bpf: update bpf.h uapi header for tools

Update tools/include/uapi/linux/bpf.h file in order to reflect the
changes for BPF helper functions documentation introduced in previous
commits.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 1380 insertions, 396 deletions

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index da8801860c7d..da77a9388947 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -377,412 +377,1396 @@ union bpf_attr {
 	};
 } __attribute__((aligned(8)));
 
-/* BPF helper function descriptions:
- *
- * void *bpf_map_lookup_elem(&map, &key)
- *     Return: Map value or NULL
- *
- * int bpf_map_update_elem(&map, &key, &value, flags)
- *     Return: 0 on success or negative error
- *
- * int bpf_map_delete_elem(&map, &key)
- *     Return: 0 on success or negative error
- *
- * int bpf_probe_read(void *dst, int size, void *src)
- *     Return: 0 on success or negative error
+/* The description below is an attempt at providing documentation to eBPF
+ * developers about the multiple available eBPF helper functions. It can be
+ * parsed and used to produce a manual page. The workflow is the following,
+ * and requires the rst2man utility:
+ *
+ *     $ ./scripts/bpf_helpers_doc.py \
+ *             --filename include/uapi/linux/bpf.h > /tmp/bpf-helpers.rst
+ *     $ rst2man /tmp/bpf-helpers.rst > /tmp/bpf-helpers.7
+ *     $ man /tmp/bpf-helpers.7
+ *
+ * Note that in order to produce this external documentation, some RST
+ * formatting is used in the descriptions to get "bold" and "italics" in
+ * manual pages. Also note that the few trailing white spaces are
+ * intentional, removing them would break paragraphs for rst2man.
+ *
+ * Start of BPF helper function descriptions:
+ *
+ * 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_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)
- *     Return: current ktime
- *
- * int bpf_trace_printk(const char *fmt, int fmt_size, ...)
- *     Return: length of buffer written or negative error
- *
- * u32 bpf_prandom_u32(void)
- *     Return: random value
- *
- * u32 bpf_raw_smp_processor_id(void)
- *     Return: SMP processor ID
- *
- * int bpf_skb_store_bytes(skb, offset, from, len, flags)
- *     store bytes into packet
- *     @skb: pointer to skb
- *     @offset: offset within packet from skb->mac_header
- *     @from: pointer where to copy bytes from
- *     @len: number of bytes to store into packet
- *     @flags: bit 0 - if true, recompute skb->csum
- *             other bits - reserved
- *     Return: 0 on success or negative error
- *
- * int bpf_l3_csum_replace(skb, offset, from, to, flags)
- *     recompute IP checksum
- *     @skb: pointer to skb
- *     @offset: offset within packet where IP checksum is located
- *     @from: old value of header field
- *     @to: new value of header field
- *     @flags: bits 0-3 - size of header field
- *             other bits - reserved
- *     Return: 0 on success or negative error
- *
- * int bpf_l4_csum_replace(skb, offset, from, to, flags)
- *     recompute TCP/UDP checksum
- *     @skb: pointer to skb
- *     @offset: offset within packet where TCP/UDP checksum is located
- *     @from: old value of header field
- *     @to: new value of header field
- *     @flags: bits 0-3 - size of header field
- *             bit 4 - is pseudo header
- *             other bits - reserved
- *     Return: 0 on success or negative error
- *
- * int bpf_tail_call(ctx, prog_array_map, index)
- *     jump into another BPF program
- *     @ctx: context pointer passed to next program
- *     @prog_array_map: pointer to map which type is BPF_MAP_TYPE_PROG_ARRAY
- *     @index: 32-bit index inside array that selects specific program to run
- *     Return: 0 on success or negative error
- *
- * int bpf_clone_redirect(skb, ifindex, flags)
- *     redirect to another netdev
- *     @skb: pointer to skb
- *     @ifindex: ifindex of the net device
- *     @flags: bit 0 - if set, redirect to ingress instead of egress
- *             other bits - reserved
- *     Return: 0 on success or negative error
+ * 	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: current->tgid << 32 | current->pid
+ * 	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: current_gid << 32 | current_uid
- *
- * int bpf_get_current_comm(char *buf, int size_of_buf)
- *     stores current->comm into buf
- *     Return: 0 on success or negative error
- *
- * u32 bpf_get_cgroup_classid(skb)
- *     retrieve a proc's classid
- *     @skb: pointer to skb
