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Documentation / printk-formats.txt




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Based on kernel version 3.9. Page generated on 2013-05-02 23:12 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		%ps	versatile_init
21		%pB	prev_fn_of_versatile_init+0x88/0x88
22	
23		For printing symbols and function pointers. The 'S' and 's' specifiers
24		result in the symbol name with ('S') or without ('s') offsets. Where
25		this is used on a kernel without KALLSYMS - the symbol address is
26		printed instead.
27	
28		The 'B' specifier results in the symbol name with offsets and should be
29		used when printing stack backtraces. The specifier takes into
30		consideration the effect of compiler optimisations which may occur
31		when tail-call's are used and marked with the noreturn GCC attribute.
32	
33		On ia64, ppc64 and parisc64 architectures function pointers are
34		actually function descriptors which must first be resolved. The 'F' and
35		'f' specifiers perform this resolution and then provide the same
36		functionality as the 'S' and 's' specifiers.
37	
38	Kernel Pointers:
39	
40		%pK	0x01234567 or 0x0123456789abcdef
41	
42		For printing kernel pointers which should be hidden from unprivileged
43		users. The behaviour of %pK depends on the kptr_restrict sysctl - see
44		Documentation/sysctl/kernel.txt for more details.
45	
46	Struct Resources:
47	
48		%pr	[mem 0x60000000-0x6fffffff flags 0x2200] or
49			[mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
50		%pR	[mem 0x60000000-0x6fffffff pref] or
51			[mem 0x0000000060000000-0x000000006fffffff pref]
52	
53		For printing struct resources. The 'R' and 'r' specifiers result in a
54		printed resource with ('R') or without ('r') a decoded flags member.
55	
56	Physical addresses:
57	
58		%pa	0x01234567 or 0x0123456789abcdef
59	
60		For printing a phys_addr_t type (and its derivatives, such as
61		resource_size_t) which can vary based on build options, regardless of
62		the width of the CPU data path. Passed by reference.
63	
64	Raw buffer as a hex string:
65		%*ph	00 01 02  ...  3f
66		%*phC	00:01:02: ... :3f
67		%*phD	00-01-02- ... -3f
68		%*phN	000102 ... 3f
69	
70		For printing a small buffers (up to 64 bytes long) as a hex string with
71		certain separator. For the larger buffers consider to use
72		print_hex_dump().
73	
74	MAC/FDDI addresses:
75	
76		%pM	00:01:02:03:04:05
77		%pMR	05:04:03:02:01:00
78		%pMF	00-01-02-03-04-05
79		%pm	000102030405
80		%pmR	050403020100
81	
82		For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
83		specifiers result in a printed address with ('M') or without ('m') byte
84		separators. The default byte separator is the colon (':').
85	
86		Where FDDI addresses are concerned the 'F' specifier can be used after
87		the 'M' specifier to use dash ('-') separators instead of the default
88		separator.
89	
90		For Bluetooth addresses the 'R' specifier shall be used after the 'M'
91		specifier to use reversed byte order suitable for visual interpretation
92		of Bluetooth addresses which are in the little endian order.
93	
94	IPv4 addresses:
95	
96		%pI4	1.2.3.4
97		%pi4	001.002.003.004
98		%p[Ii][hnbl]
99	
100		For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
101		specifiers result in a printed address with ('i4') or without ('I4')
102		leading zeros.
103	
104		The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
105		host, network, big or little endian order addresses respectively. Where
106		no specifier is provided the default network/big endian order is used.
107	
108	IPv6 addresses:
109	
110		%pI6	0001:0002:0003:0004:0005:0006:0007:0008
111		%pi6	00010002000300040005000600070008
112		%pI6c	1:2:3:4:5:6:7:8
113	
114		For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
115		specifiers result in a printed address with ('I6') or without ('i6')
116		colon-separators. Leading zeros are always used.
117	
118		The additional 'c' specifier can be used with the 'I' specifier to
119		print a compressed IPv6 address as described by
120		http://tools.ietf.org/html/rfc5952
121	
122	UUID/GUID addresses:
123	
124		%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
125		%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
126		%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
127		%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
128	
129		For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
130		'b' and 'B' specifiers are used to specify a little endian order in
131		lower ('l') or upper case ('L') hex characters - and big endian order
132		in lower ('b') or upper case ('B') hex characters.
133	
134		Where no additional specifiers are used the default little endian
135		order with lower case hex characters will be printed.
136	
137	struct va_format:
138	
139		%pV
140	
141		For printing struct va_format structures. These contain a format string
142		and va_list as follows:
143	
144		struct va_format {
145			const char *fmt;
146			va_list *va;
147		};
148	
149		Do not use this feature without some mechanism to verify the
150		correctness of the format string and va_list arguments.
151	
152	u64 SHOULD be printed with %llu/%llx, (unsigned long long):
153	
154		printk("%llu", (unsigned long long)u64_var);
155	
156	s64 SHOULD be printed with %lld/%llx, (long long):
157	
158		printk("%lld", (long long)s64_var);
159	
160	If <type> is dependent on a config option for its size (e.g., sector_t,
161	blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
162	format specifier of its largest possible type and explicitly cast to it.
163	Example:
164	
165		printk("test: sector number/total blocks: %llu/%llu\n",
166			(unsigned long long)sector, (unsigned long long)blockcount);
167	
168	Reminder: sizeof() result is of type size_t.
169	
170	Thank you for your cooperation and attention.
171	
172	
173	By Randy Dunlap <rdunlap@infradead.org> and
174	Andrew Murray <amurray@mpc-data.co.uk>
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