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PRINTF(9) 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 func- tions. 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 se- quence of bit identifiers. Each bit identifier begins with a character specifying the number of the bit (starting from 1) this identifier de- scribes. The characters from \01 to \40 can be used to specify bit numbers in the range from 1 to 32 and characters from \200 to \377 to specify bit numbers in the range from 1 to 128. The rest of the identifier is a string of characters containing the name of the bit. The identifier is terminated by either the bit number at the start of the next bit identifier or by NUL for the last bit identifier. The %D identifier is meant to assist in hexdumps. It requires two argu- ments: 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 direc- tive will specify the number of bytes to display. By default, 16 bytes of data are output. The %n conversion specifier is not supported. 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 mes- sage 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 same output will be generated by the following function: void printf_test(void) { printf("reg=%b\n", 3, "\10\201BITTWO\200BITONE"); printf("out: %4D\n", "AAZZ", ":"); } 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 sys- tem log. SEE ALSO printf(3), syslog(3) FreeBSD ports 15.1 December 19, 2025 PRINTF(9)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO
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