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1=========================================
2How to get printk format specifiers right
3=========================================
4
5.. _printk-specifiers:
6
7:Author: Randy Dunlap <rdunlap@infradead.org>
8:Author: Andrew Murray <amurray@mpc-data.co.uk>
9
10
11Integer types
12=============
13
14::
15
16 If variable is of Type, use printk format specifier:
17 ------------------------------------------------------------
18 signed char %d or %hhx
19 unsigned char %u or %x
20 char %u or %x
21 short int %d or %hx
22 unsigned short int %u or %x
23 int %d or %x
24 unsigned int %u or %x
25 long %ld or %lx
26 unsigned long %lu or %lx
27 long long %lld or %llx
28 unsigned long long %llu or %llx
29 size_t %zu or %zx
30 ssize_t %zd or %zx
31 s8 %d or %hhx
32 u8 %u or %x
33 s16 %d or %hx
34 u16 %u or %x
35 s32 %d or %x
36 u32 %u or %x
37 s64 %lld or %llx
38 u64 %llu or %llx
39
40
41If <type> is architecture-dependent for its size (e.g., cycles_t, tcflag_t) or
42is dependent on a config option for its size (e.g., blk_status_t), use a format
43specifier of its largest possible type and explicitly cast to it.
44
45Example::
46
47 printk("test: latency: %llu cycles\n", (unsigned long long)time);
48
49Reminder: sizeof() returns type size_t.
50
51The kernel's printf does not support %n. Floating point formats (%e, %f,
52%g, %a) are also not recognized, for obvious reasons. Use of any
53unsupported specifier or length qualifier results in a WARN and early
54return from vsnprintf().
55
56Pointer types
57=============
58
59A raw pointer value may be printed with %p which will hash the address
60before printing. The kernel also supports extended specifiers for printing
61pointers of different types.
62
63Some of the extended specifiers print the data on the given address instead
64of printing the address itself. In this case, the following error messages
65might be printed instead of the unreachable information::
66
67 (null) data on plain NULL address
68 (efault) data on invalid address
69 (einval) invalid data on a valid address
70
71Plain Pointers
72--------------
73
74::
75
76 %p abcdef12 or 00000000abcdef12
77
78Pointers printed without a specifier extension (i.e unadorned %p) are
79hashed to prevent leaking information about the kernel memory layout. This
80has the added benefit of providing a unique identifier. On 64-bit machines
81the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
82gathers enough entropy.
83
84When possible, use specialised modifiers such as %pS or %pB (described below)
85to avoid the need of providing an unhashed address that has to be interpreted
86post-hoc. If not possible, and the aim of printing the address is to provide
87more information for debugging, use %p and boot the kernel with the
88``no_hash_pointers`` parameter during debugging, which will print all %p
89addresses unmodified. If you *really* always want the unmodified address, see
90%px below.
91
92If (and only if) you are printing addresses as a content of a virtual file in
93e.g. procfs or sysfs (using e.g. seq_printf(), not printk()) read by a
94userspace process, use the %pK modifier described below instead of %p or %px.
95
96Error Pointers
97--------------
98
99::
100
101 %pe -ENOSPC
102
103For printing error pointers (i.e. a pointer for which IS_ERR() is true)
104as a symbolic error name. Error values for which no symbolic name is
105known are printed in decimal, while a non-ERR_PTR passed as the
106argument to %pe gets treated as ordinary %p.
107
108Symbols/Function Pointers
109-------------------------
110
111::
112
113 %pS versatile_init+0x0/0x110
114 %ps versatile_init
115 %pSR versatile_init+0x9/0x110
116 (with __builtin_extract_return_addr() translation)
117 %pB prev_fn_of_versatile_init+0x88/0x88
118
119
120The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic
121format. They result in the symbol name with (S) or without (s)
122offsets. If KALLSYMS are disabled then the symbol address is printed instead.
123
124The ``B`` specifier results in the symbol name with offsets and should be
125used when printing stack backtraces. The specifier takes into
126consideration the effect of compiler optimisations which may occur
127when tail-calls are used and marked with the noreturn GCC attribute.
