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PRINTF(9)                    OpenBSD Kernel Manual                   PRINTF(9)

NAME
     printf, sprintf, vprintf, uprintf, ttyprintf, db_printf - kernel format-
     ted output conversion

SYNOPSIS
     #include <sys/types.h>
     #include <sys/systm.h>

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

     int
     sprintf(char *buf, const char *format, ...);

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

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

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

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

DESCRIPTION
     The printf(), sprintf(), vprintf(), uprintf(), ttyprintf(), and
     db_printf() functions allow the kernel to send formatted messages to var-
     ious 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 function
     db_printf() sends formatted strings to the ddb console, and is 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 any floating point formatting speci-
     fiers.  In addition to other formatting specifiers common with the user
     space functions, the kernel functions accept the following format speci-
     fiers 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 (as an integer) and the second being a decoding direc-
           tive 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.  Recognized
           radix values (in C escape-character format) are \10 (octal), \12
           (decimal), and \20 (hexadecimal).

           The remaining characters in the decoding directive string are in-
           terpreted as a list of bit-position-description pairs.  A bit-posi-
           tion-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 posi-
           tion value of 32 (octal 40, hexadecimal 20, the ASCII space
           character) describes the most significant bit.

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

     %:    Inline format continuation.  This format specifier allows for re-
           cursive formatted output.  Its argument is the new formatting
           string to obey and the argument which follows it is a va_list argu-
           ment vector from which to obtain the data to be formatted.

     %r    Displays an integer using the current DDB radix.  This non-standard
           interpretation of %r is only available to db_printf().

     %z    Displays a signed integer using the C-style hexadecimal constant
           format.  This format specifier is only available to db_printf().

RETURN VALUES
     The sprintf() function returns the number of characters it placed in the
     buffer buf.

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>"

     Use of the %: format specifier for recursive formatting.

           void
           bail(char *fmt, ...)
           {
                   va_list ap;
                   va_start (ap, fmt);
                   printf("bailing out: %:\n", fmt, ap);
                   va_end(ap);
           }

           bail("descriptor %d is invalid.", 5)
           => "bailing out: descriptor 5 is invalid"

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

CODE REFERENCES
     sys/kern/subr_prf.c

LIMITATIONS
     The %b format specifier cannot be used to decode integers greater than 32
     bits in size.

OpenBSD 3.3                    September 1, 1998                             2