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bpf, docs: Address comments from IETF Area Directors

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This patch does the following to address IETF feedback:

* Remove mention of "program type" and reference future
  docs (and mention platform-specific docs exist) for
  helper functions and BTF. Addresses Roman Danyliw's
  comments based on GENART review from Ines Robles [0].

* Add reference for endianness as requested by John
  Scudder [1].

* Added bit numbers to top of 32-bit wide format diagrams
  as requested by Paul Wouters [2].

* Added more text about why BPF doesn't stand for anything, based
  on text from ebpf.io [3], as requested by Eric Vyncke and
  Gunter Van de Velde [4].

* Replaced "htobe16" (and similar) and the direction-specific
  description with just "be16" (and similar) and a direction-agnostic
  description, to match the direction-agnostic description in
  the Byteswap Instructions section. Based on feedback from Eric
  Vyncke [5].

[0] https://mailarchive.ietf.org/arch/msg/bpf/DvDgDWOiwk05OyNlWlAmELZFPlM/

[1] https://mailarchive.ietf.org/arch/msg/bpf/eKNXpU4jCLjsbZDSw8LjI29M3tM/

[2] https://mailarchive.ietf.org/arch/msg/bpf/hGk8HkYxeZTpdu9qW_MvbGKj7WU/

[3] https://ebpf.io/what-is-ebpf/#what-do-ebpf-and-bpf-stand-for

[4] https://mailarchive.ietf.org/arch/msg/bpf/i93lzdN3ewnzzS_JMbinCIYxAIU/

[5] https://mailarchive.ietf.org/arch/msg/bpf/KBWXbMeDcSrq4vsKR_KkBbV6hI4/

Acked-by: David Vernet <void@manifault.com>
Signed-off-by: Dave Thaler <dthaler1968@googlemail.com>
Link: https://lore.kernel.org/r/20240623150453.10613-1-dthaler1968@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Dave Thaler 2024-06-23 08:04:53 -07:00 committed by Alexei Starovoitov
parent 93265a0b79
commit 04efaebd72
1 changed files with 45 additions and 35 deletions
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80
Documentation/bpf/standardization/instruction-set.rst
View File

@ -5,12 +5,19 @@
BPF Instruction Set Architecture (ISA)
======================================
eBPF (which is no longer an acronym for anything), also commonly
eBPF, also commonly
referred to as BPF, is a technology with origins in the Linux kernel
that can run untrusted programs in a privileged context such as an
operating system kernel. This document specifies the BPF instruction
set architecture (ISA).
As a historical note, BPF originally stood for Berkeley Packet Filter,
but now that it can do so much more than packet filtering, the acronym
no longer makes sense. BPF is now considered a standalone term that
does not stand for anything. The original BPF is sometimes referred to
as cBPF (classic BPF) to distinguish it from the now widely deployed
eBPF (extended BPF).
Documentation conventions
=========================
@ -18,7 +25,7 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 `<https://www.rfc-editor.org/info/rfc2119>`_
`RFC8174 <https://www.rfc-editor.org/info/rfc8174>`_
`<https://www.rfc-editor.org/info/rfc8174>`_
when, and only when, they appear in all capitals, as shown here.
For brevity and consistency, this document refers to families
@ -59,24 +66,18 @@ numbers.
Functions
---------
* htobe16: Takes an unsigned 16-bit number in host-endian format and
returns the equivalent number as an unsigned 16-bit number in big-endian
format.
* htobe32: Takes an unsigned 32-bit number in host-endian format and
returns the equivalent number as an unsigned 32-bit number in big-endian
format.
* htobe64: Takes an unsigned 64-bit number in host-endian format and
returns the equivalent number as an unsigned 64-bit number in big-endian
format.
* htole16: Takes an unsigned 16-bit number in host-endian format and
returns the equivalent number as an unsigned 16-bit number in little-endian
format.
* htole32: Takes an unsigned 32-bit number in host-endian format and
returns the equivalent number as an unsigned 32-bit number in little-endian
format.
* htole64: Takes an unsigned 64-bit number in host-endian format and
returns the equivalent number as an unsigned 64-bit number in little-endian
format.
The following byteswap functions are direction-agnostic. That is,
the same function is used for conversion in either direction discussed
below.
* be16: Takes an unsigned 16-bit number and converts it between
host byte order and big-endian
(`IEN137 <https://www.rfc-editor.org/ien/ien137.txt>`_) byte order.
* be32: Takes an unsigned 32-bit number and converts it between
host byte order and big-endian byte order.
* be64: Takes an unsigned 64-bit number and converts it between
host byte order and big-endian byte order.
* bswap16: Takes an unsigned 16-bit number in either big- or little-endian
format and returns the equivalent number with the same bit width but
opposite endianness.
@ -86,7 +87,12 @@ Functions
* bswap64: Takes an unsigned 64-bit number in either big- or little-endian
format and returns the equivalent number with the same bit width but
opposite endianness.
* le16: Takes an unsigned 16-bit number and converts it between
host byte order and little-endian byte order.
* le32: Takes an unsigned 32-bit number and converts it between
host byte order and little-endian byte order.
* le64: Takes an unsigned 64-bit number and converts it between
host byte order and little-endian byte order.
Definitions
-----------
@ -437,8 +443,8 @@ and MUST be set to 0.
===== ======== ===== =================================================
class source value description
===== ======== ===== =================================================
ALU TO_LE 0 convert between host byte order and little endian
ALU TO_BE 1 convert between host byte order and big endian
ALU LE 0 convert between host byte order and little endian
ALU BE 1 convert between host byte order and big endian
ALU64 Reserved 0 do byte swap unconditionally
===== ======== ===== =================================================
@ -449,19 +455,19 @@ conformance group.
Examples:
``{END, TO_LE, ALU}`` with 'imm' = 16/32/64 means::
``{END, LE, ALU}`` with 'imm' = 16/32/64 means::
dst = htole16(dst)
dst = htole32(dst)
dst = htole64(dst)
dst = le16(dst)
dst = le32(dst)
dst = le64(dst)
``{END, TO_BE, ALU}`` with 'imm' = 16/32/64 means::
``{END, BE, ALU}`` with 'imm' = 16/32/64 means::
dst = htobe16(dst)
dst = htobe32(dst)
dst = htobe64(dst)
dst = be16(dst)
dst = be32(dst)
dst = be64(dst)
``{END, TO_LE, ALU64}`` with 'imm' = 16/32/64 means::
``{END, TO, ALU64}`` with 'imm' = 16/32/64 means::
dst = bswap16(dst)
dst = bswap32(dst)
@ -541,13 +547,17 @@ Helper functions are a concept whereby BPF programs can call into a
set of function calls exposed by the underlying platform.
Historically, each helper function was identified by a static ID
encoded in the 'imm' field. The available helper functions may differ
for each program type, but static IDs are unique across all program types.
encoded in the 'imm' field. Further documentation of helper functions
is outside the scope of this document and standardization is left for
future work, but use is widely deployed and more information can be
found in platform-specific documentation (e.g., Linux kernel documentation).
Platforms that support the BPF Type Format (BTF) support identifying
a helper function by a BTF ID encoded in the 'imm' field, where the BTF ID
identifies the helper name and type. Further documentation of BTF
is outside the scope of this document and is left for future work.
is outside the scope of this document and standardization is left for
future work, but use is widely deployed and more information can be
found in platform-specific documentation (e.g., Linux kernel documentation).
Program-local functions
~~~~~~~~~~~~~~~~~~~~~~~