Working on ch8

os/src/entry.asm

@@ -9,4 +9,4 @@ _start:
 boot_stack:
     .space 4096 * 16
     .globl boot_stack_top
-boot_stack_top:
+boot_stack_top:

os/src/mm/memory_set.rs

@@ -181,23 +181,7 @@ impl MemorySet {
         // map user stack with U flags
         let max_end_va: VirtAddr = max_end_vpn.into();
         let mut user_stack_bottom: usize = max_end_va.into();
-        // guard page
-        user_stack_bottom += PAGE_SIZE;
-        let user_stack_top = user_stack_bottom + USER_STACK_SIZE;
-        memory_set.push(MapArea::new(
-            user_stack_bottom.into(),
-            user_stack_top.into(),
-            MapType::Framed,
-            MapPermission::R | MapPermission::W | MapPermission::U,
-        ), None);
-        // map TrapContext
-        memory_set.push(MapArea::new(
-            TRAP_CONTEXT.into(),
-            TRAMPOLINE.into(),
-            MapType::Framed,
-            MapPermission::R | MapPermission::W,
-        ), None);
-        (memory_set, user_stack_top, elf.header.pt2.entry_point() as usize)
+        (memory_set, user_stack_bottom, elf.header.pt2.entry_point() as usize)
     }
     pub fn from_existed_user(user_space: &MemorySet) -> MemorySet {
         let mut memory_set = Self::new_bare();
@@ -355,4 +339,4 @@ pub fn remap_test() {
         false,
     );
     println!("remap_test passed!");
-}
+}

os/src/task/id.rs

@@ -0,0 +1,126 @@
+use alloc::{vec::Vec, sync::Arc};
+use lazy_static::*;
+use crate::sync::UPSafeCell;
+use crate::mm::{KERNEL_SPACE, MapPermission, VirtAddr};
+use crate::config::{
+    PAGE_SIZE,
+    TRAMPOLINE,
+    KERNEL_STACK_SIZE,
+};
+use super::ProcessControlBlock;
+
+pub struct RecycleAllocator {
+    current: usize,
+    recycled: Vec<usize>,
+}
+
+impl RecycleAllocator {
+    pub fn new() -> Self {
+        RecycleAllocator {
+            current: 0,
+            recycled: Vec::new(),
+        }
+    }
+    pub fn alloc(&mut self) -> usize {
+        if let Some(id) = self.recycled.pop() {
+            id
+        } else {
+            self.current += 1;
+            self.current - 1
+        }
+    }
+    pub fn dealloc(&mut self, id: usize) {
+        assert!(id < self.current);
+        assert!(
+            self.recycled.iter().find(|i| **i == id).is_none(),
+            "id {} has been deallocated!", id
+        );
+        self.recycled.push(id);
+    }
+}
+
+lazy_static! {
+    static ref PID_ALLOCATOR: UPSafeCell<RecycleAllocator> = unsafe {
+        UPSafeCell::new(RecycleAllocator::new())
+    };
+
+    static ref KSTACK_ALLOCATOR: UPSafeCell<RecycleAllocator> = unsafe {
+        UPSafeCell::new(RecycleAllocator::new())
+    };
+}
+
+pub struct PidHandle(pub usize);
+
+pub fn pid_alloc() -> PidHandle {
+    PidHandle(PID_ALLOCATOR.exclusive_access().alloc())
+}
+
+impl Drop for PidHandle {
+    fn drop(&mut self) {
+        PID_ALLOCATOR.exclusive_access().dealloc(self.0);
+    }
+}
+
+/// Return (bottom, top) of a kernel stack in kernel space.
+pub fn kernel_stack_position(kstack_id: usize) -> (usize, usize) {
+    let top = TRAMPOLINE - kstack_id * (KERNEL_STACK_SIZE + PAGE_SIZE);
+    let bottom = top - KERNEL_STACK_SIZE;
+    (bottom, top)
+}
+
+pub struct KernelStack(pub usize);
+
+pub fn kstack_alloc() -> KernelStack {
+    let kstack_id = KSTACK_ALLOCATOR.exclusive_access().alloc();
+    let (kstack_bottom, kstack_top) = kernel_stack_position(kstack_id);
+    KERNEL_SPACE
+        .exclusive_access()
+        .insert_framed_area(
+            kstack_bottom.into(),
+            kstack_top.into(),
+            MapPermission::R | MapPermission::W,
+        );
+    KernelStack(kstack_id)
+}
+
+impl Drop for KernelStack {
+    fn drop(&mut self) {
+        let (kernel_stack_bottom, _) = kernel_stack_position(self.0);
+        let kernel_stack_bottom_va: VirtAddr = kernel_stack_bottom.into();
+        KERNEL_SPACE
+            .exclusive_access()
+            .remove_area_with_start_vpn(kernel_stack_bottom_va.into());
+    }
+}
+
+impl KernelStack {
+    #[allow(unused)]
+    pub fn push_on_top<T>(&self, value: T) -> *mut T where
+        T: Sized, {
+        let kernel_stack_top = self.get_top();
+        let ptr_mut = (kernel_stack_top - core::mem::size_of::<T>()) as *mut T;
+        unsafe { *ptr_mut = value; }
+        ptr_mut
+    }
+    pub fn get_top(&self) -> usize {
+        let (_, kernel_stack_top) = kernel_stack_position(self.0);
+        kernel_stack_top
+    }
+}
+
+pub struct TaskUserRes {
+    pub tid: usize,
+    pub kstack: KernelStack,
+    pub process: Arc<ProcessControlBlock>,
+}
+
+impl Drop for TaskUserRes {
+    fn drop(&mut self) {
+        // dealloc tid
+        let process = self.process.inner_exclusive_access();
+        process.task_res_allocator.dealloc(self.tid);
+        // dealloc trap_cx
+        process.dealloc_trap_cx(self.tid);
+        // kstack can be deallocated automatically 
+    }
+}

