bpf-helpers

BPF-HELPERS(7)             Linux Programmer's Manual            BPF-HELPERS(7)



NAME
       BPF-HELPERS - list of eBPF helper functions

DESCRIPTION
       The extended Berkeley Packet Filter (eBPF) subsystem consists in
       programs written in a pseudo-assembly language, then attached to one of
       the several kernel hooks and run in reaction of specific events. This
       framework differs from the older, "classic" BPF (or "cBPF") in several
       aspects, one of them being the ability to call special functions (or
       "helpers") from within a program.  These functions are restricted to a
       white-list of helpers defined in the kernel.

       These helpers are used by eBPF programs to interact with the system, or
       with the context in which they work. For instance, they can be used to
       print debugging messages, to get the time since the system was booted,
       to interact with eBPF maps, or to manipulate network packets. Since
       there are several eBPF program types, and that they do not run in the
       same context, each program type can only call a subset of those
       helpers.

       Due to eBPF conventions, a helper can not have more than five
       arguments.

       Internally, eBPF programs call directly into the compiled helper
       functions without requiring any foreign-function interface. As a
       result, calling helpers introduces no overhead, thus offering excellent
       performance.

       This document is an attempt to list and document the helpers available
       to eBPF developers. They are sorted by chronological order (the oldest
       helpers in the kernel at the top).

HELPERS
       void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)

              Description
                     Perform a lookup in map for an entry associated to key.

              Return Map value associated to key, or NULL if no entry was
                     found.

       int bpf_map_update_elem(struct bpf_map *map, const void *key, const
       void *value, u64 flags)

              Description
                     Add or update the value of the entry associated to key in
                     map with value. flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the map.

                     BPF_ANY
                            No condition on the existence of the entry for
                            key.

                     Flag value BPF_NOEXIST cannot be used for maps of types
                     BPF_MAP_TYPE_ARRAY or BPF_MAP_TYPE_PERCPU_ARRAY  (all
                     elements always exist), the helper would return an error.

              Return 0 on success, or a negative error in case of failure.

       int bpf_map_delete_elem(struct bpf_map *map, const void *key)

              Description
                     Delete entry with key from map.

              Return 0 on success, or a negative error in case of failure.

       int bpf_map_push_elem(struct bpf_map *map, const void *value, u64
       flags)

              Description
                     Push an element value in map. flags is one of:

                     BPF_EXIST If the queue/stack is full, the oldest element
                     is removed to make room for this.

              Return 0 on success, or a negative error in case of failure.

       int bpf_probe_read(void *dst, u32 size, const void *src)

              Description
                     For tracing programs, safely attempt to read size bytes
                     from address src and store the data in dst.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_ktime_get_ns(void)

              Description
                     Return the time elapsed since system boot, in
                     nanoseconds.

              Return Current ktime.

       int bpf_trace_printk(const char *fmt, u32 fmt_size, ...)

              Description
                     This helper is a "printk()-like" facility for debugging.
                     It prints a message defined by format fmt (of size
                     fmt_size) to file /sys/kernel/debug/tracing/trace from
                     DebugFS, if available. It can take up to three additional
                     u64 arguments (as an eBPF helpers, the total number of
                     arguments is limited to five).

                     Each time the helper is called, it appends a line to the
                     trace.  The format of the trace is customizable, and the
                     exact output one will get depends on the options set in
                     /sys/kernel/debug/tracing/trace_options (see also the
                     README file under the same directory). However, it
                     usually defaults to something like:

                        telnet-470   [001] .N.. 419421.045894: 0x00000001: <formatted msg>

                     In the above:

                        · telnet is the name of the current task.

                        · 470 is the PID of the current task.

                        · 001 is the CPU number on which the task is running.

                        · In .N.., each character refers to a set of options
                          (whether irqs are enabled, scheduling options,
                          whether hard/softirqs are running, level of
                          preempt_disabled respectively). N means that
                          TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED are set.

                        · 419421.045894 is a timestamp.

                        · 0x00000001 is a fake value used by BPF for the
                          instruction pointer register.

                        · <formatted msg> is the message formatted with fmt.

                     The conversion specifiers supported by fmt are similar,
                     but more limited than for printk(). They are %d, %i, %u,
                     %x, %ld, %li, %lu, %lx, %lld, %lli, %llu, %llx, %p, %s.
                     No modifier (size of field, padding with zeroes, etc.) is
                     available, and the helper will return -EINVAL (but print
                     nothing) if it encounters an unknown specifier.

                     Also, note that bpf_trace_printk() is slow, and should
                     only be used for debugging purposes. For this reason, a
                     notice bloc (spanning several lines) is printed to kernel
                     logs and states that the helper should not be used "for
                     production use" the first time this helper is used (or
                     more precisely, when trace_printk() buffers are
                     allocated). For passing values to user space, perf events
                     should be preferred.

              Return The number of bytes written to the buffer, or a negative
                     error in case of failure.

       u32 bpf_get_prandom_u32(void)

              Description
                     Get a pseudo-random number.

                     From a security point of view, this helper uses its own
                     pseudo-random internal state, and cannot be used to infer
                     the seed of other random functions in the kernel.
                     However, it is essential to note that the generator used
                     by the helper is not cryptographically secure.

              Return A random 32-bit unsigned value.

       u32 bpf_get_smp_processor_id(void)

              Description
                     Get the SMP (symmetric multiprocessing) processor id.
                     Note that all programs run with preemption disabled,
                     which means that the SMP processor id is stable during
                     all the execution of the program.

              Return The SMP id of the processor running the program.

       int bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void
       *from, u32 len, u64 flags)

              Description
                     Store len bytes from address from into the packet
                     associated to skb, at offset. flags are a combination of
                     BPF_F_RECOMPUTE_CSUM (automatically recompute the
                     checksum for the packet after storing the bytes) and
                     BPF_F_INVALIDATE_HASH (set skb->hash, skb->swhash and
                     skb->l4hash to 0).

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64
       to, u64 size)

              Description
                     Recompute the layer 3 (e.g. IP) checksum for the packet
                     associated to skb. Computation is incremental, so the
                     helper must know the former value of the header field
                     that was modified (from), the new value of this field
                     (to), and the number of bytes (2 or 4) for this field,
                     stored in size.  Alternatively, it is possible to store
                     the difference between the previous and the new values of
                     the header field in to, by setting from and size to 0.
                     For both methods, offset indicates the location of the IP
                     checksum within the packet.

                     This helper works in combination with bpf_csum_diff(),
                     which does not update the checksum in-place, but offers
                     more flexibility and can handle sizes larger than 2 or 4
                     for the checksum to update.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64
       to, u64 flags)

              Description
                     Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum
                     for the packet associated to skb. Computation is
                     incremental, so the helper must know the former value of
                     the header field that was modified (from), the new value
                     of this field (to), and the number of bytes (2 or 4) for
                     this field, stored on the lowest four bits of flags.
                     Alternatively, it is possible to store the difference
                     between the previous and the new values of the header
                     field in to, by setting from and the four lowest bits of
                     flags to 0. For both methods, offset indicates the
                     location of the IP checksum within the packet. In
                     addition to the size of the field, flags can be added
                     (bitwise OR) actual flags. With BPF_F_MARK_MANGLED_0, a
                     null checksum is left untouched (unless
                     BPF_F_MARK_ENFORCE is added as well), and for updates
                     resulting in a null checksum the value is set to
                     CSUM_MANGLED_0 instead. Flag BPF_F_PSEUDO_HDR indicates
                     the checksum is to be computed against a pseudo-header.

                     This helper works in combination with bpf_csum_diff(),
                     which does not update the checksum in-place, but offers
                     more flexibility and can handle sizes larger than 2 or 4
                     for the checksum to update.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32 index)

              Description
                     This special helper is used to trigger a "tail call", or
                     in other words, to jump into another eBPF program. The
                     same stack frame is used (but values on stack and in
                     registers for the caller are not accessible to the
                     callee). This mechanism allows for program chaining,
                     either for raising the maximum number of available eBPF
                     instructions, or to execute given programs in conditional
                     blocks. For security reasons, there is an upper limit to
                     the number of successive tail calls that can be
                     performed.

                     Upon call of this helper, the program attempts to jump
                     into a program referenced at index index in
                     prog_array_map, a special map of type
                     BPF_MAP_TYPE_PROG_ARRAY, and passes ctx, a pointer to the
                     context.

