PRINTF(9) BSD Kernel Developer's Manual PRINTF(9)
printf, uprintf, tprintf, log -- formatted output conversion
printf(const char *fmt, ...);
tprintf(struct proc *p, int pri, const char *fmt, ...);
uprintf(const char *fmt, ...);
log(int pri, const char *fmt, ...);
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 ker-
nel logging facility, using the log level as indicated by pri.
Each of these related functions use the fmt parameter in the same manner as printf(3). How-
ever, 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 iden-
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 be 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
printf("reg=%b\n", 3, "\10\2BITTWO\1BITONE");
printf("out: %4D\n", "AAAA", ":");
will produce the following output:
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.
BSD September 8, 2006 BSD