os/src/task/mod.rs

@@ -3,7 +3,8 @@ mod switch;
 mod task;
 mod manager;
 mod processor;
-mod pid;
+mod id;
+mod process;
 
 use crate::fs::{open_file, OpenFlags};
 use switch::__switch;
@@ -11,8 +12,10 @@ use task::{TaskControlBlock, TaskStatus};
 use alloc::sync::Arc;
 use manager::fetch_task;
 use lazy_static::*;
-pub use context::TaskContext;
+use process::ProcessControlBlock;
+use id::RecycleAllocator;
 
+pub use context::TaskContext;
 pub use processor::{
     run_tasks,
     current_task,
@@ -22,7 +25,12 @@ pub use processor::{
     schedule,
 };
 pub use manager::add_task;
-pub use pid::{PidHandle, pid_alloc, KernelStack};
+pub use id::{
+    PidHandle,
+    pid_alloc,
+    KernelStack,
+    kstack_alloc,
+};
 
 pub fn suspend_current_and_run_next() {
     // There must be an application running.

os/src/task/pid.rs

@@ -1,108 +0,0 @@
-use alloc::vec::Vec;
-use lazy_static::*;
-use crate::sync::UPSafeCell;
-use crate::mm::{KERNEL_SPACE, MapPermission, VirtAddr};
-use crate::config::{
-    PAGE_SIZE,
-    TRAMPOLINE,
-    KERNEL_STACK_SIZE,
-};
-
-struct PidAllocator {
-    current: usize,
-    recycled: Vec<usize>,
-}
-
-impl PidAllocator {
-    pub fn new() -> Self {
-        PidAllocator {
-            current: 0,
-            recycled: Vec::new(),
-        }
-    }
-    pub fn alloc(&mut self) -> PidHandle {
-        if let Some(pid) = self.recycled.pop() {
-            PidHandle(pid)
-        } else {
-            self.current += 1;
-            PidHandle(self.current - 1)
-        }
-    }
-    pub fn dealloc(&mut self, pid: usize) {
-        assert!(pid < self.current);
-        assert!(
-            self.recycled.iter().find(|ppid| **ppid == pid).is_none(),
-            "pid {} has been deallocated!", pid
-        );
-        self.recycled.push(pid);
-    }
-}
-
-lazy_static! {
-    static ref PID_ALLOCATOR : UPSafeCell<PidAllocator> = unsafe {
-        UPSafeCell::new(PidAllocator::new())
-    };
-}
-
-pub struct PidHandle(pub usize);
-
-impl Drop for PidHandle {
-    fn drop(&mut self) {
-        //println!("drop pid {}", self.0);
-        PID_ALLOCATOR.exclusive_access().dealloc(self.0);
-    }
-}
-
-pub fn pid_alloc() -> PidHandle {
-    PID_ALLOCATOR.exclusive_access().alloc()
-}
-
-/// Return (bottom, top) of a kernel stack in kernel space.
-pub fn kernel_stack_position(app_id: usize) -> (usize, usize) {
-    let top = TRAMPOLINE - app_id * (KERNEL_STACK_SIZE + PAGE_SIZE);
-    let bottom = top - KERNEL_STACK_SIZE;
-    (bottom, top)
-}
-
-pub struct KernelStack {
-    pid: usize,
-}
-
-impl KernelStack {
-    pub fn new(pid_handle: &PidHandle) -> Self {
-        let pid = pid_handle.0;
-        let (kernel_stack_bottom, kernel_stack_top) = kernel_stack_position(pid);
-        KERNEL_SPACE
-            .exclusive_access()
-            .insert_framed_area(
-                kernel_stack_bottom.into(),
-                kernel_stack_top.into(),
-                MapPermission::R | MapPermission::W,
-            );
-        KernelStack {
-            pid: pid_handle.0,
-        }
-    }
-    #[allow(unused)]
-    pub fn push_on_top<T>(&self, value: T) -> *mut T where
-        T: Sized, {
-        let kernel_stack_top = self.get_top();
-        let ptr_mut = (kernel_stack_top - core::mem::size_of::<T>()) as *mut T;
-        unsafe { *ptr_mut = value; }
-        ptr_mut
-    }
-    pub fn get_top(&self) -> usize {
-        let (_, kernel_stack_top) = kernel_stack_position(self.pid);
-        kernel_stack_top
-    }
-}
-
-impl Drop for KernelStack {
-    fn drop(&mut self) {
-        let (kernel_stack_bottom, _) = kernel_stack_position(self.pid);
-        let kernel_stack_bottom_va: VirtAddr = kernel_stack_bottom.into();
-        KERNEL_SPACE
-            .exclusive_access()
-            .remove_area_with_start_vpn(kernel_stack_bottom_va.into());
-    }
-}

