477 lines
20 KiB
Plaintext
477 lines
20 KiB
Plaintext
drivers/syslog README File
|
|
==========================
|
|
|
|
SYSLOG 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():
|
|
|
|
syslog() and vsyslog()
|
|
----------------------
|
|
Prototypes:
|
|
|
|
int syslog(int priority, FAR const IPTR char *format, ...);
|
|
void vsyslog(int priority, FAR const IPTR char *src, va_list ap);
|
|
|
|
Description:
|
|
|
|
syslog() generates a log message. The priority argument is formed by
|
|
ORing the facility and the level values (see include/syslog.h). The
|
|
remaining arguments are a format, as in printf and any arguments to the
|
|
format.
|
|
|
|
The NuttX implementation does not support any special formatting
|
|
characters beyond those supported by printf.
|
|
|
|
The function vsyslog() performs the same task as syslog() with the
|
|
difference that it takes a set of arguments which have been obtained
|
|
using the stdarg variable argument list macros.
|
|
|
|
setlogmask()
|
|
------------
|
|
The additional setlogmask() interface can use use to filter SYSLOG output:
|
|
|
|
Prototypes:
|
|
|
|
int setlogmask(int mask);
|
|
|
|
Description:
|
|
|
|
The setlogmask() function sets the logmask and returns the previous
|
|
mask. If the mask argument is 0, the current logmask is not modified.
|
|
|
|
The SYSLOG priorities are: LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR,
|
|
LOG_WARNING, LOG_NOTICE, LOG_INFO, and LOG_DEBUG. The bit corresponding
|
|
to a priority p is LOG_MASK(p); LOG_UPTO(p) provides the mask of all
|
|
priorities in the above list up to and including p.
|
|
|
|
Per OpenGroup.org "If the maskpri argument is 0, the current log mask
|
|
is not modified." In this implementation, the value zero is permitted
|
|
in order to disable all syslog levels.
|
|
|
|
REVISIT: Per POSIX the syslog mask should be a per-process value but in
|
|
NuttX, the scope of the mask is dependent on the nature of the build:
|
|
|
|
* Flat Build: There is one, global SYSLOG mask that controls all output.
|
|
Protected Build: There are two SYSLOG masks. One within the kernel
|
|
that controls only kernel output. And one in user-space that controls
|
|
only user SYSLOG output.
|
|
* Kernel Build: The kernel build is compliant with the POSIX requirement:
|
|
There will be one mask for for each user process, controlling the
|
|
SYSLOG output only form that process. There will be a separate mask
|
|
accessable only in the kernel code to control kernel SYSLOG output.
|
|
*
|
|
|
|
These are all standard interfaces as defined at http://pubs.opengroup.org/onlinepubs/009695399/functions/closelog.html
|
|
|
|
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:
|
|
|
|
* They do not take a priority parameter; the priority is inherent in the
|
|
debug macro name.
|
|
* They decorate the output stream with information such as the file name
|
|
* They can each be disabled via configuration options.
|
|
|
|
Each debug macro has a base name that represents the priority and a prefix
|
|
that represents the sub-system. Each macro is individually initialized by
|
|
both priority and sub-system. For example, uerr() is the macro used for
|
|
error level messages from the USB subsystem and is enabled with
|
|
CONFIG_DEBUG_USB_ERROR.
|
|
|
|
The base debug macro names, their priority, and configuration variable are
|
|
summarized below:
|
|
|
|
* info(). The info() 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. The info() macro is controlled
|
|
via CONFIG_DEBUG_subsystem_INFO
|
|
* warn(). The warn() macro has medium priority (LOG_WARN) and is
|
|
controlled by CONFIG_DEBUG_subsystem_WARN. The warn() 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
|
|
by CONFIG_DEBUG_subsystem_ERROR. The err() is reserved to indicate
|
|
important error conditions.
