1 .. SPDX-License-Identifier: GPL-2.0
2
3 The tip tree handbook
4 =====================
5
6 What is the tip tree?
7 ---------------------
8
9 The tip tree is a collection of several subsystems and areas of
10 development. The tip tree is both a direct development tree and a
11 aggregation tree for several sub-maintainer trees. The tip tree gitweb URL
12 is: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
13
14 The tip tree contains the following subsystems:
15
16 - **x86 architecture**
17
18 The x86 architecture development takes place in the tip tree except
19 for the x86 KVM and XEN specific parts which are maintained in the
20 corresponding subsystems and routed directly to mainline from
21 there. It's still good practice to Cc the x86 maintainers on
22 x86-specific KVM and XEN patches.
23
24 Some x86 subsystems have their own maintainers in addition to the
25 overall x86 maintainers. Please Cc the overall x86 maintainers on
26 patches touching files in arch/x86 even when they are not called out
27 by the MAINTAINER file.
28
29 Note, that ``x86@kernel.org`` is not a mailing list. It is merely a
30 mail alias which distributes mails to the x86 top-level maintainer
31 team. Please always Cc the Linux Kernel mailing list (LKML)
32 ``linux-kernel@vger.kernel.org``, otherwise your mail ends up only in
33 the private inboxes of the maintainers.
34
35 - **Scheduler**
36
37 Scheduler development takes place in the -tip tree, in the
38 sched/core branch - with occasional sub-topic trees for
39 work-in-progress patch-sets.
40
41 - **Locking and atomics**
42
43 Locking development (including atomics and other synchronization
44 primitives that are connected to locking) takes place in the -tip
45 tree, in the locking/core branch - with occasional sub-topic trees
46 for work-in-progress patch-sets.
47
48 - **Generic interrupt subsystem and interrupt chip drivers**:
49
50 - interrupt core development happens in the irq/core branch
51
52 - interrupt chip driver development also happens in the irq/core
53 branch, but the patches are usually applied in a separate maintainer
54 tree and then aggregated into irq/core
55
56 - **Time, timers, timekeeping, NOHZ and related chip drivers**:
57
58 - timekeeping, clocksource core, NTP and alarmtimer development
59 happens in the timers/core branch, but patches are usually applied in
60 a separate maintainer tree and then aggregated into timers/core
61
62 - clocksource/event driver development happens in the timers/core
63 branch, but patches are mostly applied in a separate maintainer tree
64 and then aggregated into timers/core
65
66 - **Performance counters core, architecture support and tooling**:
67
68 - perf core and architecture support development happens in the
69 perf/core branch
70
71 - perf tooling development happens in the perf tools maintainer
72 tree and is aggregated into the tip tree.
73
74 - **CPU hotplug core**
75
76 - **RAS core**
77
78 Mostly x86-specific RAS patches are collected in the tip ras/core
79 branch.
80
81 - **EFI core**
82
83 EFI development in the efi git tree. The collected patches are
84 aggregated in the tip efi/core branch.
85
86 - **RCU**
87
88 RCU development happens in the linux-rcu tree. The resulting changes
89 are aggregated into the tip core/rcu branch.
90
91 - **Various core code components**:
92
93 - debugobjects
94
95 - objtool
96
97 - random bits and pieces
98
99
100 Patch submission notes
101 ----------------------
102
103 Selecting the tree/branch
104 ^^^^^^^^^^^^^^^^^^^^^^^^^
105
106 In general, development against the head of the tip tree master branch is
107 fine, but for the subsystems which are maintained separately, have their
108 own git tree and are only aggregated into the tip tree, development should
109 take place against the relevant subsystem tree or branch.
110
111 Bug fixes which target mainline should always be applicable against the
112 mainline kernel tree. Potential conflicts against changes which are already
113 queued in the tip tree are handled by the maintainers.
