Lab2 : system calls
作业地址：Lab: System calls (mit.edu)
- Add
$U/_traceto UPROGS in Makefile - add a prototype for the system call to
user/user.h, a stub touser/usys.pl, and a syscall number tokernel/syscall.h. The Makefile invokes the perl scriptuser/usys.pl - Add a
sys_trace()function inkernel/sysproc.cthat implements the new system call by remembering its argument in a new variable in theprocstructure (seekernel/proc.h). The functions to retrieve system call arguments from user space are inkernel/syscall.c, and you can see examples of their use inkernel/sysproc.c. - Modify
fork()(seekernel/proc.c) to copy the trace mask from the parent to the child process.
1、在用户层声明接口
2、在内核中，把用户调用的参数读入，然后传给进程结构体的参数
3、在fork中，把父进程的参数拷贝给子进程
4、在syscall统一的接口中（通过确定系统调用的编号，作为函数指针数组中的索引，进而调用到具体的函数，函数调用的参数从进程的参数中获取argint函数）
system call tracing(moderate)
用trace的mask对系统调用进行跟踪，打印进程号，系统调用名，和系统调用返回值
先定义系统调用号
/* kernel/syscall.h add call number */
#define SYS_trace 22
#define SYS_sysinfo 23
用数组存储系统调用号和函数指针的映射，用于后续调用
/* kernel/syscall.c add */
static uint64 (*syscalls[])(void) = {
[SYS_fork] sys_fork,
[SYS_exit] sys_exit,
[SYS_wait] sys_wait,
[SYS_pipe] sys_pipe,
[SYS_read] sys_read,
[SYS_kill] sys_kill,
[SYS_exec] sys_exec,
[SYS_fstat] sys_fstat,
[SYS_chdir] sys_chdir,
[SYS_dup] sys_dup,
[SYS_getpid] sys_getpid,
[SYS_sbrk] sys_sbrk,
[SYS_sleep] sys_sleep,
[SYS_uptime] sys_uptime,
[SYS_open] sys_open,
[SYS_write] sys_write,
[SYS_mknod] sys_mknod,
[SYS_unlink] sys_unlink,
[SYS_link] sys_link,
[SYS_mkdir] sys_mkdir,
[SYS_close] sys_close,[SYS_trace] sys_trace,
[SYS_sysinfo] sys_sysinfo,
};static char* syscalls_name[] = {
[SYS_fork] "fork",
[SYS_exit] "exit",
[SYS_wait] "wait",
[SYS_pipe] "pipe",
[SYS_read] "read",
[SYS_kill] "kill",
[SYS_exec] "exec",
[SYS_fstat] "fstat",
[SYS_chdir] "chdir",
[SYS_dup] "dup",
[SYS_getpid] "getpid",
[SYS_sbrk] "sbrk",
[SYS_sleep] "sleep",
[SYS_uptime] "uptime",
[SYS_open] "open",
[SYS_write] "write",
[SYS_mknod] "mknod",
[SYS_unlink] "unlink",
[SYS_link] "link",
[SYS_mkdir] "mkdir",
[SYS_close] "close",[SYS_trace] "trace",
[SYS_sysinfo] "sys_sysinfo",
};
void
syscall(void)
{int num;struct proc *p = myproc();num = p->trapframe->a7; // 读取系统调用号if(num > 0 && num < NELEM(syscalls) && syscalls[num]) {/* printf the system call debug message */p->trapframe->a0 = syscalls[num](); //记录返回值if(p->mask & (1 << num)){printf("%d: syscall %s -> %d\n", p->pid, syscalls_name[num],p->trapframe->a0); // 打印trace信息}} else {printf("%d %s: unknown sys call %d\n",p->pid, p->name, num);p->trapframe->a0 = -1;}
}
Sysinfo (moderate)
用sysinfo系统调用，记录当前的进程数量和空闲内存
定义工具方法get_nproc获取进程数量，get_free_memory获取空闲的内存数量
// 根据全局进程数组中进程状态不为
int get_nproc(void)
{// struct proc proc[NPROC]; // 全局进程数组int num = 0;for(int i = 0; i < NPROC; i++) {acquire(&(proc[i].lock));if(proc[i].state != UNUSED)num++;release(&(proc[i].lock));}return num;
}
// 空闲内存是采用链表进行维护的，链表的每个节点代表一个页的空间，最后一个空闲页的next必然为NULL
int get_free_memory(void)
{struct run *r;acquire(&kmem.lock);int num = 0;/* freelist开始计算一直链表访问，直到内存终点 */r = kmem.freelist;while(r){num += PGSIZE;r = r->next;}release(&kmem.lock);return num;
}
uint64
sys_sysinfo(void)
{/* learn sys_fstat() and filestat() to copyout */uint64 addr; // user pointer to struct sysinfoif(argaddr(0, &addr) < 0) // 读取从用户空间传入的结构体指针参数的地址return -1;// addr is a user virtual address, pointing to a struct sinfo.struct proc *p = myproc();struct sysinfo sinfo;// collect the amount of free memorysinfo.freemem = get_free_memory();// collect the number of processessinfo.nproc = get_nproc();if(copyout(p->pagetable, addr, (char *)&sinfo, sizeof(sinfo)) < 0)return -1;return 0;
}
提交
make grade
$ make qemu-gdb
trace 32 grep: OK (2.8s)
== Test trace all grep ==
$ make qemu-gdb
trace all grep: OK (0.6s)
== Test trace nothing ==
$ make qemu-gdb
trace nothing: OK (0.9s)
== Test trace children ==
$ make qemu-gdb
trace children: OK (9.1s)
== Test sysinfotest ==
$ make qemu-gdb
sysinfotest: OK (1.4s)
== Test time ==
time: OK
Score: 35/35
