linux/tools/lib/bpf
Toke Høiland-Jørgensen d1b4574a4b libbpf: Fix error handling in bpf_map__reuse_fd()
bpf_map__reuse_fd() was calling close() in the error path before returning
an error value based on errno. However, close can change errno, so that can
lead to potentially misleading error messages. Instead, explicitly store
errno in the err variable before each goto.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/157269297769.394725.12634985106772698611.stgit@toke.dk
2019-11-02 12:35:06 -07:00
..
.gitignore libbpf: Move bpf_{helpers, helper_defs, endian, tracing}.h into libbpf 2019-10-08 23:16:03 +02:00
bpf_core_read.h libbpf: Add BPF-side definitions of supported field relocation kinds 2019-10-15 16:06:05 -07:00
bpf_endian.h libbpf: Move bpf_{helpers, helper_defs, endian, tracing}.h into libbpf 2019-10-08 23:16:03 +02:00
bpf_helpers.h libbpf: Add BPF_CORE_READ/BPF_CORE_READ_INTO helpers 2019-10-08 23:16:03 +02:00
bpf_prog_linfo.c libbpf: add common min/max macro to libbpf_internal.h 2019-06-18 00:08:54 +02:00
bpf_tracing.h libbpf: Move bpf_{helpers, helper_defs, endian, tracing}.h into libbpf 2019-10-08 23:16:03 +02:00
bpf.c libbpf: Add support for prog_tracing 2019-10-31 15:16:59 +01:00
bpf.h libbpf: Add support for prog_tracing 2019-10-31 15:16:59 +01:00
btf_dump.c tools, bpf: Rename pr_warning to pr_warn to align with kernel logging 2019-10-21 14:38:41 +02:00
btf.c tools, bpf: Rename pr_warning to pr_warn to align with kernel logging 2019-10-21 14:38:41 +02:00
btf.h libbpf: Update BTF reloc support to latest Clang format 2019-10-15 16:06:05 -07:00
Build libbpf: add btf_dump API for BTF-to-C conversion 2019-05-24 14:05:58 -07:00
hashmap.c libbpf: add resizable non-thread safe internal hashmap 2019-05-24 14:05:57 -07:00
hashmap.h libbpf: fix missing __WORDSIZE definition 2019-07-29 10:18:08 -03:00
libbpf_errno.c tools/bpf: make libbpf _GNU_SOURCE friendly 2018-11-30 02:41:02 +01:00
libbpf_internal.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2019-10-26 22:57:27 -07:00
libbpf_probes.c libbpf: Add support for prog_tracing 2019-10-31 15:16:59 +01:00
libbpf_util.h libbpf: move logging helpers into libbpf_internal.h 2019-05-16 12:47:47 -07:00
libbpf.c libbpf: Fix error handling in bpf_map__reuse_fd() 2019-11-02 12:35:06 -07:00
libbpf.h libbpf: Add support for prog_tracing 2019-10-31 15:16:59 +01:00
libbpf.map libbpf: Add support for prog_tracing 2019-10-31 15:16:59 +01:00
libbpf.pc.template tools/bpf: generate pkg-config file for libbpf 2019-03-28 17:06:03 +01:00
Makefile Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2019-10-26 22:57:27 -07:00
netlink.c libbpf: Add a support for getting xdp prog id on ifindex 2019-02-01 23:37:51 +01:00
nlattr.c libbpf: relicense libbpf as LGPL-2.1 OR BSD-2-Clause 2018-10-08 10:09:48 +02:00
nlattr.h libbpf: relicense libbpf as LGPL-2.1 OR BSD-2-Clause 2018-10-08 10:09:48 +02:00
README.rst libbpf: add perf_buffer_ prefix to README 2019-07-08 15:35:43 +02:00
str_error.c libbpf: make libbpf_strerror_r agnostic to sign of error 2019-07-05 22:37:30 +02:00
str_error.h libbpf: relicense libbpf as LGPL-2.1 OR BSD-2-Clause 2018-10-08 10:09:48 +02:00
test_libbpf.c libbpf: Don't use cxx to test_libpf target 2019-10-12 16:08:59 -07:00
xsk.c libbpf: Don't use kernel-side u32 type in xsk.c 2019-10-29 06:38:12 -07:00
xsk.h libbpf: add flags to umem config 2019-08-31 01:08:26 +02:00

.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)

libbpf API naming convention
============================

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
--------------------

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.

Objects
-------

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
-------------------

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
-------------------

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 ABI
==========

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.

Symbol visibility
-----------------

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:

.. code-block:: c

        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.

ABI versionning
---------------

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:

.. code-block::
        LIBBPF_0.0.1 {
        	global:
                        bpf_func_a;
                        bpf_func_b;
        	local:
        		\*;
        };

, and a new symbol ``bpf_func_c`` is being introduced, then
``libbpf.map`` should be changed like this:

.. code-block::
        LIBBPF_0.0.1 {
        	global:
                        bpf_func_a;
                        bpf_func_b;
        	local:
        		\*;
        };
        LIBBPF_0.0.2 {
                global:
                        bpf_func_c;
        } LIBBPF_0.0.1;

, 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].

Stand-alone build
=================

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.

License
=======

libbpf is dual-licensed under LGPL 2.1 and BSD 2-Clause.

Links
=====

[1] https://www.akkadia.org/drepper/dsohowto.pdf
    (Chapter 3. Maintaining APIs and ABIs).