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Documentation / printk-formats.txt




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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 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 a hex string:
74		%*ph	00 01 02  ...  3f
75		%*phC	00:01:02: ... :3f
76		%*phD	00-01-02- ... -3f
77		%*phN	000102 ... 3f
78	
79		For printing a small buffers (up to 64 bytes long) as a hex string with
80		certain separator. For the larger buffers consider to use
81		print_hex_dump().
82	
83	MAC/FDDI addresses:
84	
85		%pM	00:01:02:03:04:05
86		%pMR	05:04:03:02:01:00
87		%pMF	00-01-02-03-04-05
88		%pm	000102030405
89		%pmR	050403020100
90	
91		For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
92		specifiers result in a printed address with ('M') or without ('m') byte
93		separators. The default byte separator is the colon (':').
94	
95		Where FDDI addresses are concerned the 'F' specifier can be used after
96		the 'M' specifier to use dash ('-') separators instead of the default
97		separator.
98	
99		For Bluetooth addresses the 'R' specifier shall be used after the 'M'
100		specifier to use reversed byte order suitable for visual interpretation
101		of Bluetooth addresses which are in the little endian order.
102	
103	IPv4 addresses:
104	
105		%pI4	1.2.3.4
106		%pi4	001.002.003.004
107		%p[Ii]4[hnbl]
108	
109		For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
110		specifiers result in a printed address with ('i4') or without ('I4')
111		leading zeros.
112	
113		The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
114		host, network, big or little endian order addresses respectively. Where
115		no specifier is provided the default network/big endian order is used.
116	
117	IPv6 addresses:
118	
119		%pI6	0001:0002:0003:0004:0005:0006:0007:0008
120		%pi6	00010002000300040005000600070008
121		%pI6c	1:2:3:4:5:6:7:8
122	
123		For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
124		specifiers result in a printed address with ('I6') or without ('i6')
125		colon-separators. Leading zeros are always used.
126	
127		The additional 'c' specifier can be used with the 'I' specifier to
128		print a compressed IPv6 address as described by
129		http://tools.ietf.org/html/rfc5952
130	
131	IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
132	
133		%pIS	1.2.3.4		or 0001:0002:0003:0004:0005:0006:0007:0008
134		%piS	001.002.003.004	or 00010002000300040005000600070008
135		%pISc	1.2.3.4		or 1:2:3:4:5:6:7:8
136		%pISpc	1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345
137		%p[Ii]S[pfschnbl]
138	
139		For printing an IP address without the need to distinguish whether it's
140		of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',
141		specified through 'IS' or 'iS', can be passed to this format specifier.
142	
143		The additional 'p', 'f', and 's' specifiers are used to specify port
144		(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,
145		flowinfo a '/' and scope a '%', each followed by the actual value.
146	
147		In case of an IPv6 address the compressed IPv6 address as described by
148		http://tools.ietf.org/html/rfc5952 is being used if the additional
149		specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in
150		case of additional specifiers 'p', 'f' or 's' as suggested by
151		https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
152	
153		In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'
154		specifiers can be used as well and are ignored in case of an IPv6
155		address.
156	
157		Further examples:
158	
159		%pISfc		1.2.3.4		or [1:2:3:4:5:6:7:8]/123456789
160		%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890
161		%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789
162	
163	UUID/GUID addresses:
164	
165		%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
166		%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
167		%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
168		%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
169	
170		For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
171		'b' and 'B' specifiers are used to specify a little endian order in
172		lower ('l') or upper case ('L') hex characters - and big endian order
173		in lower ('b') or upper case ('B') hex characters.
174	
175		Where no additional specifiers are used the default little endian
176		order with lower case hex characters will be printed.
177	
178	dentry names:
179		%pd{,2,3,4}
180		%pD{,2,3,4}
181	
182		For printing dentry name; if we race with d_move(), the name might be
183		a mix of old and new ones, but it won't oops.  %pd dentry is a safer
184		equivalent of %s dentry->d_name.name we used to use, %pd<n> prints
185		n last components.  %pD does the same thing for struct file.
186	
187	struct va_format:
188	
189		%pV
190	
191		For printing struct va_format structures. These contain a format string
192		and va_list as follows:
193	
194		struct va_format {
195			const char *fmt;
196			va_list *va;
197		};
198	
199		Do not use this feature without some mechanism to verify the
200		correctness of the format string and va_list arguments.
201	
202	u64 SHOULD be printed with %llu/%llx, (unsigned long long):
203	
204		printk("%llu", u64_var);
205	
206	s64 SHOULD be printed with %lld/%llx, (long long):
207	
208		printk("%lld", s64_var);
209	
210	If <type> is dependent on a config option for its size (e.g., sector_t,
211	blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
212	format specifier of its largest possible type and explicitly cast to it.
213	Example:
214	
215		printk("test: sector number/total blocks: %llu/%llu\n",
216			(unsigned long long)sector, (unsigned long long)blockcount);
217	
218	Reminder: sizeof() result is of type size_t.
219	
220	Thank you for your cooperation and attention.
221	
222	
223	By Randy Dunlap <rdunlap@infradead.org> and
224	Andrew Murray <amurray@mpc-data.co.uk>
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