PRINTF(9) OpenBSD Kernel Manual PRINTF(9)NAME
printf, snprintf, vprintf, vsnprintf, uprintf, ttyprintf, db_printf -
kernel formatted output conversion
SYNOPSIS
#include <sys/types.h>
#include <sys/systm.h>
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, ...);
void
db_printf(const char *format, ...);
DESCRIPTION
The printf(), snprintf(), vprintf(), vsnprintf(), uprintf(), ttyprintf(),
and db_printf() functions allow the kernel to send formatted 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 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
counterpart, 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
specifiers. In addition to other formatting specifiers common with the
user space functions, the kernel functions 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 (as an integer) 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. 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
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 significant).
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.
%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 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 ALSOrevoke(2), printf(3), ddb(4), log(9)OpenBSD 4.9 June 26, 2008 OpenBSD 4.9