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PRINTF(9)                BSD Kernel Developer's Manual               PRINTF(9)

NAME
     printf, snprintf, vprintf, vsnprintf, uprintf, ttyprintf, db_printf,
     db_vprintf -- kernel formatted output conversion

SYNOPSIS
     #include <&lt;sys/types.h>&gt;
     #include <&lt;sys/systm.h>&gt;

     int
     printf(const char *format, ...);

     int
     snprintf(char *buf, size_t size, const char *format, ...);

     int
     vprintf(const char *format, va_list ap);

     int
     vsnprintf(char *buf, size_t size, const char *fmt, va_list ap);

     void
     uprintf(const char *format, ...);

     void
     ttyprintf(struct tty *tty, const char *format, ...);

     #include <&lt;ddb/db_output.h>&gt;

     void
     db_printf(const char *format, ...);

     void
     db_vprintf(const char *format, va_list ap);

DESCRIPTION
     The printf(), snprintf(), vprintf(), vsnprintf(), uprintf(), ttyprintf(),
     db_printf(), and db_vprintf() functions allow the kernel to send format-
     ted messages to various output devices.  The functions printf() and
     vprintf() send formatted strings to the system console and to the system
     log.  The functions uprintf() and ttyprintf() send formatted strings to
     the current process's controlling tty and a specific tty, respectively.
     The functions db_printf() and db_vprintf() send formatted strings to the
     ddb console, and are only used to implement ddb(4).

     Since each of these kernel functions is a variant of its user space coun-
     terpart, this page describes only the differences between the user space
     and kernel versions.  Refer to printf(3) for functional details.

   FORMAT OPTIONS
     The kernel functions don't support as many formatting specifiers as their
     user space counterparts.  In addition to the floating point formatting
     specifiers, the following integer type specifiers are not supported in
     the format string format either :

     %hh    Argument of char type.  This format specifier is accepted by the
            kernel but will be handled as %h.

     %j     Argument of intmax_t or uintmax_t type.

     %t     Argument of ptrdiff_t type.

     The kernel functions also accept the following format specifiers in the
     format string format:

     %b     Bit field expansion.  This format specifier is useful for decoding
            bit fields in device registers.  It displays an integer using a
            specified radix (base) and an interpretation of the bits within
            that integer as though they were flags.  It requires two arguments
            from the argument vector, the first argument being the bit field
            to be decoded (of type int, unless a width modifier has been spec-
            ified) and the second being a decoding directive string.

            The decoding directive string describes how the bitfield is to be
            interpreted and displayed.  The first character of the string is a
            binary character representation of the output numeral base in
            which the bitfield will be printed before it is decoded.  Recog-
            nized radix values (in C escape-character format) are \10 (octal),
            \12 (decimal), and \20 (hexadecimal).

            The remaining characters in the decoding directive string are
            interpreted as a list of bit-position-description pairs.  A bit-
            position-description pair begins with a binary character value
            that represents the position of the bit being described.  A bit
            position value of one describes the least significant bit.
            Whereas a position value of 32 (octal 40, hexadecimal 20, the
            ASCII space character) describes the most significant bit.

            To deal with more than 32 bits, the characters 128 (octal 200,
            hexadecimal 80) through 255 (octal 377, hexadecimal FF) are used.
            The value 127 is subtracted from the character to determine the
            bit position (1 is least significant, and 128 is most signifi-
            cant).

            The remaining characters in a bit-position-description pair are
            the characters to print should the bit being described be set.
            Description strings are delimited by the next bit position value
            character encountered (distinguishable by its value being <= 32 or
            >= 128), or the end of the decoding directive string itself.

RETURN VALUES
     The printf() and vprintf() functions return the number of characters
     printed.

     The snprintf() and vsnprintf() functions return the number of characters
     that would have been put into the buffer buf if the size were unlimited.

EXAMPLES
     Use of the %b format specifier for decoding device registers.

           printf("reg=%b\n", 3, "\10\2BITTWO\1BITONE")
           => "reg=3<BITTWO,BITONE>"

           printf("enablereg=%b\n", 0xe860,
                  "\20\x10NOTBOOT\x0fFPP\x0eSDVMA\x0cVIDEO"
                  "\x0bLORES\x0aFPA\x09DIAG\x07CACHE"
                  "\x06IOCACHE\x05LOOPBACK\x04DBGCACHE")
           => "enablereg=e860<NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE>"

CODE REFERENCES
     sys/kern/subr_prf.c

SEE ALSO
     revoke(2), printf(3), ddb(4), log(9)

BSD                            December 29, 2013                           BSD