114
115 Patch subject
116 ^^^^^^^^^^^^^
117
118 The tip tree preferred format for patch subject prefixes is
119 'subsys/component:', e.g. 'x86/apic:', 'x86/mm/fault:', 'sched/fair:',
120 'genirq/core:'. Please do not use file names or complete file paths as
121 prefix. 'git log path/to/file' should give you a reasonable hint in most
122 cases.
123
124 The condensed patch description in the subject line should start with a
125 uppercase letter and should be written in imperative tone.
126
127
128 Changelog
129 ^^^^^^^^^
130
131 The general rules about changelogs in the :ref:`Submitting patches guide
132 <describe_changes>`, apply.
133
134 The tip tree maintainers set value on following these rules, especially on
135 the request to write changelogs in imperative mood and not impersonating
136 code or the execution of it. This is not just a whim of the
137 maintainers. Changelogs written in abstract words are more precise and
138 tend to be less confusing than those written in the form of novels.
139
140 It's also useful to structure the changelog into several paragraphs and not
141 lump everything together into a single one. A good structure is to explain
142 the context, the problem and the solution in separate paragraphs and this
143 order.
144
145 Examples for illustration:
146
147 Example 1::
148
149 x86/intel_rdt/mbm: Fix MBM overflow handler during hot cpu
150
151 When a CPU is dying, we cancel the worker and schedule a new worker on a
152 different CPU on the same domain. But if the timer is already about to
153 expire (say 0.99s) then we essentially double the interval.
154
155 We modify the hot cpu handling to cancel the delayed work on the dying
156 cpu and run the worker immediately on a different cpu in same domain. We
157 do not flush the worker because the MBM overflow worker reschedules the
158 worker on same CPU and scans the domain->cpu_mask to get the domain
159 pointer.
160
161 Improved version::
162
163 x86/intel_rdt/mbm: Fix MBM overflow handler during CPU hotplug
164
165 When a CPU is dying, the overflow worker is canceled and rescheduled on a
166 different CPU in the same domain. But if the timer is already about to
167 expire this essentially doubles the interval which might result in a non
168 detected overflow.
169
170 Cancel the overflow worker and reschedule it immediately on a different CPU
171 in the same domain. The work could be flushed as well, but that would
172 reschedule it on the same CPU.
173
174 Example 2::
175
176 time: POSIX CPU timers: Ensure that variable is initialized
177
178 If cpu_timer_sample_group returns -EINVAL, it will not have written into
179 *sample. Checking for cpu_timer_sample_group's return value precludes the
180 potential use of an uninitialized value of now in the following block.
181 Given an invalid clock_idx, the previous code could otherwise overwrite
182 *oldval in an undefined manner. This is now prevented. We also exploit
183 short-circuiting of && to sample the timer only if the result will
184 actually be used to update *oldval.
185
186 Improved version::
187
188 posix-cpu-timers: Make set_process_cpu_timer() more robust
189
190 Because the return value of cpu_timer_sample_group() is not checked,
191 compilers and static checkers can legitimately warn about a potential use
192 of the uninitialized variable 'now'. This is not a runtime issue as all
193 call sites hand in valid clock ids.
194
195 Also cpu_timer_sample_group() is invoked unconditionally even when the
196 result is not used because *oldval is NULL.
197
198 Make the invocation conditional and check the return value.
199
200 Example 3::
201
202 The entity can also be used for other purposes.
203
204 Let's rename it to be more generic.
205
206 Improved version::
207
208 The entity can also be used for other purposes.
209
210 Rename it to be more generic.
211
212
213 For complex scenarios, especially race conditions and memory ordering
214 issues, it is valuable to depict the scenario with a table which shows
215 the parallelism and the temporal order of events. Here is an example::
216
217 CPU0 CPU1
218 free_irq(X) interrupt X
219 spin_lock(desc->lock)
220 wake irq thread()
221 spin_unlock(desc->lock)
222 spin_lock(desc->lock)
223 remove action()
224 shutdown_irq()
225 release_resources() thread_handler()
226 spin_unlock(desc->lock) access released resources.
