Documentation/printk-formats.txt

   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 an escaped string:
  74
  75         %*pE[achnops]
  76
  77         For printing raw buffer as an escaped string. For the following buffer
  78
  79                 1b 62 20 5c 43 07 22 90 0d 5d
  80
  81         few examples show how the conversion would be done (the result string
  82         without surrounding quotes):
  83
  84                 %*pE            "\eb \C\a"\220\r]"
  85                 %*pEhp          "\x1bb \C\x07"\x90\x0d]"
  86                 %*pEa           "\e\142\040\\\103\a\042\220\r\135"
  87
  88         The conversion rules are applied according to an optional combination
  89         of flags (see string_escape_mem() kernel documentation for the
  90         details):
  91                 a - ESCAPE_ANY
  92                 c - ESCAPE_SPECIAL
  93                 h - ESCAPE_HEX
  94                 n - ESCAPE_NULL
  95                 o - ESCAPE_OCTAL
  96                 p - ESCAPE_NP
  97                 s - ESCAPE_SPACE
  98         By default ESCAPE_ANY_NP is used.
  99
 100         ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
 101         printing SSIDs.
 102
 103         If field width is omitted the 1 byte only will be escaped.
 104
 105 Raw buffer as a hex string:
 106         %*ph    00 01 02  ...  3f
 107         %*phC   00:01:02: ... :3f
 108         %*phD   00-01-02- ... -3f
 109         %*phN   000102 ... 3f
 110
 111         For printing a small buffers (up to 64 bytes long) as a hex string with
 112         certain separator. For the larger buffers consider to use
 113         print_hex_dump().
 114
 115 MAC/FDDI addresses:
 116
 117         %pM     00:01:02:03:04:05
 118         %pMR    05:04:03:02:01:00
 119         %pMF    00-01-02-03-04-05
 120         %pm     000102030405
 121         %pmR    050403020100
 122
 123         For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
 124         specifiers result in a printed address with ('M') or without ('m') byte
 125         separators. The default byte separator is the colon (':').
 126
 127         Where FDDI addresses are concerned the 'F' specifier can be used after
 128         the 'M' specifier to use dash ('-') separators instead of the default
 129         separator.
 130
 131         For Bluetooth addresses the 'R' specifier shall be used after the 'M'
 132         specifier to use reversed byte order suitable for visual interpretation
 133         of Bluetooth addresses which are in the little endian order.
 134
 135 IPv4 addresses:
 136
 137         %pI4    1.2.3.4
 138         %pi4    001.002.003.004
 139         %p[Ii]4[hnbl]
 140
 141         For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
 142         specifiers result in a printed address with ('i4') or without ('I4')
 143         leading zeros.
 144
 145         The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
 146         host, network, big or little endian order addresses respectively. Where
 147         no specifier is provided the default network/big endian order is used.
 148
 149 IPv6 addresses:
 150
 151         %pI6    0001:0002:0003:0004:0005:0006:0007:0008
 152         %pi6    00010002000300040005000600070008
 153         %pI6c   1:2:3:4:5:6:7:8
 154
 155         For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
 156         specifiers result in a printed address with ('I6') or without ('i6')
 157         colon-separators. Leading zeros are always used.
 158
 159         The additional 'c' specifier can be used with the 'I' specifier to
 160         print a compressed IPv6 address as described by
 161         http://tools.ietf.org/html/rfc5952
 162
 163 IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
 164
 165         %pIS    1.2.3.4         or 0001:0002:0003:0004:0005:0006:0007:0008
 166         %piS    001.002.003.004 or 00010002000300040005000600070008
 167         %pISc   1.2.3.4         or 1:2:3:4:5:6:7:8
 168         %pISpc  1.2.3.4:12345   or [1:2:3:4:5:6:7:8]:12345
 169         %p[Ii]S[pfschnbl]
 170
 171         For printing an IP address without the need to distinguish whether it's
 172         of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',
 173         specified through 'IS' or 'iS', can be passed to this format specifier.
 174
 175         The additional 'p', 'f', and 's' specifiers are used to specify port
 176         (IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,
 177         flowinfo a '/' and scope a '%', each followed by the actual value.
 178
 179         In case of an IPv6 address the compressed IPv6 address as described by
 180         http://tools.ietf.org/html/rfc5952 is being used if the additional
 181         specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in
 182         case of additional specifiers 'p', 'f' or 's' as suggested by
 183         https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
 184
 185         In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'
 186         specifiers can be used as well and are ignored in case of an IPv6
 187         address.
 188
 189         Further examples:
 190
 191         %pISfc          1.2.3.4         or [1:2:3:4:5:6:7:8]/123456789
 192         %pISsc          1.2.3.4         or [1:2:3:4:5:6:7:8]%1234567890
 193         %pISpfc         1.2.3.4:12345   or [1:2:3:4:5:6:7:8]:12345/123456789
 194
 195 UUID/GUID addresses:
 196
 197         %pUb    00010203-0405-0607-0809-0a0b0c0d0e0f
 198         %pUB    00010203-0405-0607-0809-0A0B0C0D0E0F
 199         %pUl    03020100-0504-0706-0809-0a0b0c0e0e0f
 200         %pUL    03020100-0504-0706-0809-0A0B0C0E0E0F
 201
 202         For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
 203         'b' and 'B' specifiers are used to specify a little endian order in
 204         lower ('l') or upper case ('L') hex characters - and big endian order
 205         in lower ('b') or upper case ('B') hex characters.
 206
 207         Where no additional specifiers are used the default little endian
 208         order with lower case hex characters will be printed.
 209
 210 dentry names:
 211         %pd{,2,3,4}
 212         %pD{,2,3,4}
 213
 214         For printing dentry name; if we race with d_move(), the name might be
 215         a mix of old and new ones, but it won't oops.  %pd dentry is a safer
 216         equivalent of %s dentry->d_name.name we used to use, %pd<n> prints
 217         n last components.  %pD does the same thing for struct file.
 218
 219 struct va_format:
 220
 221         %pV
 222
 223         For printing struct va_format structures. These contain a format string
 224         and va_list as follows:
 225
 226         struct va_format {
 227                 const char *fmt;
 228                 va_list *va;
 229         };
 230
 231         Do not use this feature without some mechanism to verify the
 232         correctness of the format string and va_list arguments.
 233
 234 u64 SHOULD be printed with %llu/%llx:
 235
 236         printk("%llu", u64_var);
 237
 238 s64 SHOULD be printed with %lld/%llx:
 239
 240         printk("%lld", s64_var);
 241
 242 If <type> is dependent on a config option for its size (e.g., sector_t,
 243 blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
 244 format specifier of its largest possible type and explicitly cast to it.
 245 Example:
 246
 247         printk("test: sector number/total blocks: %llu/%llu\n",
 248                 (unsigned long long)sector, (unsigned long long)blockcount);
 249
 250 Reminder: sizeof() result is of type size_t.
 251
 252 Thank you for your cooperation and attention.
 253
 254
 255 By Randy Dunlap <rdunlap@infradead.org> and
 256 Andrew Murray <amurray@mpc-data.co.uk>