                     If the call succeeds, the kernel immediately runs the
                     first instruction of the new program. This is not a
                     function call, and it never returns to the previous
                     program. If the call fails, then the helper has no
                     effect, and the caller continues to run its subsequent
                     instructions. A call can fail if the destination program
                     for the jump does not exist (i.e. index is superior to
                     the number of entries in prog_array_map), or if the
                     maximum number of tail calls has been reached for this
                     chain of programs. This limit is defined in the kernel by
                     the macro MAX_TAIL_CALL_CNT (not accessible to user
                     space), which is currently set to 32.

              Return 0 on success, or a negative error in case of failure.

       int bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64 flags)

              Description
                     Clone and redirect the packet associated to skb to
                     another net device of index ifindex. Both ingress and
                     egress interfaces can be used for redirection. The
                     BPF_F_INGRESS value in flags is used to make the
                     distinction (ingress path is selected if the flag is
                     present, egress path otherwise).  This is the only flag
                     supported for now.

                     In comparison with bpf_redirect() helper,
                     bpf_clone_redirect() has the associated cost of
                     duplicating the packet buffer, but this can be executed
                     out of the eBPF program. Conversely, bpf_redirect() is
                     more efficient, but it is handled through an action code
                     where the redirection happens only after the eBPF program
                     has returned.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_get_current_pid_tgid(void)

              Return A 64-bit integer containing the current tgid and pid, and
                     created as such: current_task->tgid << 32 |
                     current_task->pid.

       u64 bpf_get_current_uid_gid(void)

              Return A 64-bit integer containing the current GID and UID, and
                     created as such: current_gid << 32 | current_uid.

       int bpf_get_current_comm(char *buf, u32 size_of_buf)

              Description
                     Copy the comm attribute of the current task into buf of
                     size_of_buf. The comm attribute contains the name of the
                     executable (excluding the path) for the current task. The
                     size_of_buf must be strictly positive. On success, the
                     helper makes sure that the buf is NUL-terminated. On
                     failure, it is filled with zeroes.

              Return 0 on success, or a negative error in case of failure.

       u32 bpf_get_cgroup_classid(struct sk_buff *skb)

              Description
                     Retrieve the classid for the current task, i.e. for the
                     net_cls cgroup to which skb belongs.

                     This helper can be used on TC egress path, but not on
                     ingress.

                     The net_cls cgroup provides an interface to tag network
                     packets based on a user-provided identifier for all
                     traffic coming from the tasks belonging to the related
                     cgroup. See also the related kernel documentation,
                     available from the Linux sources in file
                     Documentation/cgroup-v1/net_cls.txt.

                     The Linux kernel has two versions for cgroups: there are
                     cgroups v1 and cgroups v2. Both are available to users,
                     who can use a mixture of them, but note that the net_cls
                     cgroup is for cgroup v1 only. This makes it incompatible
                     with BPF programs run on cgroups, which is a
                     cgroup-v2-only feature (a socket can only hold data for
                     one version of cgroups at a time).

                     This helper is only available is the kernel was compiled
                     with the CONFIG_CGROUP_NET_CLASSID configuration option
                     set to "y" or to "m".

              Return The classid, or 0 for the default unconfigured classid.

       int bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16
       vlan_tci)

              Description
                     Push a vlan_tci (VLAN tag control information) of
                     protocol vlan_proto to the packet associated to skb, then
                     update the checksum. Note that if vlan_proto is different
                     from ETH_P_8021Q and ETH_P_8021AD, it is considered to be
                     ETH_P_8021Q.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_vlan_pop(struct sk_buff *skb)

              Description
                     Pop a VLAN header from the packet associated to skb.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_get_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key
       *key, u32 size, u64 flags)

              Description
                     Get tunnel metadata. This helper takes a pointer key to
                     an empty struct bpf_tunnel_key of size, that will be
                     filled with tunnel metadata for the packet associated to
                     skb.  The flags can be set to BPF_F_TUNINFO_IPV6, which
                     indicates that the tunnel is based on IPv6 protocol
                     instead of IPv4.

                     The struct bpf_tunnel_key is an object that generalizes
                     the principal parameters used by various tunneling
                     protocols into a single struct. This way, it can be used
                     to easily make a decision based on the contents of the
                     encapsulation header, "summarized" in this struct. In
                     particular, it holds the IP address of the remote end
                     (IPv4 or IPv6, depending on the case) in key->remote_ipv4
                     or key->remote_ipv6. Also, this struct exposes the
                     key->tunnel_id, which is generally mapped to a VNI
                     (Virtual Network Identifier), making it programmable
                     together with the bpf_skb_set_tunnel_key() helper.

                     Let's imagine that the following code is part of a
                     program attached to the TC ingress interface, on one end
                     of a GRE tunnel, and is supposed to filter out all
                     messages coming from remote ends with IPv4 address other
                     than 10.0.0.1:

                        int ret;
                        struct bpf_tunnel_key key = {};

                        ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
                        if (ret < 0)
                                return TC_ACT_SHOT;     // drop packet

                        if (key.remote_ipv4 != 0x0a000001)
                                return TC_ACT_SHOT;     // drop packet

                        return TC_ACT_OK;               // accept packet

                     This interface can also be used with all encapsulation
                     devices that can operate in "collect metadata" mode:
                     instead of having one network device per specific
                     configuration, the "collect metadata" mode only requires
                     a single device where the configuration can be extracted
                     from this helper.

                     This can be used together with various tunnels such as
                     VXLan, Geneve, GRE or IP in IP (IPIP).

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_set_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key
       *key, u32 size, u64 flags)

              Description
                     Populate tunnel metadata for packet associated to skb.
                     The tunnel metadata is set to the contents of key, of
                     size. The flags can be set to a combination of the
                     following values:

                     BPF_F_TUNINFO_IPV6
                            Indicate that the tunnel is based on IPv6 protocol
                            instead of IPv4.

                     BPF_F_ZERO_CSUM_TX
                            For IPv4 packets, add a flag to tunnel metadata
                            indicating that checksum computation should be
                            skipped and checksum set to zeroes.

                     BPF_F_DONT_FRAGMENT
                            Add a flag to tunnel metadata indicating that the
                            packet should not be fragmented.

                     BPF_F_SEQ_NUMBER
                            Add a flag to tunnel metadata indicating that a
                            sequence number should be added to tunnel header
                            before sending the packet. This flag was added for
                            GRE encapsulation, but might be used with other
                            protocols as well in the future.

                     Here is a typical usage on the transmit path:

                        struct bpf_tunnel_key key;
                             populate key ...
                        bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
                        bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);

                     See also the description of the bpf_skb_get_tunnel_key()
                     helper for additional information.

              Return 0 on success, or a negative error in case of failure.

       u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)

              Description
                     Read the value of a perf event counter. This helper
                     relies on a map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY.
                     The nature of the perf event counter is selected when map
                     is updated with perf event file descriptors. The map is
                     an array whose size is the number of available CPUs, and
                     each cell contains a value relative to one CPU. The value
                     to retrieve is indicated by flags, that contains the
                     index of the CPU to look up, masked with
                     BPF_F_INDEX_MASK. Alternatively, flags can be set to
                     BPF_F_CURRENT_CPU to indicate that the value for the
                     current CPU should be retrieved.

                     Note that before Linux 4.13, only hardware perf event can
                     be retrieved.

                     Also, be aware that the newer helper
                     bpf_perf_event_read_value() is recommended over
                     bpf_perf_event_read() in general. The latter has some ABI
                     quirks where error and counter value are used as a return
                     code (which is wrong to do since ranges may overlap).
                     This issue is fixed with bpf_perf_event_read_value(),
                     which at the same time provides more features over the
                     bpf_perf_event_read() interface. Please refer to the
                     description of bpf_perf_event_read_value() for details.

              Return The value of the perf event counter read from the map, or
                     a negative error code in case of failure.

       int bpf_redirect(u32 ifindex, u64 flags)

              Description
                     Redirect the packet to another net device of index
                     ifindex.  This helper is somewhat similar to
                     bpf_clone_redirect(), except that the packet is not
                     cloned, which provides increased performance.

                     Except for XDP, both ingress and egress interfaces can be
                     used for redirection. The BPF_F_INGRESS value in flags is
                     used to make the distinction (ingress path is selected if
                     the flag is present, egress path otherwise). Currently,
                     XDP only supports redirection to the egress interface,
                     and accepts no flag at all.

                     The same effect can be attained with the more generic
                     bpf_redirect_map(), which requires specific maps to be
                     used but offers better performance.

