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Documentation / printk-formats.txt




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Based on kernel version 4.7.2. Page generated on 2016-08-22 22:47 EST.

1	If variable is of Type,		use printk format specifier:
2	---------------------------------------------------------
3			int			%d or %x
4			unsigned int		%u or %x
5			long			%ld or %lx
6			unsigned long		%lu or %lx
7			long long		%lld or %llx
8			unsigned long long	%llu or %llx
9			size_t			%zu or %zx
10			ssize_t			%zd or %zx
11			s32			%d or %x
12			u32			%u or %x
13			s64			%lld or %llx
14			u64			%llu or %llx
15	
16	If <type> is dependent on a config option for its size (e.g., sector_t,
17	blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
18	format specifier of its largest possible type and explicitly cast to it.
19	Example:
20	
21		printk("test: sector number/total blocks: %llu/%llu\n",
22			(unsigned long long)sector, (unsigned long long)blockcount);
23	
24	Reminder: sizeof() result is of type size_t.
25	
26	The kernel's printf does not support %n. For obvious reasons, floating
27	point formats (%e, %f, %g, %a) are also not recognized. Use of any
28	unsupported specifier or length qualifier results in a WARN and early
29	return from vsnprintf.
30	
31	Raw pointer value SHOULD be printed with %p. The kernel supports
32	the following extended format specifiers for pointer types:
33	
34	Symbols/Function Pointers:
35	
36		%pF	versatile_init+0x0/0x110
37		%pf	versatile_init
38		%pS	versatile_init+0x0/0x110
39		%pSR	versatile_init+0x9/0x110
40			(with __builtin_extract_return_addr() translation)
41		%ps	versatile_init
42		%pB	prev_fn_of_versatile_init+0x88/0x88
43	
44		For printing symbols and function pointers. The 'S' and 's' specifiers
45		result in the symbol name with ('S') or without ('s') offsets. Where
46		this is used on a kernel without KALLSYMS - the symbol address is
47		printed instead.
48	
49		The 'B' specifier results in the symbol name with offsets and should be
50		used when printing stack backtraces. The specifier takes into
51		consideration the effect of compiler optimisations which may occur
52		when tail-call's are used and marked with the noreturn GCC attribute.
53	
54		On ia64, ppc64 and parisc64 architectures function pointers are
55		actually function descriptors which must first be resolved. The 'F' and
56		'f' specifiers perform this resolution and then provide the same
57		functionality as the 'S' and 's' specifiers.
58	
59	Kernel Pointers:
60	
61		%pK	0x01234567 or 0x0123456789abcdef
62	
63		For printing kernel pointers which should be hidden from unprivileged
64		users. The behaviour of %pK depends on the kptr_restrict sysctl - see
65		Documentation/sysctl/kernel.txt for more details.
66	
67	Struct Resources:
68	
69		%pr	[mem 0x60000000-0x6fffffff flags 0x2200] or
70			[mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
71		%pR	[mem 0x60000000-0x6fffffff pref] or
72			[mem 0x0000000060000000-0x000000006fffffff pref]
73	
74		For printing struct resources. The 'R' and 'r' specifiers result in a
75		printed resource with ('R') or without ('r') a decoded flags member.
76		Passed by reference.
77	
78	Physical addresses types phys_addr_t:
79	
80		%pa[p]	0x01234567 or 0x0123456789abcdef
81	
82		For printing a phys_addr_t type (and its derivatives, such as
83		resource_size_t) which can vary based on build options, regardless of
84		the width of the CPU data path. Passed by reference.
85	
86	DMA addresses types dma_addr_t:
87	
88		%pad	0x01234567 or 0x0123456789abcdef
89	
90		For printing a dma_addr_t type which can vary based on build options,
91		regardless of the width of the CPU data path. Passed by reference.
