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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 char %d or %x
19 unsigned char %u or %x
20 short int %d or %x
21 unsigned short int %u or %x
22 int %d or %x
23 unsigned int %u or %x
24 long %ld or %lx
25 unsigned long %lu or %lx
26 long long %lld or %llx
27 unsigned long long %llu or %llx
28 size_t %zu or %zx
29 ssize_t %zd or %zx
30 s8 %d or %x
31 u8 %u or %x
32 s16 %d or %x
33 u16 %u or %x
34 s32 %d or %x
35 u32 %u or %x
36 s64 %lld or %llx
37 u64 %llu or %llx
38
39
40If <type> is architecture-dependent for its size (e.g., cycles_t, tcflag_t) or
41is dependent on a config option for its size (e.g., blk_status_t), use a format
42specifier of its largest possible type and explicitly cast to it.
43
44Example::
45
46 printk("test: latency: %llu cycles\n", (unsigned long long)time);
47
48Reminder: sizeof() returns type size_t.
49
50The kernel's printf does not support %n. Floating point formats (%e, %f,
51%g, %a) are also not recognized, for obvious reasons. Use of any
52unsupported specifier or length qualifier results in a WARN and early
53return from vsnprintf().
54
55Pointer types
56=============
57
58A raw pointer value may be printed with %p which will hash the address
59before printing. The kernel also supports extended specifiers for printing
60pointers of different types.
61
62Some of the extended specifiers print the data on the given address instead
63of printing the address itself. In this case, the following error messages
64might be printed instead of the unreachable information::
65
66 (null) data on plain NULL address
67 (efault) data on invalid address
68 (einval) invalid data on a valid address
69
70Plain Pointers
71--------------
72
73::
74
75 %p abcdef12 or 00000000abcdef12
76
77Pointers printed without a specifier extension (i.e unadorned %p) are
78hashed to prevent leaking information about the kernel memory layout. This
79has the added benefit of providing a unique identifier. On 64-bit machines
80the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
81gathers enough entropy.
82
83When possible, use specialised modifiers such as %pS or %pB (described below)
84to avoid the need of providing an unhashed address that has to be interpreted
85post-hoc. If not possible, and the aim of printing the address is to provide
86more information for debugging, use %p and boot the kernel with the
87``no_hash_pointers`` parameter during debugging, which will print all %p
88addresses unmodified. If you *really* always want the unmodified address, see
89%px below.
90
91If (and only if) you are printing addresses as a content of a virtual file in
92e.g. procfs or sysfs (using e.g. seq_printf(), not printk()) read by a
93userspace process, use the %pK modifier described below instead of %p or %px.
94
95Error Pointers
96--------------
97
98::
99
100 %pe -ENOSPC
101
102For printing error pointers (i.e. a pointer for which IS_ERR() is true)
103as a symbolic error name. Error values for which no symbolic name is
104known are printed in decimal, while a non-ERR_PTR passed as the
105argument to %pe gets treated as ordinary %p.
106
107Symbols/Function Pointers
108-------------------------
109
110::
111
112 %pS versatile_init+0x0/0x110
113 %ps versatile_init
114 %pSR versatile_init+0x9/0x110
115 (with __builtin_extract_return_addr() translation)
116 %pB prev_fn_of_versatile_init+0x88/0x88
117
118
119The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic
120format. They result in the symbol name with (S) or without (s)
121offsets. If KALLSYMS are disabled then the symbol address is printed instead.
122
123The ``B`` specifier results in the symbol name with offsets and should be
124used when printing stack backtraces. The specifier takes into
125consideration the effect of compiler optimisations which may occur
126when tail-calls are used and marked with the noreturn GCC attribute.
127
128If the pointer is within a module, the module name and optionally build ID is
129printed after the symbol name with an extra ``b`` appended to the end of the
130specifier.
