man/man9/kprintf.9

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.\" $FreeBSD: src/share/man/man9/printf.9,v 1.8 2006/09/08 14:05:03 ru Exp $
.\"
.Dd March 13, 2020
.Dt KPRINTF 9
.Os
.Sh NAME
.Nm kprintf ,
.Nm ksprintf ,
.Nm ksnprintf ,
.Nm kvprintf ,
.Nm kvsprintf ,
.Nm kvsnprintf ,
.Nm krateprintf ,
.Nm tprintf ,
.Nm uprintf ,
.Nm log
.Nd formatted output conversion
.Sh SYNOPSIS
.In sys/types.h
.In sys/systm.h
.Ft int
.Fn kprintf "const char *format" ...
.Ft int
.Fn ksprintf "char *str" "const char *format" ...
.Ft int
.Fn ksnprintf "char *str" "size_t size" "const char *format" ...
.Ft int
.Fn kvprintf "const char *format" "__va_list ap"
.Ft int
.Fn kvsprintf "char *str" "const char *format" "__va_list ap"
.Ft int
.Fn kvsnprintf "char *str" "size_t size" "const char *format" "__va_list ap"
.Ft int
.Fn krateprintf "struct krate *rate" "const char *format" ...
.Ft int
.Fn uprintf "const char *format" ...
.In sys/tprintf.h
.Ft int
.Fn tprintf "struct proc *p" "int pri" "const char *format" ...
.In sys/syslog.h
.Ft int
.Fn log "int pri" "const char *format" ...
.Sh DESCRIPTION
The
.Nm
family of functions are similar to the
.Xr printf 3
family of functions.
The different functions each use a different output stream.
The
.Fn uprintf
function outputs to the current process' controlling tty, while
.Fn kprintf ,
.Fn ksprintf ,
.Fn ksnprintf ,
.Fn kvprintf ,
.Fn kvsprintf
and
.Fn kvsnprintf
write to the console as well as to the logging facility.
The
.Fn tprintf
function outputs to the tty associated with the process
.Fa p
and the logging facility if
.Fa pri
is not \-1.
The
.Fn log
function sends the message to the kernel logging facility, using
the log level as indicated by
.Fa pri .
.Pp
Each of these related functions use the
.Fa format ,
.Fa str ,
.Fa size
and
.Fa ap
parameters in the same manner as
.Xr printf 3 .
However, the
.Nm
functions add another conversion specifier to
.Fa format :
.Pp
The
.Cm \&%pb%i
identifier expects two arguments: an
.Vt "char *"
and a
.Vt int .
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, \e10 gives octal and \e20 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
.Dv NUL
for the last bit identifier.
.Pp
The
.Fn log
function uses
.Xr syslog 3
level values
.Dv LOG_DEBUG
through
.Dv LOG_EMERG
for its
.Fa pri
parameter (mistakenly called
.Sq priority
here).
Alternatively, if a
.Fa pri
of \-1 is given, the message will be appended to the last log message
started by a previous call to
.Fn log .
As these messages are generated by the kernel itself, the facility will
always be
.Dv LOG_KERN .
.Pp
The
.Fn krateprintf
function is a rate controlled version of
.Fn kprintf .
The
.Fa freq
member of the
.Vt struct krate
pointed to by
.Fa rate
must be initialized with the desired reporting frequency.
A
.Fa freq
of 0 will result in no output.
Initializing
.Fa count
to a negative value allows an initial burst.
.Sh RETURN VALUES
The
.Fn kprintf ,
.Fn ksprintf ,
.Fn ksnprintf ,
.Fn kvprintf ,
.Fn kvsprintf ,
.Fn kvsnprintf ,
.Fn tprintf ,
.Fn uprintf ,
and
.Fn log
functions return the number of characters displayed.
.Pp
The
.Fn krateprintf
function returns 1 or 0, depending on whether anything was printed or not,
allowing code to issue additional
.Fn kprintf Ns s
if desired.
.Sh LOADER TUNABLES
Tunables can be set at the
.Xr loader 8
prompt before booting the kernel or stored in
.Xr loader.conf 5 .
.Bl -tag -width "xxxxxx"
.It Va kern.kprintf_logging
A bit mask that specifies the targets of
.Fn kprintf .
Supported targets are the console (0x1) and the dmesg buffer (0x4).
The default value is 5 (print to both).
.It Va kern.log_console_output
Specifies whether console output is duplicated to the syslog.
The default value is 1.
.It Va security.ptr_restrict
Specifying 1 masks out the upper bits of pointers printed  with %p, and
specifying 2 masks out pointer values altogether.
The default value is 0.
.It Va security.unprivileged_read_msgbuf
Specifies if unprivileged processes may read the kernel buffer.
The default value is 1.
.El
.Sh SYSCTL VARIABLES
The loader tunables described in
.Sx LOADER TUNABLES
are also available as sysctl(8) variables of the same names.
.Sh EXAMPLES
This example demonstrates the use of the
.Cm \&%pb%i
conversion specifier.
The function
.Bd -literal -offset indent
void
kprintf_test(void)
{
	kprintf("reg=%pb%i\en", "\e10\e2BITTWO\e1BITONE\en", 3);
}
.Ed
.Pp
will produce the following output:
.Bd -literal -offset indent
reg=3<BITTWO,BITONE>
.Ed
.Pp
The call
.Bd -literal -offset indent
log(LOG_DEBUG, "%s%d: been there.\en", sc->sc_name, sc->sc_unit);
.Ed
.Pp
will add the appropriate debug message at priority
.Dq Li kern.debug
to the system log.
.Sh SEE ALSO
.Xr printf 3 ,
.Xr syslog 3