Root/Documentation/printk-formats.txt

Source at commit fbf123cd4cc0c097fe9a99c90109ebb2a5e94a50 created 10 years 3 months ago.
By Lars-Peter Clausen, dma: jz4740: Dequeue descriptor from active list before completing it
1If 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
12Raw pointer value SHOULD be printed with %p. The kernel supports
13the following extended format specifiers for pointer types:
14
15Symbols/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
40Kernel 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
48Struct 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
58Physical 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
66DMA 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
73Raw 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
83MAC/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
103IPv4 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
117IPv6 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
131IPv4/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
163UUID/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
178dentry 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
187struct 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
202u64 SHOULD be printed with %llu/%llx:
203
204    printk("%llu", u64_var);
205
206s64 SHOULD be printed with %lld/%llx:
207
208    printk("%lld", s64_var);
209
210If <type> is dependent on a config option for its size (e.g., sector_t,
211blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
212format specifier of its largest possible type and explicitly cast to it.
213Example:
214
215    printk("test: sector number/total blocks: %llu/%llu\n",
216        (unsigned long long)sector, (unsigned long long)blockcount);
217
218Reminder: sizeof() result is of type size_t.
219
220Thank you for your cooperation and attention.
221
222
223By Randy Dunlap <rdunlap@infradead.org> and
224Andrew Murray <amurray@mpc-data.co.uk>
225

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