128
129If the pointer is within a module, the module name and optionally build ID is
130printed after the symbol name with an extra ``b`` appended to the end of the
131specifier.
132
133::
134
135 %pS versatile_init+0x0/0x110 [module_name]
136 %pSb versatile_init+0x0/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
137 %pSRb versatile_init+0x9/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
138 (with __builtin_extract_return_addr() translation)
139 %pBb prev_fn_of_versatile_init+0x88/0x88 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
140
141Probed Pointers from BPF / tracing
142----------------------------------
143
144::
145
146 %pks kernel string
147 %pus user string
148
149The ``k`` and ``u`` specifiers are used for printing prior probed memory from
150either kernel memory (k) or user memory (u). The subsequent ``s`` specifier
151results in printing a string. For direct use in regular vsnprintf() the (k)
152and (u) annotation is ignored, however, when used out of BPF's bpf_trace_printk(),
153for example, it reads the memory it is pointing to without faulting.
154
155Kernel Pointers
156---------------
157
158::
159
160 %pK 01234567 or 0123456789abcdef
161
162For printing kernel pointers which should be hidden from unprivileged
163users. The behaviour of %pK depends on the kptr_restrict sysctl - see
164Documentation/admin-guide/sysctl/kernel.rst for more details.
165
166This modifier is *only* intended when producing content of a file read by
167userspace from e.g. procfs or sysfs, not for dmesg. Please refer to the
168section about %p above for discussion about how to manage hashing pointers
169in printk().
170
171Unmodified Addresses
172--------------------
173
174::
175
176 %px 01234567 or 0123456789abcdef
177
178For printing pointers when you *really* want to print the address. Please
179consider whether or not you are leaking sensitive information about the
180kernel memory layout before printing pointers with %px. %px is functionally
181equivalent to %lx (or %lu). %px is preferred because it is more uniquely
182grep'able. If in the future we need to modify the way the kernel handles
183printing pointers we will be better equipped to find the call sites.
184
185Before using %px, consider if using %p is sufficient together with enabling the
186``no_hash_pointers`` kernel parameter during debugging sessions (see the %p
187description above). One valid scenario for %px might be printing information
188immediately before a panic, which prevents any sensitive information to be
189exploited anyway, and with %px there would be no need to reproduce the panic
190with no_hash_pointers.
191
192Pointer Differences
193-------------------
194
195::
196
197 %td 2560
198 %tx a00
199
200For printing the pointer differences, use the %t modifier for ptrdiff_t.
201
202Example::
203
204 printk("test: difference between pointers: %td\n", ptr2 - ptr1);
205
206Struct Resources
207----------------
208
209::
210
211 %pr [mem 0x60000000-0x6fffffff flags 0x2200] or
212 [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
213 %pR [mem 0x60000000-0x6fffffff pref] or
214 [mem 0x0000000060000000-0x000000006fffffff pref]
215
216For printing struct resources. The ``R`` and ``r`` specifiers result in a
217printed resource with (R) or without (r) a decoded flags member.
218
219Passed by reference.
220
221Physical address types phys_addr_t
222----------------------------------
223
224::
225
226 %pa[p] 0x01234567 or 0x0123456789abcdef
227
228For printing a phys_addr_t type (and its derivatives, such as
229resource_size_t) which can vary based on build options, regardless of the
230width of the CPU data path.
231
232Passed by reference.
233
234DMA address types dma_addr_t
235----------------------------
236
237::
238
239 %pad 0x01234567 or 0x0123456789abcdef
240
241For printing a dma_addr_t type which can vary based on build options,
242regardless of the width of the CPU data path.
243
244Passed by reference.
245
246Raw buffer as an escaped string
247-------------------------------
248
249::
250
251 %*pE[achnops]
252
253For printing raw buffer as an escaped string. For the following buffer::
254
255 1b 62 20 5c 43 07 22 90 0d 5d
256
257A few examples show how the conversion would be done (excluding surrounding
258quotes)::
259
260 %*pE "\eb \C\a"\220\r]"
261 %*pEhp "\x1bb \C\x07"\x90\x0d]"
262 %*pEa "\e\142\040\\\103\a\042\220\r\135"
263
264The conversion rules are applied according to an optional combination
265of flags (see :c:func:`string_escape_mem` kernel documentation for the
266details):
267
268 - a - ESCAPE_ANY
269 - c - ESCAPE_SPECIAL
270 - h - ESCAPE_HEX
271 - n - ESCAPE_NULL
272 - o - ESCAPE_OCTAL
273 - p - ESCAPE_NP
274 - s - ESCAPE_SPACE
275
276By default ESCAPE_ANY_NP is used.
