If variable is of Type,         use printk format specifier:
---------------------------------------------------------
                int                     %d or %x
                unsigned int            %u or %x
                long                    %ld or %lx
                unsigned long           %lu or %lx
                long long               %lld or %llx
                unsigned long long      %llu or %llx
                size_t                  %zu or %zx
                ssize_t                 %zd or %zx

Raw pointer value SHOULD be printed with %p. The kernel supports
the following extended format specifiers for pointer types:

Symbols/Function Pointers:

        %pF     versatile_init+0x0/0x110
        %pf     versatile_init
        %pS     versatile_init+0x0/0x110
        %pSR    versatile_init+0x9/0x110
                (with __builtin_extract_return_addr() translation)
        %ps     versatile_init
        %pB     prev_fn_of_versatile_init+0x88/0x88

        For printing symbols and function pointers. The 'S' and 's' specifiers
        result in the symbol name with ('S') or without ('s') offsets. Where
        this is used on a kernel without KALLSYMS - the symbol address is
        printed instead.

        The 'B' specifier results in the symbol name with offsets and should be
        used when printing stack backtraces. The specifier takes into
        consideration the effect of compiler optimisations which may occur
        when tail-call's are used and marked with the noreturn GCC attribute.

        On ia64, ppc64 and parisc64 architectures function pointers are
        actually function descriptors which must first be resolved. The 'F' and
        'f' specifiers perform this resolution and then provide the same
        functionality as the 'S' and 's' specifiers.

Kernel Pointers:

        %pK     0x01234567 or 0x0123456789abcdef

        For printing kernel pointers which should be hidden from unprivileged
        users. The behaviour of %pK depends on the kptr_restrict sysctl - see
        Documentation/sysctl/kernel.txt for more details.

Struct Resources:

        %pr     [mem 0x60000000-0x6fffffff flags 0x2200] or
                [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
        %pR     [mem 0x60000000-0x6fffffff pref] or
                [mem 0x0000000060000000-0x000000006fffffff pref]

        For printing struct resources. The 'R' and 'r' specifiers result in a
        printed resource with ('R') or without ('r') a decoded flags member.

Physical addresses:

        %pa     0x01234567 or 0x0123456789abcdef

        For printing a phys_addr_t type (and its derivatives, such as
        resource_size_t) which can vary based on build options, regardless of
        the width of the CPU data path. Passed by reference.

Raw buffer as a hex string:
        %*ph    00 01 02  ...  3f
        %*phC   00:01:02: ... :3f
        %*phD   00-01-02- ... -3f
        %*phN   000102 ... 3f

        For printing a small buffers (up to 64 bytes long) as a hex string with
        certain separator. For the larger buffers consider to use
        print_hex_dump().

MAC/FDDI addresses:

        %pM     00:01:02:03:04:05
        %pMR    05:04:03:02:01:00
        %pMF    00-01-02-03-04-05
        %pm     000102030405
        %pmR    050403020100

        For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
        specifiers result in a printed address with ('M') or without ('m') byte
        separators. The default byte separator is the colon (':').

        Where FDDI addresses are concerned the 'F' specifier can be used after
        the 'M' specifier to use dash ('-') separators instead of the default
        separator.

        For Bluetooth addresses the 'R' specifier shall be used after the 'M'
        specifier to use reversed byte order suitable for visual interpretation
        of Bluetooth addresses which are in the little endian order.

IPv4 addresses:

        %pI4    1.2.3.4
        %pi4    001.002.003.004
        %p[Ii][hnbl]

        For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
        specifiers result in a printed address with ('i4') or without ('I4')
        leading zeros.

        The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
        host, network, big or little endian order addresses respectively. Where
        no specifier is provided the default network/big endian order is used.

IPv6 addresses:

        %pI6    0001:0002:0003:0004:0005:0006:0007:0008
        %pi6    00010002000300040005000600070008
        %pI6c   1:2:3:4:5:6:7:8

        For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
        specifiers result in a printed address with ('I6') or without ('i6')
        colon-separators. Leading zeros are always used.

        The additional 'c' specifier can be used with the 'I' specifier to
        print a compressed IPv6 address as described by
        http://tools.ietf.org/html/rfc5952

IPv4/IPv6 addresses (generic, with port, flowinfo, scope):

        %pIS    1.2.3.4         or 0001:0002:0003:0004:0005:0006:0007:0008
        %piS    001.002.003.004 or 00010002000300040005000600070008
        %pISc   1.2.3.4         or 1:2:3:4:5:6:7:8
        %pISpc  1.2.3.4:12345   or [1:2:3:4:5:6:7:8]:12345
        %p[Ii]S[pfschnbl]

        For printing an IP address without the need to distinguish whether it's
        of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',
        specified through 'IS' or 'iS', can be passed to this format specifier.

        The additional 'p', 'f', and 's' specifiers are used to specify port
        (IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,
        flowinfo a '/' and scope a '%', each followed by the actual value.

        In case of an IPv6 address the compressed IPv6 address as described by
        http://tools.ietf.org/html/rfc5952 is being used if the additional
        specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in
        case of additional specifiers 'p', 'f' or 's' as suggested by
        https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07

        In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'
        specifiers can be used as well and are ignored in case of an IPv6
        address.

        Further examples:

        %pISfc          1.2.3.4         or [1:2:3:4:5:6:7:8]/123456789
        %pISsc          1.2.3.4         or [1:2:3:4:5:6:7:8]%1234567890
        %pISpfc         1.2.3.4:12345   or [1:2:3:4:5:6:7:8]:12345/123456789

UUID/GUID addresses:

        %pUb    00010203-0405-0607-0809-0a0b0c0d0e0f
        %pUB    00010203-0405-0607-0809-0A0B0C0D0E0F
        %pUl    03020100-0504-0706-0809-0a0b0c0e0e0f
        %pUL    03020100-0504-0706-0809-0A0B0C0E0E0F

        For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
        'b' and 'B' specifiers are used to specify a little endian order in
        lower ('l') or upper case ('L') hex characters - and big endian order
        in lower ('b') or upper case ('B') hex characters.

        Where no additional specifiers are used the default little endian
        order with lower case hex characters will be printed.

struct va_format:

        %pV

        For printing struct va_format structures. These contain a format string
        and va_list as follows:

        struct va_format {
                const char *fmt;
                va_list *va;
        };

        Do not use this feature without some mechanism to verify the
        correctness of the format string and va_list arguments.

u64 SHOULD be printed with %llu/%llx, (unsigned long long):

        printk("%llu", (unsigned long long)u64_var);

s64 SHOULD be printed with %lld/%llx, (long long):

        printk("%lld", (long long)s64_var);

If <type> is dependent on a config option for its size (e.g., sector_t,
blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
format specifier of its largest possible type and explicitly cast to it.
Example:

        printk("test: sector number/total blocks: %llu/%llu\n",
                (unsigned long long)sector, (unsigned long long)blockcount);

Reminder: sizeof() result is of type size_t.

Thank you for your cooperation and attention.


By Randy Dunlap <rdunlap@infradead.org> and
Andrew Murray <amurray@mpc-data.co.uk>