131
132::
133
134 %pS versatile_init+0x0/0x110 [module_name]
135 %pSb versatile_init+0x0/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
136 %pSRb versatile_init+0x9/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
137 (with __builtin_extract_return_addr() translation)
138 %pBb prev_fn_of_versatile_init+0x88/0x88 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
139
140Probed Pointers from BPF / tracing
141----------------------------------
142
143::
144
145 %pks kernel string
146 %pus user string
147
148The ``k`` and ``u`` specifiers are used for printing prior probed memory from
149either kernel memory (k) or user memory (u). The subsequent ``s`` specifier
150results in printing a string. For direct use in regular vsnprintf() the (k)
151and (u) annotation is ignored, however, when used out of BPF's bpf_trace_printk(),
152for example, it reads the memory it is pointing to without faulting.
153
154Kernel Pointers
155---------------
156
157::
158
159 %pK 01234567 or 0123456789abcdef
160
161For printing kernel pointers which should be hidden from unprivileged
162users. The behaviour of %pK depends on the kptr_restrict sysctl - see
163Documentation/admin-guide/sysctl/kernel.rst for more details.
164
165This modifier is *only* intended when producing content of a file read by
166userspace from e.g. procfs or sysfs, not for dmesg. Please refer to the
167section about %p above for discussion about how to manage hashing pointers
168in printk().
169
170Unmodified Addresses
171--------------------
172
173::
174
175 %px 01234567 or 0123456789abcdef
176
177For printing pointers when you *really* want to print the address. Please
178consider whether or not you are leaking sensitive information about the
179kernel memory layout before printing pointers with %px. %px is functionally
180equivalent to %lx (or %lu). %px is preferred because it is more uniquely
181grep'able. If in the future we need to modify the way the kernel handles
182printing pointers we will be better equipped to find the call sites.
183
184Before using %px, consider if using %p is sufficient together with enabling the
185``no_hash_pointers`` kernel parameter during debugging sessions (see the %p
186description above). One valid scenario for %px might be printing information
187immediately before a panic, which prevents any sensitive information to be
188exploited anyway, and with %px there would be no need to reproduce the panic
189with no_hash_pointers.
190
191Pointer Differences
192-------------------
193
194::
195
196 %td 2560
197 %tx a00
198
199For printing the pointer differences, use the %t modifier for ptrdiff_t.
200
201Example::
202
203 printk("test: difference between pointers: %td\n", ptr2 - ptr1);
204
205Struct Resources
206----------------
207
208::
209
210 %pr [mem 0x60000000-0x6fffffff flags 0x2200] or
211 [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
212 %pR [mem 0x60000000-0x6fffffff pref] or
213 [mem 0x0000000060000000-0x000000006fffffff pref]
214
215For printing struct resources. The ``R`` and ``r`` specifiers result in a
216printed resource with (R) or without (r) a decoded flags member.
217
218Passed by reference.
219
220Physical address types phys_addr_t
221----------------------------------
222
223::
224
225 %pa[p] 0x01234567 or 0x0123456789abcdef
226
227For printing a phys_addr_t type (and its derivatives, such as
228resource_size_t) which can vary based on build options, regardless of the
229width of the CPU data path.
230
231Passed by reference.
232
233DMA address types dma_addr_t
234----------------------------
235
236::
237
238 %pad 0x01234567 or 0x0123456789abcdef
239
240For printing a dma_addr_t type which can vary based on build options,
241regardless of the width of the CPU data path.
242
243Passed by reference.