277
278ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
279printing SSIDs.
280
281If field width is omitted then 1 byte only will be escaped.
282
283Raw buffer as a hex string
284--------------------------
285
286::
287
288 %*ph 00 01 02 ... 3f
289 %*phC 00:01:02: ... :3f
290 %*phD 00-01-02- ... -3f
291 %*phN 000102 ... 3f
292
293For printing small buffers (up to 64 bytes long) as a hex string with a
294certain separator. For larger buffers consider using
295:c:func:`print_hex_dump`.
296
297MAC/FDDI addresses
298------------------
299
300::
301
302 %pM 00:01:02:03:04:05
303 %pMR 05:04:03:02:01:00
304 %pMF 00-01-02-03-04-05
305 %pm 000102030405
306 %pmR 050403020100
307
308For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m``
309specifiers result in a printed address with (M) or without (m) byte
310separators. The default byte separator is the colon (:).
311
312Where FDDI addresses are concerned the ``F`` specifier can be used after
313the ``M`` specifier to use dash (-) separators instead of the default
314separator.
315
316For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
317specifier to use reversed byte order suitable for visual interpretation
318of Bluetooth addresses which are in the little endian order.
319
320Passed by reference.
321
322IPv4 addresses
323--------------
324
325::
326
327 %pI4 1.2.3.4
328 %pi4 001.002.003.004
329 %p[Ii]4[hnbl]
330
331For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4``
332specifiers result in a printed address with (i4) or without (I4) leading
333zeros.
334
335The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify
336host, network, big or little endian order addresses respectively. Where
337no specifier is provided the default network/big endian order is used.
338
339Passed by reference.
340
341IPv6 addresses
342--------------
343
344::
345
346 %pI6 0001:0002:0003:0004:0005:0006:0007:0008
347 %pi6 00010002000300040005000600070008
348 %pI6c 1:2:3:4:5:6:7:8
349
350For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6``
351specifiers result in a printed address with (I6) or without (i6)
352colon-separators. Leading zeros are always used.
353
354The additional ``c`` specifier can be used with the ``I`` specifier to
355print a compressed IPv6 address as described by
356https://tools.ietf.org/html/rfc5952
357
358Passed by reference.
359
360IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
361---------------------------------------------------------
362
363::
364
365 %pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008
366 %piS 001.002.003.004 or 00010002000300040005000600070008
367 %pISc 1.2.3.4 or 1:2:3:4:5:6:7:8
368 %pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345
369 %p[Ii]S[pfschnbl]
370
371For printing an IP address without the need to distinguish whether it's of
372type AF_INET or AF_INET6. A pointer to a valid struct sockaddr,
373specified through ``IS`` or ``iS``, can be passed to this format specifier.
374
375The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
376(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,
377flowinfo a ``/`` and scope a ``%``, each followed by the actual value.
378
379In case of an IPv6 address the compressed IPv6 address as described by
380https://tools.ietf.org/html/rfc5952 is being used if the additional
381specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in
382case of additional specifiers ``p``, ``f`` or ``s`` as suggested by
383https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
384
385In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``
386specifiers can be used as well and are ignored in case of an IPv6
387address.
388
389Passed by reference.
390
391Further examples::
392
393 %pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789
394 %pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890
395 %pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
396
397UUID/GUID addresses
398-------------------
399
400::
401
402 %pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
403 %pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
404 %pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
405 %pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
406
407For printing 16-byte UUID/GUIDs addresses. The additional ``l``, ``L``,
408``b`` and ``B`` specifiers are used to specify a little endian order in
409lower (l) or upper case (L) hex notation - and big endian order in lower (b)
410or upper case (B) hex notation.
