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