About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / printk-formats.txt




Custom Search

Based on kernel version 3.19. Page generated on 2015-02-13 21:22 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	
12	Raw pointer value SHOULD be printed with %p. The kernel supports
13	the following extended format specifiers for pointer types:
14	
15	Symbols/Function Pointers:
16	
17		%pF	versatile_init+0x0/0x110
18		%pf	versatile_init
19		%pS	versatile_init+0x0/0x110
20		%pSR	versatile_init+0x9/0x110
21			(with __builtin_extract_return_addr() translation)
22		%ps	versatile_init
23		%pB	prev_fn_of_versatile_init+0x88/0x88
24	
25		For printing symbols and function pointers. The 'S' and 's' specifiers
26		result in the symbol name with ('S') or without ('s') offsets. Where
27		this is used on a kernel without KALLSYMS - the symbol address is
28		printed instead.
29	
30		The 'B' specifier results in the symbol name with offsets and should be
31		used when printing stack backtraces. The specifier takes into
32		consideration the effect of compiler optimisations which may occur
33		when tail-call's are used and marked with the noreturn GCC attribute.
34	
35		On ia64, ppc64 and parisc64 architectures function pointers are
36		actually function descriptors which must first be resolved. The 'F' and
37		'f' specifiers perform this resolution and then provide the same
38		functionality as the 'S' and 's' specifiers.
39	
40	Kernel Pointers:
41	
42		%pK	0x01234567 or 0x0123456789abcdef
43	
44		For printing kernel pointers which should be hidden from unprivileged
45		users. The behaviour of %pK depends on the kptr_restrict sysctl - see
46		Documentation/sysctl/kernel.txt for more details.
47	
48	Struct Resources:
49	
50		%pr	[mem 0x60000000-0x6fffffff flags 0x2200] or
51			[mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
52		%pR	[mem 0x60000000-0x6fffffff pref] or
53			[mem 0x0000000060000000-0x000000006fffffff pref]
54	
55		For printing struct resources. The 'R' and 'r' specifiers result in a
56		printed resource with ('R') or without ('r') a decoded flags member.
57	
58	Physical addresses types phys_addr_t:
59	
60		%pa[p]	0x01234567 or 0x0123456789abcdef
61	
62		For printing a phys_addr_t type (and its derivatives, such as
63		resource_size_t) which can vary based on build options, regardless of
64		the width of the CPU data path. Passed by reference.
65	
66	DMA addresses types dma_addr_t:
67	
68		%pad	0x01234567 or 0x0123456789abcdef
69	
70		For printing a dma_addr_t type which can vary based on build options,
71		regardless of the width of the CPU data path. Passed by reference.
72	
73	Raw buffer as an escaped string:
74	
75		%*pE[achnops]
76	
77		For printing raw buffer as an escaped string. For the following buffer
78	
79			1b 62 20 5c 43 07 22 90 0d 5d
80	
81		few examples show how the conversion would be done (the result string
82		without surrounding quotes):
83	
84			%*pE		"\eb \C\a"\220\r]"
85			%*pEhp		"\x1bb \C\x07"\x90\x0d]"
86			%*pEa		"\e\142\040\\\103\a\042\220\r\135"
87	
88		The conversion rules are applied according to an optional combination
89		of flags (see string_escape_mem() kernel documentation for the
90		details):
91			a - ESCAPE_ANY
92			c - ESCAPE_SPECIAL
93			h - ESCAPE_HEX
94			n - ESCAPE_NULL
95			o - ESCAPE_OCTAL
96			p - ESCAPE_NP
97			s - ESCAPE_SPACE
98		By default ESCAPE_ANY_NP is used.
99	
100		ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
101		printing SSIDs.
102	
103		If field width is omitted the 1 byte only will be escaped.
104	
105	Raw buffer as a hex string:
106		%*ph	00 01 02  ...  3f
107		%*phC	00:01:02: ... :3f
108		%*phD	00-01-02- ... -3f
109		%*phN	000102 ... 3f
110	
111		For printing a small buffers (up to 64 bytes long) as a hex string with
112		certain separator. For the larger buffers consider to use
113		print_hex_dump().
114	
115	MAC/FDDI addresses:
116	
117		%pM	00:01:02:03:04:05
118		%pMR	05:04:03:02:01:00
119		%pMF	00-01-02-03-04-05
120		%pm	000102030405
121		%pmR	050403020100
122	
123		For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
124		specifiers result in a printed address with ('M') or without ('m') byte
125		separators. The default byte separator is the colon (':').