411
412Where no additional specifiers are used the default big endian
413order with lower case hex notation will be printed.
414
415Passed by reference.
416
417dentry names
418------------
419
420::
421
422 %pd{,2,3,4}
423 %pD{,2,3,4}
424
425For printing dentry name; if we race with :c:func:`d_move`, the name might
426be a mix of old and new ones, but it won't oops. %pd dentry is a safer
427equivalent of %s dentry->d_name.name we used to use, %pd<n> prints ``n``
428last components. %pD does the same thing for struct file.
429
430Passed by reference.
431
432block_device names
433------------------
434
435::
436
437 %pg sda, sda1 or loop0p1
438
439For printing name of block_device pointers.
440
441struct va_format
442----------------
443
444::
445
446 %pV
447
448For printing struct va_format structures. These contain a format string
449and va_list as follows::
450
451 struct va_format {
452 const char *fmt;
453 va_list *va;
454 };
455
456Implements a "recursive vsnprintf".
457
458Do not use this feature without some mechanism to verify the
459correctness of the format string and va_list arguments.
460
461Passed by reference.
462
463Device tree nodes
464-----------------
465
466::
467
468 %pOF[fnpPcCF]
469
470
471For printing device tree node structures. Default behaviour is
472equivalent to %pOFf.
473
474 - f - device node full_name
475 - n - device node name
476 - p - device node phandle
477 - P - device node path spec (name + @unit)
478 - F - device node flags
479 - c - major compatible string
480 - C - full compatible string
481
482The separator when using multiple arguments is ':'
483
484Examples::
485
486 %pOF /foo/bar@0 - Node full name
487 %pOFf /foo/bar@0 - Same as above
488 %pOFfp /foo/bar@0:10 - Node full name + phandle
489 %pOFfcF /foo/bar@0:foo,device:--P- - Node full name +
490 major compatible string +
491 node flags
492 D - dynamic
493 d - detached
494 P - Populated
495 B - Populated bus
496
497Passed by reference.
498
499Fwnode handles
500--------------
501
502::
503
504 %pfw[fP]
505
506For printing information on fwnode handles. The default is to print the full
507node name, including the path. The modifiers are functionally equivalent to
508%pOF above.
509
510 - f - full name of the node, including the path
511 - P - the name of the node including an address (if there is one)
512
513Examples (ACPI)::
514
515 %pfwf \_SB.PCI0.CIO2.port@1.endpoint@0 - Full node name
516 %pfwP endpoint@0 - Node name
517
518Examples (OF)::
519
520 %pfwf /ocp@68000000/i2c@48072000/camera@10/port/endpoint - Full name
521 %pfwP endpoint - Node name
522
523Time and date
524-------------
525
526::
527
528 %pt[RT] YYYY-mm-ddTHH:MM:SS
529 %pt[RT]s YYYY-mm-dd HH:MM:SS
530 %pt[RT]d YYYY-mm-dd
531 %pt[RT]t HH:MM:SS
532 %pt[RT][dt][r][s]
533
534For printing date and time as represented by::
535
536 R struct rtc_time structure
537 T time64_t type
538
539in human readable format.
540
541By default year will be incremented by 1900 and month by 1.
542Use %pt[RT]r (raw) to suppress this behaviour.
543
544The %pt[RT]s (space) will override ISO 8601 separator by using ' ' (space)
545instead of 'T' (Capital T) between date and time. It won't have any effect
546when date or time is omitted.
547
548Passed by reference.
549
550struct clk
551----------
552
553::
554
555 %pC pll1
556 %pCn pll1
557
558For printing struct clk structures. %pC and %pCn print the name of the clock
559(Common Clock Framework) or a unique 32-bit ID (legacy clock framework).
560
561Passed by reference.
562
563bitmap and its derivatives such as cpumask and nodemask
564-------------------------------------------------------
565
566::
567
568 %*pb 0779
569 %*pbl 0,3-6,8-10
570
571For printing bitmap and its derivatives such as cpumask and nodemask,
572%*pb outputs the bitmap with field width as the number of bits and %*pbl
573output the bitmap as range list with field width as the number of bits.
574
575The field width is passed by value, the bitmap is passed by reference.
