scripts/bpf_helpers_doc.py - linux - Git at Google

 #!/usr/bin/python3
 # SPDX-License-Identifier: GPL-2.0-only
 #
 # Copyright (C) 2018-2019 Netronome Systems, Inc.

 # In case user attempts to run with Python 2.
 from __future__ import print_function

 import argparse
 import re
 import sys, os

 class NoHelperFound(BaseException):
     pass

 class ParsingError(BaseException):
     def __init__(self, line='<line not provided>', reader=None):
         if reader:
             BaseException.__init__(self,
                                    'Error at file offset %d, parsing line: %s' %
                                    (reader.tell(), line))
         else:
             BaseException.__init__(self, 'Error parsing line: %s' % line)

 class Helper(object):
     """
     An object representing the description of an eBPF helper function.
     @proto: function prototype of the helper function
     @desc: textual description of the helper function
     @ret: description of the return value of the helper function
     """
     def __init__(self, proto='', desc='', ret=''):
         self.proto = proto
         self.desc = desc
         self.ret = ret

     def proto_break_down(self):
         """
         Break down helper function protocol into smaller chunks: return type,
         name, distincts arguments.
         """
         arg_re = re.compile('((\w+ )*?(\w+|...))( (\**)(\w+))?$')
         res = {}
         proto_re = re.compile('(.+) (\**)(\w+)\(((([^,]+)(, )?){1,5})\)$')

         capture = proto_re.match(self.proto)
         res['ret_type'] = capture.group(1)
         res['ret_star'] = capture.group(2)
         res['name']     = capture.group(3)
         res['args'] = []

         args    = capture.group(4).split(', ')
         for a in args:
             capture = arg_re.match(a)
             res['args'].append({
                 'type' : capture.group(1),
                 'star' : capture.group(5),
                 'name' : capture.group(6)
             })

         return res

 class HeaderParser(object):
     """
     An object used to parse a file in order to extract the documentation of a
     list of eBPF helper functions. All the helpers that can be retrieved are
     stored as Helper object, in the self.helpers() array.
     @filename: name of file to parse, usually include/uapi/linux/bpf.h in the
                kernel tree
     """
     def __init__(self, filename):
         self.reader = open(filename, 'r')
         self.line = ''
         self.helpers = []

     def parse_helper(self):
         proto    = self.parse_proto()
         desc     = self.parse_desc()
         ret      = self.parse_ret()
         return Helper(proto=proto, desc=desc, ret=ret)

     def parse_proto(self):
         # Argument can be of shape:
         #   - "void"
         #   - "type  name"
         #   - "type *name"
         #   - Same as above, with "const" and/or "struct" in front of type
         #   - "..." (undefined number of arguments, for bpf_trace_printk())
         # There is at least one term ("void"), and at most five arguments.
         p = re.compile(' \* ?((.+) \**\w+\((((const )?(struct )?(\w+|\.\.\.)( \**\w+)?)(, )?){1,5}\))$')
         capture = p.match(self.line)
         if not capture:
             raise NoHelperFound
         self.line = self.reader.readline()
         return capture.group(1)

     def parse_desc(self):
         p = re.compile(' \* ?(?:\t| {5,8})Description$')
         capture = p.match(self.line)
         if not capture:
             # Helper can have empty description and we might be parsing another
             # attribute: return but do not consume.
             return ''
         # Description can be several lines, some of them possibly empty, and it
         # stops when another subsection title is met.
         desc = ''
         while True:
             self.line = self.reader.readline()
             if self.line == ' *\n':
                 desc += '\n'
             else:
                 p = re.compile(' \* ?(?:\t| {5,8})(?:\t| {8})(.*)')
                 capture = p.match(self.line)
                 if capture:
                     desc += capture.group(1) + '\n'
                 else:
                     break
         return desc

     def parse_ret(self):
         p = re.compile(' \* ?(?:\t| {5,8})Return$')
         capture = p.match(self.line)
         if not capture:
             # Helper can have empty retval and we might be parsing another
             # attribute: return but do not consume.
             return ''
         # Return value description can be several lines, some of them possibly
         # empty, and it stops when another subsection title is met.
         ret = ''
         while True:
             self.line = self.reader.readline()
             if self.line == ' *\n':
                 ret += '\n'
             else:
                 p = re.compile(' \* ?(?:\t| {5,8})(?:\t| {8})(.*)')
                 capture = p.match(self.line)
                 if capture:
                     ret += capture.group(1) + '\n'
                 else:
                     break
         return ret

     def run(self):
         # Advance to start of helper function descriptions.
         offset = self.reader.read().find('* Start of BPF helper function descriptions:')
         if offset == -1:
             raise Exception('Could not find start of eBPF helper descriptions list')
         self.reader.seek(offset)
         self.reader.readline()
         self.reader.readline()
         self.line = self.reader.readline()

         while True:
             try:
                 helper = self.parse_helper()
                 self.helpers.append(helper)
             except NoHelperFound:
                 break

         self.reader.close()