              Return For XDP, the helper returns XDP_REDIRECT on success or
                     XDP_ABORTED on error. For other program types, the values
                     are TC_ACT_REDIRECT on success or TC_ACT_SHOT on error.

       u32 bpf_get_route_realm(struct sk_buff *skb)

              Description
                     Retrieve the realm or the route, that is to say the
                     tclassid field of the destination for the skb. The
                     indentifier retrieved is a user-provided tag, similar to
                     the one used with the net_cls cgroup (see description for
                     bpf_get_cgroup_classid() helper), but here this tag is
                     held by a route (a destination entry), not by a task.

                     Retrieving this identifier works with the clsact TC
                     egress hook (see also tc-bpf(8)), or alternatively on
                     conventional classful egress qdiscs, but not on TC
                     ingress path. In case of clsact TC egress hook, this has
                     the advantage that, internally, the destination entry has
                     not been dropped yet in the transmit path. Therefore, the
                     destination entry does not need to be artificially held
                     via netif_keep_dst() for a classful qdisc until the skb
                     is freed.

                     This helper is available only if the kernel was compiled
                     with CONFIG_IP_ROUTE_CLASSID configuration option.

              Return The realm of the route for the packet associated to skb,
                     or 0 if none was found.

       int bpf_perf_event_output(struct pt_reg *ctx, struct bpf_map *map, u64
       flags, void *data, u64 size)

              Description
                     Write raw data blob into a special BPF perf event held by
                     map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
                     event must have the following attributes: PERF_SAMPLE_RAW
                     as sample_type, PERF_TYPE_SOFTWARE as type, and
                     PERF_COUNT_SW_BPF_OUTPUT as config.

                     The flags are used to indicate the index in map for which
                     the value must be put, masked with BPF_F_INDEX_MASK.
                     Alternatively, flags can be set to BPF_F_CURRENT_CPU to
                     indicate that the index of the current CPU core should be
                     used.

                     The value to write, of size, is passed through eBPF stack
                     and pointed by data.

                     The context of the program ctx needs also be passed to
                     the helper.

                     On user space, a program willing to read the values needs
                     to call perf_event_open() on the perf event (either for
                     one or for all CPUs) and to store the file descriptor
                     into the map. This must be done before the eBPF program
                     can send data into it. An example is available in file
                     samples/bpf/trace_output_user.c in the Linux kernel
                     source tree (the eBPF program counterpart is in
                     samples/bpf/trace_output_kern.c).

                     bpf_perf_event_output() achieves better performance than
                     bpf_trace_printk() for sharing data with user space, and
                     is much better suitable for streaming data from eBPF
                     programs.

                     Note that this helper is not restricted to tracing use
                     cases and can be used with programs attached to TC or XDP
                     as well, where it allows for passing data to user space
                     listeners. Data can be:

                     · Only custom structs,

                     · Only the packet payload, or

                     · A combination of both.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset, void *to,
       u32 len)

              Description
                     This helper was provided as an easy way to load data from
                     a packet. It can be used to load len bytes from offset
                     from the packet associated to skb, into the buffer
                     pointed by to.

                     Since Linux 4.7, usage of this helper has mostly been
                     replaced by "direct packet access", enabling packet data
                     to be manipulated with skb->data and skb->data_end
                     pointing respectively to the first byte of packet data
                     and to the byte after the last byte of packet data.
                     However, it remains useful if one wishes to read large
                     quantities of data at once from a packet into the eBPF
                     stack.

              Return 0 on success, or a negative error in case of failure.

       int bpf_get_stackid(struct pt_reg *ctx, struct bpf_map *map, u64 flags)

              Description
                     Walk a user or a kernel stack and return its id. To
                     achieve this, the helper needs ctx, which is a pointer to
                     the context on which the tracing program is executed, and
                     a pointer to a map of type BPF_MAP_TYPE_STACK_TRACE.

                     The last argument, flags, holds the number of stack
                     frames to skip (from 0 to 255), masked with
                     BPF_F_SKIP_FIELD_MASK. The next bits can be used to set a
                     combination of the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a kernel
                            stack.

                     BPF_F_FAST_STACK_CMP
                            Compare stacks by hash only.

                     BPF_F_REUSE_STACKID
                            If two different stacks hash into the same
                            stackid, discard the old one.

                     The stack id retrieved is a 32 bit long integer handle
                     which can be further combined with other data (including
                     other stack ids) and used as a key into maps. This can be
                     useful for generating a variety of graphs (such as flame
                     graphs or off-cpu graphs).

                     For walking a stack, this helper is an improvement over
                     bpf_probe_read(), which can be used with unrolled loops
                     but is not efficient and consumes a lot of eBPF
                     instructions.  Instead, bpf_get_stackid() can collect up
                     to PERF_MAX_STACK_DEPTH both kernel and user frames. Note
                     that this limit can be controlled with the sysctl
                     program, and that it should be manually increased in
                     order to profile long user stacks (such as stacks for
                     Java programs). To do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return The positive or null stack id on success, or a negative
                     error in case of failure.

       s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32 to_size,
       __wsum seed)

              Description
                     Compute a checksum difference, from the raw buffer
                     pointed by from, of length from_size (that must be a
                     multiple of 4), towards the raw buffer pointed by to, of
                     size to_size (same remark). An optional seed can be added
                     to the value (this can be cascaded, the seed may come
                     from a previous call to the helper).

                     This is flexible enough to be used in several ways:

                     · With from_size == 0, to_size > 0 and seed set to
                       checksum, it can be used when pushing new data.

                     · With from_size > 0, to_size == 0 and seed set to
                       checksum, it can be used when removing data from a
                       packet.

                     · With from_size > 0, to_size > 0 and seed set to 0, it
                       can be used to compute a diff. Note that from_size and
                       to_size do not need to be equal.

                     This helper can be used in combination with
                     bpf_l3_csum_replace() and bpf_l4_csum_replace(), to which
                     one can feed in the difference computed with
                     bpf_csum_diff().

              Return The checksum result, or a negative error code in case of
                     failure.

       int bpf_skb_get_tunnel_opt(struct sk_buff *skb, u8 *opt, u32 size)

              Description
                     Retrieve tunnel options metadata for the packet
                     associated to skb, and store the raw tunnel option data
                     to the buffer opt of size.

                     This helper can be used with encapsulation devices that
                     can operate in "collect metadata" mode (please refer to
                     the related note in the description of
                     bpf_skb_get_tunnel_key() for more details). A particular
                     example where this can be used is in combination with the
                     Geneve encapsulation protocol, where it allows for
                     pushing (with bpf_skb_get_tunnel_opt() helper) and
                     retrieving arbitrary TLVs (Type-Length-Value headers)
                     from the eBPF program. This allows for full customization
                     of these headers.

              Return The size of the option data retrieved.

       int bpf_skb_set_tunnel_opt(struct sk_buff *skb, u8 *opt, u32 size)

              Description
                     Set tunnel options metadata for the packet associated to
                     skb to the option data contained in the raw buffer opt of
                     size.

                     See also the description of the bpf_skb_get_tunnel_opt()
                     helper for additional information.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64 flags)

              Description
                     Change the protocol of the skb to proto. Currently
                     supported are transition from IPv4 to IPv6, and from IPv6
                     to IPv4. The helper takes care of the groundwork for the
                     transition, including resizing the socket buffer. The
                     eBPF program is expected to fill the new headers, if any,
                     via skb_store_bytes() and to recompute the checksums with
                     bpf_l3_csum_replace() and bpf_l4_csum_replace(). The main
                     case for this helper is to perform NAT64 operations out
                     of an eBPF program.

                     Internally, the GSO type is marked as dodgy so that
                     headers are checked and segments are recalculated by the
                     GSO/GRO engine.  The size for GSO target is adapted as
                     well.

                     All values for flags are reserved for future usage, and
                     must be left at zero.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_change_type(struct sk_buff *skb, u32 type)

              Description
                     Change the packet type for the packet associated to skb.
                     This comes down to setting skb->pkt_type to type, except
                     the eBPF program does not have a write access to
                     skb->pkt_type beside this helper. Using a helper here
                     allows for graceful handling of errors.

                     The major use case is to change incoming skb*s to
                     **PACKET_HOST* in a programmatic way instead of having to
                     recirculate via redirect(..., BPF_F_INGRESS), for
                     example.

                     Note that type only allows certain values. At this time,
                     they are:

                     PACKET_HOST
                            Packet is for us.

                     PACKET_BROADCAST
                            Send packet to all.