227 ^^^^^^^^^^^^^^^^^^^^^^^^^
228 synchronize_irq()
229
230 Lockdep provides similar useful output to depict a possible deadlock
231 scenario::
232
233 CPU0 CPU1
234 rtmutex_lock(&rcu->rt_mutex)
235 spin_lock(&rcu->rt_mutex.wait_lock)
236 local_irq_disable()
237 spin_lock(&timer->it_lock)
238 spin_lock(&rcu->mutex.wait_lock)
239 --> Interrupt
240 spin_lock(&timer->it_lock)
241
242
243 Function references in changelogs
244 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
245
246 When a function is mentioned in the changelog, either the text body or the
247 subject line, please use the format 'function_name()'. Omitting the
248 brackets after the function name can be ambiguous::
249
250 Subject: subsys/component: Make reservation_count static
251
252 reservation_count is only used in reservation_stats. Make it static.
253
254 The variant with brackets is more precise::
255
256 Subject: subsys/component: Make reservation_count() static
257
258 reservation_count() is only called from reservation_stats(). Make it
259 static.
260
261
262 Backtraces in changelogs
263 ^^^^^^^^^^^^^^^^^^^^^^^^
264
265 See :ref:`backtraces`.
266
267 Ordering of commit tags
268 ^^^^^^^^^^^^^^^^^^^^^^^
269
270 To have a uniform view of the commit tags, the tip maintainers use the
271 following tag ordering scheme:
272
273 - Fixes: 12char-SHA1 ("sub/sys: Original subject line")
274
275 A Fixes tag should be added even for changes which do not need to be
276 backported to stable kernels, i.e. when addressing a recently introduced
277 issue which only affects tip or the current head of mainline. These tags
278 are helpful to identify the original commit and are much more valuable
279 than prominently mentioning the commit which introduced a problem in the
280 text of the changelog itself because they can be automatically
281 extracted.
282
283 The following example illustrates the difference::
284
285 Commit
286
287 abcdef012345678 ("x86/xxx: Replace foo with bar")
288
289 left an unused instance of variable foo around. Remove it.
290
291 Signed-off-by: J.Dev <j.dev@mail>
292
293 Please say instead::
294
295 The recent replacement of foo with bar left an unused instance of
296 variable foo around. Remove it.
297
298 Fixes: abcdef012345678 ("x86/xxx: Replace foo with bar")
299 Signed-off-by: J.Dev <j.dev@mail>
300
301 The latter puts the information about the patch into the focus and
302 amends it with the reference to the commit which introduced the issue
303 rather than putting the focus on the original commit in the first place.
304
305 - Reported-by: ``Reporter <reporter@mail>``
306
307 - Closes: ``URL or Message-ID of the bug report this is fixing``
308
309 - Originally-by: ``Original author <original-author@mail>``
310
311 - Suggested-by: ``Suggester <suggester@mail>``
312
313 - Co-developed-by: ``Co-author <co-author@mail>``
314
315 Signed-off-by: ``Co-author <co-author@mail>``
316
317 Note, that Co-developed-by and Signed-off-by of the co-author(s) must
318 come in pairs.
319
320 - Signed-off-by: ``Author <author@mail>``
321
322 The first Signed-off-by (SOB) after the last Co-developed-by/SOB pair is the
323 author SOB, i.e. the person flagged as author by git.
324
325 - Signed-off-by: ``Patch handler <handler@mail>``
326
327 SOBs after the author SOB are from people handling and transporting
328 the patch, but were not involved in development. SOB chains should
329 reflect the **real** route a patch took as it was propagated to us,
330 with the first SOB entry signalling primary authorship of a single
331 author. Acks should be given as Acked-by lines and review approvals
332 as Reviewed-by lines.
333
334 If the handler made modifications to the patch or the changelog, then
335 this should be mentioned **after** the changelog text and **above**
336 all commit tags in the following format::
337
338 ... changelog text ends.
339
340 [ handler: Replaced foo by bar and updated changelog ]
341
342 First-tag: .....
343
344 Note the two empty new lines which separate the changelog text and the
345 commit tags from that notice.
