Logger (logger)

A circular buffer-based logging system with automatic timestamp insertion and runtime enable/disable control, suitable for kernel and driver debug output.

Configuration

The logging system is controlled via Kconfig options:

Option	Description
CONFIG_XSTAR_LOG	Enable the logging system; the LOG macro only takes effect when enabled
CONFIG_XSTAR_LOGGER_SIZE	Circular buffer size in bytes, default 8192

How It Works

The logger maintains an internal circular buffer (buffer) managed by two pointers, head and tail:

• Write (logger_push): Writes characters one by one to the head position, advancing head; when the buffer is full, tail advances as well, overwriting the oldest data
• Flush (logger_pop): Reads from tail one by one and outputs via xos_stdio_write to stdout, until it catches up with head
• Thread Safety: All buffer operations are protected by a spinlock (spinlock), supporting multi-threaded/multi-core environments

Each call to logger() automatically prepends a microsecond-level timestamp in the format [seconds.microseconds], then formats the user input and immediately flushes the output.

API

Function	Description
LOG(fmt, arg...)	Logging output macro, same format as printf; no-op when CONFIG_XSTAR_LOG is not enabled
logger(fmt, ...)	Low-level logging function, automatically adds timestamp and outputs
logger_enable()	Enable log output
logger_disable()	Disable log output
logger_status()	Query log status, returns 1 if enabled, 0 if disabled

Usage Example

#include <kernel/core/logger.h>

/* Basic log output */
LOG("value = %d\n", value);
LOG("device %s initialized, rate = %lu\n", name, rate);

/* Runtime control */
logger_disable();  /* Temporarily disable logging */
/* ... sensitive operations ... */
logger_enable();   /* Restore logging */

/* Query status */
if(logger_status())
    LOG("logger is active\n");

Example output:

[    1.000123] value = 42
[    1.000456] device uart-pl011 initialized, rate = 115200

Notes

• The LOG macro compiles to a no-op when CONFIG_XSTAR_LOG is not enabled, with zero runtime overhead
• Timestamps are obtained via ktime_get() with microsecond precision
• When the buffer is full, the overwrite strategy retains the newest logs and discards the oldest
• logger() returns immediately in the disabled state without performing any formatting or writing
• Log output is implemented via xos_stdio_write; the actual output target depends on the platform XOS implementation