|
|
* alert(). The highest priority debug macro (LOG_EMERG) and is
|
|
controlled by CONFIG_DEBUG_ALERT. The alert() macro is reserved for
|
|
use solely by assertion and crash handling logic. It also differs
|
|
from the other macros in that it 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:
|
|
|
|
/* This structure provides the interface to a SYSLOG device */
|
|
|
|
typedef CODE int (*syslog_putc_t)(int ch);
|
|
typedef CODE int (*syslog_flush_t)(void);
|
|
|
|
struct syslog_channel_s
|
|
{
|
|
/* I/O redirection methods */
|
|
|
|
#ifdef CONFIG_SYSLOG_WRITE
|
|
syslog_write_t sc_write; /* Write multiple bytes */
|
|
#endif
|
|
syslog_putc_t sc_putc; /* Normal buffered output */
|
|
syslog_putc_t sc_force; /* Low-level output for interrupt handlers */
|
|
syslog_flush_t sc_flush; /* Flush buffered output (on crash) */
|
|
|
|
/* Implementation specific logic may follow */
|
|
};
|
|
|
|
The channel interface is instantiated by calling syslog_channel():
|
|
|
|
syslog_channel()
|
|
----------------
|
|
Prototype:
|
|
|
|
int syslog_channel(FAR const struct syslog_channel_s *channel);
|
|
|
|
Description:
|
|
|
|
Configure the SYSLOGging function to use the provided channel to
|
|
generate SYSLOG output.
|
|
|
|
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.
|
|
|
|
Input Parmeters:
|
|
|
|
* channel - Provides the interface to the channel to be used.
|
|
|
|
Returned Value:
|
|
|
|
Zero (OK) is returned on success. A negated errno value is returned
|
|
on any failure.
|
|
|
|
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:
|
|
|
|
* In-Memory Buffer (RAMLOG). Full SYSLOG capability as available at
|
|
reset.
|
|
* Serial Console. If the serial implementation provides the low-level
|
|
character output function up_putc(), then that low level serial output
|
|
is available as soon as the serial device has been configured.
|
|
* For all other SYSLOG channels, all SYSLOG output goes to the bit-
|
|
bucket until the SYSLOG channel device has been initialized.
|
|
|
|
The syslog channel device is initialized when the bring-up logic calls
|
|
syslog_initialize():
|
|
|
|
syslog_initialize()
|
|
-------------------
|
|
Prototype:
|
|
|
|
#ifndef CONFIG_ARCH_SYSLOG
|
|
int syslog_initialize(void);
|
|
#else
|
|
# define syslog_initialize()
|
|
#endif
|
|
|
|
Description:
|
|
|
|
On power up, the SYSLOG facility is non-existent or limited to very
|
|
low-level output. This function is called later in the initialization
|
|
sequence after full driver support has been initialized. It installs
|
|
the configured SYSLOG drivers and enables full SYSLOGing capability.
|
|
|
|
This function performs these basic operations:
|
|
|
|
* Initialize the SYSLOG device
|
|
* Call syslog_channel() to begin using that device.
|
|
* If CONFIG_ARCH_SYSLOG is selected, then the architecture-specific
|
|
logic will provide its own SYSLOG device initialize which must include
|
|
as a minimum a call to syslog_channel() to use the device.
|
|
|
|
Returned Value:
|
|
Zero (OK) is returned on success; a negated errno value is returned on
|
|
any failure.
|
|
|
|
Different types of SYSLOG devices have different OS initialization
|
|
requirements. Some are available immediately at reset, some are available
|
|
after some basic OS initialization, and some only after OS is fully
|
|
initialized.
|
|
|
|
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.
|
|
|
|
There are three conditions under which SYSLOG output generated from
|
|
interrupt level processing can a included the SYSLOG output stream:
|
|
|
|
1. Low-Level Serial Output
|
|
--------------------------
|
|
If you are using a SYSLOG console channel (CONFIG_SYSLOG_CONSOLE) and if
|
|
the underlying architecture supports the low-level up_putc() interface
|
|
(CONFIG_ARCH_LOWPUTC), then the SYSLOG logic will direct the output to
|
|
up_putc() which is capable of generating the serial output within the
|
|
context of an interrupt handler.
|
|
|
|
There are a few issues in doing this however:
|
|
|
|
* up_putc() is able to generate debug output in any context because it
|
|
disables serial interrupts and polls the hardware directly. These
|
|
polls may take many milliseconds and during that time, all interrupts
|
|
are disable within the interrupt handler. This, of course, interferes
|
|
with the real-time behavior of the RTOS.