 ###############################################################################

 class Printer(object):
     """
     A generic class for printers. Printers should be created with an array of
     Helper objects, and implement a way to print them in the desired fashion.
     @helpers: array of Helper objects to print to standard output
     """
     def __init__(self, helpers):
         self.helpers = helpers

     def print_header(self):
         pass

     def print_footer(self):
         pass

     def print_one(self, helper):
         pass

     def print_all(self):
         self.print_header()
         for helper in self.helpers:
             self.print_one(helper)
         self.print_footer()

 class PrinterRST(Printer):
     """
     A printer for dumping collected information about helpers as a ReStructured
     Text page compatible with the rst2man program, which can be used to
     generate a manual page for the helpers.
     @helpers: array of Helper objects to print to standard output
     """
     def print_header(self):
         header = '''\
 .. Copyright (C) All BPF authors and contributors from 2014 to present.
 .. See git log include/uapi/linux/bpf.h in kernel tree for details.
 ..
 .. %%%LICENSE_START(VERBATIM)
 .. Permission is granted to make and distribute verbatim copies of this
 .. manual provided the copyright notice and this permission notice are
 .. preserved on all copies.
 ..
 .. Permission is granted to copy and distribute modified versions of this
 .. manual under the conditions for verbatim copying, provided that the
 .. entire resulting derived work is distributed under the terms of a
 .. permission notice identical to this one.
 ..
 .. Since the Linux kernel and libraries are constantly changing, this
 .. manual page may be incorrect or out-of-date.  The author(s) assume no
 .. responsibility for errors or omissions, or for damages resulting from
 .. the use of the information contained herein.  The author(s) may not
 .. have taken the same level of care in the production of this manual,
 .. which is licensed free of charge, as they might when working
 .. professionally.
 ..
 .. Formatted or processed versions of this manual, if unaccompanied by
 .. the source, must acknowledge the copyright and authors of this work.
 .. %%%LICENSE_END
 ..
 .. Please do not edit this file. It was generated from the documentation
 .. located in file include/uapi/linux/bpf.h of the Linux kernel sources
 .. (helpers description), and from scripts/bpf_helpers_doc.py in the same
 .. repository (header and footer).

 ===========
 BPF-HELPERS
 ===========
 -------------------------------------------------------------------------------
 list of eBPF helper functions
 -------------------------------------------------------------------------------

 :Manual section: 7

 DESCRIPTION
 ===========

 The extended Berkeley Packet Filter (eBPF) subsystem consists in programs
 written in a pseudo-assembly language, then attached to one of the several
 kernel hooks and run in reaction of specific events. This framework differs
 from the older, "classic" BPF (or "cBPF") in several aspects, one of them being
 the ability to call special functions (or "helpers") from within a program.
 These functions are restricted to a white-list of helpers defined in the
 kernel.

 These helpers are used by eBPF programs to interact with the system, or with
 the context in which they work. For instance, they can be used to print
 debugging messages, to get the time since the system was booted, to interact
 with eBPF maps, or to manipulate network packets. Since there are several eBPF
 program types, and that they do not run in the same context, each program type
 can only call a subset of those helpers.

 Due to eBPF conventions, a helper can not have more than five arguments.

 Internally, eBPF programs call directly into the compiled helper functions
 without requiring any foreign-function interface. As a result, calling helpers
 introduces no overhead, thus offering excellent performance.

 This document is an attempt to list and document the helpers available to eBPF
 developers. They are sorted by chronological order (the oldest helpers in the
 kernel at the top).

 HELPERS
 =======
 '''
         print(header)

     def print_footer(self):
         footer = '''
 EXAMPLES
 ========

 Example usage for most of the eBPF helpers listed in this manual page are
 available within the Linux kernel sources, at the following locations:

 * *samples/bpf/*
 * *tools/testing/selftests/bpf/*

 LICENSE
 =======

 eBPF programs can have an associated license, passed along with the bytecode
 instructions to the kernel when the programs are loaded. The format for that
 string is identical to the one in use for kernel modules (Dual licenses, such
 as "Dual BSD/GPL", may be used). Some helper functions are only accessible to
 programs that are compatible with the GNU Privacy License (GPL).

