读understanding the linux kernel

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Chapter 3. Processes  只记录了一些记忆有点模糊的和不太懂的
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there is an upper limit on the PID values; when the kernel reaches such limit, it must start recycling the lower, unused

PIDs. By default, the maximum PID number is 32,767 (PID_MAX_DEFAULT - 1);
//进程号是有限度的，默认最大值为32767!
Linux associates a different PID with each process or lightweight process in the system.

On the other hand, Unix programmers expect threads in the same group to have a common PID. For instance, it should be

possible to a send a signal specifying a PID that affects all threads in the group.
//线程是共用一个PID的！且共享内存空间！
a wait queue represents a set of sleeping processes, which are woken up by the kernel when some condition becomes true.
//一个等待队列 代表着许多个睡眠的进程。
Process 1
The kernel thread created by process 0 executes the init( ) function, which in turn completes the initialization of the

kernel. Then init( ) invokes the execve( ) system call to load the executable program init. As a result, the init kernel

thread becomes a regular process having its own per-process kernel data structure . The init process stays alive until the

system is shut down, because it creates and monitors the activity of all processes that implement the outer layers of the

operating system.
//内核线程建立0号进程，它执行init()函数，在这个函数中，将顺序的执行代码，初始化内核。这个初始化进程建立和管理其他所有的进程
//直到关机，初始化进程也就结束了!
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Chapter 4. Interrupts and Exceptions
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All existing IRQ lines are connected to the input pins of a hardware circuit called the Programmable Interrupt Controller,

which performs the following actions:
1.Monitors the IRQ lines, checking for raised signals. If two or more IRQ lines are raised, selects the one having the lower

pin number.

2.If a raised signal occurs on an IRQ line:

a.Converts the raised signal received into a corresponding vector.

b.Stores the vector in an Interrupt Controller I/O port, thus allowing the CPU to read it via the data bus.

c.Sends a raised signal to the processor INTR pin that is, issues an interrupt.

3.Waits until the CPU acknowledges the interrupt signal by writing into one of the Programmable Interrupt Controllers (PIC)

I/O ports; when this occurs, clears the INTR line.

4 . Goes back to step 1.
//所有的中断线都和可编程中断控制器相连，可编程中断控制器负责检查中断，然后做一系列的通知工作！
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