新增rust版本的lockref (#135)

* new:Rust封装cpu_relax(),通过pause指令，让cpu休息一会儿。降低空转功耗

* new: Rust版本的lockref

* Rust的RawSpinlock新增is_locked()和set_value()方法。

* lockref文档

kernel/src/arch/x86_64/asm/cmpxchg.c

@@ -0,0 +1,7 @@
+#include <arch/x86_64/include/asm/cmpxchg.h>
+
+bool __try_cmpxchg_q(uint64_t *ptr, uint64_t *old_ptr, uint64_t *new_ptr)
+{
+    bool success = __raw_try_cmpxchg(ptr, old_ptr, *new_ptr, 8);
+    return success;
+}

kernel/src/arch/x86_64/asm/cmpxchg.rs

@@ -0,0 +1,12 @@
+// 该函数在cmpxchg.c中实现
+extern "C" {
+    fn __try_cmpxchg_q(ptr: *mut u64, old_ptr: *mut u64, new_ptr: *mut u64) -> bool;
+}
+
+/// @brief 封装lock cmpxchg指令
+/// 由于Rust实现这部分的内联汇编比较麻烦（实在想不出办法），因此使用C的实现。
+#[inline]
+pub unsafe fn try_cmpxchg_q(ptr: *mut u64, old_ptr: *mut u64, new_ptr: *mut u64) -> bool {
+    let retval = __try_cmpxchg_q(ptr, old_ptr, new_ptr);
+    return retval;
+}

kernel/src/arch/x86_64/asm/mod.rs

@@ -2,4 +2,5 @@ pub mod irqflags;
 #[macro_use]
 pub mod current;
 pub mod ptrace;
-pub mod bitops;
+pub mod bitops;
+pub mod cmpxchg;

kernel/src/arch/x86_64/cpu.rs

@@ -14,3 +14,10 @@ pub fn arch_current_apic_id() -> u8 {
     }
     return (cpuid_res >> 24) as u8;
 }
+
+/// @brief 通过pause指令，让cpu休息一会儿。降低空转功耗
+pub fn cpu_relax() {
+    unsafe {
+        asm!("pause");
+    }
+}

kernel/src/arch/x86_64/include/asm/cmpxchg.h

@@ -79,3 +79,5 @@ extern void __cmpxchg_wrong_size(void) __compiletime_error("Bad argument size fo
 
 #define arch_try_cmpxchg(ptr, old_ptr, new_ptr) \
     __raw_try_cmpxchg((ptr), (old_ptr), (new_ptr), sizeof(*ptr))
+
+bool __try_cmpxchg_q(uint64_t *ptr, uint64_t *old_ptr, uint64_t *new_ptr);