 In order to use such helpers, the eBPF program must be loaded with the correct
 license string passed (via **attr**) to the **bpf**\ () system call, and this
 generally translates into the C source code of the program containing a line
 similar to the following:

 ::

 	char ____license[] __attribute__((section("license"), used)) = "GPL";

 IMPLEMENTATION
 ==============

 This manual page is an effort to document the existing eBPF helper functions.
 But as of this writing, the BPF sub-system is under heavy development. New eBPF
 program or map types are added, along with new helper functions. Some helpers
 are occasionally made available for additional program types. So in spite of
 the efforts of the community, this page might not be up-to-date. If you want to
 check by yourself what helper functions exist in your kernel, or what types of
 programs they can support, here are some files among the kernel tree that you
 may be interested in:

 * *include/uapi/linux/bpf.h* is the main BPF header. It contains the full list
   of all helper functions, as well as many other BPF definitions including most
   of the flags, structs or constants used by the helpers.
 * *net/core/filter.c* contains the definition of most network-related helper
   functions, and the list of program types from which they can be used.
 * *kernel/trace/bpf_trace.c* is the equivalent for most tracing program-related
   helpers.
 * *kernel/bpf/verifier.c* contains the functions used to check that valid types
   of eBPF maps are used with a given helper function.
 * *kernel/bpf/* directory contains other files in which additional helpers are
   defined (for cgroups, sockmaps, etc.).

 Compatibility between helper functions and program types can generally be found
 in the files where helper functions are defined. Look for the **struct
 bpf_func_proto** objects and for functions returning them: these functions
 contain a list of helpers that a given program type can call. Note that the
 **default:** label of the **switch ... case** used to filter helpers can call
 other functions, themselves allowing access to additional helpers. The
 requirement for GPL license is also in those **struct bpf_func_proto**.

 Compatibility between helper functions and map types can be found in the
 **check_map_func_compatibility**\ () function in file *kernel/bpf/verifier.c*.

 Helper functions that invalidate the checks on **data** and **data_end**
 pointers for network processing are listed in function
 **bpf_helper_changes_pkt_data**\ () in file *net/core/filter.c*.

 SEE ALSO
 ========

 **bpf**\ (2),
 **cgroups**\ (7),
 **ip**\ (8),
 **perf_event_open**\ (2),
 **sendmsg**\ (2),
 **socket**\ (7),
 **tc-bpf**\ (8)'''
         print(footer)

     def print_proto(self, helper):
         """
         Format function protocol with bold and italics markers. This makes RST
         file less readable, but gives nice results in the manual page.
         """
         proto = helper.proto_break_down()

         print('**%s %s%s(' % (proto['ret_type'],
                               proto['ret_star'].replace('*', '\\*'),
                               proto['name']),
               end='')

         comma = ''
         for a in proto['args']:
             one_arg = '{}{}'.format(comma, a['type'])
             if a['name']:
                 if a['star']:
                     one_arg += ' {}**\ '.format(a['star'].replace('*', '\\*'))
                 else:
                     one_arg += '** '
                 one_arg += '*{}*\\ **'.format(a['name'])
             comma = ', '
             print(one_arg, end='')

         print(')**')

     def print_one(self, helper):
         self.print_proto(helper)

         if (helper.desc):
             print('\tDescription')
             # Do not strip all newline characters: formatted code at the end of
             # a section must be followed by a blank line.
             for line in re.sub('\n$', '', helper.desc, count=1).split('\n'):
                 print('{}{}'.format('\t\t' if line else '', line))

         if (helper.ret):
             print('\tReturn')
             for line in helper.ret.rstrip().split('\n'):
                 print('{}{}'.format('\t\t' if line else '', line))

         print('')

 class PrinterHelpers(Printer):
     """
     A printer for dumping collected information about helpers as C header to
     be included from BPF program.
     @helpers: array of Helper objects to print to standard output
     """

     type_fwds = [
             'struct bpf_fib_lookup',
             'struct bpf_perf_event_data',
             'struct bpf_perf_event_value',
             'struct bpf_sock',
             'struct bpf_sock_addr',
             'struct bpf_sock_ops',
             'struct bpf_sock_tuple',
             'struct bpf_spin_lock',
             'struct bpf_sysctl',
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',
             'struct tcphdr',