346
347 If a patch is sent to the mailing list by a handler then the author has
348 to be noted in the first line of the changelog with::
349
350 From: Author <author@mail>
351
352 Changelog text starts here....
353
354 so the authorship is preserved. The 'From:' line has to be followed
355 by a empty newline. If that 'From:' line is missing, then the patch
356 would be attributed to the person who sent (transported, handled) it.
357 The 'From:' line is automatically removed when the patch is applied
358 and does not show up in the final git changelog. It merely affects
359 the authorship information of the resulting Git commit.
360
361 - Tested-by: ``Tester <tester@mail>``
362
363 - Reviewed-by: ``Reviewer <reviewer@mail>``
364
365 - Acked-by: ``Acker <acker@mail>``
366
367 - Cc: ``cc-ed-person <person@mail>``
368
369 If the patch should be backported to stable, then please add a '``Cc:
370 stable@vger.kernel.org``' tag, but do not Cc stable when sending your
371 mail.
372
373 - Link: ``https://link/to/information``
374
375 For referring to an email posted to the kernel mailing lists, please
376 use the lore.kernel.org redirector URL::
377
378 Link: https://lore.kernel.org/email-message-id@here
379
380 This URL should be used when referring to relevant mailing list
381 topics, related patch sets, or other notable discussion threads.
382 A convenient way to associate ``Link:`` trailers with the commit
383 message is to use markdown-like bracketed notation, for example::
384
385 A similar approach was attempted before as part of a different
386 effort [1], but the initial implementation caused too many
387 regressions [2], so it was backed out and reimplemented.
388
389 Link: https://lore.kernel.org/some-msgid@here # [1]
390 Link: https://bugzilla.example.org/bug/12345 # [2]
391
392 You can also use ``Link:`` trailers to indicate the origin of the
393 patch when applying it to your git tree. In that case, please use the
394 dedicated ``patch.msgid.link`` domain instead of ``lore.kernel.org``.
395 This practice makes it possible for automated tooling to identify
396 which link to use to retrieve the original patch submission. For
397 example::
398
399 Link: https://patch.msgid.link/patch-source-message-id@here
400
401 Please do not use combined tags, e.g. ``Reported-and-tested-by``, as
402 they just complicate automated extraction of tags.
403
404
405 Links to documentation
406 ^^^^^^^^^^^^^^^^^^^^^^
407
408 Providing links to documentation in the changelog is a great help to later
409 debugging and analysis. Unfortunately, URLs often break very quickly
410 because companies restructure their websites frequently. Non-'volatile'
411 exceptions include the Intel SDM and the AMD APM.
412
413 Therefore, for 'volatile' documents, please create an entry in the kernel
414 bugzilla https://bugzilla.kernel.org and attach a copy of these documents
415 to the bugzilla entry. Finally, provide the URL of the bugzilla entry in
416 the changelog.
417
418 Patch resend or reminders
419 ^^^^^^^^^^^^^^^^^^^^^^^^^
420
421 See :ref:`resend_reminders`.
422
423 Merge window
424 ^^^^^^^^^^^^
425
426 Please do not expect patches to be reviewed or merged by tip
427 maintainers around or during the merge window. The trees are closed
428 to all but urgent fixes during this time. They reopen once the merge
429 window closes and a new -rc1 kernel has been released.
430
431 Large series should be submitted in mergeable state *at* *least* a week
432 before the merge window opens. Exceptions are made for bug fixes and
433 *sometimes* for small standalone drivers for new hardware or minimally
434 invasive patches for hardware enablement.
435
436 During the merge window, the maintainers instead focus on following the
437 upstream changes, fixing merge window fallout, collecting bug fixes, and
438 allowing themselves a breath. Please respect that.
439
440 So called _urgent_ branches will be merged into mainline during the
441 stabilization phase of each release.
442
443
444 Git
445 ^^^
446
447 The tip maintainers accept git pull requests from maintainers who provide
448 subsystem changes for aggregation in the tip tree.