244
245Raw buffer as an escaped string
246-------------------------------
247
248::
249
250 %*pE[achnops]
251
252For printing raw buffer as an escaped string. For the following buffer::
253
254 1b 62 20 5c 43 07 22 90 0d 5d
255
256A few examples show how the conversion would be done (excluding surrounding
257quotes)::
258
259 %*pE "\eb \C\a"\220\r]"
260 %*pEhp "\x1bb \C\x07"\x90\x0d]"
261 %*pEa "\e\142\040\\\103\a\042\220\r\135"
262
263The conversion rules are applied according to an optional combination
264of flags (see :c:func:`string_escape_mem` kernel documentation for the
265details):
266
267 - a - ESCAPE_ANY
268 - c - ESCAPE_SPECIAL
269 - h - ESCAPE_HEX
270 - n - ESCAPE_NULL
271 - o - ESCAPE_OCTAL
272 - p - ESCAPE_NP
273 - s - ESCAPE_SPACE
274
275By default ESCAPE_ANY_NP is used.
276
277ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
278printing SSIDs.
279
280If field width is omitted then 1 byte only will be escaped.
281
282Raw buffer as a hex string
283--------------------------
284
285::
286
287 %*ph 00 01 02 ... 3f
288 %*phC 00:01:02: ... :3f
289 %*phD 00-01-02- ... -3f
290 %*phN 000102 ... 3f
291
292For printing small buffers (up to 64 bytes long) as a hex string with a
293certain separator. For larger buffers consider using
294:c:func:`print_hex_dump`.
295
296MAC/FDDI addresses
297------------------
298
299::
300
301 %pM 00:01:02:03:04:05
302 %pMR 05:04:03:02:01:00
303 %pMF 00-01-02-03-04-05
304 %pm 000102030405
305 %pmR 050403020100
306
307For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m``
308specifiers result in a printed address with (M) or without (m) byte
309separators. The default byte separator is the colon (:).
310
311Where FDDI addresses are concerned the ``F`` specifier can be used after
312the ``M`` specifier to use dash (-) separators instead of the default
313separator.
314
315For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
316specifier to use reversed byte order suitable for visual interpretation
317of Bluetooth addresses which are in the little endian order.
318
319Passed by reference.
320
321IPv4 addresses
322--------------
323
324::
325
326 %pI4 1.2.3.4
327 %pi4 001.002.003.004
328 %p[Ii]4[hnbl]
329
330For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4``
331specifiers result in a printed address with (i4) or without (I4) leading
332zeros.
333
334The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify
335host, network, big or little endian order addresses respectively. Where
336no specifier is provided the default network/big endian order is used.
337
338Passed by reference.
339
340IPv6 addresses
341--------------
342
343::
344
345 %pI6 0001:0002:0003:0004:0005:0006:0007:0008
346 %pi6 00010002000300040005000600070008
347 %pI6c 1:2:3:4:5:6:7:8
348
349For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6``
350specifiers result in a printed address with (I6) or without (i6)
351colon-separators. Leading zeros are always used.
352
353The additional ``c`` specifier can be used with the ``I`` specifier to
354print a compressed IPv6 address as described by
355https://tools.ietf.org/html/rfc5952
356
357Passed by reference.
358
359IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
360---------------------------------------------------------
361
362::
363
364 %pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008
365 %piS 001.002.003.004 or 00010002000300040005000600070008
366 %pISc 1.2.3.4 or 1:2:3:4:5:6:7:8
367 %pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345
368 %p[Ii]S[pfschnbl]
369
370For printing an IP address without the need to distinguish whether it's of
371type AF_INET or AF_INET6. A pointer to a valid struct sockaddr,
372specified through ``IS`` or ``iS``, can be passed to this format specifier.
373
374The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
375(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,
376flowinfo a ``/`` and scope a ``%``, each followed by the actual value.
377
378In case of an IPv6 address the compressed IPv6 address as described by
379https://tools.ietf.org/html/rfc5952 is being used if the additional
380specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in
381case of additional specifiers ``p``, ``f`` or ``s`` as suggested by
382https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
383
384In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``
385specifiers can be used as well and are ignored in case of an IPv6
386address.
387
388Passed by reference.