             'struct __sk_buff',
             'struct sk_msg_md',
             'struct xdp_md',
     ]
     known_types = {
             '...',
             'void',
             'const void',
             'char',
             'const char',
             'int',
             'long',
             'unsigned long',

             '__be16',
             '__be32',
             '__wsum',

             'struct bpf_fib_lookup',
             'struct bpf_perf_event_data',
             'struct bpf_perf_event_value',
             'struct bpf_sock',
             'struct bpf_sock_addr',
             'struct bpf_sock_ops',
             'struct bpf_sock_tuple',
             'struct bpf_spin_lock',
             'struct bpf_sysctl',
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',
             'struct tcphdr',
     }
     mapped_types = {
             'u8': '__u8',
             'u16': '__u16',
             'u32': '__u32',
             'u64': '__u64',
             's8': '__s8',
             's16': '__s16',
             's32': '__s32',
             's64': '__s64',
             'size_t': 'unsigned long',
             'struct bpf_map': 'void',
             'struct sk_buff': 'struct __sk_buff',
             'const struct sk_buff': 'const struct __sk_buff',
             'struct sk_msg_buff': 'struct sk_msg_md',
             'struct xdp_buff': 'struct xdp_md',
     }

     def print_header(self):
         header = '''\
 /* This is auto-generated file. See bpf_helpers_doc.py for details. */

 /* Forward declarations of BPF structs */'''

         print(header)
         for fwd in self.type_fwds:
             print('%s;' % fwd)
         print('')

     def print_footer(self):
         footer = ''
         print(footer)

     def map_type(self, t):
         if t in self.known_types:
             return t
         if t in self.mapped_types:
             return self.mapped_types[t]
         print("Unrecognized type '%s', please add it to known types!" % t,
               file=sys.stderr)
         sys.exit(1)

     seen_helpers = set()

     def print_one(self, helper):
         proto = helper.proto_break_down()

         if proto['name'] in self.seen_helpers:
             return
         self.seen_helpers.add(proto['name'])

         print('/*')
         print(" * %s" % proto['name'])
         print(" *")
         if (helper.desc):
             # Do not strip all newline characters: formatted code at the end of
             # a section must be followed by a blank line.
             for line in re.sub('\n$', '', helper.desc, count=1).split('\n'):
                 print(' *{}{}'.format(' \t' if line else '', line))

         if (helper.ret):
             print(' *')
             print(' * Returns')
             for line in helper.ret.rstrip().split('\n'):
                 print(' *{}{}'.format(' \t' if line else '', line))

         print(' */')
         print('static %s %s(*%s)(' % (self.map_type(proto['ret_type']),
                                       proto['ret_star'], proto['name']), end='')
         comma = ''
         for i, a in enumerate(proto['args']):
             t = a['type']
             n = a['name']
             if proto['name'] == 'bpf_get_socket_cookie' and i == 0:
                     t = 'void'
                     n = 'ctx'
             one_arg = '{}{}'.format(comma, self.map_type(t))
             if n:
                 if a['star']:
                     one_arg += ' {}'.format(a['star'])
                 else:
                     one_arg += ' '
                 one_arg += '{}'.format(n)
             comma = ', '
             print(one_arg, end='')

         print(') = (void *) %d;' % len(self.seen_helpers))
         print('')

 ###############################################################################

 # If script is launched from scripts/ from kernel tree and can access
 # ../include/uapi/linux/bpf.h, use it as a default name for the file to parse,
 # otherwise the --filename argument will be required from the command line.
 script = os.path.abspath(sys.argv[0])
 linuxRoot = os.path.dirname(os.path.dirname(script))
 bpfh = os.path.join(linuxRoot, 'include/uapi/linux/bpf.h')

 argParser = argparse.ArgumentParser(description="""
 Parse eBPF header file and generate documentation for eBPF helper functions.
 The RST-formatted output produced can be turned into a manual page with the
 rst2man utility.
 """)
 argParser.add_argument('--header', action='store_true',
                        help='generate C header file')
 if (os.path.isfile(bpfh)):
     argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h',
                            default=bpfh)
 else:
     argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h')
 args = argParser.parse_args()

 # Parse file.
 headerParser = HeaderParser(args.filename)
 headerParser.run()

 # Print formatted output to standard output.
 if args.header:
     printer = PrinterHelpers(headerParser.helpers)
 else:
     printer = PrinterRST(headerParser.helpers)
 printer.print_all()
	#!/usr/bin/python3
	# SPDX-License-Identifier: GPL-2.0-only
	#
	# Copyright (C) 2018-2019 Netronome Systems, Inc.

