76 lines
3.7 KiB
Plaintext
76 lines
3.7 KiB
Plaintext
drivers/syslog README File
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==========================
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This README file discusses the SYLOG drivers that can be found in the
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drivers/syslog directory. The syslogging interfaces are defined in the
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header file include/syslog.h. In NuttX, "syslog output" is really
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synonymous to "debug output" and, therefore, the debugging interfaces
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defined in the header file include/debug.h are also sysloggin interfaces.
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By default, all system log output goes to console (/dev/console). But that
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behavior can be changed by the defining CONFIG_SYSLOG in the NuttX
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configuration. In that, case all low-level debug output will go through
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syslog_putc().
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One version of syslog_putc() is defined in fs/fs_syslog.c; that version is
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used when CONFIG_SYSLOG_CHAR is defined. That version of syslog_putc()
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just integrates with the file system to re-direct debug output to a
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character device or to a file. A disadvantage of using the generic character
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device for the SYSLOG is that it cannot handle debug output generated from
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interrupt level handles.
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If CONFIG_SYSLOG_CHAR is not defined, then other custom SYSLOG drivers
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can be used. These custom SYSLOG drivers can do things like handle
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unusual logging media and since they can avoid the general file system
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interfaces, can be designed to support debug output from interrupt handlers.
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Those custom SYSLOG drivers reside in this directory.
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ramlog.c
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--------
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The RAM logging driver is a driver that was intended to support debugging
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output (aka, syslogging). It might be used when the normal serial output
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is not available. For example, if you are using a Telnet or USB serial
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console, the debug output will get lost since the USB Telnet session does
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not use the serial console.
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The RAM logginc driver is also useful when debug output on the serial
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console would interfere with performance or with usability. The debug
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output is write to RAM very quickly and so interferes less with realtime
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performance. And since the output does not appear on the serial console
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until you want it to, it does not interfere with the usability of the
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serial console. The NuttShell (NSH), for eample, supports a 'dmesg'
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command that can be used to dump the buffered output when you want to
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see it.
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The RAM logging driver is similar to a pipe in that it saves the
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debugging output in a FIFO in RAM. It differs from a pipe in numerous
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details as needed to support logging.
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This driver is built when CONFIG_RAMLOG is defined in the Nuttx
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configuration.
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Configuration options:
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CONFIG_RAMLOG - Enables the RAM logging feature
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CONFIG_RAMLOG_CONSOLE - Use the RAM logging device as a system console.
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If this feature is enabled (along with CONFIG_DEV_CONSOLE), then all
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console output will be re-directed to a circular buffer in RAM. This
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is useful, for example, if the only console is a Telnet console. Then
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in that case, console output from non-Telnet threads will go to the
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circular buffer and can be viewed using the NSH 'dmesg' command.
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CONFIG_RAMLOG_SYSLOG - Use the RAM logging device for the syslogging
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interface. If this feature is enabled (along with CONFIG_SYSLOG),
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then all debug output (only) will be re-directed to the circular
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buffer in RAM. This RAM log can be view from NSH using the 'dmesg'
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command. NOTE: Unlike the limited, generic character driver SYSLOG
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device, the RAMLOG *can* be used to generate debug output from interrupt
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level handlers.
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CONFIG_RAMLOG_NPOLLWAITERS - The number of threads than can be waiting
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for this driver on poll(). Default: 4
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If CONFIG_RAMLOG_CONSOLE or CONFIG_RAMLOG_SYSLOG is selected, then the
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following may also be provided:
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CONFIG_RAMLOG_BUFSIZE - Size of the console RAM log. Default: 1024
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