                     PACKET_MULTICAST
                            Send packet to group.

                     PACKET_OTHERHOST
                            Send packet to someone else.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map *map, u32
       index)

              Description
                     Check whether skb is a descendant of the cgroup2 held by
                     map of type BPF_MAP_TYPE_CGROUP_ARRAY, at index.

              Return The return value depends on the result of the test, and
                     can be:

                     · 0, if the skb failed the cgroup2 descendant test.

                     · 1, if the skb succeeded the cgroup2 descendant test.

                     · A negative error code, if an error occurred.

       u32 bpf_get_hash_recalc(struct sk_buff *skb)

              Description
                     Retrieve the hash of the packet, skb->hash. If it is not
                     set, in particular if the hash was cleared due to
                     mangling, recompute this hash. Later accesses to the hash
                     can be done directly with skb->hash.

                     Calling bpf_set_hash_invalid(), changing a packet
                     prototype with bpf_skb_change_proto(), or calling
                     bpf_skb_store_bytes() with the BPF_F_INVALIDATE_HASH are
                     actions susceptible to clear the hash and to trigger a
                     new computation for the next call to
                     bpf_get_hash_recalc().

              Return The 32-bit hash.

       u64 bpf_get_current_task(void)

              Return A pointer to the current task struct.

       int bpf_probe_write_user(void *dst, const void *src, u32 len)

              Description
                     Attempt in a safe way to write len bytes from the buffer
                     src to dst in memory. It only works for threads that are
                     in user context, and dst must be a valid user space
                     address.

                     This helper should not be used to implement any kind of
                     security mechanism because of TOC-TOU attacks, but rather
                     to debug, divert, and manipulate execution of
                     semi-cooperative processes.

                     Keep in mind that this feature is meant for experiments,
                     and it has a risk of crashing the system and running
                     programs.  Therefore, when an eBPF program using this
                     helper is attached, a warning including PID and process
                     name is printed to kernel logs.

              Return 0 on success, or a negative error in case of failure.

       int bpf_current_task_under_cgroup(struct bpf_map *map, u32 index)

              Description
                     Check whether the probe is being run is the context of a
                     given subset of the cgroup2 hierarchy. The cgroup2 to
                     test is held by map of type BPF_MAP_TYPE_CGROUP_ARRAY, at
                     index.

              Return The return value depends on the result of the test, and
                     can be:

                     · 0, if the skb task belongs to the cgroup2.

                     · 1, if the skb task does not belong to the cgroup2.

                     · A negative error code, if an error occurred.

       int bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)

              Description
                     Resize (trim or grow) the packet associated to skb to the
                     new len. The flags are reserved for future usage, and
                     must be left at zero.

                     The basic idea is that the helper performs the needed
                     work to change the size of the packet, then the eBPF
                     program rewrites the rest via helpers like
                     bpf_skb_store_bytes(), bpf_l3_csum_replace(),
                     bpf_l3_csum_replace() and others. This helper is a slow
                     path utility intended for replies with control messages.
                     And because it is targeted for slow path, the helper
                     itself can afford to be slow: it implicitly linearizes,
                     unclones and drops offloads from the skb.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_pull_data(struct sk_buff *skb, u32 len)

              Description
                     Pull in non-linear data in case the skb is non-linear and
                     not all of len are part of the linear section. Make len
                     bytes from skb readable and writable. If a zero value is
                     passed for len, then the whole length of the skb is
                     pulled.

                     This helper is only needed for reading and writing with
                     direct packet access.

                     For direct packet access, testing that offsets to access
                     are within packet boundaries (test on skb->data_end) is
                     susceptible to fail if offsets are invalid, or if the
                     requested data is in non-linear parts of the skb. On
                     failure the program can just bail out, or in the case of
                     a non-linear buffer, use a helper to make the data
                     available. The bpf_skb_load_bytes() helper is a first
                     solution to access the data. Another one consists in
                     using bpf_skb_pull_data to pull in once the non-linear
                     parts, then retesting and eventually access the data.

                     At the same time, this also makes sure the skb is
                     uncloned, which is a necessary condition for direct
                     write. As this needs to be an invariant for the write
                     part only, the verifier detects writes and adds a
                     prologue that is calling bpf_skb_pull_data() to
                     effectively unclone the skb from the very beginning in
                     case it is indeed cloned.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)

              Description
                     Add the checksum csum into skb->csum in case the driver
                     has supplied a checksum for the entire packet into that
                     field. Return an error otherwise. This helper is intended
                     to be used in combination with bpf_csum_diff(), in
                     particular when the checksum needs to be updated after
                     data has been written into the packet through direct
                     packet access.

              Return The checksum on success, or a negative error code in case
                     of failure.

       void bpf_set_hash_invalid(struct sk_buff *skb)

              Description
                     Invalidate the current skb->hash. It can be used after
                     mangling on headers through direct packet access, in
                     order to indicate that the hash is outdated and to
                     trigger a recalculation the next time the kernel tries to
                     access this hash or when the bpf_get_hash_recalc() helper
                     is called.

       int bpf_get_numa_node_id(void)

              Description
                     Return the id of the current NUMA node. The primary use
                     case for this helper is the selection of sockets for the
                     local NUMA node, when the program is attached to sockets
                     using the SO_ATTACH_REUSEPORT_EBPF option (see also
                     socket(7)), but the helper is also available to other
                     eBPF program types, similarly to
                     bpf_get_smp_processor_id().

              Return The id of current NUMA node.

       int bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)

              Description
                     Grows headroom of packet associated to skb and adjusts
                     the offset of the MAC header accordingly, adding len
                     bytes of space. It automatically extends and reallocates
                     memory as required.

                     This helper can be used on a layer 3 skb to push a MAC
                     header for redirection into a layer 2 device.

                     All values for flags are reserved for future usage, and
                     must be left at zero.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust (move) xdp_md->data by delta bytes. Note that it
                     is possible to use a negative value for delta. This
                     helper can be used to prepare the packet for pushing or
                     popping headers.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_probe_read_str(void *dst, int size, const void *unsafe_ptr)

              Description
                     Copy a NUL terminated string from an unsafe address
                     unsafe_ptr to dst. The size should include the
                     terminating NUL byte. In case the string length is
                     smaller than size, the target is not padded with further
                     NUL bytes. If the string length is larger than size, just
                     size-1 bytes are copied and the last byte is set to NUL.

                     On success, the length of the copied string is returned.
                     This makes this helper useful in tracing programs for
                     reading strings, and more importantly to get its length
                     at runtime. See the following snippet:

                        SEC("kprobe/sys_open")
                        void bpf_sys_open(struct pt_regs *ctx)
                                char buf[PATHLEN]; // PATHLEN is defined to 256
                                int res = bpf_probe_read_str(buf, sizeof(buf),
                                                             ctx->di);

                                // Consume buf, for example push it to
                                // userspace via bpf_perf_event_output(); we
                                // can use res (the string length) as event
                                // size, after checking its boundaries.

                     In comparison, using bpf_probe_read() helper here instead
                     to read the string would require to estimate the length
                     at compile time, and would often result in copying more
                     memory than necessary.

                     Another useful use case is when parsing individual
                     process arguments or individual environment variables
                     navigating current->mm->arg_start and
                     current->mm->env_start: using this helper and the return
                     value, one can quickly iterate at the right offset of the
                     memory area.

              Return On success, the strictly positive length of the string,
                     including the trailing NUL character. On error, a
                     negative value.

       u64 bpf_get_socket_cookie(struct sk_buff *skb)

              Description
                     If the struct sk_buff pointed by skb has a known socket,
                     retrieve the cookie (generated by the kernel) of this
                     socket.  If no cookie has been set yet, generate a new
                     cookie. Once generated, the socket cookie remains stable
                     for the life of the socket. This helper can be useful for
                     monitoring per socket networking traffic statistics as it
                     provides a unique socket identifier per namespace.

              Return A 8-byte long non-decreasing number on success, or 0 if
                     the socket field is missing inside skb.

       u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)

              Description
                     Equivalent to bpf_get_socket_cookie() helper that accepts
                     skb, but gets socket from struct bpf_sock_addr contex.

              Return A 8-byte long non-decreasing number.

       u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)

              Description
                     Equivalent to bpf_get_socket_cookie() helper that accepts
                     skb, but gets socket from struct bpf_sock_ops contex.

