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Documentation / printk-formats.txt




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Based on kernel version 3.4. Page generated on 2012-05-21 22:09 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	MAC/FDDI addresses:
57	
58		%pM	00:01:02:03:04:05
59		%pMF	00-01-02-03-04-05
60		%pm	000102030405
61	
62		For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
63		specifiers result in a printed address with ('M') or without ('m') byte
64		separators. The default byte separator is the colon (':').
65	
66		Where FDDI addresses are concerned the 'F' specifier can be used after
67		the 'M' specifier to use dash ('-') separators instead of the default
68		separator.
69	
70	IPv4 addresses:
71	
72		%pI4	1.2.3.4
73		%pi4	001.002.003.004
74		%p[Ii][hnbl]
75	
76		For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
77		specifiers result in a printed address with ('i4') or without ('I4')
78		leading zeros.
79	
80		The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
81		host, network, big or little endian order addresses respectively. Where
82		no specifier is provided the default network/big endian order is used.
83	
84	IPv6 addresses:
85	
86		%pI6	0001:0002:0003:0004:0005:0006:0007:0008
87		%pi6	00010002000300040005000600070008
88		%pI6c	1:2:3:4:5:6:7:8
89	
90		For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
91		specifiers result in a printed address with ('I6') or without ('i6')
92		colon-separators. Leading zeros are always used.
93	
94		The additional 'c' specifier can be used with the 'I' specifier to
95		print a compressed IPv6 address as described by
96		http://tools.ietf.org/html/rfc5952
97	
98	UUID/GUID addresses:
99	
100		%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
101		%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
102		%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
103		%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
104	
105		For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
106		'b' and 'B' specifiers are used to specify a little endian order in
107		lower ('l') or upper case ('L') hex characters - and big endian order
108		in lower ('b') or upper case ('B') hex characters.
109	
110		Where no additional specifiers are used the default little endian
111		order with lower case hex characters will be printed.
112	
113	struct va_format:
114	
115		%pV
116	
117		For printing struct va_format structures. These contain a format string
118		and va_list as follows:
119	
120		struct va_format {
121			const char *fmt;
122			va_list *va;
123		};
124	
125		Do not use this feature without some mechanism to verify the
126		correctness of the format string and va_list arguments.
127	
128	u64 SHOULD be printed with %llu/%llx, (unsigned long long):
129	
130		printk("%llu", (unsigned long long)u64_var);
131	
132	s64 SHOULD be printed with %lld/%llx, (long long):
133	
134		printk("%lld", (long long)s64_var);
135	
136	If <type> is dependent on a config option for its size (e.g., sector_t,
137	blkcnt_t, phys_addr_t, resource_size_t) or is architecture-dependent
138	for its size (e.g., tcflag_t), use a format specifier of its largest
139	possible type and explicitly cast to it.  Example:
140	
141		printk("test: sector number/total blocks: %llu/%llu\n",
142			(unsigned long long)sector, (unsigned long long)blockcount);
143	
144	Reminder: sizeof() result is of type size_t.
145	
146	Thank you for your cooperation and attention.
147	
148	
149	By Randy Dunlap <rdunlap@xenotime.net> and
150	Andrew Murray <amurray@mpc-data.co.uk>
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