安徽平台网站建设制作,列表页面设计模板,如何选择网站托管公司,汽车网页设计论文一、参考
Message logging with printk — The Linux Kernel documentation
如何获得正确的printk格式占位符 — The Linux Kernel documentation
使用printk记录消息 — The Linux Kernel documentation
printk 内核打印 – 人人都懂物联网 (getiot.tech)
内核printk原理…一、参考
Message logging with printk — The Linux Kernel documentation
如何获得正确的printk格式占位符 — The Linux Kernel documentation
使用printk记录消息 — The Linux Kernel documentation
printk 内核打印 – 人人都懂物联网 (getiot.tech)
内核printk原理介绍 - 知乎 (zhihu.com)
Linux kernel log与调试_内核log_hui_zh的博客-CSDN博客
linux内核日志的存储与读取 | QZJ (eathanq.github.io)
二、printk概述
printk 函数主要做两件事情
将信息记录到 log 中调用控制台驱动来将信息输出。
从上图可看出其核心是一个叫做log buffer的循环缓冲区printk作为生产者将消息存入该缓冲区右边的log服务模块作为消费者可从log buffer中读取消息。这样设计有以下几个优点
1、控制台和日志模块初始化前内核的启动日志可以暂存到log buffer中。待它们初始化完成后再输出相应信息。
2、在printk log输出太快而log服务的处理速度不足时防止log信息丢失。
3、将log输入模块和log输出模块解耦增加设计的灵活性。
三、log buffer
在内核启动初期系统内存布局和log buffer大小cpu核心数等因素决定不确定导致无法动态分配内存。为了支持printk内核通过全局变量方式定义一个log buffer全局变量被定义在数据段中会在内核镜像映射过程中被映射其定义如下
// kernel/printk/printk.c/* record buffer */
#define LOG_ALIGN __alignof__(unsigned long)
#define __LOG_BUF_LEN (1 CONFIG_LOG_BUF_SHIFT)
#define LOG_BUF_LEN_MAX (u32)(1 31)
static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
static char *log_buf __log_buf;
static u32 log_buf_len __LOG_BUF_LEN;当必要信息初始化完成后在 start_kernel 函数中调用 setup_log_buf(0) 函数动态分配 log buffer。
void __init setup_log_buf(int early)
{……log_buf_len new_log_buf_len;log_buf new_log_buf;new_log_buf_len 0;……
}四、printk_ringbuffer
log buffer通过数据结构printk_ringbuffer维护其状态信息其主要成员的关系如下图
// kernel/printk/printk_ringbuffer.h/** Meta information about each stored message.** All fields are set by the printk code except for seq, which is* set by the ringbuffer code.*/
struct printk_info {u64 seq; /* sequence number */u64 ts_nsec; /* timestamp in nanoseconds */u16 text_len; /* length of text message */u8 facility; /* syslog facility */u8 flags:5; /* internal record flags */u8 level:3; /* syslog level */u32 caller_id; /* thread id or processor id */struct dev_printk_info dev_info;
};
/** A structure providing the buffers, used by writers and readers.** Writers:* Using prb_rec_init_wr(), a writer sets text_buf_size before calling* prb_reserve(). On success, prb_reserve() sets info and text_buf to* buffers reserved for that writer.** Readers:* Using prb_rec_init_rd(), a reader sets all fields before calling* prb_read_valid(). Note that the reader provides the info and text_buf,* buffers. On success, the struct pointed to by info will be filled and* the char array pointed to by text_buf will be filled with text data.*/
struct printk_record {struct printk_info *info;char *text_buf;unsigned int text_buf_size;
};/* Specifies the logical position and span of a data block. */
struct prb_data_blk_lpos {unsigned long begin;unsigned long next;
};
/** A descriptor: the complete meta-data for a record.** state_var: A bitwise combination of descriptor ID and descriptor state.*/
struct prb_desc {atomic_long_t state_var;struct prb_data_blk_lpos text_blk_lpos;
};/* A ringbuffer of ID data elements. */
struct prb_data_ring {unsigned int size_bits;char *data;atomic_long_t head_lpos;atomic_long_t tail_lpos;
};/* A ringbuffer of struct prb_desc elements. */
struct prb_desc_ring {unsigned int count_bits;struct prb_desc *descs;struct printk_info *infos;atomic_long_t head_id;atomic_long_t tail_id;atomic_long_t last_finalized_id;
};/** The high level structure representing the printk ringbuffer.** fail: Count of failed prb_reserve() calls where not even a data-less* record was created.*/
struct printk_ringbuffer {struct prb_desc_ring desc_ring;struct prb_data_ring text_data_ring;atomic_long_t fail;
};五、日志等级
日志级别的设置用来控制 printk 打印的这条信息是否在终端上显示的当日志级别的数值小于控制台级别时printk 要打印的信息才会在控制台打印出来否则不会显示在控制台
在我们内核中一共有8种级别他们分别为
// include/linux/kern_levels.h#define KERN_EMERG KERN_SOH 0 /* system is unusable */
#define KERN_ALERT KERN_SOH 1 /* action must be taken immediately */
#define KERN_CRIT KERN_SOH 2 /* critical conditions */
#define KERN_ERR KERN_SOH 3 /* error conditions */
#define KERN_WARNING KERN_SOH 4 /* warning conditions */
#define KERN_NOTICE KERN_SOH 5 /* normal but significant condition */
#define KERN_INFO KERN_SOH 6 /* informational */
#define KERN_DEBUG KERN_SOH 7 /* debug-level messages */六、控制台级别
// .config#
# printk and dmesg options
#
CONFIG_PRINTK_TIMEy
# CONFIG_PRINTK_CALLER is not set
# CONFIG_STACKTRACE_BUILD_ID is not set
CONFIG_CONSOLE_LOGLEVEL_DEFAULT7
CONFIG_CONSOLE_LOGLEVEL_QUIET4
CONFIG_MESSAGE_LOGLEVEL_DEFAULT4// include/linux/printk.h/* printks without a loglevel use this.. */
#define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT/* We show everything that is MORE important than this.. */
#define CONSOLE_LOGLEVEL_SILENT 0 /* Mums the word */
#define CONSOLE_LOGLEVEL_MIN 1 /* Minimum loglevel we let people use */
#define CONSOLE_LOGLEVEL_DEBUG 10 /* issue debug messages */
#define CONSOLE_LOGLEVEL_MOTORMOUTH 15 /* You cant shut this one up *//** Default used to be hard-coded at 7, quiet used to be hardcoded at 4,* were now allowing both to be set from kernel config.*/
#define CONSOLE_LOGLEVEL_DEFAULT CONFIG_CONSOLE_LOGLEVEL_DEFAULT
#define CONSOLE_LOGLEVEL_QUIET CONFIG_CONSOLE_LOGLEVEL_QUIET// kernel/printk/printk.cint console_printk[4] {CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
};
EXPORT_SYMBOL_GPL(console_printk);七、常用的日志函数
