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PRINTF(9) FreeBSD Kernel Developer's Manual PRINTF(9)
NAME
printf, uprintf, tprintf, log - formatted output conversion
SYNOPSIS
#include <sys/types.h>
#include <sys/systm.h>
int
printf(const char *fmt, ...);
void
tprintf(struct proc *p, int pri, const char *fmt, ...);
int
uprintf(const char *fmt, ...);
int
vprintf(const char *fmt, va_list ap);
#include <sys/syslog.h>
void
log(int pri, const char *fmt, ...);
void
vlog(int pri, const char *fmt, va_list ap);
DESCRIPTION
The printf family of functions are similar to the printf(3) family of
functions. The different functions each use a different output stream.
The uprintf() function outputs to the current process' controlling tty,
while printf() writes to the console as well as to the logging facility.
The tprintf() function outputs to the tty associated with the process p
and the logging facility if pri is not -1. The log() function sends the
message to the kernel logging facility, using the log level as indicated
by pri, and to the console if no process is yet reading the log.
Each of these related functions use the fmt parameter in the same manner
as printf(3). However, printf adds two other conversion specifiers and
omits one.
The %b identifier expects two arguments: an int and a char *. These are
used as a register value and a print mask for decoding bitmasks. The
print mask is made up of two parts: the base and the arguments. The base
value is the output base (radix) expressed as an octal value; for
example, \10 gives octal and \20 gives hexadecimal. The arguments are
made up of a sequence of bit identifiers. Each bit identifier begins
with an octal value which is the number of the bit (starting from 1) this
identifier describes. The rest of the identifier is a string of
characters containing the name of the bit. The string is terminated by
either the bit number at the start of the next bit identifier or NUL for
the last bit identifier.
The %D identifier is meant to assist in hexdumps. It requires two
arguments: a u_char * pointer and a char * string. The memory pointed to
by the pointer is output in hexadecimal one byte at a time. The string
is used as a delimiter between individual bytes. If present, a width
Alternatively, if a pri of -1 is given, the message will be appended to
the last log message started by a previous call to log(). As these
messages are generated by the kernel itself, the facility will always be
LOG_KERN.
RETURN VALUES
The printf() and the uprintf() functions return the number of characters
displayed.
EXAMPLES
This example demonstrates the use of the %b and %D conversion specifiers.
The function
void
printf_test(void)
{
printf("reg=%b\n", 3, "\10\2BITTWO\1BITONE");
printf("out: %4D\n", "AAZZ", ":");
}
will produce the following output:
reg=3<BITTWO,BITONE>
out: 41:41:5a:5a
The call
log(LOG_DEBUG, "%s%d: been there.\n", sc->sc_name, sc->sc_unit);
will add the appropriate debug message at priority "kern.debug" to the
system log.
SEE ALSO
printf(3), syslog(3)
FreeBSD 14.0-RELEASE-p11 April 25, 2023 FreeBSD 14.0-RELEASE-p11