diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-09-13 12:27:00 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-09-13 12:27:00 -0700 |
| commit | 22098763a10d9c1340827fcf6edab66f153b27f0 (patch) | |
| tree | 3962f95a34df034652ff93686cdd156c7197f2d9 /Documentation/bpf/libbpf | |
| download | linux-stable-22098763a10d9c1340827fcf6edab66f153b27f0.tar.gz linux-stable-22098763a10d9c1340827fcf6edab66f153b27f0.zip | |
Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted
Pull tracing fixes from Steven Rostedt:
- Don't destroy user event fields when removal fails
User event fields are destroyed before the event is removed from
visibility. But that can fail leaving the still visible event with no
fields. Move the destroying of the fields to after the event is
successfully removed from visibility.
- Initialize function graph state is fork before calling
copy_exec_state()
For non-CLONE_VM forks, copy_exec_state() allocates a new
task_exec_state. If that allocation fails, ftrace_graph_exit_task()
will free the tasks ret_stack pointer. Since that pointer is still
using the parent's ret_stack, it mistakenly frees the parent's
pointer too.
Call ftrace_graph_init() on the task first which will NULL out the
new tasks's ret_stack and if the copy fails, it will not free
anything.
- Remove FGRAPH_MAX_INDEX
The macro FGRAPH_MAX_INDEX was added but never used. Remove it.
- Save ent_size in function graph printing of nested functions
The function graph tracer needs to look at the next event to see if
the next event is the return of the current function entry. If it is,
it prints a single line:
ktime_get();
Otherwise it prints it like a nested function:
tick_nohz_irq_exit() {
ktime_get();
kcpustat_irq_exit();
}
In order to look at the next event, it must save the current event so
that it has the information to print from it. It saves the event in
the iterator descriptor called "ent". What it doesn't save is the
ent_size of the event which is now used to know if the function graph
arguments are to be printed. The peek doesn't save the size so the
size used happens to be that of the size of the last event that was
seen.
Save the entry event size in the iterator descriptor so that the
correct size is used.
- Fix several errors with freeing data in the histogram code
The histogram code had a lot of leaked or or incorrect accounting
when failures happen. Correct them.
- Fix histogram regression of .percent and .graph modifiers
Up until 6.3 histogram values could have "percent" or "graph"
modifiers that changed how they were printed. But a change that added
restricting histograms values from being strings, stack traces and
other modifiers inadvertently prevented them from using the percent
and graph modifiers, which were legal use cases for values.
Put back the percent and graph modifiers.
- Fix various typos in the comments
- Set the trace_clock before initializing a histogram with clock
argument
The histogram API allows the user to specific which trace clock to
use via a "clock=" string. The histogram is set up first before the
clock is checked. If the passed in clock is not valid, it exits
without fully fixing up the histogram leaving it on the list and a
use-after-free can trigger.
Update the clock argument first and if it fails then exit gracefully
before the histogram trigger is placed on any lists.
- Restore :mod: trailer after parsing in ftrace_set_clr_event
The function ftrace_set_clr_event() modifies the parse string and
needs to put it back to what was passed in. It searches for ":mod:"
via a strsep() but fails to put back the first ':' in the string.
Add back the ':' in the passed in string.
- Take trace_array reference when opening a tracer options file
The options files are dynamically created and some tracers add their
own options. When a tracer adds their own list of options, the
trace_array holding them has an array to hold the list of options for
each tracer. This array increases in size via a krealloc(), and the
new entry gets a newly allocated array to hold the options of the new
tracer being added.
The element in each entry of the tracer's option array holds a
pointer back to the trace_array, a pointer to the tracer it is
associated to, a pointer to the flags of the option.
The issue is that these arrays are freed when the trace_array is
freed when its instance it represents is removed from the instances
directory. There's a race that an open of one of these options files
can happen when the instance is being removed.
Add a new helper function to be called by the open function of the
options file to iterate all existing trace_arrays under a lock and
find the one that has the given option element in one of it's tracer
arrays. If found, then update the associated trace_array's reference
counter to keep it from being freed. If not found, have the open call
return -ENODEV.
- Disable interrupts when acquiring the lock in rb_wake_up_waiters()
The function rb_wake_up_waiters() assumes it will be called in
interrupt context and does not disable irqs when taking
cpu_buffer->reader_lock, which can be called in hard interrupt
context. The issue is in PREEMPT_RT, this function is called in
thread context leaving this lock open to a deadlock.