576Helper macros cpumask_pr_args() and nodemask_pr_args() are available to ease
577printing cpumask and nodemask.
578
579Flags bitfields such as page flags, page_type, gfp_flags
580--------------------------------------------------------
581
582::
583
584 %pGp 0x17ffffc0002036(referenced|uptodate|lru|active|private|node=0|zone=2|lastcpupid=0x1fffff)
585 %pGt 0xffffff7f(buddy)
586 %pGg GFP_USER|GFP_DMA32|GFP_NOWARN
587 %pGv read|exec|mayread|maywrite|mayexec|denywrite
588
589For printing flags bitfields as a collection of symbolic constants that
590would construct the value. The type of flags is given by the third
591character. Currently supported are:
592
593 - p - [p]age flags, expects value of type (``unsigned long *``)
594 - t - page [t]ype, expects value of type (``unsigned int *``)
595 - v - [v]ma_flags, expects value of type (``unsigned long *``)
596 - g - [g]fp_flags, expects value of type (``gfp_t *``)
597
598The flag names and print order depends on the particular type.
599
600Note that this format should not be used directly in the
601:c:func:`TP_printk()` part of a tracepoint. Instead, use the show_*_flags()
602functions from <trace/events/mmflags.h>.
603
604Passed by reference.
605
606Network device features
607-----------------------
608
609::
610
611 %pNF 0x000000000000c000
612
613For printing netdev_features_t.
614
615Passed by reference.
616
617V4L2 and DRM FourCC code (pixel format)
618---------------------------------------
619
620::
621
622 %p4cc
623
624Print a FourCC code used by V4L2 or DRM, including format endianness and
625its numerical value as hexadecimal.
626
627Passed by reference.
628
629Examples::
630
631 %p4cc BG12 little-endian (0x32314742)
632 %p4cc Y10 little-endian (0x20303159)
633 %p4cc NV12 big-endian (0xb231564e)
634
635Rust
636----
637
638::
639
640 %pA
641
642Only intended to be used from Rust code to format ``core::fmt::Arguments``.
643Do *not* use it from C.
644
645Thanks
646======
647
648If you add other %p extensions, please extend <lib/test_printf.c> with
649one or more test cases, if at all feasible.
650
651Thank you for your cooperation and attention.
1=========================================
2How to get printk format specifiers right
3=========================================
4
5:Author: Randy Dunlap <rdunlap@infradead.org>
6:Author: Andrew Murray <amurray@mpc-data.co.uk>
7
8
9Integer types
10=============
11
12::
13
14 If variable is of Type, use printk format specifier:
15 ------------------------------------------------------------
16 char %d or %x
17 unsigned char %u or %x
18 short int %d or %x
19 unsigned short int %u or %x
20 int %d or %x
21 unsigned int %u or %x
22 long %ld or %lx
23 unsigned long %lu or %lx
24 long long %lld or %llx
25 unsigned long long %llu or %llx
26 size_t %zu or %zx
27 ssize_t %zd or %zx
28 s8 %d or %x
29 u8 %u or %x
30 s16 %d or %x
31 u16 %u or %x
32 s32 %d or %x
33 u32 %u or %x
34 s64 %lld or %llx
35 u64 %llu or %llx
36
37
38If <type> is dependent on a config option for its size (e.g., sector_t,
39blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
40format specifier of its largest possible type and explicitly cast to it.
41
42Example::
43
44 printk("test: sector number/total blocks: %llu/%llu\n",
45 (unsigned long long)sector, (unsigned long long)blockcount);
46
47Reminder: sizeof() returns type size_t.
48
49The kernel's printf does not support %n. Floating point formats (%e, %f,
50%g, %a) are also not recognized, for obvious reasons. Use of any
51unsupported specifier or length qualifier results in a WARN and early
52return from vsnprintf().
53
54Pointer types
55=============
56
57A raw pointer value may be printed with %p which will hash the address
58before printing. The kernel also supports extended specifiers for printing
59pointers of different types.