              Return A 8-byte long non-decreasing number.

       u32 bpf_get_socket_uid(struct sk_buff *skb)

              Return The owner UID of the socket associated to skb. If the
                     socket is NULL, or if it is not a full socket (i.e. if it
                     is a time-wait or a request socket instead), overflowuid
                     value is returned (note that overflowuid might also be
                     the actual UID value for the socket).

       u32 bpf_set_hash(struct sk_buff *skb, u32 hash)

              Description
                     Set the full hash for skb (set the field skb->hash) to
                     value hash.

              Return

       int bpf_setsockopt(struct bpf_sock_ops *bpf_socket, int level, int
       optname, char *optval, int optlen)

              Description
                     Emulate a call to setsockopt() on the socket associated
                     to bpf_socket, which must be a full socket. The level at
                     which the option resides and the name optname of the
                     option must be specified, see setsockopt(2) for more
                     information.  The option value of length optlen is
                     pointed by optval.

                     This helper actually implements a subset of setsockopt().
                     It supports the following levels:

                     · SOL_SOCKET, which supports the following optnames:
                       SO_RCVBUF, SO_SNDBUF, SO_MAX_PACING_RATE, SO_PRIORITY,
                       SO_RCVLOWAT, SO_MARK.

                     · IPPROTO_TCP, which supports the following optnames:
                       TCP_CONGESTION, TCP_BPF_IW, TCP_BPF_SNDCWND_CLAMP.

                     · IPPROTO_IP, which supports optname IP_TOS.

                     · IPPROTO_IPV6, which supports optname IPV6_TCLASS.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32 mode,
       u64 flags)

              Description
                     Grow or shrink the room for data in the packet associated
                     to skb by len_diff, and according to the selected mode.

                     There is a single supported mode at this time:

                     · BPF_ADJ_ROOM_NET: Adjust room at the network layer
                       (room space is added or removed below the layer 3
                       header).

                     All values for flags are reserved for future usage, and
                     must be left at zero.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)

              Description
                     Redirect the packet to the endpoint referenced by map at
                     index key. Depending on its type, this map can contain
                     references to net devices (for forwarding packets through
                     other ports), or to CPUs (for redirecting XDP frames to
                     another CPU; but this is only implemented for native XDP
                     (with driver support) as of this writing).

                     All values for flags are reserved for future usage, and
                     must be left at zero.

                     When used to redirect packets to net devices, this helper
                     provides a high performance increase over bpf_redirect().
                     This is due to various implementation details of the
                     underlying mechanisms, one of which is the fact that
                     bpf_redirect_map() tries to send packet as a "bulk" to
                     the device.

              Return XDP_REDIRECT on success, or XDP_ABORTED on error.

       int bpf_sk_redirect_map(struct bpf_map *map, u32 key, u64 flags)

              Description
                     Redirect the packet to the socket referenced by map (of
                     type BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress and
                     egress interfaces can be used for redirection. The
                     BPF_F_INGRESS value in flags is used to make the
                     distinction (ingress path is selected if the flag is
                     present, egress path otherwise). This is the only flag
                     supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       int bpf_sock_map_update(struct bpf_sock_ops *skops, struct bpf_map
       *map, void *key, u64 flags)

              Description
                     Add an entry to, or update a map referencing sockets. The
                     skops is used as a new value for the entry associated to
                     key. flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the map.

                     BPF_ANY
                            No condition on the existence of the entry for
                            key.

                     If the map has eBPF programs (parser and verdict), those
                     will be inherited by the socket being added. If the
                     socket is already attached to eBPF programs, this results
                     in an error.

              Return 0 on success, or a negative error in case of failure.

       int bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust the address pointed by xdp_md->data_meta by delta
                     (which can be positive or negative). Note that this
                     operation modifies the address stored in xdp_md->data, so
                     the latter must be loaded only after the helper has been
                     called.

                     The use of xdp_md->data_meta is optional and programs are
                     not required to use it. The rationale is that when the
                     packet is processed with XDP (e.g. as DoS filter), it is
                     possible to push further meta data along with it before
                     passing to the stack, and to give the guarantee that an
                     ingress eBPF program attached as a TC classifier on the
                     same device can pick this up for further post-processing.
                     Since TC works with socket buffers, it remains possible
                     to set from XDP the mark or priority pointers, or other
                     pointers for the socket buffer.  Having this scratch
                     space generic and programmable allows for more
                     flexibility as the user is free to store whatever meta
                     data they need.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_perf_event_read_value(struct bpf_map *map, u64 flags, struct
       bpf_perf_event_value *buf, u32 buf_size)

              Description
                     Read the value of a perf event counter, and store it into
                     buf of size buf_size. This helper relies on a map of type
                     BPF_MAP_TYPE_PERF_EVENT_ARRAY. The nature of the perf
                     event counter is selected when map is updated with perf
                     event file descriptors. The map is an array whose size is
                     the number of available CPUs, and each cell contains a
                     value relative to one CPU. The value to retrieve is
                     indicated by flags, that contains the index of the CPU to
                     look up, masked with BPF_F_INDEX_MASK. Alternatively,
                     flags can be set to BPF_F_CURRENT_CPU to indicate that
                     the value for the current CPU should be retrieved.

                     This helper behaves in a way close to
                     bpf_perf_event_read() helper, save that instead of just
                     returning the value observed, it fills the buf structure.
                     This allows for additional data to be retrieved: in
                     particular, the enabled and running times (in
                     buf->enabled and buf->running, respectively) are copied.
                     In general, bpf_perf_event_read_value() is recommended
                     over bpf_perf_event_read(), which has some ABI issues and
                     provides fewer functionalities.

                     These values are interesting, because hardware PMU
                     (Performance Monitoring Unit) counters are limited
                     resources. When there are more PMU based perf events
                     opened than available counters, kernel will multiplex
                     these events so each event gets certain percentage (but
                     not all) of the PMU time. In case that multiplexing
                     happens, the number of samples or counter value will not
                     reflect the case compared to when no multiplexing occurs.
                     This makes comparison between different runs difficult.
                     Typically, the counter value should be normalized before
                     comparing to other experiments. The usual normalization
                     is done as follows.

                        normalized_counter = counter * t_enabled / t_running

                     Where t_enabled is the time enabled for event and
                     t_running is the time running for event since last
                     normalization. The enabled and running times are
                     accumulated since the perf event open. To achieve scaling
                     factor between two invocations of an eBPF program, users
                     can can use CPU id as the key (which is typical for perf
                     array usage model) to remember the previous value and do
                     the calculation inside the eBPF program.

              Return 0 on success, or a negative error in case of failure.

       int bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx, struct
       bpf_perf_event_value *buf, u32 buf_size)

              Description
                     For en eBPF program attached to a perf event, retrieve
                     the value of the event counter associated to ctx and
                     store it in the structure pointed by buf and of size
                     buf_size. Enabled and running times are also stored in
                     the structure (see description of helper
                     bpf_perf_event_read_value() for more details).

              Return 0 on success, or a negative error in case of failure.

       int bpf_getsockopt(struct bpf_sock_ops *bpf_socket, int level, int
       optname, char *optval, int optlen)

              Description
                     Emulate a call to getsockopt() on the socket associated
                     to bpf_socket, which must be a full socket. The level at
                     which the option resides and the name optname of the
                     option must be specified, see getsockopt(2) for more
                     information.  The retrieved value is stored in the
                     structure pointed by opval and of length optlen.

                     This helper actually implements a subset of getsockopt().
                     It supports the following levels:

                     · IPPROTO_TCP, which supports optname TCP_CONGESTION.

                     · IPPROTO_IP, which supports optname IP_TOS.

                     · IPPROTO_IPV6, which supports optname IPV6_TCLASS.

              Return 0 on success, or a negative error in case of failure.

       int bpf_override_return(struct pt_reg *regs, u64 rc)

              Description
                     Used for error injection, this helper uses kprobes to
                     override the return value of the probed function, and to
                     set it to rc.  The first argument is the context regs on
                     which the kprobe works.

                     This helper works by setting setting the PC (program
                     counter) to an override function which is run in place of
                     the original probed function. This means the probed
                     function is not run at all. The replacement function just
                     returns with the required value.

                     This helper has security implications, and thus is
                     subject to restrictions. It is only available if the
                     kernel was compiled with the CONFIG_BPF_KPROBE_OVERRIDE
                     configuration option, and in this case it only works on
                     functions tagged with ALLOW_ERROR_INJECTION in the kernel
                     code.

                     Also, the helper is only available for the architectures
                     having the CONFIG_FUNCTION_ERROR_INJECTION option. As of
                     this writing, x86 architecture is the only one to support
                     this feature.