os/src/task/process.rs

@@ -0,0 +1,213 @@
+use crate::mm::{
+    MemorySet,
+    KERNEL_SPACE, 
+    VirtAddr,
+    translated_refmut,
+};
+use crate::trap::{TrapContext, trap_handler};
+use crate::config::TRAP_CONTEXT;
+use crate::sync::UPSafeCell;
+use core::cell::RefMut;
+use super::id::RecycleAllocator;
+use super::{TaskContext, TaskControlBlock};
+use super::{PidHandle, pid_alloc, KernelStack, kstack_alloc};
+use alloc::sync::{Weak, Arc};
+use alloc::vec;
+use alloc::vec::Vec;
+use alloc::string::String;
+use crate::fs::{File, Stdin, Stdout};
+
+pub struct ProcessControlBlock {
+    // immutable
+    pub pid: PidHandle,
+    // mutable
+    inner: UPSafeCell<ProcessControlBlockInner>,
+}
+
+pub struct ProcessControlBlockInner {
+    pub base_size: usize,
+    pub is_zombie: bool,
+    pub memory_set: MemorySet,
+    pub parent: Option<Weak<ProcessControlBlock>>,
+    pub children: Vec<Arc<ProcessControlBlock>>,
+    pub exit_code: i32,
+    pub fd_table: Vec<Option<Arc<dyn File + Send + Sync>>>,
+    pub tasks: Vec<Option<Weak<TaskControlBlock>>>,
+    pub task_res_allocator: RecycleAllocator,
+}
+
+impl ProcessControlBlockInner {
+    pub fn get_user_token(&self) -> usize {
+        self.memory_set.token()
+    }
+    pub fn alloc_fd(&mut self) -> usize {
+        if let Some(fd) = (0..self.fd_table.len())
+            .find(|fd| self.fd_table[*fd].is_none()) {
+            fd
+        } else {
+            self.fd_table.push(None);
+            self.fd_table.len() - 1
+        }
+    }
+    pub fn dealloc_trap_cx(&mut self, tid: usize) {
+        unimplemented!();
+        //self.memory_set.remove_area_with_start_vpn()
+    }
+}
+
+impl ProcessControlBlock {
+    pub fn inner_exclusive_access(&self) -> RefMut<'_, ProcessControlBlockInner> {
+        self.inner.exclusive_access()
+    }
+
+    pub fn new(elf_data: &[u8]) -> Self {
+        // memory_set with elf program headers/trampoline/trap context/user stack
+        let (memory_set, user_sp, entry_point) = MemorySet::from_elf(elf_data);
+        let trap_cx_ppn = memory_set
+            .translate(VirtAddr::from(TRAP_CONTEXT).into())
+            .unwrap()
+            .ppn();
+        // alloc a pid and a kernel stack in kernel space
+        let pid_handle = pid_alloc();
+        let kstack = kstack_alloc();
+        let kernel_stack_top = kstack.get_top();
+        let task_control_block = Self {
+            pid: pid_handle,
+            kernel_stack,
+            inner: unsafe { UPSafeCell::new(TaskControlBlockInner {
+                trap_cx_ppn,
+                base_size: user_sp,
+                task_cx: TaskContext::goto_trap_return(kernel_stack_top),
+                task_status: TaskStatus::Ready,
+                memory_set,
+                parent: None,
+                children: Vec::new(),
+                exit_code: 0,
+                fd_table: vec![
+                    // 0 -> stdin
+                    Some(Arc::new(Stdin)),
+                    // 1 -> stdout
+                    Some(Arc::new(Stdout)),
+                    // 2 -> stderr
+                    Some(Arc::new(Stdout)),
+                ],
+            })},
+        };
+        // prepare TrapContext in user space
+        let trap_cx = task_control_block.inner_exclusive_access().get_trap_cx();
+        *trap_cx = TrapContext::app_init_context(
+            entry_point,
+            user_sp,
+            KERNEL_SPACE.exclusive_access().token(),
+            kernel_stack_top,
+            trap_handler as usize,
+        );
+        task_control_block
+    }
+    pub fn exec(&self, elf_data: &[u8], args: Vec<String>) {
+        // memory_set with elf program headers/trampoline/trap context/user stack
+        let (memory_set, mut user_sp, entry_point) = MemorySet::from_elf(elf_data);
+        let trap_cx_ppn = memory_set
+            .translate(VirtAddr::from(TRAP_CONTEXT).into())
