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Documentation / printk-formats.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 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:
59	
60		%pa	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	Raw buffer as a hex string:
67		%*ph	00 01 02  ...  3f
68		%*phC	00:01:02: ... :3f
69		%*phD	00-01-02- ... -3f
70		%*phN	000102 ... 3f
71	
72		For printing a small buffers (up to 64 bytes long) as a hex string with
73		certain separator. For the larger buffers consider to use
74		print_hex_dump().
75	
76	MAC/FDDI addresses:
77	
78		%pM	00:01:02:03:04:05
79		%pMR	05:04:03:02:01:00
80		%pMF	00-01-02-03-04-05
81		%pm	000102030405
82		%pmR	050403020100
83	
84		For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
85		specifiers result in a printed address with ('M') or without ('m') byte
86		separators. The default byte separator is the colon (':').
87	
88		Where FDDI addresses are concerned the 'F' specifier can be used after
89		the 'M' specifier to use dash ('-') separators instead of the default
90		separator.
91	
92		For Bluetooth addresses the 'R' specifier shall be used after the 'M'
93		specifier to use reversed byte order suitable for visual interpretation
94		of Bluetooth addresses which are in the little endian order.
95	
96	IPv4 addresses:
97	
98		%pI4	1.2.3.4
99		%pi4	001.002.003.004
100		%p[Ii]4[hnbl]
101	
102		For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
103		specifiers result in a printed address with ('i4') or without ('I4')
104		leading zeros.
105	
106		The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
107		host, network, big or little endian order addresses respectively. Where
108		no specifier is provided the default network/big endian order is used.
109	
110	IPv6 addresses:
111	
112		%pI6	0001:0002:0003:0004:0005:0006:0007:0008
113		%pi6	00010002000300040005000600070008
114		%pI6c	1:2:3:4:5:6:7:8
115	
116		For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
117		specifiers result in a printed address with ('I6') or without ('i6')
118		colon-separators. Leading zeros are always used.
119	
120		The additional 'c' specifier can be used with the 'I' specifier to
121		print a compressed IPv6 address as described by
122		http://tools.ietf.org/html/rfc5952
123	
124	IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
125	
126		%pIS	1.2.3.4		or 0001:0002:0003:0004:0005:0006:0007:0008
127		%piS	001.002.003.004	or 00010002000300040005000600070008
128		%pISc	1.2.3.4		or 1:2:3:4:5:6:7:8
129		%pISpc	1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345
130		%p[Ii]S[pfschnbl]
131	
132		For printing an IP address without the need to distinguish whether it's
133		of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',
134		specified through 'IS' or 'iS', can be passed to this format specifier.
135	
136		The additional 'p', 'f', and 's' specifiers are used to specify port
137		(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,
138		flowinfo a '/' and scope a '%', each followed by the actual value.
139	
140		In case of an IPv6 address the compressed IPv6 address as described by
141		http://tools.ietf.org/html/rfc5952 is being used if the additional
142		specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in
143		case of additional specifiers 'p', 'f' or 's' as suggested by
144		https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
145	
146		In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'
147		specifiers can be used as well and are ignored in case of an IPv6
148		address.
149	
150		Further examples:
151	
152		%pISfc		1.2.3.4		or [1:2:3:4:5:6:7:8]/123456789
153		%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890
154		%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789
155	
156	UUID/GUID addresses:
157	
158		%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
159		%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
160		%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
161		%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
162	
163		For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
164		'b' and 'B' specifiers are used to specify a little endian order in
165		lower ('l') or upper case ('L') hex characters - and big endian order
166		in lower ('b') or upper case ('B') hex characters.
167	
168		Where no additional specifiers are used the default little endian
169		order with lower case hex characters will be printed.
170	
171	dentry names:
172		%pd{,2,3,4}
173		%pD{,2,3,4}
174	
175		For printing dentry name; if we race with d_move(), the name might be
176		a mix of old and new ones, but it won't oops.  %pd dentry is a safer
177		equivalent of %s dentry->d_name.name we used to use, %pd<n> prints
178		n last components.  %pD does the same thing for struct file.
179	
180	struct va_format:
181	
182		%pV
183	
184		For printing struct va_format structures. These contain a format string
185		and va_list as follows:
186	
187		struct va_format {
188			const char *fmt;
189			va_list *va;
190		};
191	
192		Do not use this feature without some mechanism to verify the
193		correctness of the format string and va_list arguments.
194	
195	u64 SHOULD be printed with %llu/%llx, (unsigned long long):
196	
197		printk("%llu", u64_var);
198	
199	s64 SHOULD be printed with %lld/%llx, (long long):
200	
201		printk("%lld", s64_var);
202	
203	If <type> is dependent on a config option for its size (e.g., sector_t,
204	blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
205	format specifier of its largest possible type and explicitly cast to it.
206	Example:
207	
208		printk("test: sector number/total blocks: %llu/%llu\n",
209			(unsigned long long)sector, (unsigned long long)blockcount);
210	
211	Reminder: sizeof() result is of type size_t.
212	
213	Thank you for your cooperation and attention.
214	
215	
216	By Randy Dunlap <rdunlap@infradead.org> and
217	Andrew Murray <amurray@mpc-data.co.uk>
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