389
390Further examples::
391
392 %pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789
393 %pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890
394 %pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
395
396UUID/GUID addresses
397-------------------
398
399::
400
401 %pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
402 %pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
403 %pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
404 %pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
405
406For printing 16-byte UUID/GUIDs addresses. The additional ``l``, ``L``,
407``b`` and ``B`` specifiers are used to specify a little endian order in
408lower (l) or upper case (L) hex notation - and big endian order in lower (b)
409or upper case (B) hex notation.
410
411Where no additional specifiers are used the default big endian
412order with lower case hex notation will be printed.
413
414Passed by reference.
415
416dentry names
417------------
418
419::
420
421 %pd{,2,3,4}
422 %pD{,2,3,4}
423
424For printing dentry name; if we race with :c:func:`d_move`, the name might
425be a mix of old and new ones, but it won't oops. %pd dentry is a safer
426equivalent of %s dentry->d_name.name we used to use, %pd<n> prints ``n``
427last components. %pD does the same thing for struct file.
428
429Passed by reference.
430
431block_device names
432------------------
433
434::
435
436 %pg sda, sda1 or loop0p1
437
438For printing name of block_device pointers.
439
440struct va_format
441----------------
442
443::
444
445 %pV
446
447For printing struct va_format structures. These contain a format string
448and va_list as follows::
449
450 struct va_format {
451 const char *fmt;
452 va_list *va;
453 };
454
455Implements a "recursive vsnprintf".
456
457Do not use this feature without some mechanism to verify the
458correctness of the format string and va_list arguments.
459
460Passed by reference.
461
462Device tree nodes
463-----------------
464
465::
466
467 %pOF[fnpPcCF]
468
469
470For printing device tree node structures. Default behaviour is
471equivalent to %pOFf.
472
473 - f - device node full_name
474 - n - device node name
475 - p - device node phandle
476 - P - device node path spec (name + @unit)
477 - F - device node flags
478 - c - major compatible string
479 - C - full compatible string
480
481The separator when using multiple arguments is ':'
482
483Examples::
484
485 %pOF /foo/bar@0 - Node full name
486 %pOFf /foo/bar@0 - Same as above
487 %pOFfp /foo/bar@0:10 - Node full name + phandle
488 %pOFfcF /foo/bar@0:foo,device:--P- - Node full name +
489 major compatible string +
490 node flags
491 D - dynamic
492 d - detached
493 P - Populated
494 B - Populated bus
495
496Passed by reference.
497
498Fwnode handles
499--------------
500
501::
502
503 %pfw[fP]
504
505For printing information on fwnode handles. The default is to print the full
506node name, including the path. The modifiers are functionally equivalent to
507%pOF above.
508
509 - f - full name of the node, including the path
510 - P - the name of the node including an address (if there is one)
511
512Examples (ACPI)::
513
514 %pfwf \_SB.PCI0.CIO2.port@1.endpoint@0 - Full node name
515 %pfwP endpoint@0 - Node name
516
517Examples (OF)::
518
519 %pfwf /ocp@68000000/i2c@48072000/camera@10/port/endpoint - Full name
520 %pfwP endpoint - Node name
521
522Time and date
523-------------
524
525::
526
527 %pt[RT] YYYY-mm-ddTHH:MM:SS
528 %pt[RT]s YYYY-mm-dd HH:MM:SS
529 %pt[RT]d YYYY-mm-dd
530 %pt[RT]t HH:MM:SS
531 %pt[RT][dt][r][s]
532
533For printing date and time as represented by::
534
535 R struct rtc_time structure
536 T time64_t type
537
538in human readable format.
539
540By default year will be incremented by 1900 and month by 1.
541Use %pt[RT]r (raw) to suppress this behaviour.
542
543The %pt[RT]s (space) will override ISO 8601 separator by using ' ' (space)
544instead of 'T' (Capital T) between date and time. It won't have any effect
545when date or time is omitted.
546
547Passed by reference.