+            .unwrap()
+            .ppn();
+        // push arguments on user stack
+        user_sp -= (args.len() + 1) * core::mem::size_of::<usize>();
+        let argv_base = user_sp;
+        let mut argv: Vec<_> = (0..=args.len())
+            .map(|arg| {
+                translated_refmut(
+                    memory_set.token(),
+                    (argv_base + arg * core::mem::size_of::<usize>()) as *mut usize
+                )
+            })
+            .collect();
+        *argv[args.len()] = 0;
+        for i in 0..args.len() {
+            user_sp -= args[i].len() + 1;
+            *argv[i] = user_sp;
+            let mut p = user_sp;
+            for c in args[i].as_bytes() {
+                *translated_refmut(memory_set.token(), p as *mut u8) = *c;
+                p += 1;
+            }
+            *translated_refmut(memory_set.token(), p as *mut u8) = 0;
+        }
+        // make the user_sp aligned to 8B for k210 platform
+        user_sp -= user_sp % core::mem::size_of::<usize>();
+
+        // **** access current TCB exclusively
+        let mut inner = self.inner_exclusive_access();
+        // substitute memory_set
+        inner.memory_set = memory_set;
+        // update trap_cx ppn
+        inner.trap_cx_ppn = trap_cx_ppn;
+        // initialize trap_cx
+        let mut trap_cx = TrapContext::app_init_context(
+            entry_point,
+            user_sp,
+            KERNEL_SPACE.exclusive_access().token(),
+            self.kernel_stack.get_top(),
+            trap_handler as usize,
+        );
+        trap_cx.x[10] = args.len();
+        trap_cx.x[11] = argv_base;
+        *inner.get_trap_cx() = trap_cx;
+        // **** release current PCB
+    }
+    pub fn fork(self: &Arc<TaskControlBlock>) -> Arc<TaskControlBlock> {
+        // ---- hold parent PCB lock
+        let mut parent_inner = self.inner_exclusive_access();
+        // copy user space(include trap context)
+        let memory_set = MemorySet::from_existed_user(
+            &parent_inner.memory_set
+        );
+        let trap_cx_ppn = memory_set
+            .translate(VirtAddr::from(TRAP_CONTEXT).into())
+            .unwrap()
+            .ppn();
+        // alloc a pid and a kernel stack in kernel space
+        let pid_handle = pid_alloc();
+        let kernel_stack = KernelStack::new(&pid_handle);
+        let kernel_stack_top = kernel_stack.get_top();
+        // copy fd table
+        let mut new_fd_table: Vec<Option<Arc<dyn File + Send + Sync>>> = Vec::new();
+        for fd in parent_inner.fd_table.iter() {
+            if let Some(file) = fd {
+                new_fd_table.push(Some(file.clone()));
+            } else {
+                new_fd_table.push(None);
+            }
+        }
+        let task_control_block = Arc::new(TaskControlBlock {
+            pid: pid_handle,
+            kernel_stack,
+            inner: unsafe { UPSafeCell::new(TaskControlBlockInner {
+                trap_cx_ppn,
+                base_size: parent_inner.base_size,
+                task_cx: TaskContext::goto_trap_return(kernel_stack_top),
+                task_status: TaskStatus::Ready,
+                memory_set,
+                parent: Some(Arc::downgrade(self)),
+                children: Vec::new(),
+                exit_code: 0,
+                fd_table: new_fd_table,
+            })},
+        });
+        // add child
+        parent_inner.children.push(task_control_block.clone());
+        // modify kernel_sp in trap_cx
+        // **** access child PCB exclusively
+        let trap_cx = task_control_block.inner_exclusive_access().get_trap_cx();
+        trap_cx.kernel_sp = kernel_stack_top;
+        // return
+        task_control_block
+        // **** release child PCB
+        // ---- release parent PCB
+    }
+    pub fn getpid(&self) -> usize {
+        self.pid.0
+    }
+
+}
+