	# In case user attempts to run with Python 2.
	from __future__ import print_function

	import argparse
	import re
	import sys, os

	class NoHelperFound(BaseException):
	pass

	class ParsingError(BaseException):
	def __init__(self, line='<line not provided>', reader=None):
	if reader:
	BaseException.__init__(self,
	'Error at file offset %d, parsing line: %s' %
	(reader.tell(), line))
	else:
	BaseException.__init__(self, 'Error parsing line: %s' % line)

	class Helper(object):
	"""
	An object representing the description of an eBPF helper function.
	@proto: function prototype of the helper function
	@desc: textual description of the helper function
	@ret: description of the return value of the helper function
	"""
	def __init__(self, proto='', desc='', ret=''):
	self.proto = proto
	self.desc = desc
	self.ret = ret

	def proto_break_down(self):
	"""
	Break down helper function protocol into smaller chunks: return type,
	name, distincts arguments.
	"""
	arg_re = re.compile('((\w+ )?(\w+\|...))( (\*)(\w+))?$')
	res = {}
	proto_re = re.compile('(.+) (\**)(\w+)\(((([^,]+)(, )?){1,5})\)$')

	capture = proto_re.match(self.proto)
	res['ret_type'] = capture.group(1)
	res['ret_star'] = capture.group(2)
	res['name'] = capture.group(3)
	res['args'] = []

	args = capture.group(4).split(', ')
	for a in args:
	capture = arg_re.match(a)
	res['args'].append({
	'type' : capture.group(1),
	'star' : capture.group(5),
	'name' : capture.group(6)
	})

	return res

	class HeaderParser(object):
	"""
	An object used to parse a file in order to extract the documentation of a
	list of eBPF helper functions. All the helpers that can be retrieved are
	stored as Helper object, in the self.helpers() array.
	@filename: name of file to parse, usually include/uapi/linux/bpf.h in the
	kernel tree
	"""
	def __init__(self, filename):
	self.reader = open(filename, 'r')
	self.line = ''
	self.helpers = []

	def parse_helper(self):
	proto = self.parse_proto()
	desc = self.parse_desc()
	ret = self.parse_ret()
	return Helper(proto=proto, desc=desc, ret=ret)

	def parse_proto(self):
	# Argument can be of shape:
	# - "void"
	# - "type name"
	# - "type *name"
	# - Same as above, with "const" and/or "struct" in front of type
	# - "..." (undefined number of arguments, for bpf_trace_printk())
	# There is at least one term ("void"), and at most five arguments.
	p = re.compile(' \* ?((.+) \\w+\((((const )?(struct )?(\w+\|\.\.\.)( \\w+)?)(, )?){1,5}\))$')
	capture = p.match(self.line)
	if not capture:
	raise NoHelperFound
	self.line = self.reader.readline()
	return capture.group(1)

	def parse_desc(self):
	p = re.compile(' \* ?(?:\t\| {5,8})Description$')
	capture = p.match(self.line)
	if not capture:
	# Helper can have empty description and we might be parsing another
	# attribute: return but do not consume.
	return ''
	# Description can be several lines, some of them possibly empty, and it
	# stops when another subsection title is met.
	desc = ''
	while True:
	self.line = self.reader.readline()
	if self.line == ' *\n':
	desc += '\n'
	else:
	p = re.compile(' \* ?(?:\t\| {5,8})(?:\t\| {8})(.*)')
	capture = p.match(self.line)
	if capture:
	desc += capture.group(1) + '\n'
	else:
	break
	return desc

	def parse_ret(self):
	p = re.compile(' \* ?(?:\t\| {5,8})Return$')
	capture = p.match(self.line)
	if not capture:
	# Helper can have empty retval and we might be parsing another
	# attribute: return but do not consume.
	return ''
	# Return value description can be several lines, some of them possibly
	# empty, and it stops when another subsection title is met.
	ret = ''
	while True:
	self.line = self.reader.readline()
	if self.line == ' *\n':
	ret += '\n'
	else:
	p = re.compile(' \* ?(?:\t\| {5,8})(?:\t\| {8})(.*)')
	capture = p.match(self.line)
	if capture:
	ret += capture.group(1) + '\n'
	else:
	break
	return ret

	def run(self):
	# Advance to start of helper function descriptions.
	offset = self.reader.read().find('* Start of BPF helper function descriptions:')
	if offset == -1:
	raise Exception('Could not find start of eBPF helper descriptions list')
	self.reader.seek(offset)
	self.reader.readline()
	self.reader.readline()
	self.line = self.reader.readline()

	while True:
	try:
	helper = self.parse_helper()
	self.helpers.append(helper)
	except NoHelperFound:
	break

	self.reader.close()

