Linux Kernel Development (2nd) - Study Notes

It is important to initialize hardware and register an interrupt handler in the proper order to prevent the interrupt handler from running before the device is fully initialized.

初始化硬件和注册中断处理程序的顺序必须正确，以防止中断处理程序在设备初始化完成之前就开始执行。

The process can access a memory address only in a valid memory area. Memory areas have associated permissions, such as readable, writable, and executable, that the associated process must respect. If a process accesses a memory address not in a valid memory area, or if it accesses a valid area in an invalid manner, the kernel kills the process with the dreaded “Segmentation Fault” message.

进程只能访问有效范围内的内存地址。每个内存区域也具有相应进程必须遵循的特定访问属性，如只读、只写、可执行等属性。如果一个进程访问了不在有效范围中的地址，或以不正确的方式访问有效地址，那么内核就会终止改进程，并返回“段错误”信息。

Internally, the kobject reference counting is provided by the kref structure, which is defined in <linux/kref.h>:
struct kref {
atomic_t refcount;
};
The lone member is an atomic variable used to hold the reference count.A structure is used simply to provide type checking.

那为什么采用结构体？这是为了便于进行类型检测。

syslogd and klogd
On a standard Linux system, the user-space klogd daemon retrieves the kernel messages from the log buffer and feeds them into the system log file via the syslogd daemon.To read the log, the klogd program can either read the /proc/kmsg file or call the syslog() system call. By default, it uses the /proc approach. In either case, klogd blocks until there are new kernel messages to read. It then wakes up, reads any new messages, and processes them. By default, it sends the messages to the syslogd daemon.
The syslogd daemon appends all the messages it receives to a file, which is by default /var/log/messages. It is configurable via /etc/syslog.conf.
You can have klogd change the console loglevel when it loads by specifying the -c flag when you start it.

在标准的Linux系统上，用户空间的守护进程klogd从纪录缓冲区中获取内核消息，再通过syslogd守护进程把这些消息保存在系统日志文件中。klogd进程既可以从/proc/kmsg文件中，也可以通过syslog()系统调用读取这些消息。默认情况下，它选择读取/proc方式实现。klogd守护进程在消息缓冲区有新的消息之前，一直处于阻塞状态。一旦有新的内核消息，klogd被唤醒，读出内核消息并进行处理。默认情况下，处理例程就是把内核消息传给syslogd守护进程。

   syslogd守护进程一般把接收到的消息写入/var/log/messages文件中。不过，还是可以通过/etc/syslog.conf文件来进行配置，可以选择其他的输出文件。

图1 X光了此过程：

 

参考文献

1. Linux内核调试 - 一般人儿我都不告诉他