548
549struct clk
550----------
551
552::
553
554 %pC pll1
555 %pCn pll1
556
557For printing struct clk structures. %pC and %pCn print the name of the clock
558(Common Clock Framework) or a unique 32-bit ID (legacy clock framework).
559
560Passed by reference.
561
562bitmap and its derivatives such as cpumask and nodemask
563-------------------------------------------------------
564
565::
566
567 %*pb 0779
568 %*pbl 0,3-6,8-10
569
570For printing bitmap and its derivatives such as cpumask and nodemask,
571%*pb outputs the bitmap with field width as the number of bits and %*pbl
572output the bitmap as range list with field width as the number of bits.
573
574The field width is passed by value, the bitmap is passed by reference.
575Helper macros cpumask_pr_args() and nodemask_pr_args() are available to ease
576printing cpumask and nodemask.
577
578Flags bitfields such as page flags, gfp_flags
579---------------------------------------------
580
581::
582
583 %pGp 0x17ffffc0002036(referenced|uptodate|lru|active|private|node=0|zone=2|lastcpupid=0x1fffff)
584 %pGg GFP_USER|GFP_DMA32|GFP_NOWARN
585 %pGv read|exec|mayread|maywrite|mayexec|denywrite
586
587For printing flags bitfields as a collection of symbolic constants that
588would construct the value. The type of flags is given by the third
589character. Currently supported are [p]age flags, [v]ma_flags (both
590expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag
591names and print order depends on the particular type.
592
593Note that this format should not be used directly in the
594:c:func:`TP_printk()` part of a tracepoint. Instead, use the show_*_flags()
595functions from <trace/events/mmflags.h>.
596
597Passed by reference.
598
599Network device features
600-----------------------
601
602::
603
604 %pNF 0x000000000000c000
605
606For printing netdev_features_t.
607
608Passed by reference.
609
610V4L2 and DRM FourCC code (pixel format)
611---------------------------------------
612
613::
614
615 %p4cc
616
617Print a FourCC code used by V4L2 or DRM, including format endianness and
618its numerical value as hexadecimal.
619
620Passed by reference.
621
622Examples::
623
624 %p4cc BG12 little-endian (0x32314742)
625 %p4cc Y10 little-endian (0x20303159)
626 %p4cc NV12 big-endian (0xb231564e)
627
628Rust
629----
630
631::
632
633 %pA
634
635Only intended to be used from Rust code to format ``core::fmt::Arguments``.
636Do *not* use it from C.
637
638Thanks
639======
640
641If you add other %p extensions, please extend <lib/test_printf.c> with
642one or more test cases, if at all feasible.
643
644Thank 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 int %d or %x
17 unsigned int %u or %x
18 long %ld or %lx
19 unsigned long %lu or %lx
20 long long %lld or %llx
21 unsigned long long %llu or %llx
22 size_t %zu or %zx
23 ssize_t %zd or %zx
24 s32 %d or %x
25 u32 %u or %x
26 s64 %lld or %llx
27 u64 %llu or %llx
28
29
30If <type> is dependent on a config option for its size (e.g., sector_t,
31blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
32format specifier of its largest possible type and explicitly cast to it.
33
34Example::
35
36 printk("test: sector number/total blocks: %llu/%llu\n",
37 (unsigned long long)sector, (unsigned long long)blockcount);
38
39Reminder: sizeof() returns type size_t.
40
41The kernel's printf does not support %n. Floating point formats (%e, %f,
42%g, %a) are also not recognized, for obvious reasons. Use of any
43unsupported specifier or length qualifier results in a WARN and early
44return from vsnprintf().
45
46Pointer types
47=============
48
49A raw pointer value may be printed with %p which will hash the address
50before printing. The kernel also supports extended specifiers for printing
51pointers of different types.
52
53Plain Pointers
54--------------
55
56::
57
58 %p abcdef12 or 00000000abcdef12
59
60Pointers printed without a specifier extension (i.e unadorned %p) are
61hashed to prevent leaking information about the kernel memory layout. This
62has the added benefit of providing a unique identifier. On 64-bit machines
63the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
64gathers enough entropy. If you *really* want the address see %px below.
