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SYSLOG
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Interfaces
Standard SYSLOG Interfaces
The NuttX SYSLOG is an architecture for getting debug and status information from the system. The syslogging interfaces are defined in the header file include/syslog.h. The primary interface to SYSLOG sub-system is the function syslog() and, to a lesser extent, its companion vsyslog():
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These are all standard interfaces as defined at OpenGroup.org.
Debug Interfaces
In NuttX, syslog output is really synonymous to debug output and, therefore, the debugging interface macros defined in the header file include/debug.h are also syslogging interfaces. Those macros are simply wrappers around syslog(). The debugging interfaces differ from the syslog interfaces in that:
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info(). Theinfo()macro is the lowest priority (LOG_INFO) and is intended to provide general information about the flow of program execution so that you can get an overview of the behavior of the program.info()is often very chatty and voluminous and usually more information than you may want to see. Theinfo()macro is controlled viaCONFIG_DEBUG+subsystem+INFOwarn(). Thewarn()macro has medium priority (LOG_WARN) and is controlled byCONFIG_DEBUG+subsystem+WARN. Thewarn()is intended to note exceptional or unexpected conditions that meigh be potential errors or, perhaps, minor errors that easily recovered.err(). This is a high priority debug macro (LOG_ERROR) and controlled byCONFIG_DEBUG+subsystem+ERROR. Theerr()is reserved to indicate important error conditions.alert(). The highest priority debug macro (LOG_EMERG) and is controlled byCONFIG_DEBUG_ALERT. Thealert()macro is reserved for use solely by assertion and crash handling logic. It also differs from the other macros in that it is global and cannot be enabled or disabled per subsystem.
SYSLOG Channels
SYSLOG Channel Interfaces
In the NuttX SYSLOG implementation, the underlying device logic the supports the SYSLOG output is referred to as a SYSLOG channel. Each SYSLOG channel is represented by an interface defined in include/nuttx/syslog/syslog.h:
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syslog_channel() is a non-standard, internal OS interface and is not available to applications. It may be called numerous times as necessary to change channel interfaces. By default, all system log output goes to console (/dev/console).
SYSLOG Channel Initialization
The initial, default SYSLOG channel is established with statically initialized global variables so that some level of SYSLOG output may be available immediately upon reset. This initialized data is in the file drivers/syslog/syslog_channel.c. The initial SYSLOG capability is determined by the selected SYSLOG channel:
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There are other types of SYSLOG channel devices that may require even further initialization. For example, the file SYSLOG channel (described below) cannot be initialized until the necessary file systems have been mounted.
Interrupt Level SYSLOG Output
As a general statement, SYSLOG output only supports normal output from NuttX tasks. However, for debugging purposes, it is also useful to get SYSLOG output from interrupt level logic. In an embedded system, that is often where the most critical operations are performed.
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The SYSLOG interrupt buffer is enabled with CONFIG_SYSLOG_INTBUFFER. When the interrupt buffer is enabled, you must also provide the size of the interrupt buffer with CONFIG_SYSLOG_INTBUFSIZE.
SYSLOG Channel Options
SYSLOG Console Device
The typical SYSLOG device is the system console. If you are using a serial console, for example, then the SYSLOG output will appear on that serial port.
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References: drivers/syslog/syslog_consolechannel.c and drivers/syslog/syslog_device.c
SYSLOG Character Device
The system console device, /dev/console, is a character driver with some special properties. However, any character driver may be used as the SYSLOG output channel. For example, suppose you have a serial console on /dev/ttyS0 and you want SYSLOG output on /dev/ttyS1. Or suppose you support only a Telnet console but want to capture debug output /dev/ttyS0.
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References: drivers/syslog/syslog_devchannel.c and drivers/syslog/syslog_device.c
SYSLOG File Device
Files can also be used as the sink for SYSLOG output. There is, however, a very fundamental difference in using a file as opposed the system console, a RAM buffer, or character device: You must first mount the file system that supports the SYSLOG file. That difference means that the file SYSLOG channel cannot be supported during the boot-up phase but can be instantiated later when board level logic configures the application environment, including mounting of the file systems.
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References: drivers/syslog/syslog_filechannel.c, drivers/syslog/syslog_device.c, and include/nuttx/syslog/syslog.h.
SYSLOG RAMLOG Device
The RAMLOG is a standalone feature that can be used to buffer any character data in memory. There are, however, special configurations that can be used to configure the RAMLOG as a SYSLOG channel. The RAMLOG functionality is described in a more general way in the following paragraphs.
RAM Logging Device
The RAM logging driver is a driver that was intended to support debugging output (SYSLOG) when the normal serial output is not available. For example, if you are using a Telnet or USB serial console, the debug output will get lost – or worse. For example, what if you want to debug the network over Telnet?
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This driver is built when CONFIG_RAMLOG is defined in the Nuttx configuration.
dmesg
When the RAMLOG (with SYSLOG) is enabled, a new NuttShell (NSH) command will appear: dmesg. The dmsg command will dump the contents of the circular buffer to the console (and also clear the circular buffer).
RAMLOG Configuration options
CONFIG_RAMLOG- Enables the RAM logging feature
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CONFIG_RAMLOG_NPOLLWAITERS- The maximum number of threads that may be waiting on the poll method.
SYSLOG (Input) Character Device
If the option CONFIG_SYSLOG_CHARDEV is selected then support for a special character device at /dev/syslog is supported. The function {{ syslog_register()}} can be used to register that character device:
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