Take the lock with interrupts disabled.
- Use rcu_assign_pointer() for tmp_ops filter hash
The tmp_ops used in update_ftrace_direct_mod() assigns its
filter_hash field directly, but that field is annotated as __rcu and
sparse complains. Assign it with rcu_assign_pointer()
- Fix use-after-free in enable_trigger_private_data_free()
The trace_event_call is accessed through the event_trigger_data's
trace_event_file pointer to put the trace_event_call on freeing. The
issue is that the trace_event_file data may have been freed already
causing a use-after-free. Add a field to the event_trigger_data that
points directly to the trace_event_call so that it can decrement its
reference directly without needing to go through the
trace_event_file.
- Fix accounting of buffer data remote headers
trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
the number of pages is needed for the asked for size as it doesn't
take into account the meta data on each page. Add a helper function
to do the calculation properly and use that in these functions.
- Catch nr_page_va overflow in ring_buffer_desc sizing
The number of pages per remote ring buffer is capped by
ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
overflow that field would silently allocate a descriptor smaller than
what was asked for.
- Do not resize the subbuf order if any per_cpu buffer is disabled
The mmapping of ring buffers disables resizing the subbuffers, but it
is done per-cpu whereas the subbuf size change is done for all the
per_cpu buffers under the buffer->mutex. It could change the size of
some while the mapping is happening on others. Have the resize of the
subbuf order check all the per_cpu buffers under the lock to see if
any of them is disabled before starting and causing an inconsistency
between buffers that are being mapped.
* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
ring-buffer: Check resize_disabled before publishing the new subbuf order
tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
tracing/remotes: Account for ring buffer page header in size calculation
tracing: Don't dereference trace_event_file in deferred trigger free
ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
tracing: Take trace_array reference when opening a tracer options file
tracing: Fix ring_buffer_read_page_size() kernel-doc
tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
tracing: Fix memory corruption from a "STACKTRACE" histogram key
tracing: Fix memory corruption from the histogram stacktrace modifier
tracing: Undo the registration when enabling the histogram trigger fails
tracing: Take the reference before publishing the named histogram trigger
tracing: Set the trace clock before registering the histogram trigger
tracing: Fix typo "preceeded" in comment
tracing: Fix typo "availabe" in comment
tracing: Let histogram values keep the percent and graph modifiers
tracing: Keep the entry count when the histogram stats allocation fails
tracing: Free histogram the field rejected for a bad modifier
tracing: Free histogram the var ref when its initialization fails
...
Diffstat (limited to 'Documentation/bpf/libbpf')
| -rw-r--r-- | Documentation/bpf/libbpf/index.rst | 33 | ||||
| -rw-r--r-- | Documentation/bpf/libbpf/libbpf_build.rst | 37 | ||||
| -rw-r--r-- | Documentation/bpf/libbpf/libbpf_naming_convention.rst | 193 | ||||
| -rw-r--r-- | Documentation/bpf/libbpf/libbpf_overview.rst | 236 | ||||
| -rw-r--r-- | Documentation/bpf/libbpf/program_types.rst | 257 |
5 files changed, 756 insertions, 0 deletions
diff --git a/Documentation/bpf/libbpf/index.rst b/Documentation/bpf/libbpf/index.rst new file mode 100644 index 000000000..7545a2049 --- /dev/null +++ b/Documentation/bpf/libbpf/index.rst @@ -0,0 +1,33 @@ +.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) + +.. _libbpf: + +====== +libbpf +====== + +If you are looking to develop BPF applications using the libbpf library, this +directory contains important documentation that you should read. + +To get started, it is recommended to begin with the :doc:`libbpf Overview +<libbpf_overview>` document, which provides a high-level understanding of the +libbpf APIs and their usage. This will give you a solid foundation to start +exploring and utilizing the various features of libbpf to develop your BPF +applications. + +.. toctree:: + :maxdepth: 1 + + libbpf_overview + API Documentation <https://libbpf.readthedocs.io/en/latest/api.html> + program_types + libbpf_naming_convention + libbpf_build + + +All general BPF questions, including kernel functionality, libbpf APIs and their +application, should be sent to bpf@vger.kernel.org mailing list. You can +`subscribe <http://vger.kernel.org/vger-lists.html#bpf>`_ to the mailing list +search its `archive <https://lore.kernel.org/bpf/>`_. Please search the archive +before asking new questions. It may be that this was already addressed or +answered before. diff --git a/Documentation/bpf/libbpf/libbpf_build.rst b/Documentation/bpf/libbpf/libbpf_build.rst new file mode 100644 index 000000000..8e8c23e80 --- /dev/null +++ b/Documentation/bpf/libbpf/libbpf_build.rst @@ -0,0 +1,37 @@ +.