65
66Symbols/Function Pointers
67-------------------------
68
69::
70
71 %pS versatile_init+0x0/0x110
72 %ps versatile_init
73 %pF versatile_init+0x0/0x110
74 %pf versatile_init
75 %pSR versatile_init+0x9/0x110
76 (with __builtin_extract_return_addr() translation)
77 %pB prev_fn_of_versatile_init+0x88/0x88
78
79
80The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic
81format. They result in the symbol name with (S) or without (s)
82offsets. If KALLSYMS are disabled then the symbol address is printed instead.
83
84Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``)
85and thus deprecated. We have ``F`` and ``f`` because on ia64, ppc64 and
86parisc64 function pointers are indirect and, in fact, are function
87descriptors, which require additional dereferencing before we can lookup
88the symbol. As of now, ``S`` and ``s`` perform dereferencing on those
89platforms (when needed), so ``F`` and ``f`` exist for compatibility
90reasons only.
91
92The ``B`` specifier results in the symbol name with offsets and should be
93used when printing stack backtraces. The specifier takes into
94consideration the effect of compiler optimisations which may occur
95when tail-calls are used and marked with the noreturn GCC attribute.
96
97Kernel Pointers
98---------------
99
100::
101
102 %pK 01234567 or 0123456789abcdef
103
104For printing kernel pointers which should be hidden from unprivileged
105users. The behaviour of %pK depends on the kptr_restrict sysctl - see
106Documentation/sysctl/kernel.txt for more details.
107
108Unmodified Addresses
109--------------------
110
111::
112
113 %px 01234567 or 0123456789abcdef
114
115For printing pointers when you *really* want to print the address. Please
116consider whether or not you are leaking sensitive information about the
117kernel memory layout before printing pointers with %px. %px is functionally
118equivalent to %lx (or %lu). %px is preferred because it is more uniquely
119grep'able. If in the future we need to modify the way the kernel handles
120printing pointers we will be better equipped to find the call sites.
121
122Struct Resources
123----------------
124
125::
126
127 %pr [mem 0x60000000-0x6fffffff flags 0x2200] or
128 [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
129 %pR [mem 0x60000000-0x6fffffff pref] or
130 [mem 0x0000000060000000-0x000000006fffffff pref]
131
132For printing struct resources. The ``R`` and ``r`` specifiers result in a
133printed resource with (R) or without (r) a decoded flags member.
134
135Passed by reference.
136
137Physical address types phys_addr_t
138----------------------------------
139
140::
141
142 %pa[p] 0x01234567 or 0x0123456789abcdef
143
144For printing a phys_addr_t type (and its derivatives, such as
145resource_size_t) which can vary based on build options, regardless of the
146width of the CPU data path.
147
148Passed by reference.
149
150DMA address types dma_addr_t
151----------------------------
152
153::
154
155 %pad 0x01234567 or 0x0123456789abcdef
156
157For printing a dma_addr_t type which can vary based on build options,
158regardless of the width of the CPU data path.
159
160Passed by reference.
161
162Raw buffer as an escaped string
163-------------------------------
164
165::
166
167 %*pE[achnops]
168
169For printing raw buffer as an escaped string. For the following buffer::
170
171 1b 62 20 5c 43 07 22 90 0d 5d
172
173A few examples show how the conversion would be done (excluding surrounding
174quotes)::
175
176 %*pE "\eb \C\a"\220\r]"
177 %*pEhp "\x1bb \C\x07"\x90\x0d]"
178 %*pEa "\e\142\040\\\103\a\042\220\r\135"
179
180The conversion rules are applied according to an optional combination
181of flags (see :c:func:`string_escape_mem` kernel documentation for the
182details):
183
184 - a - ESCAPE_ANY
185 - c - ESCAPE_SPECIAL
186 - h - ESCAPE_HEX
187 - n - ESCAPE_NULL
188 - o - ESCAPE_OCTAL
189 - p - ESCAPE_NP
190 - s - ESCAPE_SPACE
191
192By default ESCAPE_ANY_NP is used.