126	
127		Where FDDI addresses are concerned the 'F' specifier can be used after
128		the 'M' specifier to use dash ('-') separators instead of the default
129		separator.
130	
131		For Bluetooth addresses the 'R' specifier shall be used after the 'M'
132		specifier to use reversed byte order suitable for visual interpretation
133		of Bluetooth addresses which are in the little endian order.
134	
135	IPv4 addresses:
136	
137		%pI4	1.2.3.4
138		%pi4	001.002.003.004
139		%p[Ii]4[hnbl]
140	
141		For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
142		specifiers result in a printed address with ('i4') or without ('I4')
143		leading zeros.
144	
145		The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
146		host, network, big or little endian order addresses respectively. Where
147		no specifier is provided the default network/big endian order is used.
148	
149	IPv6 addresses:
150	
151		%pI6	0001:0002:0003:0004:0005:0006:0007:0008
152		%pi6	00010002000300040005000600070008
153		%pI6c	1:2:3:4:5:6:7:8
154	
155		For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
156		specifiers result in a printed address with ('I6') or without ('i6')
157		colon-separators. Leading zeros are always used.
158	
159		The additional 'c' specifier can be used with the 'I' specifier to
160		print a compressed IPv6 address as described by
161		http://tools.ietf.org/html/rfc5952
162	
163	IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
164	
165		%pIS	1.2.3.4		or 0001:0002:0003:0004:0005:0006:0007:0008
166		%piS	001.002.003.004	or 00010002000300040005000600070008
167		%pISc	1.2.3.4		or 1:2:3:4:5:6:7:8
168		%pISpc	1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345
169		%p[Ii]S[pfschnbl]
170	
171		For printing an IP address without the need to distinguish whether it's
172		of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',
173		specified through 'IS' or 'iS', can be passed to this format specifier.
174	
175		The additional 'p', 'f', and 's' specifiers are used to specify port
176		(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,
177		flowinfo a '/' and scope a '%', each followed by the actual value.
178	
179		In case of an IPv6 address the compressed IPv6 address as described by
180		http://tools.ietf.org/html/rfc5952 is being used if the additional
181		specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in
182		case of additional specifiers 'p', 'f' or 's' as suggested by
183		https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
184	
185		In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'
186		specifiers can be used as well and are ignored in case of an IPv6
187		address.
188	
189		Further examples:
190	
191		%pISfc		1.2.3.4		or [1:2:3:4:5:6:7:8]/123456789
192		%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890
193		%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789
194	
195	UUID/GUID addresses:
196	
197		%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
198		%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
199		%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
200		%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
201	
202		For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
203		'b' and 'B' specifiers are used to specify a little endian order in
204		lower ('l') or upper case ('L') hex characters - and big endian order
205		in lower ('b') or upper case ('B') hex characters.
206	
207		Where no additional specifiers are used the default little endian
208		order with lower case hex characters will be printed.
209	
210	dentry names:
211		%pd{,2,3,4}
212		%pD{,2,3,4}
213	
214		For printing dentry name; if we race with d_move(), the name might be
215		a mix of old and new ones, but it won't oops.  %pd dentry is a safer
216		equivalent of %s dentry->d_name.name we used to use, %pd<n> prints
217		n last components.  %pD does the same thing for struct file.
218	
219	struct va_format:
220	
221		%pV
222	
223		For printing struct va_format structures. These contain a format string
224		and va_list as follows:
225	
226		struct va_format {
227			const char *fmt;
228			va_list *va;
229		};
230	
231		Do not use this feature without some mechanism to verify the
232		correctness of the format string and va_list arguments.
233	
234	u64 SHOULD be printed with %llu/%llx:
235	
236		printk("%llu", u64_var);
237	
238	s64 SHOULD be printed with %lld/%llx:
239	
240		printk("%lld", s64_var);
241	
242	If <type> is dependent on a config option for its size (e.g., sector_t,
243	blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
244	format specifier of its largest possible type and explicitly cast to it.
245	Example:
246	
247		printk("test: sector number/total blocks: %llu/%llu\n",
248			(unsigned long long)sector, (unsigned long long)blockcount);
249	
250	Reminder: sizeof() result is of type size_t.
251	
252	Thank you for your cooperation and attention.
253	
254	
255	By Randy Dunlap <rdunlap@infradead.org> and
256	Andrew Murray <amurray@mpc-data.co.uk>
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.