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COMP421 Lab2 - Yalnix Kernel Xiaoyu Chen (xc12) and Jiafang Jiang (jj26)

• All implementations of the yalnix kernel locate in yalnix.c, except for the idle program which locates in idle.c.

Struct cei (Child Exit Info): Each struct contains pid and exit status of one exited child process, and the pointer to the next cei (NULL if none), which enables each parent process to record all cei's in a FIFO linked list. Note that only when a child process exits will it add its corresponding cei to its parent's linked list.

Struct pcb (Process Control Block): Each process has one until it exits. It contains all necessary bookkeeping variables, whose names themselves are self-explanatory enough. Still, two of them needs some more explanation. 'time_to_switch' is meaningful for two kinds of processes. For the currently running process, it represents the time that the process needs to be context switched if it has not already done so through kernel calls during two clock clicks. In other words, when a process is context switched to, its time_to_switch will be set to current system 'time' plus 2. The other kind of process is delayed process. When a process calls Delay, Its 'time_to_switch' will be set to current system 'time' plus the amount of clock clicks it wants to delay. The other variable 'next' also has different meanings in different circumstances. When a process is in ready queue, its 'next' points to the the next ready process in ready queue (NULL if none). Similarly, when a process is in other queues, its 'next' points to the next process in that specific queue.

Struct line: Struct line represents an input line of user from a specific terminal that has not been read by any programs. So each terminal has its own queue of lines. 'buf' contains the actual line of inputs. 'cur' is the current cursor on the line. 'len' is the length of the line. 'next' makes the queue as a linked list.