193
194ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
195printing SSIDs.
196
197If field width is omitted then 1 byte only will be escaped.
198
199Raw buffer as a hex string
200--------------------------
201
202::
203
204 %*ph 00 01 02 ... 3f
205 %*phC 00:01:02: ... :3f
206 %*phD 00-01-02- ... -3f
207 %*phN 000102 ... 3f
208
209For printing small buffers (up to 64 bytes long) as a hex string with a
210certain separator. For larger buffers consider using
211:c:func:`print_hex_dump`.
212
213MAC/FDDI addresses
214------------------
215
216::
217
218 %pM 00:01:02:03:04:05
219 %pMR 05:04:03:02:01:00
220 %pMF 00-01-02-03-04-05
221 %pm 000102030405
222 %pmR 050403020100
223
224For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m``
225specifiers result in a printed address with (M) or without (m) byte
226separators. The default byte separator is the colon (:).
227
228Where FDDI addresses are concerned the ``F`` specifier can be used after
229the ``M`` specifier to use dash (-) separators instead of the default
230separator.
231
232For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
233specifier to use reversed byte order suitable for visual interpretation
234of Bluetooth addresses which are in the little endian order.
235
236Passed by reference.
237
238IPv4 addresses
239--------------
240
241::
242
243 %pI4 1.2.3.4
244 %pi4 001.002.003.004
245 %p[Ii]4[hnbl]
246
247For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4``
248specifiers result in a printed address with (i4) or without (I4) leading
249zeros.
250
251The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify
252host, network, big or little endian order addresses respectively. Where
253no specifier is provided the default network/big endian order is used.
254
255Passed by reference.
256
257IPv6 addresses
258--------------
259
260::
261
262 %pI6 0001:0002:0003:0004:0005:0006:0007:0008
263 %pi6 00010002000300040005000600070008
264 %pI6c 1:2:3:4:5:6:7:8
265
266For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6``
267specifiers result in a printed address with (I6) or without (i6)
268colon-separators. Leading zeros are always used.
269
270The additional ``c`` specifier can be used with the ``I`` specifier to
271print a compressed IPv6 address as described by
272http://tools.ietf.org/html/rfc5952
273
274Passed by reference.
275
276IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
277---------------------------------------------------------
278
279::
280
281 %pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008
282 %piS 001.002.003.004 or 00010002000300040005000600070008
283 %pISc 1.2.3.4 or 1:2:3:4:5:6:7:8
284 %pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345
285 %p[Ii]S[pfschnbl]
286
287For printing an IP address without the need to distinguish whether it's of
288type AF_INET or AF_INET6. A pointer to a valid struct sockaddr,
289specified through ``IS`` or ``iS``, can be passed to this format specifier.
290
291The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
292(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,
293flowinfo a ``/`` and scope a ``%``, each followed by the actual value.
294
295In case of an IPv6 address the compressed IPv6 address as described by
296http://tools.ietf.org/html/rfc5952 is being used if the additional
297specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in
298case of additional specifiers ``p``, ``f`` or ``s`` as suggested by
299https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
300
301In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``
302specifiers can be used as well and are ignored in case of an IPv6
303address.
304
305Passed by reference.
306
307Further examples::
308
309 %pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789
310 %pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890
311 %pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
312
313UUID/GUID addresses
314-------------------
315
316::
317
318 %pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
319 %pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
320 %pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
321 %pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
322
323For printing 16-byte UUID/GUIDs addresses. The additional ``l``, ``L``,
324``b`` and ``B`` specifiers are used to specify a little endian order in
325lower (l) or upper case (L) hex notation - and big endian order in lower (b)
326or upper case (B) hex notation.
