--- /dev/null
+================
+bpftool-gen
+================
+-------------------------------------------------------------------------------
+tool for BPF code-generation
+-------------------------------------------------------------------------------
+
+:Manual section: 8
+
+SYNOPSIS
+========
+
+ **bpftool** [*OPTIONS*] **gen** *COMMAND*
+
+ *OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] }
+
+ *COMMAND* := { **skeleton | **help** }
+
+GEN COMMANDS
+=============
+
+| **bpftool** **gen skeleton** *FILE*
+| **bpftool** **gen help**
+
+DESCRIPTION
+===========
+ **bpftool gen skeleton** *FILE*
+ Generate BPF skeleton C header file for a given *FILE*.
+
+ BPF skeleton is an alternative interface to existing libbpf
+ APIs for working with BPF objects. Skeleton code is intended
+ to significantly shorten and simplify code to load and work
+ with BPF programs from userspace side. Generated code is
+ tailored to specific input BPF object *FILE*, reflecting its
+ structure by listing out available maps, program, variables,
+ etc. Skeleton eliminates the need to lookup mentioned
+ components by name. Instead, if skeleton instantiation
+ succeeds, they are populated in skeleton structure as valid
+ libbpf types (e.g., struct bpf_map pointer) and can be
+ passed to existing generic libbpf APIs.
+
+ In addition to simple and reliable access to maps and
+ programs, skeleton provides a storage for BPF links (struct
+ bpf_link) for each BPF program within BPF object. When
+ requested, supported BPF programs will be automatically
+ attached and resulting BPF links stored for further use by
+ user in pre-allocated fields in skeleton struct. For BPF
+ programs that can't be automatically attached by libbpf,
+ user can attach them manually, but store resulting BPF link
+ in per-program link field. All such set up links will be
+ automatically destroyed on BPF skeleton destruction. This
+ eliminates the need for users to manage links manually and
+ rely on libbpf support to detach programs and free up
+ resources.
+
+ Another facility provided by BPF skeleton is an interface to
+ global variables of all supported kinds: mutable, read-only,
+ as well as extern ones. This interface allows to pre-setup
+ initial values of variables before BPF object is loaded and
+ verified by kernel. For non-read-only variables, the same
+ interface can be used to fetch values of global variables on
+ userspace side, even if they are modified by BPF code.
+
+ During skeleton generation, contents of source BPF object
+ *FILE* is embedded within generated code and is thus not
+ necessary to keep around. This ensures skeleton and BPF
+ object file are matching 1-to-1 and always stay in sync.
+ Generated code is dual-licensed under LGPL-2.1 and
+ BSD-2-Clause licenses.
+
+ It is a design goal and guarantee that skeleton interfaces
+ are interoperable with generic libbpf APIs. User should
+ always be able to use skeleton API to create and load BPF
+ object, and later use libbpf APIs to keep working with
+ specific maps, programs, etc.
+
+ As part of skeleton, few custom functions are generated.
+ Each of them is prefixed with object name, derived from
+ object file name. I.e., if BPF object file name is
+ **example.o**, BPF object name will be **example**. The
+ following custom functions are provided in such case:
+
+ - **example__open** and **example__open_opts**.
+ These functions are used to instantiate skeleton. It
+ corresponds to libbpf's **bpf_object__open()** API.
+ **_opts** variants accepts extra **bpf_object_open_opts**
+ options.
+
+ - **example__load**.
+ This function creates maps, loads and verifies BPF
+ programs, initializes global data maps. It corresponds to
+ libppf's **bpf_object__load** API.
+
+ - **example__open_and_load** combines **example__open** and
+ **example__load** invocations in one commonly used
+ operation.
+
+ - **example__attach** and **example__detach**
+ This pair of functions allow to attach and detach,
+ correspondingly, already loaded BPF object. Only BPF
+ programs of types supported by libbpf for auto-attachment
+ will be auto-attached and their corresponding BPF links
+ instantiated. For other BPF programs, user can manually
+ create a BPF link and assign it to corresponding fields in
+ skeleton struct. **example__detach** will detach both
+ links created automatically, as well as those populated by
+ user manually.
+
+ - **example__destroy**
+ Detach and unload BPF programs, free up all the resources
+ used by skeleton and BPF object.
+
+ If BPF object has global variables, corresponding structs
+ with memory layout corresponding to global data data section
+ layout will be created. Currently supported ones are: .data,
+ .bss, .rodata, and .extern structs/data sections. These
+ data sections/structs can be used to set up initial values of
+ variables, if set before **example__load**. Afterwards, if
+ target kernel supports memory-mapped BPF arrays, same
+ structs can be used to fetch and update (non-read-only)
+ data from userspace, with same simplicity as for BPF side.
+
+ **bpftool gen help**
+ Print short help message.
+
+OPTIONS
+=======
+ -h, --help
+ Print short generic help message (similar to **bpftool help**).