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) + +Building libbpf +=============== + +libelf and zlib are internal dependencies of libbpf and thus are required to link +against and must be installed on the system for applications to work. +pkg-config is used by default to find libelf, and the program called +can be overridden with PKG_CONFIG. + +If using pkg-config at build time is not desired, it can be disabled by +setting NO_PKG_CONFIG=1 when calling make. + +To build both static libbpf.a and shared libbpf.so: + +.. code-block:: bash + + $ cd src + $ make + +To build only static libbpf.a library in directory build/ and install them +together with libbpf headers in a staging directory root/: + +.. code-block:: bash + + $ cd src + $ mkdir build root + $ BUILD_STATIC_ONLY=y OBJDIR=build DESTDIR=root make install + +To build both static libbpf.a and shared libbpf.so against a custom libelf +dependency installed in /build/root/ and install them together with libbpf +headers in a build directory /build/root/: + +.. code-block:: bash + + $ cd src + $ PKG_CONFIG_PATH=/build/root/lib64/pkgconfig DESTDIR=/build/root make
\ No newline at end of file diff --git a/Documentation/bpf/libbpf/libbpf_naming_convention.rst b/Documentation/bpf/libbpf/libbpf_naming_convention.rst new file mode 100644 index 000000000..b5b41b61b --- /dev/null +++ b/Documentation/bpf/libbpf/libbpf_naming_convention.rst @@ -0,0 +1,193 @@ +.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) + +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_``, ``btf_dump_``, +``ring_buffer_``, ``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 to 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. + +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``. + +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 versioning +-------------- + +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:: none + + 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:: none + + 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. + + +API documentation convention +============================ + +The libbpf API is documented via comments above definitions in +header files. These comments can be rendered by doxygen and sphinx +for well organized html output. This section describes the +convention in which these comments should be formatted. + +Here is an example from btf.h: + +.. code-block:: c + + /** + * @brief **btf__new()** creates a new instance of a BTF object from the raw + * bytes of an ELF's BTF section + * @param data raw bytes + * @param size number of bytes passed in `data` + * @return new BTF object instance which has to be eventually freed with + * **btf__free()** + * + * On error, error-code-encoded-as-pointer is returned, not a NULL. To extract + * error code from such a pointer `libbpf_get_error()` should be used. If + * `libbpf_set_strict_mode(LIBBPF_STRICT_CLEAN_PTRS)` is enabled, NULL is + * returned on error instead. In both cases thread-local `errno` variable is + * always set to error code as well. + */ + +The comment must start with a block comment of the form '/\*\*'. + +The documentation always starts with a @brief directive. This line is a short +description about this API. It starts with the name of the API, denoted in bold +like so: **api_name**. Please include an open and close parenthesis if this is a +function. Follow with the short description of the API. A longer form description +can be added below the last directive, at the bottom of the comment. + +Parameters are denoted with the @param directive, there should be one for each +parameter. If this is a function with a non-void return, use the @return directive +to document it. + +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). diff --git a/Documentation/bpf/libbpf/libbpf_overview.rst b/Documentation/bpf/libbpf/libbpf_overview.rst new file mode 100644 index 000000000..f4d22f0c6 --- /dev/null +++ b/Documentation/bpf/libbpf/libbpf_overview.rst @@ -0,0 +1,236 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +libbpf Overview +=============== + +libbpf is a C-based library containing a BPF loader that takes compiled BPF +object files and prepares and loads them into the Linux kernel. libbpf takes the +heavy lifting of loading, verifying, and attaching BPF programs to various +kernel hooks, allowing BPF application developers to focus only on BPF program +correctness and performance. + +The following