|
|
* The output generated by up_putc() is immediate and in real-time. The
|
|
normal SYSLOG output, on the other hand, is buffered in the serial
|
|
driver and may be delayed with respect to the immediate output by many
|
|
lines. Therefore, the interrupt level SYSLOG output provided through
|
|
up_putc() is grossly out of synchronization with other debug output
|
|
|
|
2. In-Memory Buffering
|
|
----------------------
|
|
If the RAMLOG SYSLOG channel is supported, then all SYSLOG output is
|
|
buffered in memory. Interrupt level SYSLOG output is no different than
|
|
normal SYSLOG output in this case.
|
|
|
|
3. Serialization Buffer
|
|
-----------------------
|
|
A final option is the use the an "interrupt buffer" to buffer the
|
|
interrupt level SYSLOG output. In this case:
|
|
|
|
* SYSLOG output generated from interrupt level process in not sent to
|
|
the SYSLOG channel immediately. Rather, it is buffered in the
|
|
interrupt serialization buffer.
|
|
* Later, when the next normal syslog output is generated, it will first
|
|
empty the content of the interrupt buffer to the SYSLOG device in the
|
|
proper context. It will then be followed by the normal syslog output.
|
|
In this case, the interrupt level SYSLOG output will interrupt the
|
|
normal output stream and the interrupt level SYSLOG output will be
|
|
inserted into the correct position in the SYSLOG output when the next
|
|
normal SYSLOG output is generated.
|
|
|
|
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.
|
|
|
|
This SYSLOG channel is automatically selected by syslog_initialize() in
|
|
the LATE initialization phase based on configuration options. The
|
|
configuration options that affect this channel selection include:
|
|
|
|
* CONFIG_DEV_CONSOLE. This setting indicates that the system supports a
|
|
console device, i.e., that the character device /dev/console exists.
|
|
* CONFIG_SERIAL_CONSOLE. This configuration option is automatically
|
|
selected when a UART or USART is configured as the system console.
|
|
There is no user selection.
|
|
* CONFIG_SYSLOG_CONSOLE. This configuration option is manually selected
|
|
from the SYSLOG menu. This is the option that acutally enables the
|
|
SYSLOG console device. It depends on CONFIG_DEV_CONSOLE.
|
|
* CONFIG_ARCH_LOWPUTC. This is an indication from the architecture
|
|
configuration that the platform supports the up_putc() interface.
|
|
up_putc() is a very low level UART interface that can even be used from
|
|
interrupt handling.
|
|
|
|
Interrupt level SYSLOG output will be lost unless: (1) the interrupt buffer
|
|
is enabled to support serialization, or (2) a serial console is used and
|
|
up_putc() is supported.
|
|
|
|
NOTE: The console channel uses the fixed character device at /dev/console.
|
|
The console channel is not synonymous with stdout (or file descriptor 1).
|
|
stdout is the current output from a task when, say, printf() if used.
|
|
Initially, stdout does, indeed, use the /dev/console device. However,
|
|
stdout may subsequently be redirected to some other device or file. This
|
|
is always the case, for example, when a transient device is used for a
|
|
console -- such as a USB console or a Telnet console. The SYSLOG channel
|
|
is not redirected as stdout is; the SYSLOG channel will stayed fixed (unless
|
|
it is explicitly changed via syslog_channel()).
|
|
|
|
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.
|
|
|
|
This SYSLOG device channel is selected with CONFIG_SYSLOG_CHAR and has no
|
|
other dependencies. Differences from the SYSLOG console channel include:
|
|
|
|
* CONFIG_SYSLOG_DEVPATH. This configuration option string must be set
|
|
provide the full path to the character device to be used.
|
|
* The forced SYSLOG output always goes to the bit-bucket. This means
|
|
that interrupt level SYSLOG output will be lost unless the interrupt
|
|
buffer is enabled to support serialization.
|
|
* CONFIG_SYSLOG_CHAR_CRLF. If CONFIG_SYSLOG_CHAR_CRLF is selected, then
|
|
linefeeds in the SYSLOG output will be expanded to Carriage Return +
|
|
Linefeed. Since the character device is not a console device, the
|
|
addition of carriage returns to line feeds would not be performed
|
|
otherwise. You would probably want this expansion if you use a serial
|
|
terminal program with the character device output.
