The Dlog API provides functions for sending log output.

DLog is the default logging interface for Tizen. The core interface is just `dlog_print`, which is completely standalone and has essentially no preconditions. Logs can later be retrieved using the `dlogutil` CLI tool or `libdlogutil` library.

Required Header

#include <dlog.h>

Overview

Sending log message to circular buffer. Dlog APIs include Priority and Tag. By using priority and Tag, we can easily filtered messages what we want to see.

priority

priority level indicates the urgency of log message

Priority	Description
DLOG_VERBOSE	Verbose, use to let users track what's going on with extra detail. Usually you'll want to gate this behind a `--verbose` flag or similar.
DLOG_DEBUG	Debug, meant for tracking execution details during development. Usually gets compiled out for non-debug builds.
DLOG_INFO	Info, for when something remarkable happens during normal operation.
DLOG_WARN	Warning, for suspicious activity or something that may warrant attention that isn't yet an error. Most tools' default filtering passes this level and above through.
DLOG_ERROR	Error, use when something fails. Avoid using this level as a generic "high priority" message because errors look scary to everybody else; on the other hand if you're writing a tool that parses logs remember that this is how it often gets used in practice.
DLOG_FATAL	Fatal, when an error is hard enough not to be recoverable. Depending on system configuration, dlog can automatically kill the program.
DLOG_SILENT	Silent, for use in filtering tools to "silence" logs, by being higher than the highest "real" level.

Macro example for useful usage

The Dlog APIs can be used by defining own macros. The macros can be defined like below examples. Thus, developers can use appropriate method as a matter of convenience.

#undef LOG_TAG
#define LOG_TAG "APP_TAG"

#define LOGI(fmt, arg...) \
    ({ do { \
        dlog_print(DLOG_INFO, LOG_TAG, "%s: %s(%d) > " fmt, __MODULE__, __func__, __LINE__, ##arg); \
    } while (0); })
#define LOGW(fmt, arg...) \
    ({ do { \
        dlog_print(DLOG_WARN, LOG_TAG, "%s: %s(%d) > " fmt, __MODULE__, __func__, __LINE__, ##arg); \
    } while (0); })
#define LOGE(fmt, arg...) \
    ({ do { \
        dlog_print(DLOG_ERROR, LOG_TAG, "%s: %s(%d) > " fmt, __MODULE__, __func__, __LINE__, ##arg); \
    } while (0); })

Signal

For technical reasons, libdlog blocks the SIGPIPE signal on initialization. If you need to receive it, feel free to reenable it, but note that you may receive the SIGPIPE signal spuriously when writing logs.

dlogutil CLI

dlogutil is a utility that can be utilized to read stored logs.

The most rudimentary way to use it is to run it with no parameters; it then prints all stored logs to the standard output and awaits more.

Parameters exist to change behaviour:

PARAM	DESCRIPTION
-s	Set default filter to *:s (see later for details)
-f filename	Output to given file instead of stdout
-r kbytes	Rotate log file every this many kilobytes.
-n files	Keep this many old rotations
-v	Set log output format.
-b buffer	Select another buffer
-c	Clear the selected buffers
-d	Exit when no more logs are currently available
-t count	Similar to -d, except only print this many logs from the end
-g	Get the size of selected buffers instead of printing logs
-h, --help	Show help info

Additionally, you can specify filters. Filters go behind the parameters and are used to decide which logs are shown.
Each log line has priority and a tag. Filters are specified in the format TAG[:PRIO]. Only logs with given tags and priorities are shown.
You can specify * as the tag to match anything. Beware: only a single asterisk works that way, asterisk is not otherwise expanded. For example, "T*G" filter will NOT match "TAG", only literal "T*G".
If you don't specify any filter, it defaults to *:I
If you specify just * as the tag, without priority, its priority defaults to D
If you specify any other tag without priority, the priority defaults to V

dlogutil allows you to specify buffers. These are:

NAME	REMARKS
main	the default, for general platform logging
system	for system logs
radio	for radio logs
apps	for applications
kmsg	a copy of kernel messages (dmesg)

There are also priorities to be specified. These are one letter abbreviations of the following levels:

LEVEL	DESCRIPTION
V	verbose
D	debug
I	info
W	warning
E	error
F	fatal
S	silent

Depending on products, some of priorities (e.g., V and D) can be disabled by default to prevent too many logs.