os/src/task/task.rs

@@ -1,224 +1,39 @@
-use crate::mm::{
-    MemorySet,
-    PhysPageNum,
-    KERNEL_SPACE, 
-    VirtAddr,
-    translated_refmut,
+use alloc::sync::Arc;
+use crate::{mm::PhysPageNum, sync::UPSafeCell};
+use crate::trap::TrapContext;
+use super::{
+    KernelStack,
+    ProcessControlBlock,
+    TaskContext
 };
-use crate::trap::{TrapContext, trap_handler};
-use crate::config::TRAP_CONTEXT;
-use crate::sync::UPSafeCell;
-use core::cell::RefMut;
-use super::TaskContext;
-use super::{PidHandle, pid_alloc, KernelStack};
-use alloc::sync::{Weak, Arc};
-use alloc::vec;
-use alloc::vec::Vec;
-use alloc::string::String;
-use crate::fs::{File, Stdin, Stdout};
 
 pub struct TaskControlBlock {
     // immutable
-    pub pid: PidHandle,
-    pub kernel_stack: KernelStack,
+    pub tid: usize,
+    pub kstack: KernelStack,
+    pub process: Arc<ProcessControlBlock>,
     // mutable
     inner: UPSafeCell<TaskControlBlockInner>,
 }
 
 pub struct TaskControlBlockInner {
     pub trap_cx_ppn: PhysPageNum,
-    pub base_size: usize,
     pub task_cx: TaskContext,
     pub task_status: TaskStatus,
-    pub memory_set: MemorySet,
-    pub parent: Option<Weak<TaskControlBlock>>,
-    pub children: Vec<Arc<TaskControlBlock>>,
     pub exit_code: i32,
-    pub fd_table: Vec<Option<Arc<dyn File + Send + Sync>>>,
 }
 
