| PRINTF(9) | Kernel Developer's Manual | PRINTF(9) |
printf, uprintf,
tprintf, log —
formatted output conversion
#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);
The printf(9) 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(9) adds two other conversion specifiers.
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 expressed as an integer 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 integer 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 directive will
specify the number of bytes to display. By default, 16 bytes of data are
output.
The
log() function
uses syslog(3) level values
LOG_DEBUG through LOG_EMERG
for its pri parameter (mistakenly called
‘priority’ here). 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.
The printf() and the
uprintf() functions return the number of characters
displayed.
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", "AAAA", ":");
}
will produce the following output:
reg=3<BITTWO,BITONE> out: 41:41:41:41
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.
| November 18, 2015 | Debian |