              Return

       int bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, int
       argval)

              Description
                     Attempt to set the value of the bpf_sock_ops_cb_flags
                     field for the full TCP socket associated to bpf_sock_ops
                     to argval.

                     The primary use of this field is to determine if there
                     should be calls to eBPF programs of type
                     BPF_PROG_TYPE_SOCK_OPS at various points in the TCP code.
                     A program of the same type can change its value, per
                     connection and as necessary, when the connection is
                     established. This field is directly accessible for
                     reading, but this helper must be used for updates in
                     order to return an error if an eBPF program tries to set
                     a callback that is not supported in the current kernel.

                     The supported callback values that argval can combine
                     are:

                     · BPF_SOCK_OPS_RTO_CB_FLAG (retransmission time out)

                     · BPF_SOCK_OPS_RETRANS_CB_FLAG (retransmission)

                     · BPF_SOCK_OPS_STATE_CB_FLAG (TCP state change)

                     Here are some examples of where one could call such eBPF
                     program:

                     · When RTO fires.

                     · When a packet is retransmitted.

                     · When the connection terminates.

                     · When a packet is sent.

                     · When a packet is received.

              Return Code -EINVAL if the socket is not a full TCP socket;
                     otherwise, a positive number containing the bits that
                     could not be set is returned (which comes down to 0 if
                     all bits were set as required).

       int bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map *map,
       u32 key, u64 flags)

              Description
                     This helper is used in programs implementing policies at
                     the socket level. If the message msg is allowed to pass
                     (i.e. if the verdict eBPF program returns SK_PASS),
                     redirect it to the socket referenced by map (of type
                     BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress and
                     egress interfaces can be used for redirection. The
                     BPF_F_INGRESS value in flags is used to make the
                     distinction (ingress path is selected if the flag is
                     present, egress path otherwise). This is the only flag
                     supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       int bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)

              Description
                     For socket policies, apply the verdict of the eBPF
                     program to the next bytes (number of bytes) of message
                     msg.

                     For example, this helper can be used in the following
                     cases:

                     · A single sendmsg() or sendfile() system call contains
                       multiple logical messages that the eBPF program is
                       supposed to read and for which it should apply a
                       verdict.

                     · An eBPF program only cares to read the first bytes of a
                       msg. If the message has a large payload, then setting
                       up and calling the eBPF program repeatedly for all
                       bytes, even though the verdict is already known, would
                       create unnecessary overhead.

                     When called from within an eBPF program, the helper sets
                     a counter internal to the BPF infrastructure, that is
                     used to apply the last verdict to the next bytes. If
                     bytes is smaller than the current data being processed
                     from a sendmsg() or sendfile() system call, the first
                     bytes will be sent and the eBPF program will be re-run
                     with the pointer for start of data pointing to byte
                     number bytes + 1. If bytes is larger than the current
                     data being processed, then the eBPF verdict will be
                     applied to multiple sendmsg() or sendfile() calls until
                     bytes are consumed.

                     Note that if a socket closes with the internal counter
                     holding a non-zero value, this is not a problem because
                     data is not being buffered for bytes and is sent as it is
                     received.

              Return

       int bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)

              Description
                     For socket policies, prevent the execution of the verdict
                     eBPF program for message msg until bytes (byte number)
                     have been accumulated.

                     This can be used when one needs a specific number of
                     bytes before a verdict can be assigned, even if the data
                     spans multiple sendmsg() or sendfile() calls. The extreme
                     case would be a user calling sendmsg() repeatedly with
                     1-byte long message segments. Obviously, this is bad for
                     performance, but it is still valid. If the eBPF program
                     needs bytes bytes to validate a header, this helper can
                     be used to prevent the eBPF program to be called again
                     until bytes have been accumulated.

              Return

       int bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end, u64
       flags)

              Description
                     For socket policies, pull in non-linear data from user
                     space for msg and set pointers msg->data and
                     msg->data_end to start and end bytes offsets into msg,
                     respectively.

                     If a program of type BPF_PROG_TYPE_SK_MSG is run on a msg
                     it can only parse data that the (data, data_end) pointers
                     have already consumed. For sendmsg() hooks this is likely
                     the first scatterlist element. But for calls relying on
                     the sendpage handler (e.g. sendfile()) this will be the
                     range (0, 0) because the data is shared with user space
                     and by default the objective is to avoid allowing user
                     space to modify data while (or after) eBPF verdict is
                     being decided. This helper can be used to pull in data
                     and to set the start and end pointer to given values.
                     Data will be copied if necessary (i.e. if data was not
                     linear and if start and end pointers do not point to the
                     same chunk).

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

                     All values for flags are reserved for future usage, and
                     must be left at zero.

              Return 0 on success, or a negative error in case of failure.

       int bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr, int
       addr_len)

              Description
                     Bind the socket associated to ctx to the address pointed
                     by addr, of length addr_len. This allows for making
                     outgoing connection from the desired IP address, which
                     can be useful for example when all processes inside a
                     cgroup should use one single IP address on a host that
                     has multiple IP configured.

                     This helper works for IPv4 and IPv6, TCP and UDP sockets.
                     The domain (addr->sa_family) must be AF_INET (or
                     AF_INET6). Looking for a free port to bind to can be
                     expensive, therefore binding to port is not permitted by
                     the helper: addr->sin_port (or sin6_port, respectively)
                     must be set to zero.

              Return 0 on success, or a negative error in case of failure.

       int bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)

              Description
                     Adjust (move) xdp_md->data_end by delta bytes. It is only
                     possible to shrink the packet as of this writing,
                     therefore delta must be a negative integer.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_skb_get_xfrm_state(struct sk_buff *skb, u32 index, struct
       bpf_xfrm_state *xfrm_state, u32 size, u64 flags)

              Description
                     Retrieve the XFRM state (IP transform framework, see also
                     ip-xfrm(8)) at index in XFRM "security path" for skb.

                     The retrieved value is stored in the struct
                     bpf_xfrm_state pointed by xfrm_state and of length size.

                     All values for flags are reserved for future usage, and
                     must be left at zero.

                     This helper is available only if the kernel was compiled
                     with CONFIG_XFRM configuration option.

              Return 0 on success, or a negative error in case of failure.

       int bpf_get_stack(struct pt_regs *regs, void *buf, u32 size, u64 flags)

              Description
                     Return a user or a kernel stack in bpf program provided
                     buffer.  To achieve this, the helper needs ctx, which is
                     a pointer to the context on which the tracing program is
                     executed.  To store the stacktrace, the bpf program
                     provides buf with a nonnegative size.

                     The last argument, flags, holds the number of stack
                     frames to skip (from 0 to 255), masked with
                     BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
                     the following flags:

                     BPF_F_USER_STACK
                            Collect a user space stack instead of a kernel
                            stack.

                     BPF_F_USER_BUILD_ID
                            Collect buildid+offset instead of ips for user
                            stack, only valid if BPF_F_USER_STACK is also
                            specified.

                     bpf_get_stack() can collect up to PERF_MAX_STACK_DEPTH
                     both kernel and user frames, subject to sufficient large
                     buffer size. Note that this limit can be controlled with
                     the sysctl program, and that it should be manually
                     increased in order to profile long user stacks (such as
                     stacks for Java programs). To do so, use:

                        # sysctl kernel.perf_event_max_stack=<new value>

              Return A non-negative value equal to or less than size on
                     success, or a negative error in case of failure.

       int bpf_skb_load_bytes_relative(const struct sk_buff *skb, u32 offset,
       void *to, u32 len, u32 start_header)

              Description
                     This helper is similar to bpf_skb_load_bytes() in that it
                     provides an easy way to load len bytes from offset from
                     the packet associated to skb, into the buffer pointed by
                     to. The difference to bpf_skb_load_bytes() is that a
                     fifth argument start_header exists in order to select a
                     base offset to start from. start_header can be one of:

                     BPF_HDR_START_MAC
                            Base offset to load data from is skb's mac header.

                     BPF_HDR_START_NET
                            Base offset to load data from is skb's network
                            header.

                     In general, "direct packet access" is the preferred
                     method to access packet data, however, this helper is in
                     particular useful in socket filters where skb->data does
                     not always point to the start of the mac header and where
                     "direct packet access" is not available.