 impl TaskControlBlockInner {
     pub fn get_trap_cx(&self) -> &'static mut TrapContext {
         self.trap_cx_ppn.get_mut()
     }
-    pub fn get_user_token(&self) -> usize {
-        self.memory_set.token()
-    }
     fn get_status(&self) -> TaskStatus {
         self.task_status
     }
-    pub fn is_zombie(&self) -> bool {
-        self.get_status() == TaskStatus::Zombie
-    }
-    pub fn alloc_fd(&mut self) -> usize {
-        if let Some(fd) = (0..self.fd_table.len())
-            .find(|fd| self.fd_table[*fd].is_none()) {
-            fd
-        } else {
-            self.fd_table.push(None);
-            self.fd_table.len() - 1
-        }
-    }
-}
-
-impl TaskControlBlock {
-    pub fn inner_exclusive_access(&self) -> RefMut<'_, TaskControlBlockInner> {
-        self.inner.exclusive_access()
-    }
-    pub fn new(elf_data: &[u8]) -> Self {
-        // memory_set with elf program headers/trampoline/trap context/user stack
-        let (memory_set, user_sp, entry_point) = MemorySet::from_elf(elf_data);
-        let trap_cx_ppn = memory_set
-            .translate(VirtAddr::from(TRAP_CONTEXT).into())
-            .unwrap()
-            .ppn();
-        // alloc a pid and a kernel stack in kernel space
-        let pid_handle = pid_alloc();
-        let kernel_stack = KernelStack::new(&pid_handle);
-        let kernel_stack_top = kernel_stack.get_top();
-        let task_control_block = Self {
-            pid: pid_handle,
-            kernel_stack,
-            inner: unsafe { UPSafeCell::new(TaskControlBlockInner {
-                trap_cx_ppn,
-                base_size: user_sp,
-                task_cx: TaskContext::goto_trap_return(kernel_stack_top),
-                task_status: TaskStatus::Ready,
-                memory_set,
-                parent: None,
-                children: Vec::new(),
-                exit_code: 0,
-                fd_table: vec![
-                    // 0 -> stdin
-                    Some(Arc::new(Stdin)),
-                    // 1 -> stdout
-                    Some(Arc::new(Stdout)),
-                    // 2 -> stderr
-                    Some(Arc::new(Stdout)),
-                ],
-            })},
-        };
-        // prepare TrapContext in user space
-        let trap_cx = task_control_block.inner_exclusive_access().get_trap_cx();
-        *trap_cx = TrapContext::app_init_context(
-            entry_point,
-            user_sp,
-            KERNEL_SPACE.exclusive_access().token(),
-            kernel_stack_top,
-            trap_handler as usize,
-        );
-        task_control_block
-    }
-    pub fn exec(&self, elf_data: &[u8], args: Vec<String>) {
-        // memory_set with elf program headers/trampoline/trap context/user stack
-        let (memory_set, mut user_sp, entry_point) = MemorySet::from_elf(elf_data);
-        let trap_cx_ppn = memory_set
-            .translate(VirtAddr::from(TRAP_CONTEXT).into())
-            .unwrap()
-            .ppn();
-        // push arguments on user stack
-        user_sp -= (args.len() + 1) * core::mem::size_of::<usize>();
-        let argv_base = user_sp;
-        let mut argv: Vec<_> = (0..=args.len())
-            .map(|arg| {
-                translated_refmut(
-                    memory_set.token(),
-                    (argv_base + arg * core::mem::size_of::<usize>()) as *mut usize
-                )
-            })
-            .collect();
-        *argv[args.len()] = 0;