92	
93	Raw buffer as an escaped string:
94	
95		%*pE[achnops]
96	
97		For printing raw buffer as an escaped string. For the following buffer
98	
99			1b 62 20 5c 43 07 22 90 0d 5d
100	
101		few examples show how the conversion would be done (the result string
102		without surrounding quotes):
103	
104			%*pE		"\eb \C\a"\220\r]"
105			%*pEhp		"\x1bb \C\x07"\x90\x0d]"
106			%*pEa		"\e\142\040\\\103\a\042\220\r\135"
107	
108		The conversion rules are applied according to an optional combination
109		of flags (see string_escape_mem() kernel documentation for the
110		details):
111			a - ESCAPE_ANY
112			c - ESCAPE_SPECIAL
113			h - ESCAPE_HEX
114			n - ESCAPE_NULL
115			o - ESCAPE_OCTAL
116			p - ESCAPE_NP
117			s - ESCAPE_SPACE
118		By default ESCAPE_ANY_NP is used.
119	
120		ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
121		printing SSIDs.
122	
123		If field width is omitted the 1 byte only will be escaped.
124	
125	Raw buffer as a hex string:
126	
127		%*ph	00 01 02  ...  3f
128		%*phC	00:01:02: ... :3f
129		%*phD	00-01-02- ... -3f
130		%*phN	000102 ... 3f
131	
132		For printing a small buffers (up to 64 bytes long) as a hex string with
133		certain separator. For the larger buffers consider to use
134		print_hex_dump().
135	
136	MAC/FDDI addresses:
137	
138		%pM	00:01:02:03:04:05
139		%pMR	05:04:03:02:01:00
140		%pMF	00-01-02-03-04-05
141		%pm	000102030405
142		%pmR	050403020100
143	
144		For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
145		specifiers result in a printed address with ('M') or without ('m') byte
146		separators. The default byte separator is the colon (':').
147	
148		Where FDDI addresses are concerned the 'F' specifier can be used after
149		the 'M' specifier to use dash ('-') separators instead of the default
150		separator.
151	
152		For Bluetooth addresses the 'R' specifier shall be used after the 'M'
153		specifier to use reversed byte order suitable for visual interpretation
154		of Bluetooth addresses which are in the little endian order.
155	
156		Passed by reference.
157	
158	IPv4 addresses:
159	
160		%pI4	1.2.3.4
161		%pi4	001.002.003.004
162		%p[Ii]4[hnbl]
163	
164		For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
165		specifiers result in a printed address with ('i4') or without ('I4')
166		leading zeros.
167	
168		The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
169		host, network, big or little endian order addresses respectively. Where
170		no specifier is provided the default network/big endian order is used.
171	
172		Passed by reference.
173	
174	IPv6 addresses:
175	
176		%pI6	0001:0002:0003:0004:0005:0006:0007:0008
177		%pi6	00010002000300040005000600070008
178		%pI6c	1:2:3:4:5:6:7:8
179	
180		For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
181		specifiers result in a printed address with ('I6') or without ('i6')
182		colon-separators. Leading zeros are always used.
183	
184		The additional 'c' specifier can be used with the 'I' specifier to
185		print a compressed IPv6 address as described by
186		http://tools.ietf.org/html/rfc5952
187	
188		Passed by reference.
189	
190	IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
191	
192		%pIS	1.2.3.4		or 0001:0002:0003:0004:0005:0006:0007:0008
193		%piS	001.002.003.004	or 00010002000300040005000600070008
194		%pISc	1.2.3.4		or 1:2:3:4:5:6:7:8
195		%pISpc	1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345
196		%p[Ii]S[pfschnbl]
197	
198		For printing an IP address without the need to distinguish whether it's
199		of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',
200		specified through 'IS' or 'iS', can be passed to this format specifier.
201	
202		The additional 'p', 'f', and 's' specifiers are used to specify port
203		(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,
204		flowinfo a '/' and scope a '%', each followed by the actual value.
