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 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>