libbpf API provides access to a few logically separated groups of functions and types. Every group has its own naming convention described here. It's recommended to follow these conventions whenever a new function or type is added to keep libbpf API clean and consistent.
All types and functions provided by libbpf API should have one of the
following prefixes: bpf_, btf_, libbpf_, xsk_,
perf_buffer_.
System call wrappers are simple wrappers for commands supported by
sys_bpf system call. These wrappers should go to bpf.h header file
and map one-on-one to corresponding commands.
For example bpf_map_lookup_elem wraps BPF_MAP_LOOKUP_ELEM
command of sys_bpf, bpf_prog_attach wraps BPF_PROG_ATTACH, etc.
Another class of types and functions provided by libbpf API is "objects"
and functions to work with them. Objects are high-level abstractions
such as BPF program or BPF map. They're represented by corresponding
structures such as struct bpf_object, struct bpf_program,
struct bpf_map, etc.
Structures are forward declared and access to their fields should be provided via corresponding getters and setters rather than directly.
These objects are associated with corresponding parts of ELF object that contains compiled BPF programs.
For example struct bpf_object represents ELF object itself created
from an ELF file or from a buffer, struct bpf_program represents a
program in ELF object and struct bpf_map is a map.
Functions that work with an object have names built from object name, double underscore and part that describes function purpose.
For example bpf_object__open consists of the name of corresponding
object, bpf_object, double underscore and open that defines the
purpose of the function to open ELF file and create bpf_object from
it.
Another example: bpf_program__load is named for corresponding
object, bpf_program, that is separated from other part of the name
by double underscore.
All objects and corresponding functions other than BTF related should go
to libbpf.h. BTF types and functions should go to btf.h.
Auxiliary functions and types that don't fit well in any of categories
described above should have libbpf_ prefix, e.g.
libbpf_get_error or libbpf_prog_type_by_name.
AF_XDP functions should have an xsk_ prefix, e.g.
xsk_umem__get_data or xsk_umem__create. The interface consists
of both low-level ring access functions and high-level configuration
functions. These can be mixed and matched. Note that these functions
are not reentrant for performance reasons.
Please take a look at Documentation/networking/af_xdp.rst in the Linux kernel source tree on how to use XDP sockets and for some common mistakes in case you do not get any traffic up to user space.
libbpf can be both linked statically or used as DSO. To avoid possible conflicts with other libraries an application is linked with, all non-static libbpf symbols should have one of the prefixes mentioned in API documentation above. See API naming convention to choose the right name for a new symbol.
libbpf follow the model when all global symbols have visibility "hidden"
by default and to make a symbol visible it has to be explicitly
attributed with LIBBPF_API macro. For example:
LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);This prevents from accidentally exporting a symbol, that is not supposed to be a part of ABI what, in turn, improves both libbpf developer- and user-experiences.
To make future ABI extensions possible libbpf ABI is versioned.
Versioning is implemented by libbpf.map version script that is
passed to linker.
Version name is LIBBPF_ prefix + three-component numeric version,
starting from 0.0.1.
Every time ABI is being changed, e.g. because a new symbol is added or semantic of existing symbol is changed, ABI version should be bumped. This bump in ABI version is at most once per kernel development cycle.
For example, if current state of libbpf.map is:
, and a new symbol bpf_func_c is being introduced, then
libbpf.map should be changed like this:
, where new version LIBBPF_0.0.2 depends on the previous
LIBBPF_0.0.1.
Format of version script and ways to handle ABI changes, including incompatible ones, described in details in [1].
Under https://github.com/libbpf/libbpf there is a (semi-)automated mirror of the mainline's version of libbpf for a stand-alone build.
However, all changes to libbpf's code base must be upstreamed through the mainline kernel tree.
libbpf is dual-licensed under LGPL 2.1 and BSD 2-Clause.
- [1] https://www.akkadia.org/drepper/dsohowto.pdf
- (Chapter 3. Maintaining APIs and ABIs).