linux/Documentation/printk-formats.txt
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   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:
  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
  66Raw 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
  76MAC/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
  96IPv4 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
 110IPv6 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
 124IPv4/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
 156UUID/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
 171dentry 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
 180struct 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
 195u64 SHOULD be printed with %llu/%llx, (unsigned long long):
 196
 197        printk("%llu", u64_var);
 198
 199s64 SHOULD be printed with %lld/%llx, (long long):
 200
 201        printk("%lld", s64_var);
 202
 203If <type> is dependent on a config option for its size (e.g., sector_t,
 204blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
 205format specifier of its largest possible type and explicitly cast to it.
 206Example:
 207
 208        printk("test: sector number/total blocks: %llu/%llu\n",
 209                (unsigned long long)sector, (unsigned long long)blockcount);
 210
 211Reminder: sizeof() result is of type size_t.
 212
 213Thank you for your cooperation and attention.
 214
 215
 216By Randy Dunlap <rdunlap@infradead.org> and
 217Andrew Murray <amurray@mpc-data.co.uk>
 218
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