are the high-level features supported by libbpf: + +* Provides high-level and low-level APIs for user space programs to interact + with BPF programs. The low-level APIs wrap all the bpf system call + functionality, which is useful when users need more fine-grained control + over the interactions between user space and BPF programs. +* Provides overall support for the BPF object skeleton generated by bpftool. + The skeleton file simplifies the process for the user space programs to access + global variables and work with BPF programs. +* Provides BPF-side APIS, including BPF helper definitions, BPF maps support, + and tracing helpers, allowing developers to simplify BPF code writing. +* Supports BPF CO-RE mechanism, enabling BPF developers to write portable + BPF programs that can be compiled once and run across different kernel + versions. + +This document will delve into the above concepts in detail, providing a deeper +understanding of the capabilities and advantages of libbpf and how it can help +you develop BPF applications efficiently. + +BPF App Lifecycle and libbpf APIs +================================== + +A BPF application consists of one or more BPF programs (either cooperating or +completely independent), BPF maps, and global variables. The global +variables are shared between all BPF programs, which allows them to cooperate on +a common set of data. libbpf provides APIs that user space programs can use to +manipulate the BPF programs by triggering different phases of a BPF application +lifecycle. + +The following section provides a brief overview of each phase in the BPF life +cycle: + +* **Open phase**: In this phase, libbpf parses the BPF + object file and discovers BPF maps, BPF programs, and global variables. After + a BPF app is opened, user space apps can make additional adjustments + (setting BPF program types, if necessary; pre-setting initial values for + global variables, etc.) before all the entities are created and loaded. + +* **Load phase**: In the load phase, libbpf creates BPF + maps, resolves various relocations, and verifies and loads BPF programs into + the kernel. At this point, libbpf validates all the parts of a BPF application + and loads the BPF program into the kernel, but no BPF program has yet been + executed. After the load phase, it’s possible to set up the initial BPF map + state without racing with the BPF program code execution. + +* **Attachment phase**: In this phase, libbpf + attaches BPF programs to various BPF hook points (e.g., tracepoints, kprobes, + cgroup hooks, network packet processing pipeline, etc.). During this + phase, BPF programs perform useful work such as processing + packets, or updating BPF maps and global variables that can be read from user + space. + +* **Tear down phase**: In the tear down phase, + libbpf detaches BPF programs and unloads them from the kernel. BPF maps are + destroyed, and all the resources used by the BPF app are freed. + +BPF Object Skeleton File +======================== + +BPF skeleton is an alternative interface to libbpf APIs for working with BPF +objects. Skeleton code abstract away generic libbpf APIs to significantly +simplify code for manipulating BPF programs from user space. Skeleton code +includes a bytecode representation of the BPF object file, simplifying the +process of distributing your BPF code. With BPF bytecode embedded, there are no +extra files to deploy along with your application binary. + +You can generate the skeleton header file ``(.skel.h)`` for a specific object +file by passing the BPF object to the bpftool. The generated BPF skeleton +provides the following custom functions that correspond to the BPF lifecycle, +each of them prefixed with the specific object name: + +* ``<name>__open()`` – creates and opens BPF application (``<name>`` stands for + the specific bpf object name) +* ``<name>__load()`` – instantiates, loads,and verifies BPF application parts +* ``<name>__attach()`` – attaches all auto-attachable BPF programs (it’s + optional, you can have more control by using libbpf APIs directly) +* ``<name>__destroy()`` – detaches all BPF programs and + frees up all used resources + +Using the skeleton code is the recommended way to work with bpf programs. Keep +in mind, BPF skeleton provides access to the underlying BPF object, so whatever +was possible to do with generic libbpf APIs is still possible even when the BPF +skeleton is used. It's an additive convenience feature, with no syscalls, and no +cumbersome code. + +Other Advantages of Using Skeleton File +--------------------------------------- + +* BPF skeleton provides an interface for user space programs to work with BPF + global variables. The skeleton code memory maps global variables as a struct + into user