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Linux 6.18.37 · Core API

Netlink notes for kernel developers

Kernel Netlink family 설계 시 enum, reply와 notification ID, echo와 dump consistency, validation policy 및 attribute 길이 검사를 정리합니다.

Source pathDocumentation/core-api/netlink.rst
Source versionLinux v6.18.37
TranslationDUJINLABS 전문 번역 + 해설

요약·해설과 원문, 전문 번역을 서로 분리했습니다. API 이름, symbol, source path는 원문 표기를 사용합니다.

1. 요약·해설

원문의 핵심 논리와 kernel programming 관점의 보충 설명입니다. 아래의 전문 번역과는 별도로 작성했습니다.

2. 영어 원문 전체

번역 기준이 된 Linux v6.18.37 원문입니다. 줄 번호는 이 버전의 파일 좌표입니다.

원문 전체 펼치기
1 .. SPDX-License-Identifier: BSD-3-Clause
2
3 .. _kernel_netlink:
4
5 ===================================
6 Netlink notes for kernel developers
7 ===================================
8
9 General guidance
10 ================
11
12 Attribute enums
13 ---------------
14
15 Older families often define "null" attributes and commands with value
16 of ``0`` and named ``unspec``. This is supported (``type: unused``)
17 but should be avoided in new families. The ``unspec`` enum values are
18 not used in practice, so just set the value of the first attribute to ``1``.
19
20 Message enums
21 -------------
22
23 Use the same command IDs for requests and replies. This makes it easier
24 to match them up, and we have plenty of ID space.
25
26 Use separate command IDs for notifications. This makes it easier to
27 sort the notifications from replies (and present them to the user
28 application via a different API than replies).
29
30 Answer requests
31 ---------------
32
33 Older families do not reply to all of the commands, especially NEW / ADD
34 commands. User only gets information whether the operation succeeded or
35 not via the ACK. Try to find useful data to return. Once the command is
36 added whether it replies with a full message or only an ACK is uAPI and
37 cannot be changed. It's better to err on the side of replying.
38
39 Specifically NEW and ADD commands should reply with information identifying
40 the created object such as the allocated object's ID (without having to
41 resort to using ``NLM_F_ECHO``).
42
43 NLM_F_ECHO
44 ----------
45
46 Make sure to pass the request info to genl_notify() to allow ``NLM_F_ECHO``
47 to take effect. This is useful for programs that need precise feedback
48 from the kernel (for example for logging purposes).
49
50 Support dump consistency
51 ------------------------
52
53 If iterating over objects during dump may skip over objects or repeat
54 them - make sure to report dump inconsistency with ``NLM_F_DUMP_INTR``.
55 This is usually implemented by maintaining a generation id for the
56 structure and recording it in the ``seq`` member of struct netlink_callback.
57
58 Netlink specification
59 =====================
60
61 Documentation of the Netlink specification parts which are only relevant
62 to the kernel space.
63
64 Globals
65 -------
66
67 kernel-policy
68 ~~~~~~~~~~~~~
69
70 Defines whether the kernel validation policy is ``global`` i.e. the same for all
71 operations of the family, defined for each operation individually - ``per-op``,
72 or separately for each operation and operation type (do vs dump) - ``split``.
73 New families should use ``per-op`` (default) to be able to narrow down the
74 attributes accepted by a specific command.
75
76 checks
77 ------
78
79 Documentation for the ``checks`` sub-sections of attribute specs.
80
81 unterminated-ok
82 ~~~~~~~~~~~~~~~
83
84 Accept strings without the null-termination (for legacy families only).
85 Switches from the ``NLA_NUL_STRING`` to ``NLA_STRING`` policy type.
86
87 max-len
88 ~~~~~~~
89
90 Defines max length for a binary or string attribute (corresponding
91 to the ``len`` member of struct nla_policy). For string attributes terminating
92 null character is not counted towards ``max-len``.
93
94 The field may either be a literal integer value or a name of a defined
95 constant. String types may reduce the constant by one
96 (i.e. specify ``max-len: CONST - 1``) to reserve space for the terminating
97 character so implementations should recognize such pattern.
98
99 min-len
100 ~~~~~~~
101
102 Similar to ``max-len`` but defines minimum length.
103

3. 한국어 전문 번역

영어 원문의 문단 순서와 의미를 유지한 전체 번역입니다. 코드, 함수명, symbol과 URL은 원문 표기를 유지합니다.