Formats, and what they look like:

NAME	SPECIFICATION	EXAMPLE
brief	PRI/TAG(PID): MSG	E/TEST_APP(123): FOO
process	PRI(PID) MSG (TAG)	E(123) FOO (TEST_APP)
tag	PRI/TAG: MSG	E/TEST_APP: FOO
thread	PRI('P'PID, 'T'TID) MSG	E(P123, T456) FOO
raw	MSG	FOO
time	REALTIME PRI/TAG(PID): MSG	12-31 23:59:59.999 +0200 E/TEST_APP(123): FOO
threadtime	REALTIME PRI/TAG('P'PID, 'T'TID): MSG	12-31 23:59:59.999 +0200 E/TEST_APP(P123, T456): FOO
kerneltime	BOOTTIME PRI/TAG('P'PID, 'T'TID): MSG	0.123 E/TEST_APP(P123, T456): FOO
long	[REALTIME PRI/TAG 'P'PID, 'T'TID] MSG	[12-31 23:59:59.999 +0200 E/TEST_APP P123, T456] FOO

Functions
int	dlog_print (log_priority prio, const char tag, const char fmt,...)
	Sends a log message with given priority and tag, using printf formatting.
int	dlog_vprint (log_priority prio, const char tag, const char fmt, va_list ap)
	Sends a log message with given priority and tag label, using variadic args.

Enumeration Type Documentation

enum dlog_error_e

Enumeration for Dlog Errors, returned by API calls.

Some of DLog API calls can return these to denote what happened.

Since :: 2.3

Enumerator:

DLOG_ERROR_NONE	Successful
DLOG_ERROR_INVALID_PARAMETER	Invalid parameter
DLOG_ERROR_NOT_PERMITTED	Operation not permitted

enum log_priority

Enumeration for log priority values in ascending priority order.

Priority level controls how important a message is. This is both a way to a developer to gauge it and for tools to filter for it.

Since :: 2.3

Enumerator:

DLOG_VERBOSE	Verbose, use to let users track what's going on with extra detail. Usually you'll want to gate this behind a `--verbose` flag or similar.
DLOG_DEBUG	Debug, meant for tracking execution details during development. Usually gets compiled out for non-debug builds.
DLOG_INFO	Info, for when something remarkable happens during normal operation.
DLOG_WARN	Warning, for suspicious activity or something that may warrant attention that isn't yet an error. Default filtering passes this level and above through.
DLOG_ERROR	Error, use when something fails.
DLOG_FATAL	Fatal, when an error is hard enough not to be recoverable. Depending on system configuration, dlog can automatically kill the program.
DLOG_SILENT	Silent, for use in filtering tools to "silence" logs, by being higher than the highest "real" level.

Function Documentation

int dlog_print	(	log_priority	prio,
		const char *	tag,
		const char *	fmt,
			...
	)

Sends a log message with given priority and tag, using printf formatting.

Produces a log and sends it to be stored on the DLog backend for later retrieval via dlogutil CLI tool.

Since :: 2.3

Parameters:

[in]	prio	priority level of type log_priority
[in]	tag	tag - a null-terminated string
[in]	fmt	format string - same as printf

Returns:: On success, the function returns the number of bytes written. On error, a negative errno-style error code

Return values:

DLOG_ERROR_INVALID_PARAMETER	Invalid parameter
DLOG_ERROR_NOT_PERMITTED	Operation not permitted

Precondition:: none

Postcondition:: none

See also:: dlog_vprint

#include<dlog.h>
int main(void)
{
    int integer = 21;
    char string[] = "test dlog";

    dlog_print(DLOG_INFO, "USR_TAG", "test dlog");
    dlog_print(DLOG_INFO, "USR_TAG", "%s, %d", string, integer);
    return 0;
}

int dlog_vprint	(	log_priority	prio,
		const char *	tag,
		const char *	fmt,
		va_list	ap
	)

Sends a log message with given priority and tag label, using variadic args.