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         %ps     versatile_init
  21         %pB     prev_fn_of_versatile_init+0x88/0x88
  22
  23         For printing symbols and function pointers. The 'S' and 's' specifiers
  24         result in the symbol name with ('S') or without ('s') offsets. Where
  25         this is used on a kernel without KALLSYMS - the symbol address is
  26         printed instead.
  27
  28         The 'B' specifier results in the symbol name with offsets and should be
  29         used when printing stack backtraces. The specifier takes into
  30         consideration the effect of compiler optimisations which may occur
  31         when tail-call's are used and marked with the noreturn GCC attribute.
  32
  33         On ia64, ppc64 and parisc64 architectures function pointers are
  34         actually function descriptors which must first be resolved. The 'F' and
  35         'f' specifiers perform this resolution and then provide the same
  36         functionality as the 'S' and 's' specifiers.
  37
  38 Kernel Pointers:
  39
  40         %pK     0x01234567 or 0x0123456789abcdef
  41
  42         For printing kernel pointers which should be hidden from unprivileged
  43         users. The behaviour of %pK depends on the kptr_restrict sysctl - see
  44         Documentation/sysctl/kernel.txt for more details.
  45
  46 Struct Resources:
  47
  48         %pr     [mem 0x60000000-0x6fffffff flags 0x2200] or
  49                 [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
  50         %pR     [mem 0x60000000-0x6fffffff pref] or
  51                 [mem 0x0000000060000000-0x000000006fffffff pref]
  52
  53         For printing struct resources. The 'R' and 'r' specifiers result in a
  54         printed resource with ('R') or without ('r') a decoded flags member.
  55
  56 Physical addresses:
  57
  58         %pa     0x01234567 or 0x0123456789abcdef
  59
  60         For printing a phys_addr_t type (and its derivatives, such as
  61         resource_size_t) which can vary based on build options, regardless of
  62         the width of the CPU data path. Passed by reference.
  63
  64 Raw buffer as a hex string:
  65         %*ph    00 01 02  ...  3f
  66         %*phC   00:01:02: ... :3f
  67         %*phD   00-01-02- ... -3f
  68         %*phN   000102 ... 3f
  69
  70         For printing a small buffers (up to 64 bytes long) as a hex string with
  71         certain separator. For the larger buffers consider to use
  72         print_hex_dump().
  73
  74 MAC/FDDI addresses:
  75
  76         %pM     00:01:02:03:04:05
  77         %pMR    05:04:03:02:01:00
  78         %pMF    00-01-02-03-04-05
  79         %pm     000102030405
  80         %pmR    050403020100
  81
  82         For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
  83         specifiers result in a printed address with ('M') or without ('m') byte
  84         separators. The default byte separator is the colon (':').
  85
  86         Where FDDI addresses are concerned the 'F' specifier can be used after
  87         the 'M' specifier to use dash ('-') separators instead of the default
  88         separator.
  89
  90         For Bluetooth addresses the 'R' specifier shall be used after the 'M'
  91         specifier to use reversed byte order suitable for visual interpretation
  92         of Bluetooth addresses which are in the little endian order.
  93
  94 IPv4 addresses:
  95
  96         %pI4    1.2.3.4
  97         %pi4    001.002.003.004
  98         %p[Ii][hnbl]
  99
 100         For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
 101         specifiers result in a printed address with ('i4') or without ('I4')
 102         leading zeros.
 103
 104         The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
 105         host, network, big or little endian order addresses respectively. Where
 106         no specifier is provided the default network/big endian order is used.
 107
 108 IPv6 addresses:
 109
 110         %pI6    0001:0002:0003:0004:0005:0006:0007:0008
 111         %pi6    00010002000300040005000600070008
 112         %pI6c   1:2:3:4:5:6:7:8
 113
 114         For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
 115         specifiers result in a printed address with ('I6') or without ('i6')
 116         colon-separators. Leading zeros are always used.
 117
 118         The additional 'c' specifier can be used with the 'I' specifier to
 119         print a compressed IPv6 address as described by
 120         http://tools.ietf.org/html/rfc5952
 121
 122 UUID/GUID addresses:
 123
 124         %pUb    00010203-0405-0607-0809-0a0b0c0d0e0f
 125         %pUB    00010203-0405-0607-0809-0A0B0C0D0E0F
 126         %pUl    03020100-0504-0706-0809-0a0b0c0e0e0f
 127         %pUL    03020100-0504-0706-0809-0A0B0C0E0E0F
 128
 129         For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
 130         'b' and 'B' specifiers are used to specify a little endian order in
 131         lower ('l') or upper case ('L') hex characters - and big endian order
 132         in lower ('b') or upper case ('B') hex characters.
 133
 134         Where no additional specifiers are used the default little endian
 135         order with lower case hex characters will be printed.
 136
 137 struct va_format:
 138
 139         %pV
 140
 141         For printing struct va_format structures. These contain a format string
 142         and va_list as follows:
 143
 144         struct va_format {
 145                 const char *fmt;
 146                 va_list *va;
 147         };
 148
 149         Do not use this feature without some mechanism to verify the
 150         correctness of the format string and va_list arguments.
 151
 152 u64 SHOULD be printed with %llu/%llx, (unsigned long long):
 153
 154         printk("%llu", (unsigned long long)u64_var);
 155
 156 s64 SHOULD be printed with %lld/%llx, (long long):
 157
 158         printk("%lld", (long long)s64_var);
 159
 160 If <type> is dependent on a config option for its size (e.g., sector_t,
 161 blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
 162 format specifier of its largest possible type and explicitly cast to it.
 163 Example:
 164
 165         printk("test: sector number/total blocks: %llu/%llu\n",
 166                 (unsigned long long)sector, (unsigned long long)blockcount);
 167
 168 Reminder: sizeof() result is of type size_t.
 169
 170 Thank you for your cooperation and attention.
 171
 172
 173 By Randy Dunlap <rdunlap@infradead.org> and
 174 Andrew Murray <amurray@mpc-data.co.uk>