+
+ -V, --version
+ Print version number (similar to **bpftool version**).
+
+ -j, --json
+ Generate JSON output. For commands that cannot produce JSON,
+ this option has no effect.
+
+ -p, --pretty
+ Generate human-readable JSON output. Implies **-j**.
+
+ -d, --debug
+ Print all logs available from libbpf, including debug-level
+ information.
+
+EXAMPLES
+========
+**$ cat example.c**
+::
+
+ #include <stdbool.h>
+ #include <linux/ptrace.h>
+ #include <linux/bpf.h>
+ #include "bpf_helpers.h"
+
+ const volatile int param1 = 42;
+ bool global_flag = true;
+ struct { int x; } data = {};
+
+ struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(max_entries, 128);
+ __type(key, int);
+ __type(value, long);
+ } my_map SEC(".maps");
+
+ SEC("raw_tp/sys_enter")
+ int handle_sys_enter(struct pt_regs *ctx)
+ {
+ static long my_static_var;
+ if (global_flag)
+ my_static_var++;
+ else
+ data.x += param1;
+ return 0;
+ }
+
+ SEC("raw_tp/sys_exit")
+ int handle_sys_exit(struct pt_regs *ctx)
+ {
+ int zero = 0;
+ bpf_map_lookup_elem(&my_map, &zero);
+ return 0;
+ }
+
+This is example BPF application with two BPF programs and a mix of BPF maps
+and global variables.
+
+**$ bpftool gen skeleton example.o**
+::
+
+ /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+ /* THIS FILE IS AUTOGENERATED! */
+ #ifndef __EXAMPLE_SKEL_H__
+ #define __EXAMPLE_SKEL_H__
+
+ #include <stdlib.h>
+ #include <libbpf.h>
+
+ struct example {
+ struct bpf_object_skeleton *skeleton;
+ struct bpf_object *obj;
+ struct {
+ struct bpf_map *rodata;
+ struct bpf_map *data;
+ struct bpf_map *bss;
+ struct bpf_map *my_map;
+ } maps;
+ struct {
+ struct bpf_program *handle_sys_enter;
+ struct bpf_program *handle_sys_exit;
+ } progs;
+ struct {
+ struct bpf_link *handle_sys_enter;
+ struct bpf_link *handle_sys_exit;
+ } links;
+ struct example__bss {
+ struct {
+ int x;
+ } data;
+ } *bss;
+ struct example__data {
+ _Bool global_flag;
+ long int handle_sys_enter_my_static_var;
+ } *data;
+ struct example__rodata {
+ int param1;
+ } *rodata;
+ };
+
+ static void example__destroy(struct example *obj);
+ static inline struct example *example__open_opts(
+ const struct bpf_object_open_opts *opts);
+ static inline struct example *example__open();
+ static inline int example__load(struct example *obj);
+ static inline struct example *example__open_and_load();
+ static inline int example__attach(struct example *obj);
+ static inline void example__detach(struct example *obj);
+
+ #endif /* __EXAMPLE_SKEL_H__ */
+
+**$ cat example_user.c**
+::
+
+ #include "example.skel.h"
+
+ int main()
+ {
+ struct example *skel;
+ int err = 0;
+
+ skel = example__open();
+ if (!skel)
+ goto cleanup;
+
+ skel->rodata->param1 = 128;
+
+ err = example__load(skel);
+ if (err)
+ goto cleanup;
+
+ err = example__attach(skel);
+ if (err)
+ goto cleanup;
+
+ /* all libbpf APIs are usable */
+ printf("my_map name: %s\n", bpf_map__name(skel->maps.my_map));
+ printf("sys_enter prog FD: %d\n",
+ bpf_program__fd(skel->progs.handle_sys_enter));
+
+ /* detach and re-attach sys_exit program */
+ bpf_link__destroy(skel->links.handle_sys_exit);
+ skel->links.handle_sys_exit =
+ bpf_program__attach(skel->progs.handle_sys_exit);
+
+ printf("my_static_var: %ld\n",
+ skel->bss->handle_sys_enter_my_static_var);
+
+ cleanup:
+ example__destroy(skel);
+ return err;
+ }
+
+**# ./example_user**
+::
+
+ my_map name: my_map
+ sys_enter prog FD: 8
+ my_static_var: 7
+
+This is a stripped-out version of skeleton generated for above example code.
+
+SEE ALSO
+========
+ **bpf**\ (2),
+ **bpf-helpers**\ (7),
+ **bpftool**\ (8),
+ **bpftool-map**\ (8),
+ **bpftool-prog**\ (8),
+ **bpftool-cgroup**\ (8),
+ **bpftool-feature**\ (8),
+ **bpftool-net**\ (8),
+ **bpftool-perf**\ (8),
+ **bpftool-btf**\ (8)
projects / openwrt / staging / blogic.git / commitdiff