the object have been

       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.  The JIT com-
       piler  is  disabled  by default, but its operation can be controlled by
       writing	one  of	 the   following   integer   strings   to   the	  file

       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

       JIT compiler for eBPF is currently available for the x86-64, arm64, and
       s390 architectures.

       seccomp(2), socket(7), tc(8), tc-bpf(8)

       Both  classic  and extended BPF are explained in the kernel source file

       This page is part of release 4.10 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

Linux				  2016-10-08				BPF(2)