- *     Return: classid if != 0
- *
- * int bpf_skb_vlan_push(skb, vlan_proto, vlan_tci)
- *     Return: 0 on success or negative error
- *
- * int bpf_skb_vlan_pop(skb)
- *     Return: 0 on success or negative error
- *
- * int bpf_skb_get_tunnel_key(skb, key, size, flags)
- * int bpf_skb_set_tunnel_key(skb, key, size, flags)
- *     retrieve or populate tunnel metadata
- *     @skb: pointer to skb
- *     @key: pointer to 'struct bpf_tunnel_key'
- *     @size: size of 'struct bpf_tunnel_key'
- *     @flags: room for future extensions
- *     Return: 0 on success or negative error
- *
- * u64 bpf_perf_event_read(map, flags)
- *     read perf event counter value
- *     @map: pointer to perf_event_array map
- *     @flags: index of event in the map or bitmask flags
- *     Return: value of perf event counter read or error code
- *
- * int bpf_redirect(ifindex, flags)
- *     redirect to another netdev
- *     @ifindex: ifindex of the net device
- *     @flags:
- *	  cls_bpf:
- *          bit 0 - if set, redirect to ingress instead of egress
- *          other bits - reserved
- *	  xdp_bpf:
- *	    all bits - reserved
- *     Return: cls_bpf: TC_ACT_REDIRECT on success or TC_ACT_SHOT on error
- *	       xdp_bfp: XDP_REDIRECT on success or XDP_ABORT on error
- * int bpf_redirect_map(map, key, flags)
- *     redirect to endpoint in map
- *     @map: pointer to dev map
- *     @key: index in map to lookup
- *     @flags: --
- *     Return: XDP_REDIRECT on success or XDP_ABORT on error
- *
- * u32 bpf_get_route_realm(skb)
- *     retrieve a dst's tclassid
- *     @skb: pointer to skb
- *     Return: realm if != 0
- *
- * int bpf_perf_event_output(ctx, map, flags, data, size)
- *     output perf raw sample
- *     @ctx: struct pt_regs*
- *     @map: pointer to perf_event_array map
- *     @flags: index of event in the map or bitmask flags
- *     @data: data on stack to be output as raw data
- *     @size: size of data
- *     Return: 0 on success or negative error
- *
- * int bpf_get_stackid(ctx, map, flags)
- *     walk user or kernel stack and return id
- *     @ctx: struct pt_regs*
- *     @map: pointer to stack_trace map
- *     @flags: bits 0-7 - numer of stack frames to skip
- *             bit 8 - collect user stack instead of kernel
- *             bit 9 - compare stacks by hash only
- *             bit 10 - if two different stacks hash into the same stackid
- *                      discard old
- *             other bits - reserved
- *     Return: >= 0 stackid on success or negative error
- *
- * s64 bpf_csum_diff(from, from_size, to, to_size, seed)
- *     calculate csum diff
- *     @from: raw from buffer
- *     @from_size: length of from buffer
- *     @to: raw to buffer
- *     @to_size: length of to buffer
- *     @seed: optional seed
- *     Return: csum result or negative error code
- *
- * int bpf_skb_get_tunnel_opt(skb, opt, size)
- *     retrieve tunnel options metadata
- *     @skb: pointer to skb
- *     @opt: pointer to raw tunnel option data
- *     @size: size of @opt
- *     Return: option size
- *
- * int bpf_skb_set_tunnel_opt(skb, opt, size)
- *     populate tunnel options metadata
- *     @skb: pointer to skb
- *     @opt: pointer to raw tunnel option data
- *     @size: size of @opt
- *     Return: 0 on success or negative error
- *
- * int bpf_skb_change_proto(skb, proto, flags)
- *     Change protocol of the skb. Currently supported is v4 -> v6,
- *     v6 -> v4 transitions. The helper will also resize the skb. eBPF
- *     program is expected to fill the new headers via skb_store_bytes
- *     and lX_csum_replace.
- *     @skb: pointer to skb
- *     @proto: new skb->protocol type
- *     @flags: reserved
- *     Return: 0 on success or negative error
- *
- * int bpf_skb_change_type(skb, type)
- *     Change packet type of skb.
- *     @skb: pointer to skb
- *     @type: new skb->pkt_type type
- *     Return: 0 on success or negative error
- *
- * int bpf_skb_under_cgroup(skb, map, index)
- *     Check cgroup2 membership of skb
- *     @skb: pointer to skb
- *     @map: pointer to bpf_map in BPF_MAP_TYPE_CGROUP_ARRAY type
- *     @index: index of the cgroup in the bpf_map
- *     Return:
- *       == 0 skb failed the cgroup2 descendant test
- *       == 1 skb succeeded the cgroup2 descendant test
- *        < 0 error
- *
- * u32 bpf_get_hash_recalc(skb)
- *     Retrieve and possibly recalculate skb->hash.
- *     @skb: pointer to skb
- *     Return: hash
+ * 	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