60
61Some of the extended specifiers print the data on the given address instead
62of printing the address itself. In this case, the following error messages
63might be printed instead of the unreachable information::
64
65 (null) data on plain NULL address
66 (efault) data on invalid address
67 (einval) invalid data on a valid address
68
69Plain Pointers
70--------------
71
72::
73
74 %p abcdef12 or 00000000abcdef12
75
76Pointers printed without a specifier extension (i.e unadorned %p) are
77hashed to prevent leaking information about the kernel memory layout. This
78has the added benefit of providing a unique identifier. On 64-bit machines
79the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
80gathers enough entropy. If you *really* want the address see %px below.
81
82Symbols/Function Pointers
83-------------------------
84
85::
86
87 %pS versatile_init+0x0/0x110
88 %ps versatile_init
89 %pF versatile_init+0x0/0x110
90 %pf versatile_init
91 %pSR versatile_init+0x9/0x110
92 (with __builtin_extract_return_addr() translation)
93 %pB prev_fn_of_versatile_init+0x88/0x88
94
95
96The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic
97format. They result in the symbol name with (S) or without (s)
98offsets. If KALLSYMS are disabled then the symbol address is printed instead.
99
100Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``)
101and thus deprecated. We have ``F`` and ``f`` because on ia64, ppc64 and
102parisc64 function pointers are indirect and, in fact, are function
103descriptors, which require additional dereferencing before we can lookup
104the symbol. As of now, ``S`` and ``s`` perform dereferencing on those
105platforms (when needed), so ``F`` and ``f`` exist for compatibility
106reasons only.
107
108The ``B`` specifier results in the symbol name with offsets and should be
109used when printing stack backtraces. The specifier takes into
110consideration the effect of compiler optimisations which may occur
111when tail-calls are used and marked with the noreturn GCC attribute.
112
113Kernel Pointers
114---------------
115
116::
117
118 %pK 01234567 or 0123456789abcdef
119
120For printing kernel pointers which should be hidden from unprivileged
121users. The behaviour of %pK depends on the kptr_restrict sysctl - see
122Documentation/admin-guide/sysctl/kernel.rst for more details.
123
124Unmodified Addresses
125--------------------
126
127::
128
129 %px 01234567 or 0123456789abcdef
130
131For printing pointers when you *really* want to print the address. Please
132consider whether or not you are leaking sensitive information about the
133kernel memory layout before printing pointers with %px. %px is functionally
134equivalent to %lx (or %lu). %px is preferred because it is more uniquely
135grep'able. If in the future we need to modify the way the kernel handles
136printing pointers we will be better equipped to find the call sites.
137
138Struct Resources
139----------------
140
141::
142
143 %pr [mem 0x60000000-0x6fffffff flags 0x2200] or
144 [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
145 %pR [mem 0x60000000-0x6fffffff pref] or
146 [mem 0x0000000060000000-0x000000006fffffff pref]
147
148For printing struct resources. The ``R`` and ``r`` specifiers result in a
149printed resource with (R) or without (r) a decoded flags member.
150
151Passed by reference.
152
153Physical address types phys_addr_t
154----------------------------------
155
156::
157
158 %pa[p] 0x01234567 or 0x0123456789abcdef
159
160For printing a phys_addr_t type (and its derivatives, such as
161resource_size_t) which can vary based on build options, regardless of the
162width of the CPU data path.
163
164Passed by reference.
165
166DMA address types dma_addr_t
167----------------------------
168
169::
170
171 %pad 0x01234567 or 0x0123456789abcdef
172
173For printing a dma_addr_t type which can vary based on build options,
174regardless of the width of the CPU data path.
175
176Passed by reference.
177
178Raw buffer as an escaped string
179-------------------------------
180
181::
182
183 %*pE[achnops]
184
185For printing raw buffer as an escaped string. For the following buffer::
186
187 1b 62 20 5c 43 07 22 90 0d 5d
188
189A few examples show how the conversion would be done (excluding surrounding
190quotes)::
191
192 %*pE "\eb \C\a"\220\r]"
193 %*pEhp "\x1bb \C\x07"\x90\x0d]"
194 %*pEa "\e\142\040\\\103\a\042\220\r\135"
195
196The conversion rules are applied according to an optional combination
197of flags (see :c:func:`string_escape_mem` kernel documentation for the
198details):
199
200 - a - ESCAPE_ANY
201 - c - ESCAPE_SPECIAL
202 - h - ESCAPE_HEX
203 - n - ESCAPE_NULL
204 - o - ESCAPE_OCTAL
205 - p - ESCAPE_NP
206 - s - ESCAPE_SPACE
207
208By default ESCAPE_ANY_NP is used.