space. The struct interface allows user space programs to initialize + BPF programs before the BPF load phase and fetch and update data from user + space afterward. + +* The ``skel.h`` file reflects the object file structure by listing out the + available maps, programs, etc. BPF skeleton provides direct access to all the + BPF maps and BPF programs as struct fields. This eliminates the need for + string-based lookups with ``bpf_object_find_map_by_name()`` and + ``bpf_object_find_program_by_name()`` APIs, reducing errors due to BPF source + code and user-space code getting out of sync. + +* The embedded bytecode representation of the object file ensures that the + skeleton and the BPF object file are always in sync. + +BPF Helpers +=========== + +libbpf provides BPF-side APIs that BPF programs can use to interact with the +system. The BPF helpers definition allows developers to use them in BPF code as +any other plain C function. For example, there are helper functions to print +debugging messages, get the time since the system was booted, interact with BPF +maps, manipulate network packets, etc. + +For a complete description of what the helpers do, the arguments they take, and +the return value, see the `bpf-helpers +<https://man7.org/linux/man-pages/man7/bpf-helpers.7.html>`_ man page. + +BPF CO-RE (Compile Once – Run Everywhere) +========================================= + +BPF programs work in the kernel space and have access to kernel memory and data +structures. One limitation that BPF applications come across is the lack of +portability across different kernel versions and configurations. `BCC +<https://github.com/iovisor/bcc/>`_ is one of the solutions for BPF +portability. However, it comes with runtime overhead and a large binary size +from embedding the compiler with the application. + +libbpf steps up the BPF program portability by supporting the BPF CO-RE concept. +BPF CO-RE brings together BTF type information, libbpf, and the compiler to +produce a single executable binary that you can run on multiple kernel versions +and configurations. + +To make BPF programs portable libbpf relies on the BTF type information of the +running kernel. Kernel also exposes this self-describing authoritative BTF +information through ``sysfs`` at ``/sys/kernel/btf/vmlinux``. + +You can generate the BTF information for the running kernel with the following +command: + +:: + + $ bpftool btf dump file /sys/kernel/btf/vmlinux format c > vmlinux.h + +The command generates a ``vmlinux.h`` header file with all kernel types +(:doc:`BTF types <../btf>`) that the running kernel uses. Including +``vmlinux.h`` in your BPF program eliminates dependency on system-wide kernel +headers. + +libbpf enables portability of BPF programs by looking at the BPF program’s +recorded BTF type and relocation information and matching them to BTF +information (vmlinux) provided by the running kernel. libbpf then resolves and +matches all the types and fields, and updates necessary offsets and other +relocatable data to ensure that BPF program’s logic functions correctly for a +specific kernel on the host. BPF CO-RE concept thus eliminates overhead +associated with BPF development and allows developers to write portable BPF +applications without modifications and runtime source code compilation on the +target machine. + +The following code snippet shows how to read the parent field of a kernel +``task_struct`` using BPF CO-RE and libbf. The basic helper to read a field in a +CO-RE relocatable manner is ``bpf_core_read(dst, sz, src)``, which will read +``sz`` bytes from the field referenced by ``src`` into the memory pointed to by +``dst``. + +.. code-block:: C + :emphasize-lines: 6 + + //... + struct task_struct *task = (void *)bpf_get_current_task(); + struct task_struct *parent_task; + int err; + + err = bpf_core_read(&parent_task, sizeof(void *), &task->parent); + if (err) { + /* handle error */ + } + + /* parent_task contains the value of task->parent pointer */ + +In the code snippet, we first get a pointer to the current ``task_struct`` using +``bpf_get_current_task()``. We then use ``bpf_core_read()`` to read the parent +field of task struct into the ``parent_task`` variable. ``bpf_core_read()`` is +just like ``bpf_probe_read_kernel()`` BPF helper, except it records information +about the field that should be relocated on the target kernel. i.e, if the +``parent`` field gets shifted to a different offset within +``struct task_struct`` due to some new field added in front of it, libbpf will +automatically adjust the actual offset to the proper value. + +Getting Started with libbpf +=========================== + +Check out the `libbpf-bootstrap <https://github.com/libbpf/libbpf-bootstrap>`_ +repository with simple examples