449
450 Pull requests for new patch submissions are usually not accepted and do not
451 replace proper patch submission to the mailing list. The main reason for
452 this is that the review workflow is email based.
453
454 If you submit a larger patch series it is helpful to provide a git branch
455 in a private repository which allows interested people to easily pull the
456 series for testing. The usual way to offer this is a git URL in the cover
457 letter of the patch series.
458
459 Testing
460 ^^^^^^^
461
462 Code should be tested before submitting to the tip maintainers. Anything
463 other than minor changes should be built, booted and tested with
464 comprehensive (and heavyweight) kernel debugging options enabled.
465
466 These debugging options can be found in kernel/configs/x86_debug.config
467 and can be added to an existing kernel config by running:
468
469 make x86_debug.config
470
471 Some of these options are x86-specific and can be left out when testing
472 on other architectures.
473
474 .. _maintainer-tip-coding-style:
475
476 Coding style notes
477 ------------------
478
479 Comment style
480 ^^^^^^^^^^^^^
481
482 Sentences in comments start with an uppercase letter.
483
484 Single line comments::
485
486 /* This is a single line comment */
487
488 Multi-line comments::
489
490 /*
491 * This is a properly formatted
492 * multi-line comment.
493 *
494 * Larger multi-line comments should be split into paragraphs.
495 */
496
497 No tail comments (see below):
498
499 Please refrain from using tail comments. Tail comments disturb the
500 reading flow in almost all contexts, but especially in code::
501
502 if (somecondition_is_true) /* Don't put a comment here */
503 dostuff(); /* Neither here */
504
505 seed = MAGIC_CONSTANT; /* Nor here */
506
507 Use freestanding comments instead::
508
509 /* This condition is not obvious without a comment */
510 if (somecondition_is_true) {
511 /* This really needs to be documented */
512 dostuff();
513 }
514
515 /* This magic initialization needs a comment. Maybe not? */
516 seed = MAGIC_CONSTANT;
517
518 Use C++ style, tail comments when documenting structs in headers to
519 achieve a more compact layout and better readability::
520
521 // eax
522 u32 x2apic_shift : 5, // Number of bits to shift APIC ID right
523 // for the topology ID at the next level
524 : 27; // Reserved
525 // ebx
526 u32 num_processors : 16, // Number of processors at current level
527 : 16; // Reserved
528
529 versus::
530
531 /* eax */
532 /*
533 * Number of bits to shift APIC ID right for the topology ID
534 * at the next level
535 */
536 u32 x2apic_shift : 5,
537 /* Reserved */
538 : 27;
539
540 /* ebx */
541 /* Number of processors at current level */
542 u32 num_processors : 16,
543 /* Reserved */
544 : 16;
545
546 Comment the important things:
547
548 Comments should be added where the operation is not obvious. Documenting
549 the obvious is just a distraction::
550
551 /* Decrement refcount and check for zero */
552 if (refcount_dec_and_test(&p->refcnt)) {
553 do;
554 lots;
555 of;
556 magic;
557 things;
558 }
559
560 Instead, comments should explain the non-obvious details and document
561 constraints::
562
563 if (refcount_dec_and_test(&p->refcnt)) {
564 /*
565 * Really good explanation why the magic things below
566 * need to be done, ordering and locking constraints,
567 * etc..
568 */
569 do;
570 lots;
571 of;
572 magic;
573 /* Needs to be the last operation because ... */
574 things;
575 }
576
577 Function documentation comments:
578
579 To document functions and their arguments please use kernel-doc format
580 and not free form comments::
581
582 /**
583 * magic_function - Do lots of magic stuff
584 * @magic: Pointer to the magic data to operate on
585 * @offset: Offset in the data array of @magic
586 *
587 * Deep explanation of mysterious things done with @magic along
588 * with documentation of the return values.
589 *
590 * Note, that the argument descriptors above are arranged
591 * in a tabular fashion.