209
210ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
211printing SSIDs.
212
213If field width is omitted then 1 byte only will be escaped.
214
215Raw buffer as a hex string
216--------------------------
217
218::
219
220 %*ph 00 01 02 ... 3f
221 %*phC 00:01:02: ... :3f
222 %*phD 00-01-02- ... -3f
223 %*phN 000102 ... 3f
224
225For printing small buffers (up to 64 bytes long) as a hex string with a
226certain separator. For larger buffers consider using
227:c:func:`print_hex_dump`.
228
229MAC/FDDI addresses
230------------------
231
232::
233
234 %pM 00:01:02:03:04:05
235 %pMR 05:04:03:02:01:00
236 %pMF 00-01-02-03-04-05
237 %pm 000102030405
238 %pmR 050403020100
239
240For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m``
241specifiers result in a printed address with (M) or without (m) byte
242separators. The default byte separator is the colon (:).
243
244Where FDDI addresses are concerned the ``F`` specifier can be used after
245the ``M`` specifier to use dash (-) separators instead of the default
246separator.
247
248For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
249specifier to use reversed byte order suitable for visual interpretation
250of Bluetooth addresses which are in the little endian order.
251
252Passed by reference.
253
254IPv4 addresses
255--------------
256
257::
258
259 %pI4 1.2.3.4
260 %pi4 001.002.003.004
261 %p[Ii]4[hnbl]
262
263For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4``
264specifiers result in a printed address with (i4) or without (I4) leading
265zeros.
266
267The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify
268host, network, big or little endian order addresses respectively. Where
269no specifier is provided the default network/big endian order is used.
270
271Passed by reference.
272
273IPv6 addresses
274--------------
275
276::
277
278 %pI6 0001:0002:0003:0004:0005:0006:0007:0008
279 %pi6 00010002000300040005000600070008
280 %pI6c 1:2:3:4:5:6:7:8
281
282For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6``
283specifiers result in a printed address with (I6) or without (i6)
284colon-separators. Leading zeros are always used.
285
286The additional ``c`` specifier can be used with the ``I`` specifier to
287print a compressed IPv6 address as described by
288http://tools.ietf.org/html/rfc5952
289
290Passed by reference.
291
292IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
293---------------------------------------------------------
294
295::
296
297 %pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008
298 %piS 001.002.003.004 or 00010002000300040005000600070008
299 %pISc 1.2.3.4 or 1:2:3:4:5:6:7:8
300 %pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345
301 %p[Ii]S[pfschnbl]
302
303For printing an IP address without the need to distinguish whether it's of
304type AF_INET or AF_INET6. A pointer to a valid struct sockaddr,
305specified through ``IS`` or ``iS``, can be passed to this format specifier.
306
307The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
308(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,
309flowinfo a ``/`` and scope a ``%``, each followed by the actual value.
310
311In case of an IPv6 address the compressed IPv6 address as described by
312http://tools.ietf.org/html/rfc5952 is being used if the additional
313specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in
314case of additional specifiers ``p``, ``f`` or ``s`` as suggested by
315https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
316
317In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``
318specifiers can be used as well and are ignored in case of an IPv6
319address.
320
321Passed by reference.
322
323Further examples::
324
325 %pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789
326 %pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890
327 %pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
328
329UUID/GUID addresses
330-------------------
331
332::
333
334 %pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
335 %pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
336 %pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
337 %pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
338
339For printing 16-byte UUID/GUIDs addresses. The additional ``l``, ``L``,
340``b`` and ``B`` specifiers are used to specify a little endian order in
341lower (l) or upper case (L) hex notation - and big endian order in lower (b)
342or upper case (B) hex notation.
343
344Where no additional specifiers are used the default big endian
345order with lower case hex notation will be printed.
346
347Passed by reference.