	###############################################################################

	class Printer(object):
	"""
	A generic class for printers. Printers should be created with an array of
	Helper objects, and implement a way to print them in the desired fashion.
	@helpers: array of Helper objects to print to standard output
	"""
	def __init__(self, helpers):
	self.helpers = helpers

	def print_header(self):
	pass

	def print_footer(self):
	pass

	def print_one(self, helper):
	pass

	def print_all(self):
	self.print_header()
	for helper in self.helpers:
	self.print_one(helper)
	self.print_footer()

	class PrinterRST(Printer):
	"""
	A printer for dumping collected information about helpers as a ReStructured
	Text page compatible with the rst2man program, which can be used to
	generate a manual page for the helpers.
	@helpers: array of Helper objects to print to standard output
	"""
	def print_header(self):
	header = '''\
	.. Copyright (C) All BPF authors and contributors from 2014 to present.
	.. See git log include/uapi/linux/bpf.h in kernel tree for details.
	..
	.. %%%LICENSE_START(VERBATIM)
	.. Permission is granted to make and distribute verbatim copies of this
	.. manual provided the copyright notice and this permission notice are
	.. preserved on all copies.
	..
	.. Permission is granted to copy and distribute modified versions of this
	.. manual under the conditions for verbatim copying, provided that the
	.. entire resulting derived work is distributed under the terms of a
	.. permission notice identical to this one.
	..
	.. Since the Linux kernel and libraries are constantly changing, this
	.. manual page may be incorrect or out-of-date. The author(s) assume no
	.. responsibility for errors or omissions, or for damages resulting from
	.. the use of the information contained herein. The author(s) may not
	.. have taken the same level of care in the production of this manual,
	.. which is licensed free of charge, as they might when working
	.. professionally.
	..
	.. Formatted or processed versions of this manual, if unaccompanied by
	.. the source, must acknowledge the copyright and authors of this work.
	.. %%%LICENSE_END
	..
	.. Please do not edit this file. It was generated from the documentation
	.. located in file include/uapi/linux/bpf.h of the Linux kernel sources
	.. (helpers description), and from scripts/bpf_helpers_doc.py in the same
	.. repository (header and footer).

	===========
	BPF-HELPERS
	===========
	-------------------------------------------------------------------------------
	list of eBPF helper functions
	-------------------------------------------------------------------------------

	:Manual section: 7

	DESCRIPTION
	===========

	The extended Berkeley Packet Filter (eBPF) subsystem consists in programs
	written in a pseudo-assembly language, then attached to one of the several
	kernel hooks and run in reaction of specific events. This framework differs
	from the older, "classic" BPF (or "cBPF") in several aspects, one of them being
	the ability to call special functions (or "helpers") from within a program.
	These functions are restricted to a white-list of helpers defined in the
	kernel.

	These helpers are used by eBPF programs to interact with the system, or with
	the context in which they work. For instance, they can be used to print
	debugging messages, to get the time since the system was booted, to interact
	with eBPF maps, or to manipulate network packets. Since there are several eBPF
	program types, and that they do not run in the same context, each program type
	can only call a subset of those helpers.

	Due to eBPF conventions, a helper can not have more than five arguments.

	Internally, eBPF programs call directly into the compiled helper functions
	without requiring any foreign-function interface. As a result, calling helpers
	introduces no overhead, thus offering excellent performance.

	This document is an attempt to list and document the helpers available to eBPF
	developers. They are sorted by chronological order (the oldest helpers in the
	kernel at the top).

	HELPERS
	=======
	'''
	print(header)

	def print_footer(self):
	footer = '''
	EXAMPLES
	========

	Example usage for most of the eBPF helpers listed in this manual page are
	available within the Linux kernel sources, at the following locations:

	* samples/bpf/
	* tools/testing/selftests/bpf/

	LICENSE
	=======

	eBPF programs can have an associated license, passed along with the bytecode
	instructions to the kernel when the programs are loaded. The format for that
	string is identical to the one in use for kernel modules (Dual licenses, such
	as "Dual BSD/GPL", may be used). Some helper functions are only accessible to
	programs that are compatible with the GNU Privacy License (GPL).