592 */
593
594 This applies especially to globally visible functions and inline
595 functions in public header files. It might be overkill to use kernel-doc
596 format for every (static) function which needs a tiny explanation. The
597 usage of descriptive function names often replaces these tiny comments.
598 Apply common sense as always.
599
600
601 Documenting locking requirements
602 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
603 Documenting locking requirements is a good thing, but comments are not
604 necessarily the best choice. Instead of writing::
605
606 /* Caller must hold foo->lock */
607 void func(struct foo *foo)
608 {
609 ...
610 }
611
612 Please use::
613
614 void func(struct foo *foo)
615 {
616 lockdep_assert_held(&foo->lock);
617 ...
618 }
619
620 In PROVE_LOCKING kernels, lockdep_assert_held() emits a warning
621 if the caller doesn't hold the lock. Comments can't do that.
622
623 Bracket rules
624 ^^^^^^^^^^^^^
625
626 Brackets should be omitted only if the statement which follows 'if', 'for',
627 'while' etc. is truly a single line::
628
629 if (foo)
630 do_something();
631
632 The following is not considered to be a single line statement even
633 though C does not require brackets::
634
635 for (i = 0; i < end; i++)
636 if (foo[i])
637 do_something(foo[i]);
638
639 Adding brackets around the outer loop enhances the reading flow::
640
641 for (i = 0; i < end; i++) {
642 if (foo[i])
643 do_something(foo[i]);
644 }
645
646
647 Variable declarations
648 ^^^^^^^^^^^^^^^^^^^^^
649
650 The preferred ordering of variable declarations at the beginning of a
651 function is reverse fir tree order::
652
653 struct long_struct_name *descriptive_name;
654 unsigned long foo, bar;
655 unsigned int tmp;
656 int ret;
657
658 The above is faster to parse than the reverse ordering::
659
660 int ret;
661 unsigned int tmp;
662 unsigned long foo, bar;
663 struct long_struct_name *descriptive_name;
664
665 And even more so than random ordering::
666
667 unsigned long foo, bar;
668 int ret;
669 struct long_struct_name *descriptive_name;
670 unsigned int tmp;
671
672 Also please try to aggregate variables of the same type into a single
673 line. There is no point in wasting screen space::
674
675 unsigned long a;
676 unsigned long b;
677 unsigned long c;
678 unsigned long d;
679
680 It's really sufficient to do::
681
682 unsigned long a, b, c, d;
683
684 Please also refrain from introducing line splits in variable declarations::
685
686 struct long_struct_name *descriptive_name = container_of(bar,
687 struct long_struct_name,
688 member);
689 struct foobar foo;
690
691 It's way better to move the initialization to a separate line after the
692 declarations::
693
694 struct long_struct_name *descriptive_name;
695 struct foobar foo;
696
697 descriptive_name = container_of(bar, struct long_struct_name, member);
698
699
700 Variable types
701 ^^^^^^^^^^^^^^
702
703 Please use the proper u8, u16, u32, u64 types for variables which are meant
704 to describe hardware or are used as arguments for functions which access
705 hardware. These types are clearly defining the bit width and avoid
706 truncation, expansion and 32/64-bit confusion.
707
708 u64 is also recommended in code which would become ambiguous for 32-bit
709 kernels when 'unsigned long' would be used instead. While in such
710 situations 'unsigned long long' could be used as well, u64 is shorter
711 and also clearly shows that the operation is required to be 64 bits wide
712 independent of the target CPU.
713
714 Please use 'unsigned int' instead of 'unsigned'.
715
716
717 Constants
718 ^^^^^^^^^
719
720 Please do not use literal (hexa)decimal numbers in code or initializers.
721 Either use proper defines which have descriptive names or consider using
722 an enum.
