Implement sys_read && allocate pid and kernel stack dynamically.

os/src/task/pid.rs

@@ -0,0 +1,104 @@
+use alloc::vec::Vec;
+use lazy_static::*;
+use spin::Mutex;
+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 : Mutex<PidAllocator> = Mutex::new(PidAllocator::new());
+}
+
+pub struct PidHandle(pub usize);
+
+impl Drop for PidHandle {
+    fn drop(&mut self) {
+        PID_ALLOCATOR.lock().dealloc(self.0);
+    }
+}
+
+pub fn pid_alloc() -> PidHandle {
+    PID_ALLOCATOR.lock().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
+            .lock()
+            .insert_framed_area(
+                kernel_stack_bottom.into(),
+                kernel_stack_top.into(),
+                MapPermission::R | MapPermission::W,
+            );
+        KernelStack {
+            pid: pid_handle.0,
+        }
+    }
+    pub fn push_on_top<T>(&self, value: T) -> *mut T where
+        T: Sized, {
+        let (_, kernel_stack_top) = kernel_stack_position(self.pid);
+        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
+            .lock()
+            .remove_area_with_start_vpn(kernel_stack_bottom_va.into());
+    }
+}