              Return 0 on success, or a negative error in case of failure.

       int bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int plen,
       u32 flags)

              Description
                     Do FIB lookup in kernel tables using parameters in
                     params.  If lookup is successful and result shows packet
                     is to be forwarded, the neighbor tables are searched for
                     the nexthop.  If successful (ie., FIB lookup shows
                     forwarding and nexthop is resolved), the nexthop address
                     is returned in ipv4_dst or ipv6_dst based on family, smac
                     is set to mac address of egress device, dmac is set to
                     nexthop mac address, rt_metric is set to metric from
                     route (IPv4/IPv6 only), and ifindex is set to the device
                     index of the nexthop from the FIB lookup.

                     plen argument is the size of the passed in struct.  flags
                     argument can be a combination of one or more of the
                     following values:

                     BPF_FIB_LOOKUP_DIRECT
                            Do a direct table lookup vs full lookup using FIB
                            rules.

                     BPF_FIB_LOOKUP_OUTPUT
                            Perform lookup from an egress perspective (default
                            is ingress).

                     ctx is either struct xdp_md for XDP programs or struct
                     sk_buff tc cls_act programs.

              Return

                     · < 0 if any input argument is invalid

                     · 0 on success (packet is forwarded, nexthop neighbor
                       exists)

                     · > 0 one of BPF_FIB_LKUP_RET_ codes explaining why the
                       packet is not forwarded or needs assist from full stack

       int bpf_sock_hash_update(struct bpf_sock_ops_kern *skops, struct
       bpf_map *map, void *key, u64 flags)

              Description
                     Add an entry to, or update a sockhash map referencing
                     sockets.  The skops is used as a new value for the entry
                     associated to key. flags is one of:

                     BPF_NOEXIST
                            The entry for key must not exist in the map.

                     BPF_EXIST
                            The entry for key must already exist in the map.

                     BPF_ANY
                            No condition on the existence of the entry for
                            key.

                     If the map has eBPF programs (parser and verdict), those
                     will be inherited by the socket being added. If the
                     socket is already attached to eBPF programs, this results
                     in an error.

              Return 0 on success, or a negative error in case of failure.

       int bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct bpf_map *map,
       void *key, u64 flags)

              Description
                     This helper is used in programs implementing policies at
                     the socket level. If the message msg is allowed to pass
                     (i.e. if the verdict eBPF program returns SK_PASS),
                     redirect it to the socket referenced by map (of type
                     BPF_MAP_TYPE_SOCKHASH) using hash key. Both ingress and
                     egress interfaces can be used for redirection. The
                     BPF_F_INGRESS value in flags is used to make the
                     distinction (ingress path is selected if the flag is
                     present, egress path otherwise). This is the only flag
                     supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       int bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map, void
       *key, u64 flags)

              Description
                     This helper is used in programs implementing policies at
                     the skb socket level. If the sk_buff skb is allowed to
                     pass (i.e.  if the verdeict eBPF program returns
                     SK_PASS), redirect it to the socket referenced by map (of
                     type BPF_MAP_TYPE_SOCKHASH) using hash key. Both ingress
                     and egress interfaces can be used for redirection. The
                     BPF_F_INGRESS value in flags is used to make the
                     distinction (ingress path is selected if the flag is
                     present, egress otherwise). This is the only flag
                     supported for now.

              Return SK_PASS on success, or SK_DROP on error.

       int bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr, u32
       len)

              Description
                     Encapsulate the packet associated to skb within a Layer 3
                     protocol header. This header is provided in the buffer at
                     address hdr, with len its size in bytes. type indicates
                     the protocol of the header and can be one of:

                     BPF_LWT_ENCAP_SEG6
                            IPv6 encapsulation with Segment Routing Header
                            (struct ipv6_sr_hdr). hdr only contains the SRH,
                            the IPv6 header is computed by the kernel.

                     BPF_LWT_ENCAP_SEG6_INLINE
                            Only works if skb contains an IPv6 packet. Insert
                            a Segment Routing Header (struct ipv6_sr_hdr)
                            inside the IPv6 header.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset, const
       void *from, u32 len)

              Description
                     Store len bytes from address from into the packet
                     associated to skb, at offset. Only the flags, tag and
                     TLVs inside the outermost IPv6 Segment Routing Header can
                     be modified through this helper.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32 delta)

              Description
                     Adjust the size allocated to TLVs in the outermost IPv6
                     Segment Routing Header contained in the packet associated
                     to skb, at position offset by delta bytes. Only offsets
                     after the segments are accepted. delta can be as well
                     positive (growing) as negative (shrinking).

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void *param,
       u32 param_len)

              Description
                     Apply an IPv6 Segment Routing action of type action to
                     the packet associated to skb. Each action takes a
                     parameter contained at address param, and of length
                     param_len bytes.  action can be one of:

                     SEG6_LOCAL_ACTION_END_X
                            End.X action: Endpoint with Layer-3 cross-connect.
                            Type of param: struct in6_addr.

                     SEG6_LOCAL_ACTION_END_T
                            End.T action: Endpoint with specific IPv6 table
                            lookup.  Type of param: int.

                     SEG6_LOCAL_ACTION_END_B6
                            End.B6 action: Endpoint bound to an SRv6 policy.
                            Type of param: struct ipv6_sr_hdr.

                     SEG6_LOCAL_ACTION_END_B6_ENCAP
                            End.B6.Encap action: Endpoint bound to an SRv6
                            encapsulation policy.  Type of param: struct
                            ipv6_sr_hdr.

                     A call to this helper is susceptible to change the
                     underlaying packet buffer. Therefore, at load time, all
                     checks on pointers previously done by the verifier are
                     invalidated and must be performed again, if the helper is
                     used in combination with direct packet access.

              Return 0 on success, or a negative error in case of failure.

       int bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32 toggle)

              Description
                     This helper is used in programs implementing IR decoding,
                     to report a successfully decoded key press with scancode,
                     toggle value in the given protocol. The scancode will be
                     translated to a keycode using the rc keymap, and reported
                     as an input key down event. After a period a key up event
                     is generated. This period can be extended by calling
                     either bpf_rc_keydown() again with the same values, or
                     calling bpf_rc_repeat().

                     Some protocols include a toggle bit, in case the button
                     was released and pressed again between consecutive
                     scancodes.

                     The ctx should point to the lirc sample as passed into
                     the program.

                     The protocol is the decoded protocol number (see enum
                     rc_proto for some predefined values).

                     This helper is only available is the kernel was compiled
                     with the CONFIG_BPF_LIRC_MODE2 configuration option set
                     to "y".

              Return

       int bpf_rc_repeat(void *ctx)

              Description
                     This helper is used in programs implementing IR decoding,
                     to report a successfully decoded repeat key message. This
                     delays the generation of a key up event for previously
                     generated key down event.

                     Some IR protocols like NEC have a special IR message for
                     repeating last button, for when a button is held down.

                     The ctx should point to the lirc sample as passed into
                     the program.

                     This helper is only available is the kernel was compiled
                     with the CONFIG_BPF_LIRC_MODE2 configuration option set
                     to "y".

              Return

       uint64_t bpf_skb_cgroup_id(struct sk_buff *skb)

              Description
                     Return the cgroup v2 id of the socket associated with the
                     skb.  This is roughly similar to the
                     bpf_get_cgroup_classid() helper for cgroup v1 by
                     providing a tag resp. identifier that can be matched on
                     or used for map lookups e.g. to implement policy. The
                     cgroup v2 id of a given path in the hierarchy is exposed
                     in user space through the f_handle API in order to get to
                     the same 64-bit id.

                     This helper can be used on TC egress path, but not on
                     ingress, and is available only if the kernel was compiled
                     with the CONFIG_SOCK_CGROUP_DATA configuration option.

              Return The id is returned or 0 in case the id could not be
                     retrieved.

       u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, int ancestor_level)

              Description
                     Return id of cgroup v2 that is ancestor of cgroup
                     associated with the skb at the ancestor_level.  The root
                     cgroup is at ancestor_level zero and each step down the
                     hierarchy increments the level. If ancestor_level ==
                     level of cgroup associated with skb, then return value
                     will be same as that of bpf_skb_cgroup_id().

                     The helper is useful to implement policies based on
                     cgroups that are upper in hierarchy than immediate cgroup
                     associated with skb.

                     The format of returned id and helper limitations are same
                     as in bpf_skb_cgroup_id().

