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KPRINTF(9) Kernel Developer's Manual KPRINTF(9)

device_printf, printf, printf_nolog, snprintf, vasprintf, vprintf, vsnprintf, uprintf, ttyprintf, tprintf_open, tprintf, tprintf_close, aprint_normal, aprint_naive, aprint_verbose, aprint_debug, aprint_error, aprint_normal_dev, aprint_naive_dev, aprint_verbose_dev, aprint_debug_dev, aprint_error_dev, aprint_normal_ifnet, aprint_naive_ifnet, aprint_verbose_ifnet, aprint_debug_ifnet, aprint_error_ifnet, aprint_get_error_count — kernel formatted output conversion

#include <sys/systm.h>

void
device_printf(device_t, const char *format, ...);

void
printf(const char *format, ...);

void
printf_nolog(const char *format, ...);

int
snprintf(char *buf, size_t size, const char *format, ...);

int
vasprintf(char **buf, const char *format, va_list ap);

void
vprintf(const char *format, va_list ap);

int
vsnprintf(char *buf, size_t size, const char *format, va_list ap);

void
uprintf(const char *format, ...);

void
ttyprintf(struct tty *tty, const char *format, ...);

#include <sys/tprintf.h>

tpr_t
tprintf_open(struct proc *p);

void
tprintf(tpr_t tpr, const char *format, ...);

void
tprintf_close(tpr_t tpr);

void
aprint_normal(const char *format, ...);

void
aprint_naive(const char *format, ...);

void
aprint_verbose(const char *format, ...);

void
aprint_debug(const char *format, ...);

void
aprint_error(const char *format, ...);

void
aprint_normal_dev(device_t, const char *format, ...);

void
aprint_naive_dev(device_t, const char *format, ...);

void
aprint_verbose_dev(device_t, const char *format, ...);

void
aprint_debug_dev(device_t, const char *format, ...);

void
aprint_error_dev(device_t, const char *format, ...);

void
aprint_normal_ifnet(struct ifnet *, const char *format, ...);

void
aprint_naive_ifnet(struct ifnet *, const char *format, ...);

void
aprint_verbose_ifnet(struct ifnet *, const char *format, ...);

void
aprint_debug_ifnet(struct ifnet *, const char *format, ...);

void
aprint_error_ifnet(struct ifnet *, const char *format, ...);

int
aprint_get_error_count(void);

The () family of functions allows the kernel to send formatted messages to various output devices. The functions printf() and () send formatted strings to the system console. The () function is identical to printf(), except that it prefixes the log message with the corresponding device name. The () function is identical to printf(), except it does not send the data to the system log. The functions (), (), and () write output to a string buffer. These five functions work similarly to their user space counterparts, and are not described in detail here. The vasprintf() function allocates memory with kmem_alloc(9) and it is the caller's responsibility to free the returned string with kmem_free(9).

The functions () and () send formatted strings to the current process's controlling tty and a specific tty, respectively.

The () function sends formatted strings to a process's controlling tty, via a handle of type tpr_t. This allows multiple write operations to the tty with a guarantee that the tty will be valid across calls. A handle is acquired by calling () with the target process as an argument. This handle must be closed with a matching call to ().

The functions (), (), (), (), and () are intended to be used to print autoconf(9) messages. Their verbosity depends on flags set in the boothowto variable, through options passed during bootstrap; see boothowto(9) and Interactive mode in boot(8):

silent mode, enabled by boot -z.
quiet mode, enabled by boot -q.
verbose mode, enabled by boot -v.
debug mode, enabled by boot -x.

The () functions have the following behaviour, based on the above mentioned flags:

aprint_normal()
Sends to the console unless AB_QUIET is set. Always sends to the log.
aprint_naive()
Sends to the console only if AB_QUIET is set. Never sends to the log.
aprint_verbose()
Sends to the console only if AB_VERBOSE is set. Always sends to the log.
aprint_debug()
Sends to the console and the log only if AB_DEBUG is set.
aprint_error()
Like aprint_normal(), but also keeps track of the number of times called. This allows a subsystem to report the number of errors that occurred during a quiet or silent initialization phase.

For the () functions there are two additional families of functions with the suffixes _dev and _ifnet which work like their counterparts without the suffixes, except that they take a device_t and struct ifnet *, respectively, as first argument, and prefix the log message with the corresponding device or interface name.

The () function reports the number of errors and resets the counter to 0.

If AB_SILENT is set, none of the autoconfiguration message printing routines send output to the console. The AB_VERBOSE and AB_DEBUG flags override AB_SILENT.

The snprintf() and vsnprintf() functions return the number of characters that would have been placed in the buffer buf. if there was enough space in the buffer, not including the trailing NUL character used to terminate output strings like the user-space functions of the same name.

The tprintf_open() function returns NULL if no terminal handle could be acquired.

sys/kern/subr_prf.c

printf(1), printf(3), snprintb(3), boot(8), autoconf(9), boothowto(9)

In NetBSD 1.5 and earlier, printf() supported more format strings than the user space printf(). These nonstandard format strings are no longer supported. For the functionality provided by the former %b format string, see snprintb(3).

The aprint_normal(), aprint_naive(), aprint_verbose(), and aprint_debug() functions first appeared in BSD/OS.

The uprintf() and ttyprintf() functions should be used sparingly, if at all. Where multiple lines of output are required to reach a process's controlling terminal, tprintf() is preferred.

May 20, 2019 NetBSD-9.2