|
|
|
|
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.
|
|
|
|
The interface syslog_file_channel() is used to configure the SYSLOG file
|
|
channel:
|
|
|
|
syslog_file_channel()
|
|
---------------------
|
|
Prototype:
|
|
|
|
#ifdef CONFIG_SYSLOG_FILE
|
|
int syslog_file_channel(FAR const char *devpath);
|
|
#endif
|
|
|
|
Description:
|
|
|
|
Configure to use a file in a mounted file system at 'devpath' as the
|
|
SYSLOG channel.
|
|
|
|
This tiny function is simply a wrapper around syslog_dev_initialize()
|
|
and syslog_channel(). It calls syslog_dev_initialize() to configure
|
|
the character file at 'devpath' and then calls syslog_channel() to use
|
|
that device as the SYSLOG output channel.
|
|
|
|
File SYSLOG channels differ from other SYSLOG channels in that they
|
|
cannot be established until after fully booting and mounting the target
|
|
file system. This function would need to be called from board-specific
|
|
bring-up logic AFTER mounting the file system containing 'devpath'.
|
|
|
|
SYSLOG data generated prior to calling syslog_file_channel will, of
|
|
course, not be included in the file.
|
|
|
|
NOTE interrupt level SYSLOG output will be lost in this case unless
|
|
the interrupt buffer is used.
|
|
|
|
Input Parameters:
|
|
|
|
* devpath - The full path to the file to be used for SYSLOG output.
|
|
This may be an existing file or not. If the file exists,
|
|
syslog_file_channel() will append new SYSLOG data to the end of the
|
|
file. If it does not, then syslog_file_channel() will create the
|
|
file.
|
|
|
|
Returned Value:
|
|
|
|
Zero (OK) is returned on success; a negated errno value is returned on
|
|
any failure.
|
|
|
|
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?
|
|
|
|
The RAM logging driver can also accept debug output data from interrupt
|
|
handler with no special serialization buffering. As an added benefit, the
|
|
RAM logging driver is much less invasive. Since no actual I/O is performed
|
|
with the debug output is generated, the RAM logger tends to be much faster
|
|
and will interfere much less when used with time critical drivers.
|
|
|
|
The RAM logging driver is similar to a pipe in that it saves the debugging
|
|
output in a circular buffer in RAM. It differs from a pipe in numerous
|
|
details as needed to support logging.
|
|
|
|
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
|
|
* CONFIG_RAMLOG_SYSLOG - Use the RAM logging device for the syslogging
|
|
interface. If this feature is enabled, then all debug output (only)
|
|
will be re-directed to the circular buffer in RAM. This RAM log can
|
|
be viewed from NSH using the 'dmesg' command. NOTE: Unlike the
|
|
limited, generic character driver SYSLOG device, the RAMLOG *can* be
|
|
used to capture debug output from interrupt level handlers.
|
|
* CONFIG_RAMLOG_NPOLLWAITERS - The number of threads than can be waiting
|
|
for this driver on poll(). Default: 4
|
|
|
|
If CONFIG_RAMLOG_SYSLOG is selected, then the following must also be
|
|
provided:
|
|
|
|
* CONFIG_RAMLOG_BUFSIZE - The size of the circular buffer to use.
|
|
Default: 1024 bytes.
|
|
|
|
Other miscellaneous settings
|
|
|
|
* CONFIG_RAMLOG_CRLF - Pre-pend a carriage return before every linefeed
|
|
that goes into the RAM log.
|
|
* CONFIG_RAMLOG_NONBLOCKING - Reading from the RAMLOG will never block
|
|
if the RAMLOG is empty. If the RAMLOG is empty, then zero is returned
|
|
(usually interpreted as end-of-file). If you do not define this, the
|
|
NSH 'dmsg' command will lock up when called! So you probably do want
|
|
this!
|
|
* CONFIG_RAMLOG_NPOLLWAITERS - The maximum number of threads that may be
|
|
waiting on the poll method.
|