of using libbpf to build various BPF +applications. + +See also `libbpf API documentation +<https://libbpf.readthedocs.io/en/latest/api.html>`_. + +libbpf and Rust +=============== + +If you are building BPF applications in Rust, it is recommended to use the +`Libbpf-rs <https://github.com/libbpf/libbpf-rs>`_ library instead of bindgen +bindings directly to libbpf. Libbpf-rs wraps libbpf functionality in +Rust-idiomatic interfaces and provides libbpf-cargo plugin to handle BPF code +compilation and skeleton generation. Using Libbpf-rs will make building user +space part of the BPF application easier. Note that the BPF program themselves +must still be written in plain C. + +libbpf logging +============== + +By default, libbpf logs informational and warning messages to stderr. The +verbosity of these messages can be controlled by setting the environment +variable LIBBPF_LOG_LEVEL to either warn, info, or debug. A custom log +callback can be set using ``libbpf_set_print()``. + +Additional Documentation +======================== + +* `Program types and ELF Sections <https://libbpf.readthedocs.io/en/latest/program_types.html>`_ +* `API naming convention <https://libbpf.readthedocs.io/en/latest/libbpf_naming_convention.html>`_ +* `Building libbpf <https://libbpf.readthedocs.io/en/latest/libbpf_build.html>`_ +* `API documentation Convention <https://libbpf.readthedocs.io/en/latest/libbpf_naming_convention.html#api-documentation-convention>`_ diff --git a/Documentation/bpf/libbpf/program_types.rst b/Documentation/bpf/libbpf/program_types.rst new file mode 100644 index 000000000..3a07ce3b7 --- /dev/null +++ b/Documentation/bpf/libbpf/program_types.rst @@ -0,0 +1,257 @@ +.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) + +.. _program_types_and_elf: + +Program Types and ELF Sections +============================== + +The table below lists the program types, their attach types where relevant and the ELF section +names supported by libbpf for them. The ELF section names follow these rules: + +- ``type`` is an exact match, e.g. ``SEC("socket")`` +- ``type+`` means it can be either exact ``SEC("type")`` or well-formed ``SEC("type/extras")`` + with a '``/``' separator between ``type`` and ``extras``. + +When ``extras`` are specified, they provide details of how to auto-attach the BPF program. The +format of ``extras`` depends on the program type, e.g. ``SEC("tracepoint/<category>/<name>")`` +for tracepoints or ``SEC("usdt/<path>:<provider>:<name>")`` for USDT probes. The extras are +described in more detail in the footnotes. + + ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| Program Type | Attach Type | ELF Section Name | Sleepable | ++===========================================+========================================+==================================+===========+ +| ``BPF_PROG_TYPE_CGROUP_DEVICE`` | ``BPF_CGROUP_DEVICE`` | ``cgroup/dev`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_CGROUP_SKB`` | | ``cgroup/skb`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET_EGRESS`` | ``cgroup_skb/egress`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET_INGRESS`` | ``cgroup_skb/ingress`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_CGROUP_SOCKOPT`` | ``BPF_CGROUP_GETSOCKOPT`` | ``cgroup/getsockopt`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_SETSOCKOPT`` | ``cgroup/setsockopt`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_CGROUP_SOCK_ADDR`` | ``BPF_CGROUP_INET4_BIND`` | ``cgroup/bind4`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET4_CONNECT`` | ``cgroup/connect4`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET4_GETPEERNAME`` | ``cgroup/getpeername4`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET4_GETSOCKNAME`` | ``cgroup/getsockname4`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET6_BIND`` | ``cgroup/bind6`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET6_CONNECT`` | ``cgroup/connect6`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET6_GETPEERNAME`` | ``cgroup/getpeername6`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET6_GETSOCKNAME`` | ``cgroup/getsockname6`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UDP4_RECVMSG`` | ``cgroup/recvmsg4`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UDP4_SENDMSG`` | ``cgroup/sendmsg4`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UDP6_RECVMSG`` | ``cgroup/recvmsg6`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UDP6_SENDMSG`` | ``cgroup/sendmsg6`` | | +| +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UNIX_CONNECT`` | ``cgroup/connect_unix`` | | +| +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UNIX_SENDMSG`` | ``cgroup/sendmsg_unix`` | | +| +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UNIX_RECVMSG`` | ``cgroup/recvmsg_unix`` | | +| +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UNIX_GETPEERNAME`` | ``cgroup/getpeername_unix`` | | +| +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_UNIX_GETSOCKNAME`` | ``cgroup/getsockname_unix`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_CGROUP_SOCK`` | ``BPF_CGROUP_INET4_POST_BIND`` | ``cgroup/post_bind4`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET6_POST_BIND`` | ``cgroup/post_bind6`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET_SOCK_CREATE`` | ``cgroup/sock_create`` | | ++ + +----------------------------------+-----------+ +| | | ``cgroup/sock`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_CGROUP_INET_SOCK_RELEASE`` | ``cgroup/sock_release`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_CGROUP_SYSCTL`` | ``BPF_CGROUP_SYSCTL`` | ``cgroup/sysctl`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_EXT`` | | ``freplace+`` [#fentry]_ | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_FLOW_DISSECTOR`` | ``BPF_FLOW_DISSECTOR`` | ``flow_dissector`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_KPROBE`` | | ``kprobe+`` [#kprobe]_ | | ++ + +----------------------------------+-----------+ +| | | ``kretprobe+`` [#kprobe]_ | | ++ + +----------------------------------+-----------+ +| | | ``ksyscall+`` [#ksyscall]_ | | ++ + +----------------------------------+-----------+ +| | | ``kretsyscall+`` [#ksyscall]_ | | ++ + +----------------------------------+-----------+ +| | | ``uprobe+`` [#uprobe]_ | | ++ + +----------------------------------+-----------+ +| | | ``uprobe.s+`` [#uprobe]_ | Yes | ++ + +----------------------------------+-----------+ +| | | ``uretprobe+`` [#uprobe]_ | | ++ + +----------------------------------+-----------+ +| | | ``uretprobe.s+`` [#uprobe]_ | Yes | ++ + +----------------------------------+-----------+ +| | | ``usdt+`` [#usdt]_ | | ++ + +----------------------------------+-----------+ +| | | ``usdt.s+`` [#usdt]_ | Yes | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_KPROBE_MULTI`` | ``kprobe.multi+`` [#kpmulti]_ | | ++ + +----------------------------------+-----------+ +| | | ``kretprobe.multi+`` [#kpmulti]_ | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_KPROBE_SESSION`` | ``kprobe.session+`` [#kpmulti]_ | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_UPROBE_MULTI`` | ``uprobe.multi+`` [#upmul]_ | | ++ + +----------------------------------+-----------+ +| | | ``uprobe.multi.s+`` [#upmul]_ | Yes | ++ + +----------------------------------+-----------+ +| | | ``uretprobe.multi+`` [#upmul]_ | | ++ + +----------------------------------+-----------+ +| | | ``uretprobe.multi.s+`` [#upmul]_ | Yes | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_UPROBE_SESSION`` | ``uprobe.session+`` [#upmul]_ | | ++ + +----------------------------------+-----------+ +| | | ``uprobe.session.s+`` [#upmul]_ | Yes | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_LIRC_MODE2`` | ``BPF_LIRC_MODE2`` | ``lirc_mode2`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_LSM`` | ``BPF_LSM_CGROUP`` | ``lsm_cgroup+`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_LSM_MAC`` | ``lsm+`` [#lsm]_ | | ++ + +----------------------------------+-----------+ +| | | ``lsm.s+`` [#lsm]_ | Yes | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_LWT_IN`` | | ``lwt_in`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_LWT_OUT`` | | ``lwt_out`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_LWT_SEG6LOCAL`` | | ``lwt_seg6local`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_LWT_XMIT`` | | ``lwt_xmit`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_NETFILTER`` | | ``netfilter`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_PERF_EVENT`` | | ``perf_event`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE`` | | ``raw_tp.w+`` [#rawtp]_ | | ++ + +----------------------------------+-----------+ +| | | ``raw_tracepoint.w+`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_RAW_TRACEPOINT`` | | ``raw_tp+`` [#rawtp]_ | | ++ + +----------------------------------+-----------+ +| | | ``raw_tracepoint+`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SCHED_ACT`` | | ``action`` [#tc_legacy]_ | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SCHED_CLS`` | | ``classifier`` [#tc_legacy]_ | | ++ + +----------------------------------+-----------+ +| | | ``tc`` [#tc_legacy]_ | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_NETKIT_PRIMARY`` | ``netkit/primary`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_NETKIT_PEER`` | ``netkit/peer`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TCX_INGRESS`` | ``tc/ingress`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TCX_EGRESS`` | ``tc/egress`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TCX_INGRESS`` | ``tcx/ingress`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TCX_EGRESS`` | ``tcx/egress`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SK_LOOKUP`` | ``BPF_SK_LOOKUP`` | ``sk_lookup`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SK_MSG`` | ``BPF_SK_MSG_VERDICT`` | ``sk_msg`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SK_REUSEPORT`` | ``BPF_SK_REUSEPORT_SELECT_OR_MIGRATE`` | ``sk_reuseport/migrate`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_SK_REUSEPORT_SELECT`` | ``sk_reuseport`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SK_SKB`` | | ``sk_skb`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_SK_SKB_STREAM_PARSER`` | ``sk_skb/stream_parser`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_SK_SKB_STREAM_VERDICT`` | ``sk_skb/stream_verdict`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SOCKET_FILTER`` | | ``socket`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SOCK_OPS`` | ``BPF_CGROUP_SOCK_OPS`` | ``sockops`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_STRUCT_OPS`` | | ``struct_ops+`` [#struct_ops]_ | | ++ + +----------------------------------+-----------+ +| | | ``struct_ops.s+`` [#struct_ops]_ | Yes | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_SYSCALL`` | | ``syscall`` | Yes | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_TRACEPOINT`` | | ``tp+`` [#tp]_ | | ++ + +----------------------------------+-----------+ +| | | ``tracepoint+`` [#tp]_ | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_TRACING`` | ``BPF_MODIFY_RETURN`` | ``fmod_ret+`` [#fentry]_ | | ++ + +----------------------------------+-----------+ +| | | ``fmod_ret.s+`` [#fentry]_ | Yes | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_FENTRY`` | ``fentry+`` [#fentry]_ | | ++ + +----------------------------------+-----------+ +| | | ``fentry.s+`` [#fentry]_ | Yes | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_FEXIT`` | ``fexit+`` [#fentry]_ | | ++ + +----------------------------------+-----------+ +| | | ``fexit.s+`` [#fentry]_ | Yes | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_FSESSION`` | ``fsession+`` [#fentry]_ | | ++ + +----------------------------------+-----------+ +| | | ``fsession.s+`` [#fentry]_ | Yes | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_ITER`` | ``iter+`` [#iter]_ | | ++ + +----------------------------------+-----------+ +| | | ``iter.s+`` [#iter]_ | Yes | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_TRACE_RAW_TP`` | ``tp_btf+`` [#fentry]_ | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ +| ``BPF_PROG_TYPE_XDP`` | ``BPF_XDP_CPUMAP`` | ``xdp.frags/cpumap`` | | ++ + +----------------------------------+-----------+ +| | | ``xdp/cpumap`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_XDP_DEVMAP`` | ``xdp.frags/devmap`` | | ++ + +----------------------------------+-----------+ +| | | ``xdp/devmap`` | | ++ +----------------------------------------+----------------------------------+-----------+ +| | ``BPF_XDP`` | ``xdp.frags`` | | ++ + +----------------------------------+-----------+ +| | | ``xdp`` | | ++-------------------------------------------+----------------------------------------+----------------------------------+-----------+ + + +.. rubric:: Footnotes + +.. [#fentry] The ``fentry`` attach format is ``fentry[.s]/<function>``. +.. [#kprobe] The ``kprobe`` attach format is ``kprobe/<function>[+<offset>]``. Valid + characters for ``function`` are ``a-zA-Z0-9_.`` and ``offset`` must be a valid + non-negative integer. +.. [#ksyscall] The ``ksyscall`` attach format is ``ksyscall/<syscall>``. +.. [#uprobe] The ``uprobe`` attach format is ``uprobe[.s]/<path>:<function>[+<offset>]``. +.. [#upmul] The ``uprobe.multi`` attach format is ``uprobe.multi[.s]/<path>:<function-pattern>`` + where ``function-pattern`` supports ``*`` and ``?`` wildcards. +.. [#usdt] The ``usdt`` attach format is ``usdt/<path>:<provider>:<name>``. +.. [#kpmulti] The ``kprobe.multi`` attach format is ``kprobe.multi/<pattern>`` where ``pattern`` + supports ``*`` and ``?`` wildcards. Valid characters for pattern are + ``a-zA-Z0-9_.*?``. +.. [#lsm] The ``lsm`` attachment format is ``lsm[.s]/<hook>``. +.. [#rawtp] The ``raw_tp`` attach format is ``raw_tracepoint[.w]/<tracepoint>``. +.. [#tc_legacy] The ``tc``, ``classifier`` and ``action`` attach types are deprecated, use + ``tcx/*`` instead. +.. [#struct_ops] The ``struct_ops`` attach format supports ``struct_ops[.s]/<name>`` convention, + but ``name`` is ignored and it is recommended to just use plain + ``SEC("struct_ops[.s]")``. The attachments are defined in a struct initializer + that is tagged with ``SEC(".struct_ops[.link]")``. +.. [#tp] The ``tracepoint`` attach format is ``tracepoint/<category>/<name>``. +.. [#iter] The ``iter`` attach format is ``iter[.s]/<struct-name>``. |