348
349dentry names
350------------
351
352::
353
354 %pd{,2,3,4}
355 %pD{,2,3,4}
356
357For printing dentry name; if we race with :c:func:`d_move`, the name might
358be a mix of old and new ones, but it won't oops. %pd dentry is a safer
359equivalent of %s dentry->d_name.name we used to use, %pd<n> prints ``n``
360last components. %pD does the same thing for struct file.
361
362Passed by reference.
363
364block_device names
365------------------
366
367::
368
369 %pg sda, sda1 or loop0p1
370
371For printing name of block_device pointers.
372
373struct va_format
374----------------
375
376::
377
378 %pV
379
380For printing struct va_format structures. These contain a format string
381and va_list as follows::
382
383 struct va_format {
384 const char *fmt;
385 va_list *va;
386 };
387
388Implements a "recursive vsnprintf".
389
390Do not use this feature without some mechanism to verify the
391correctness of the format string and va_list arguments.
392
393Passed by reference.
394
395Device tree nodes
396-----------------
397
398::
399
400 %pOF[fnpPcCF]
401
402
403For printing device tree node structures. Default behaviour is
404equivalent to %pOFf.
405
406 - f - device node full_name
407 - n - device node name
408 - p - device node phandle
409 - P - device node path spec (name + @unit)
410 - F - device node flags
411 - c - major compatible string
412 - C - full compatible string
413
414The separator when using multiple arguments is ':'
415
416Examples::
417
418 %pOF /foo/bar@0 - Node full name
419 %pOFf /foo/bar@0 - Same as above
420 %pOFfp /foo/bar@0:10 - Node full name + phandle
421 %pOFfcF /foo/bar@0:foo,device:--P- - Node full name +
422 major compatible string +
423 node flags
424 D - dynamic
425 d - detached
426 P - Populated
427 B - Populated bus
428
429Passed by reference.
430
431Time and date (struct rtc_time)
432-------------------------------
433
434::
435
436 %ptR YYYY-mm-ddTHH:MM:SS
437 %ptRd YYYY-mm-dd
438 %ptRt HH:MM:SS
439 %ptR[dt][r]
440
441For printing date and time as represented by struct rtc_time structure in
442human readable format.
443
444By default year will be incremented by 1900 and month by 1. Use %ptRr (raw)
445to suppress this behaviour.
446
447Passed by reference.
448
449struct clk
450----------
451
452::
453
454 %pC pll1
455 %pCn pll1
456
457For printing struct clk structures. %pC and %pCn print the name of the clock
458(Common Clock Framework) or a unique 32-bit ID (legacy clock framework).
459
460Passed by reference.
461
462bitmap and its derivatives such as cpumask and nodemask
463-------------------------------------------------------
464
465::
466
467 %*pb 0779
468 %*pbl 0,3-6,8-10
469
470For printing bitmap and its derivatives such as cpumask and nodemask,
471%*pb outputs the bitmap with field width as the number of bits and %*pbl
472output the bitmap as range list with field width as the number of bits.
473
474Passed by reference.
475
476Flags bitfields such as page flags, gfp_flags
477---------------------------------------------
478
479::
480
481 %pGp referenced|uptodate|lru|active|private
482 %pGg GFP_USER|GFP_DMA32|GFP_NOWARN
483 %pGv read|exec|mayread|maywrite|mayexec|denywrite
484
485For printing flags bitfields as a collection of symbolic constants that
486would construct the value. The type of flags is given by the third
487character. Currently supported are [p]age flags, [v]ma_flags (both
488expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag
489names and print order depends on the particular type.
490
491Note that this format should not be used directly in the
492:c:func:`TP_printk()` part of a tracepoint. Instead, use the show_*_flags()
493functions from <trace/events/mmflags.h>.
494
495Passed by reference.
496
497Network device features
498-----------------------
499
500::
501
502 %pNF 0x000000000000c000
503
504For printing netdev_features_t.
505
506Passed by reference.
507
508Thanks
509======
510
511If you add other %p extensions, please extend <lib/test_printf.c> with
512one or more test cases, if at all feasible.
513
514Thank you for your cooperation and attention.