327
328Where no additional specifiers are used the default big endian
329order with lower case hex notation will be printed.
330
331Passed by reference.
332
333dentry names
334------------
335
336::
337
338 %pd{,2,3,4}
339 %pD{,2,3,4}
340
341For printing dentry name; if we race with :c:func:`d_move`, the name might
342be a mix of old and new ones, but it won't oops. %pd dentry is a safer
343equivalent of %s dentry->d_name.name we used to use, %pd<n> prints ``n``
344last components. %pD does the same thing for struct file.
345
346Passed by reference.
347
348block_device names
349------------------
350
351::
352
353 %pg sda, sda1 or loop0p1
354
355For printing name of block_device pointers.
356
357struct va_format
358----------------
359
360::
361
362 %pV
363
364For printing struct va_format structures. These contain a format string
365and va_list as follows::
366
367 struct va_format {
368 const char *fmt;
369 va_list *va;
370 };
371
372Implements a "recursive vsnprintf".
373
374Do not use this feature without some mechanism to verify the
375correctness of the format string and va_list arguments.
376
377Passed by reference.
378
379kobjects
380--------
381
382::
383
384 %pOF[fnpPcCF]
385
386
387For printing kobject based structs (device nodes). Default behaviour is
388equivalent to %pOFf.
389
390 - f - device node full_name
391 - n - device node name
392 - p - device node phandle
393 - P - device node path spec (name + @unit)
394 - F - device node flags
395 - c - major compatible string
396 - C - full compatible string
397
398The separator when using multiple arguments is ':'
399
400Examples::
401
402 %pOF /foo/bar@0 - Node full name
403 %pOFf /foo/bar@0 - Same as above
404 %pOFfp /foo/bar@0:10 - Node full name + phandle
405 %pOFfcF /foo/bar@0:foo,device:--P- - Node full name +
406 major compatible string +
407 node flags
408 D - dynamic
409 d - detached
410 P - Populated
411 B - Populated bus
412
413Passed by reference.
414
415struct clk
416----------
417
418::
419
420 %pC pll1
421 %pCn pll1
422 %pCr 1560000000
423
424For printing struct clk structures. %pC and %pCn print the name
425(Common Clock Framework) or address (legacy clock framework) of the
426structure; %pCr prints the current clock rate.
427
428Passed by reference.
429
430bitmap and its derivatives such as cpumask and nodemask
431-------------------------------------------------------
432
433::
434
435 %*pb 0779
436 %*pbl 0,3-6,8-10
437
438For printing bitmap and its derivatives such as cpumask and nodemask,
439%*pb outputs the bitmap with field width as the number of bits and %*pbl
440output the bitmap as range list with field width as the number of bits.
441
442Passed by reference.
443
444Flags bitfields such as page flags, gfp_flags
445---------------------------------------------
446
447::
448
449 %pGp referenced|uptodate|lru|active|private
450 %pGg GFP_USER|GFP_DMA32|GFP_NOWARN
451 %pGv read|exec|mayread|maywrite|mayexec|denywrite
452
453For printing flags bitfields as a collection of symbolic constants that
454would construct the value. The type of flags is given by the third
455character. Currently supported are [p]age flags, [v]ma_flags (both
456expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag
457names and print order depends on the particular type.
458
459Note that this format should not be used directly in the
460:c:func:`TP_printk()` part of a tracepoint. Instead, use the show_*_flags()
461functions from <trace/events/mmflags.h>.
462
463Passed by reference.
464
465Network device features
466-----------------------
467
468::
469
470 %pNF 0x000000000000c000
471
472For printing netdev_features_t.
473
474Passed by reference.
475
476Thanks
477======
478
479If you add other %p extensions, please extend <lib/test_printf.c> with
480one or more test cases, if at all feasible.
481
482Thank you for your cooperation and attention.