723
724
725 Struct declarations and initializers
726 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
727
728 Struct declarations should align the struct member names in a tabular
729 fashion::
730
731 struct bar_order {
732 unsigned int guest_id;
733 int ordered_item;
734 struct menu *menu;
735 };
736
737 Please avoid documenting struct members within the declaration, because
738 this often results in strangely formatted comments and the struct members
739 become obfuscated::
740
741 struct bar_order {
742 unsigned int guest_id; /* Unique guest id */
743 int ordered_item;
744 /* Pointer to a menu instance which contains all the drinks */
745 struct menu *menu;
746 };
747
748 Instead, please consider using the kernel-doc format in a comment preceding
749 the struct declaration, which is easier to read and has the added advantage
750 of including the information in the kernel documentation, for example, as
751 follows::
752
753
754 /**
755 * struct bar_order - Description of a bar order
756 * @guest_id: Unique guest id
757 * @ordered_item: The item number from the menu
758 * @menu: Pointer to the menu from which the item
759 * was ordered
760 *
761 * Supplementary information for using the struct.
762 *
763 * Note, that the struct member descriptors above are arranged
764 * in a tabular fashion.
765 */
766 struct bar_order {
767 unsigned int guest_id;
768 int ordered_item;
769 struct menu *menu;
770 };
771
772 Static struct initializers must use C99 initializers and should also be
773 aligned in a tabular fashion::
774
775 static struct foo statfoo = {
776 .a = 0,
777 .plain_integer = CONSTANT_DEFINE_OR_ENUM,
778 .bar = &statbar,
779 };
780
781 Note that while C99 syntax allows the omission of the final comma,
782 we recommend the use of a comma on the last line because it makes
783 reordering and addition of new lines easier, and makes such future
784 patches slightly easier to read as well.
785
786 Line breaks
787 ^^^^^^^^^^^
788
789 Restricting line length to 80 characters makes deeply indented code hard to
790 read. Consider breaking out code into helper functions to avoid excessive
791 line breaking.
792
793 The 80 character rule is not a strict rule, so please use common sense when
794 breaking lines. Especially format strings should never be broken up.
795
796 When splitting function declarations or function calls, then please align
797 the first argument in the second line with the first argument in the first
798 line::
799
800 static int long_function_name(struct foobar *barfoo, unsigned int id,
801 unsigned int offset)
802 {
803
804 if (!id) {
805 ret = longer_function_name(barfoo, DEFAULT_BARFOO_ID,
806 offset);
807 ...
808
809 Namespaces
810 ^^^^^^^^^^
811
812 Function/variable namespaces improve readability and allow easy
813 grepping. These namespaces are string prefixes for globally visible
814 function and variable names, including inlines. These prefixes should
815 combine the subsystem and the component name such as 'x86_comp\_',
816 'sched\_', 'irq\_', and 'mutex\_'.
817
818 This also includes static file scope functions that are immediately put
819 into globally visible driver templates - it's useful for those symbols
820 to carry a good prefix as well, for backtrace readability.
821
822 Namespace prefixes may be omitted for local static functions and
823 variables. Truly local functions, only called by other local functions,
824 can have shorter descriptive names - our primary concern is greppability
825 and backtrace readability.
826
827 Please note that 'xxx_vendor\_' and 'vendor_xxx_` prefixes are not
828 helpful for static functions in vendor-specific files. After all, it
829 is already clear that the code is vendor-specific. In addition, vendor
830 names should only be for truly vendor-specific functionality.
831
832 As always apply common sense and aim for consistency and readability.
833
834
835 Commit notifications
836 --------------------
837
838 The tip tree is monitored by a bot for new commits. The bot sends an email
839 for each new commit to a dedicated mailing list
840 (``linux-tip-commits@vger.kernel.org``) and Cc's all people who are
841 mentioned in one of the commit tags. It uses the email message ID from the
842 Link tag at the end of the tag list to set the In-Reply-To email header so
843 the message is properly threaded with the patch submission email.
844
845 The tip maintainers and submaintainers try to reply to the submitter
846 when merging a patch, but they sometimes forget or it does not fit the
847 workflow of the moment. While the bot message is purely mechanical, it
848 also implies a 'Thank you! Applied.'.
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