.\"	$OpenBSD: printf.9,v 1.18 2011/09/19 10:25:37 miod Exp $
.\"     $NetBSD: kprintf.9,v 1.6 1999/03/16 00:40:47 garbled Exp $
.\"
.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jeremy Cooper.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\"
.Dd $Mdocdate: September 19 2011 $
.Dt PRINTF 9
.Os
.Sh NAME
.Nm printf ,
.Nm snprintf ,
.Nm vprintf ,
.Nm vsnprintf ,
.Nm uprintf ,
.Nm ttyprintf ,
.Nm db_printf
.Nd kernel formatted output conversion
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/systm.h>
.Ft int
.Fo "printf"
.Fa "const char *format"
.Fa "..."
.Fc
.Ft int
.Fo "snprintf"
.Fa "char *buf"
.Fa "size_t size"
.Fa "const char *format"
.Fa "..."
.Fc
.Ft int
.Fo "vprintf"
.Fa "const char *format"
.Fa "va_list ap"
.Fc
.Ft int
.Fo "vsnprintf"
.Fa "char *buf"
.Fa "size_t size"
.Fa "const char *fmt"
.Fa "va_list ap"
.Fc
.Ft void
.Fo "uprintf"
.Fa "const char *format"
.Fa "..."
.Fc
.Ft void
.Fo "ttyprintf"
.Fa "struct tty *tty"
.Fa "const char *format"
.Fa "..."
.Fc
.Ft void
.Fn db_printf "const char *format" ...
.Sh DESCRIPTION
The
.Fn printf ,
.Fn snprintf ,
.Fn vprintf ,
.Fn vsnprintf ,
.Fn uprintf ,
.Fn ttyprintf ,
and
.Fn db_printf
functions allow the kernel to send formatted messages to various output
devices.
The functions
.Fn printf
and
.Fn vprintf
send formatted strings to the system console and to the system log.
The functions
.Fn uprintf
and
.Fn ttyprintf
send formatted strings to the current process's controlling tty and a specific
tty,
respectively.
The function
.Fn db_printf
sends formatted strings to the ddb console, and is only used to implement
.Xr ddb 4 .
.Pp
Since each of these kernel functions is a variant of its user space
counterpart, this page describes only the differences between the user
space and kernel versions.
Refer to
.Xr printf 3
for functional details.
.Ss FORMAT OPTIONS
The kernel functions don't support as many formatting specifiers as their
user space counterparts.
In addition to the floating point formatting specifiers,
the following integer type specifiers are not supported in the format string
.Fa format
either :
.Bl -tag -width 5n
.It Li %hh
Argument of
.Li char
type.
This format specifier is accepted by the kernel but will be handled as
.Li %h .
.It Li %j
Argument of
.Li intmax_t
or
.Li uintmax_t
type.
.It Li %t
Argument of
.Li ptrdiff_t
type.
.El
.Pp
The kernel functions also accept the following format specifiers
in the format string
.Fa format :
.Bl -tag -width 5n
.It Li %b
Bit field expansion.
This format specifier is useful for decoding bit fields in device registers.
It displays an integer using a specified radix
.Pq 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
(of type
.Li int ,
unless a width modifier has been specified)
and the second being a decoding directive string.
.Pp
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
.Pq "in C escape-character format"
are
.Li \e10
.Pq octal ,
.Li \e12
.Pq decimal ,
and
.Li \e20
.Pq hexadecimal .
.Pp
The remaining characters in the decoding directive string are interpreted as a
list of bit-position\(endescription pairs.
A bit-position\(endescription 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 position value of 32
.Pq "octal 40, hexadecimal 20, the ASCII space character"
describes the most significant bit.
.Pp
To deal with more than 32 bits, the characters 128
.Pq "octal 200, hexadecimal 80"
through 255
.Pq "octal 377, hexadecimal FF"
are used.
The value 127 is subtracted from the character to determine the
bit position (1 is least significant, and 128 is most significant).
.Pp
The remaining characters in a bit-position\(endescription pair are the
characters to print should the bit being described be set.
Description strings are delimited by the next bit position value character
encountered
.Po
distinguishable by its value being \*(Le 32 or \*(Ge 128
.Pc ,
or the end of the decoding directive string itself.
.El
.Sh RETURN VALUES
The
.Fn printf
and
.Fn vprintf
functions return the number of characters printed.
.Pp
The
.Fn snprintf
and
.Fn vsnprintf
functions return the number of characters that would have been put into
the buffer
.Fa buf
if the
.Fa size
were unlimited.
.Sh EXAMPLES
Use of the
.Li %b
format specifier for decoding device registers.
.Bd -literal -offset indent
printf("reg=%b\en", 3, "\e10\e2BITTWO\e1BITONE")
\(rA "reg=3<BITTWO,BITONE>"

printf("enablereg=%b\en", 0xe860,
       "\e20\ex10NOTBOOT\ex0fFPP\ex0eSDVMA\ex0cVIDEO"
       "\ex0bLORES\ex0aFPA\ex09DIAG\ex07CACHE"
       "\ex06IOCACHE\ex05LOOPBACK\ex04DBGCACHE")
\(rA "enablereg=e860<NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE>"
.Ed
.Sh CODE REFERENCES
.Pa sys/kern/subr_prf.c
.Sh SEE ALSO
.Xr revoke 2 ,
.Xr printf 3 ,
.Xr ddb 4 ,
.Xr log 9