-        for i in 0..args.len() {
-            user_sp -= args[i].len() + 1;
-            *argv[i] = user_sp;
-            let mut p = user_sp;
-            for c in args[i].as_bytes() {
-                *translated_refmut(memory_set.token(), p as *mut u8) = *c;
-                p += 1;
-            }
-            *translated_refmut(memory_set.token(), p as *mut u8) = 0;
-        }
-        // make the user_sp aligned to 8B for k210 platform
-        user_sp -= user_sp % core::mem::size_of::<usize>();
-
-        // **** access current TCB exclusively
-        let mut inner = self.inner_exclusive_access();
-        // substitute memory_set
-        inner.memory_set = memory_set;
-        // update trap_cx ppn
-        inner.trap_cx_ppn = trap_cx_ppn;
-        // initialize trap_cx
-        let mut trap_cx = TrapContext::app_init_context(
-            entry_point,
-            user_sp,
-            KERNEL_SPACE.exclusive_access().token(),
-            self.kernel_stack.get_top(),
-            trap_handler as usize,
-        );
-        trap_cx.x[10] = args.len();
-        trap_cx.x[11] = argv_base;
-        *inner.get_trap_cx() = trap_cx;
-        // **** release current PCB
-    }
-    pub fn fork(self: &Arc<TaskControlBlock>) -> Arc<TaskControlBlock> {
-        // ---- hold parent PCB lock
-        let mut parent_inner = self.inner_exclusive_access();
-        // copy user space(include trap context)
-        let memory_set = MemorySet::from_existed_user(
-            &parent_inner.memory_set
-        );
-        let trap_cx_ppn = memory_set
-            .translate(VirtAddr::from(TRAP_CONTEXT).into())
-            .unwrap()
-            .ppn();
-        // alloc a pid and a kernel stack in kernel space
-        let pid_handle = pid_alloc();
-        let kernel_stack = KernelStack::new(&pid_handle);
-        let kernel_stack_top = kernel_stack.get_top();
-        // copy fd table
-        let mut new_fd_table: Vec<Option<Arc<dyn File + Send + Sync>>> = Vec::new();
-        for fd in parent_inner.fd_table.iter() {
-            if let Some(file) = fd {
-                new_fd_table.push(Some(file.clone()));
-            } else {
-                new_fd_table.push(None);
-            }
-        }
-        let task_control_block = Arc::new(TaskControlBlock {
-            pid: pid_handle,
-            kernel_stack,
-            inner: unsafe { UPSafeCell::new(TaskControlBlockInner {
-                trap_cx_ppn,
-                base_size: parent_inner.base_size,
-                task_cx: TaskContext::goto_trap_return(kernel_stack_top),
-                task_status: TaskStatus::Ready,
-                memory_set,
-                parent: Some(Arc::downgrade(self)),
-                children: Vec::new(),
-                exit_code: 0,
-                fd_table: new_fd_table,
-            })},
-        });
-        // add child
-        parent_inner.children.push(task_control_block.clone());
-        // modify kernel_sp in trap_cx
-        // **** access child PCB exclusively
-        let trap_cx = task_control_block.inner_exclusive_access().get_trap_cx();
-        trap_cx.kernel_sp = kernel_stack_top;
-        // return
-        task_control_block
-        // **** release child PCB
-        // ---- release parent PCB
-    }
-    pub fn getpid(&self) -> usize {
-        self.pid.0
-    }
-
 }
 
 #[derive(Copy, Clone, PartialEq)]
 pub enum TaskStatus {
     Ready,
     Running,
-    Zombie,
-}
+}