              Return The id is returned or 0 in case the id could not be
                     retrieved.

       u64 bpf_get_current_cgroup_id(void)

              Return A 64-bit integer containing the current cgroup id based
                     on the cgroup within which the current task is running.

       void* get_local_storage(void *map, u64 flags)

              Description
                     Get the pointer to the local storage area.  The type and
                     the size of the local storage is defined by the map
                     argument.  The flags meaning is specific for each map
                     type, and has to be 0 for cgroup local storage.

                     Depending on the BPF program type, a local storage area
                     can be shared between multiple instances of the BPF
                     program, running simultaneously.

                     A user should care about the synchronization by themself.
                     For example, by using the BPF_STX_XADD instruction to
                     alter the shared data.

              Return A pointer to the local storage area.

       int bpf_sk_select_reuseport(struct sk_reuseport_md *reuse, struct
       bpf_map *map, void *key, u64 flags)

              Description
                     Select a SO_REUSEPORT socket from a
                     BPF_MAP_TYPE_REUSEPORT_ARRAY map.  It checks the selected
                     socket is matching the incoming request in the socket
                     buffer.

              Return 0 on success, or a negative error in case of failure.

       struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple
       *tuple, u32 tuple_size, u64 netns, u64 flags)

              Description
                     Look for TCP socket matching tuple, optionally in a child
                     network namespace netns. The return value must be
                     checked, and if non-NULL, released via bpf_sk_release().

                     The ctx should point to the context of the program, such
                     as the skb or socket (depending on the hook in use). This
                     is used to determine the base network namespace for the
                     lookup.

                     tuple_size must be one of:

                     sizeof(tuple->ipv4)
                            Look for an IPv4 socket.

                     sizeof(tuple->ipv6)
                            Look for an IPv6 socket.

                     If the netns is a negative signed 32-bit integer, then
                     the socket lookup table in the netns associated with the
                     ctx will will be used. For the TC hooks, this is the
                     netns of the device in the skb. For socket hooks, this is
                     the netns of the socket.  If netns is any other signed
                     32-bit value greater than or equal to zero then it
                     specifies the ID of the netns relative to the netns
                     associated with the ctx. netns values beyond the range of
                     32-bit integers are reserved for future use.

                     All values for flags are reserved for future usage, and
                     must be left at zero.

                     This helper is available only if the kernel was compiled
                     with CONFIG_NET configuration option.

              Return Pointer to struct bpf_sock, or NULL in case of failure.
                     For sockets with reuseport option, the struct bpf_sock
                     result is from reuse->socks[] using the hash of the
                     tuple.

       struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple
       *tuple, u32 tuple_size, u64 netns, u64 flags)

              Description
                     Look for UDP socket matching tuple, optionally in a child
                     network namespace netns. The return value must be
                     checked, and if non-NULL, released via bpf_sk_release().

                     The ctx should point to the context of the program, such
                     as the skb or socket (depending on the hook in use). This
                     is used to determine the base network namespace for the
                     lookup.

                     tuple_size must be one of:

                     sizeof(tuple->ipv4)
                            Look for an IPv4 socket.

                     sizeof(tuple->ipv6)
                            Look for an IPv6 socket.

                     If the netns is a negative signed 32-bit integer, then
                     the socket lookup table in the netns associated with the
                     ctx will will be used. For the TC hooks, this is the
                     netns of the device in the skb. For socket hooks, this is
                     the netns of the socket.  If netns is any other signed
                     32-bit value greater than or equal to zero then it
                     specifies the ID of the netns relative to the netns
                     associated with the ctx. netns values beyond the range of
                     32-bit integers are reserved for future use.

                     All values for flags are reserved for future usage, and
                     must be left at zero.

                     This helper is available only if the kernel was compiled
                     with CONFIG_NET configuration option.

              Return Pointer to struct bpf_sock, or NULL in case of failure.
                     For sockets with reuseport option, the struct bpf_sock
                     result is from reuse->socks[] using the hash of the
                     tuple.

       int bpf_sk_release(struct bpf_sock *sock)

              Description
                     Release the reference held by sock. sock must be a
                     non-NULL pointer that was returned from
                     bpf_sk_lookup_xxx().

              Return 0 on success, or a negative error in case of failure.

       int bpf_map_pop_elem(struct bpf_map *map, void *value)

              Description
                     Pop an element from map.

              Return 0 on success, or a negative error in case of failure.

       int bpf_map_peek_elem(struct bpf_map *map, void *value)

              Description
                     Get an element from map without removing it.

              Return 0 on success, or a negative error in case of failure.

       int bpf_msg_push_data(struct sk_buff *skb, u32 start, u32 len, u64
       flags)

              Description
                     For socket policies, insert len bytes into msg at offset
                     start.

                     If a program of type BPF_PROG_TYPE_SK_MSG is run on a msg
                     it may want to insert metadata or options into the msg.
                     This can later be read and used by any of the lower layer
                     BPF hooks.

                     This helper may fail if under memory pressure (a malloc
                     fails) in these cases BPF programs will get an
                     appropriate error and BPF programs will need to handle
                     them.

              Return 0 on success, or a negative error in case of failure.

       int bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32 pop, u64
       flags)

              Description
                     Will remove pop bytes from a msg starting at byte start.
                     This may result in ENOMEM errors under certain situations
                     if an allocation and copy are required due to a full ring
                     buffer.  However, the helper will try to avoid doing the
                     allocation if possible. Other errors can occur if input
                     parameters are invalid either due to start byte not being
                     valid part of msg payload and/or pop value being to
                     large.

              Return 0 on success, or a negative error in case of failure.

       int bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)

              Description
                     This helper is used in programs implementing IR decoding,
                     to report a successfully decoded pointer movement.

                     The ctx should point to the lirc sample as passed into
                     the program.

                     This helper is only available is the kernel was compiled
                     with the CONFIG_BPF_LIRC_MODE2 configuration option set
                     to "y".

              Return

EXAMPLES
       Example usage for most of the eBPF helpers listed in this manual page
       are available within the Linux kernel sources, at the following
       locations:

       · samples/bpf/

       · tools/testing/selftests/bpf/

LICENSE
       eBPF programs can have an associated license, passed along with the
       bytecode instructions to the kernel when the programs are loaded. The
       format for that string is identical to the one in use for kernel
       modules (Dual licenses, such as "Dual BSD/GPL", may be used). Some
       helper functions are only accessible to programs that are compatible
       with the GNU Privacy License (GPL).

       In order to use such helpers, the eBPF program must be loaded with the
       correct license string passed (via attr) to the bpf() system call, and
       this generally translates into the C source code of the program
       containing a line similar to the following:

          char ____license[] __attribute__((section("license"), used)) = "GPL";

IMPLEMENTATION
       This manual page is an effort to document the existing eBPF helper
       functions.  But as of this writing, the BPF sub-system is under heavy
       development. New eBPF program or map types are added, along with new
       helper functions. Some helpers are occasionally made available for
       additional program types. So in spite of the efforts of the community,
       this page might not be up-to-date. If you want to check by yourself
       what helper functions exist in your kernel, or what types of programs
       they can support, here are some files among the kernel tree that you
       may be interested in:

       · include/uapi/linux/bpf.h is the main BPF header. It contains the full
         list of all helper functions, as well as many other BPF definitions
         including most of the flags, structs or constants used by the
         helpers.

       · net/core/filter.c contains the definition of most network-related
         helper functions, and the list of program types from which they can
         be used.

       · kernel/trace/bpf_trace.c is the equivalent for most tracing
         program-related helpers.

       · kernel/bpf/verifier.c contains the functions used to check that valid
         types of eBPF maps are used with a given helper function.

       · kernel/bpf/ directory contains other files in which additional
         helpers are defined (for cgroups, sockmaps, etc.).

       Compatibility between helper functions and program types can generally
       be found in the files where helper functions are defined. Look for the
       struct bpf_func_proto objects and for functions returning them: these
       functions contain a list of helpers that a given program type can call.
       Note that the default: label of the switch ... case used to filter
       helpers can call other functions, themselves allowing access to
       additional helpers. The requirement for GPL license is also in those
       struct bpf_func_proto.

       Compatibility between helper functions and map types can be found in
       the check_map_func_compatibility() function in file
       kernel/bpf/verifier.c.

       Helper functions that invalidate the checks on data and data_end
       pointers for network processing are listed in function
       bpf_helper_changes_pkt_data() in file net/core/filter.c.

SEE ALSO
       bpf(2), cgroups(7), ip(8), perf_event_open(2), sendmsg(2), socket(7),
       tc-bpf(8)

COLOPHON
       This page is part of release 5.03 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                             2019-03-06                    BPF-HELPERS(7)