205	
206		In case of an IPv6 address the compressed IPv6 address as described by
207		http://tools.ietf.org/html/rfc5952 is being used if the additional
208		specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in
209		case of additional specifiers 'p', 'f' or 's' as suggested by
210		https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
211	
212		In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'
213		specifiers can be used as well and are ignored in case of an IPv6
214		address.
215	
216		Passed by reference.
217	
218		Further examples:
219	
220		%pISfc		1.2.3.4		or [1:2:3:4:5:6:7:8]/123456789
221		%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890
222		%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789
223	
224	UUID/GUID addresses:
225	
226		%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
227		%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
228		%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
229		%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
230	
231		For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
232		'b' and 'B' specifiers are used to specify a little endian order in
233		lower ('l') or upper case ('L') hex characters - and big endian order
234		in lower ('b') or upper case ('B') hex characters.
235	
236		Where no additional specifiers are used the default big endian
237		order with lower case hex characters will be printed.
238	
239		Passed by reference.
240	
241	dentry names:
242	
243		%pd{,2,3,4}
244		%pD{,2,3,4}
245	
246		For printing dentry name; if we race with d_move(), the name might be
247		a mix of old and new ones, but it won't oops.  %pd dentry is a safer
248		equivalent of %s dentry->d_name.name we used to use, %pd<n> prints
249		n last components.  %pD does the same thing for struct file.
250	
251		Passed by reference.
252	
253	block_device names:
254	
255		%pg	sda, sda1 or loop0p1
256	
257		For printing name of block_device pointers.
258	
259	struct va_format:
260	
261		%pV
262	
263		For printing struct va_format structures. These contain a format string
264		and va_list as follows:
265	
266		struct va_format {
267			const char *fmt;
268			va_list *va;
269		};
270	
271		Implements a "recursive vsnprintf".
272	
273		Do not use this feature without some mechanism to verify the
274		correctness of the format string and va_list arguments.
275	
276		Passed by reference.
277	
278	struct clk:
279	
280		%pC	pll1
281		%pCn	pll1
282		%pCr	1560000000
283	
284		For printing struct clk structures. '%pC' and '%pCn' print the name
285		(Common Clock Framework) or address (legacy clock framework) of the
286		structure; '%pCr' prints the current clock rate.
287	
288		Passed by reference.
289	
290	bitmap and its derivatives such as cpumask and nodemask:
291	
292		%*pb	0779
293		%*pbl	0,3-6,8-10
294	
295		For printing bitmap and its derivatives such as cpumask and nodemask,
296		%*pb output the bitmap with field width as the number of bits and %*pbl
297		output the bitmap as range list with field width as the number of bits.
298	
299		Passed by reference.
300	
301	Flags bitfields such as page flags, gfp_flags:
302	
303		%pGp	referenced|uptodate|lru|active|private
304		%pGg	GFP_USER|GFP_DMA32|GFP_NOWARN
305		%pGv	read|exec|mayread|maywrite|mayexec|denywrite
306	
307		For printing flags bitfields as a collection of symbolic constants that
308		would construct the value. The type of flags is given by the third
309		character. Currently supported are [p]age flags, [v]ma_flags (both
310		expect unsigned long *) and [g]fp_flags (expects gfp_t *). The flag
311		names and print order depends on the particular	type.
312	
313		Note that this format should not be used directly in TP_printk() part
314		of a tracepoint. Instead, use the show_*_flags() functions from
315		<trace/events/mmflags.h>.
316	
317		Passed by reference.
318	
319	Network device features:
320	
321		%pNF	0x000000000000c000
322	
323		For printing netdev_features_t.
324	
325		Passed by reference.
326	
327	If you add other %p extensions, please extend lib/test_printf.c with
328	one or more test cases, if at all feasible.
329	
330	
331	Thank you for your cooperation and attention.
332	
333	
334	By Randy Dunlap <rdunlap@infradead.org> and
335	Andrew Murray <amurray@mpc-data.co.uk>
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