	In order to use such helpers, the eBPF program must be loaded with the correct
	license string passed (via attr) to the bpf\ () system call, and this
	generally translates into the C source code of the program containing a line
	similar to the following:

	::

	char ____license[] __attribute__((section("license"), used)) = "GPL";

	IMPLEMENTATION
	==============

	This manual page is an effort to document the existing eBPF helper functions.
	But as of this writing, the BPF sub-system is under heavy development. New eBPF
	program or map types are added, along with new helper functions. Some helpers
	are occasionally made available for additional program types. So in spite of
	the efforts of the community, this page might not be up-to-date. If you want to
	check by yourself what helper functions exist in your kernel, or what types of
	programs they can support, here are some files among the kernel tree that you
	may be interested in:

	* include/uapi/linux/bpf.h is the main BPF header. It contains the full list
	of all helper functions, as well as many other BPF definitions including most
	of the flags, structs or constants used by the helpers.
	* net/core/filter.c contains the definition of most network-related helper
	functions, and the list of program types from which they can be used.
	* kernel/trace/bpf_trace.c is the equivalent for most tracing program-related
	helpers.
	* kernel/bpf/verifier.c contains the functions used to check that valid types
	of eBPF maps are used with a given helper function.
	* kernel/bpf/ directory contains other files in which additional helpers are
	defined (for cgroups, sockmaps, etc.).

	Compatibility between helper functions and program types can generally be found
	in the files where helper functions are defined. Look for the **struct
	bpf_func_proto** objects and for functions returning them: these functions
	contain a list of helpers that a given program type can call. Note that the
	default: label of the switch ... case used to filter helpers can call
	other functions, themselves allowing access to additional helpers. The
	requirement for GPL license is also in those struct bpf_func_proto.

	Compatibility between helper functions and map types can be found in the
	check_map_func_compatibility\ () function in file kernel/bpf/verifier.c.

	Helper functions that invalidate the checks on data and data_end
	pointers for network processing are listed in function
	bpf_helper_changes_pkt_data\ () in file net/core/filter.c.

	SEE ALSO
	========

	bpf\ (2),
	cgroups\ (7),
	ip\ (8),
	perf_event_open\ (2),
	sendmsg\ (2),
	socket\ (7),
	tc-bpf\ (8)'''
	print(footer)

	def print_proto(self, helper):
	"""
	Format function protocol with bold and italics markers. This makes RST
	file less readable, but gives nice results in the manual page.
	"""
	proto = helper.proto_break_down()

	print('**%s %s%s(' % (proto['ret_type'],
	proto['ret_star'].replace('', '\\'),
	proto['name']),
	end='')

	comma = ''
	for a in proto['args']:
	one_arg = '{}{}'.format(comma, a['type'])
	if a['name']:
	if a['star']:
	one_arg += ' {}*\ '.format(a['star'].replace('', '\\*'))
	else:
	one_arg += '** '
	one_arg += '{}\\ **'.format(a['name'])
	comma = ', '
	print(one_arg, end='')

	print(')**')

	def print_one(self, helper):
	self.print_proto(helper)

	if (helper.desc):
	print('\tDescription')
	# Do not strip all newline characters: formatted code at the end of
	# a section must be followed by a blank line.
	for line in re.sub('\n$', '', helper.desc, count=1).split('\n'):
	print('{}{}'.format('\t\t' if line else '', line))

	if (helper.ret):
	print('\tReturn')
	for line in helper.ret.rstrip().split('\n'):
	print('{}{}'.format('\t\t' if line else '', line))

	print('')

	class PrinterHelpers(Printer):
	"""
	A printer for dumping collected information about helpers as C header to
	be included from BPF program.
	@helpers: array of Helper objects to print to standard output
	"""

	type_fwds = [
	'struct bpf_fib_lookup',
	'struct bpf_perf_event_data',
	'struct bpf_perf_event_value',
	'struct bpf_sock',
	'struct bpf_sock_addr',
	'struct bpf_sock_ops',
	'struct bpf_sock_tuple',
	'struct bpf_spin_lock',
	'struct bpf_sysctl',
	'struct bpf_tcp_sock',
	'struct bpf_tunnel_key',
	'struct bpf_xfrm_state',
	'struct pt_regs',
	'struct sk_reuseport_md',
	'struct sockaddr',
	'struct tcphdr',

	'struct __sk_buff',
	'struct sk_msg_md',
	'struct xdp_md',
	]
	known_types = {
	'...',
	'void',
	'const void',
	'char',
	'const char',
	'int',
	'long',
	'unsigned long',

	'__be16',
	'__be32',
	'__wsum',

	'struct bpf_fib_lookup',
	'struct bpf_perf_event_data',
	'struct bpf_perf_event_value',
	'struct bpf_sock',
	'struct bpf_sock_addr',
	'struct bpf_sock_ops',
	'struct bpf_sock_tuple',
	'struct bpf_spin_lock',
	'struct bpf_sysctl',
	'struct bpf_tcp_sock',
	'struct bpf_tunnel_key',
	'struct bpf_xfrm_state',
	'struct pt_regs',
	'struct sk_reuseport_md',
	'struct sockaddr',
	'struct tcphdr',
	}
	mapped_types = {
	'u8': '__u8',
	'u16': '__u16',
	'u32': '__u32',
	'u64': '__u64',
	's8': '__s8',
	's16': '__s16',
	's32': '__s32',
	's64': '__s64',
	'size_t': 'unsigned long',
	'struct bpf_map': 'void',
	'struct sk_buff': 'struct __sk_buff',
	'const struct sk_buff': 'const struct __sk_buff',
	'struct sk_msg_buff': 'struct sk_msg_md',
	'struct xdp_buff': 'struct xdp_md',
	}

	def print_header(self):
	header = '''\
	/* This is auto-generated file. See bpf_helpers_doc.py for details. */

	/* Forward declarations of BPF structs */'''

	print(header)
	for fwd in self.type_fwds:
	print('%s;' % fwd)
	print('')

	def print_footer(self):
	footer = ''
	print(footer)

	def map_type(self, t):
	if t in self.known_types:
	return t
	if t in self.mapped_types:
	return self.mapped_types[t]
	print("Unrecognized type '%s', please add it to known types!" % t,
	file=sys.stderr)
	sys.exit(1)

	seen_helpers = set()

	def print_one(self, helper):
	proto = helper.proto_break_down()

	if proto['name'] in self.seen_helpers:
	return
	self.seen_helpers.add(proto['name'])

	print('/*')
	print(" * %s" % proto['name'])
	print(" *")
	if (helper.desc):
	# Do not strip all newline characters: formatted code at the end of
	# a section must be followed by a blank line.
	for line in re.sub('\n$', '', helper.desc, count=1).split('\n'):
	print(' *{}{}'.format(' \t' if line else '', line))

	if (helper.ret):
	print(' *')
	print(' * Returns')
	for line in helper.ret.rstrip().split('\n'):
	print(' *{}{}'.format(' \t' if line else '', line))

	print(' */')
	print('static %s %s(*%s)(' % (self.map_type(proto['ret_type']),
	proto['ret_star'], proto['name']), end='')
	comma = ''
	for i, a in enumerate(proto['args']):
	t = a['type']
	n = a['name']
	if proto['name'] == 'bpf_get_socket_cookie' and i == 0:
	t = 'void'
	n = 'ctx'
	one_arg = '{}{}'.format(comma, self.map_type(t))
	if n:
	if a['star']:
	one_arg += ' {}'.format(a['star'])
	else:
	one_arg += ' '
	one_arg += '{}'.format(n)
	comma = ', '
	print(one_arg, end='')

	print(') = (void *) %d;' % len(self.seen_helpers))
	print('')

	###############################################################################

	# If script is launched from scripts/ from kernel tree and can access
	# ../include/uapi/linux/bpf.h, use it as a default name for the file to parse,
	# otherwise the --filename argument will be required from the command line.
	script = os.path.abspath(sys.argv[0])
	linuxRoot = os.path.dirname(os.path.dirname(script))
	bpfh = os.path.join(linuxRoot, 'include/uapi/linux/bpf.h')

	argParser = argparse.ArgumentParser(description="""
	Parse eBPF header file and generate documentation for eBPF helper functions.
	The RST-formatted output produced can be turned into a manual page with the
	rst2man utility.
	""")
	argParser.add_argument('--header', action='store_true',
	help='generate C header file')
	if (os.path.isfile(bpfh)):
	argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h',
	default=bpfh)
	else:
	argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h')
	args = argParser.parse_args()

	# Parse file.
	headerParser = HeaderParser(args.filename)
	headerParser.run()

	# Print formatted output to standard output.
	if args.header:
	printer = PrinterHelpers(headerParser.helpers)
	else:
	printer = PrinterRST(headerParser.helpers)
	printer.print_all()