121 lines
2.9 KiB
ReStructuredText
121 lines
2.9 KiB
ReStructuredText
|
系统调用表实现方案
|
|||
|
|
====================
|
|||
|
|
|
|||
|
|
.. note::
|
|||
|
|
Author: longjin <longjin@dragonos.org>
|
|||
|
|
|
|||
|
|
Date: 2025/05/13
|
|||
|
|
|
|||
|
|
概述
|
|||
|
|
----
|
|||
|
|
|
|||
|
|
.. mermaid::
|
|||
|
|
:align: center
|
|||
|
|
:caption: 系统调用表架构
|
|||
|
|
|
|||
|
|
classDiagram
|
|||
|
|
class Syscall {
|
|||
|
|
<<trait>>
|
|||
|
|
+num_args() usize
|
|||
|
|
+handle(args, from_user) Result<usize, SystemError>
|
|||
|
|
+entry_format(args) Vec<FormattedSyscallParam>
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
class SyscallHandle {
|
|||
|
|
+nr: usize
|
|||
|
|
+inner_handle: &dyn Syscall
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
class SyscallTable {
|
|||
|
|
-entries: [Option<&SyscallHandle>; 512]
|
|||
|
|
+get(nr) Option<&dyn Syscall>
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
Syscall <|.. SysXXXXXXHandle
|
|||
|
|
SyscallHandle "1" *-- "1" Syscall
|
|||
|
|
SyscallTable "1" *-- "512" SyscallHandle
|
|||
|
|
|
|||
|
|
相比于将原本集中在一个大match中的系统调用分发，本方案采用基于trait和系统调用表的实现。主要优势包括：
|
|||
|
|
|
|||
|
|
- 降低栈内存使用：避免单个大函数占用过多栈空间
|
|||
|
|
- 支持参数打印：通过统一的参数格式化接口
|
|||
|
|
- 更好的扩展性：新增系统调用无需修改分发逻辑
|
|||
|
|
|
|||
|
|
核心设计
|
|||
|
|
--------
|
|||
|
|
|
|||
|
|
Syscall Trait
|
|||
|
|
~~~~~~~~~~~~~
|
|||
|
|
|
|||
|
|
所有系统调用处理函数都需要实现 `Syscall` trait：
|
|||
|
|
|
|||
|
|
.. code-block:: rust
|
|||
|
|
|
|||
|
|
pub trait Syscall: Send + Sync + 'static {
|
|||
|
|
fn num_args(&self) -> usize;
|
|||
|
|
fn handle(&self, args: &[usize], from_user: bool) -> Result<usize, SystemError>;
|
|||
|
|
fn entry_format(&self, args: &[usize]) -> Vec<FormattedSyscallParam>;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
- `num_args()`: 返回该系统调用需要的参数数量
|
|||
|
|
- `handle()`: 实际执行系统调用处理
|
|||
|
|
- `entry_format()`: 格式化参数用于调试打印
|
|||
|
|
|
|||
|
|
SyscallHandle
|
|||
|
|
~~~~~~~~~~~~~
|
|||
|
|
|
|||
|
|
`SyscallHandle` 结构体将系统调用号与处理函数关联：
|
|||
|
|
|
|||
|
|
.. code-block:: rust
|
|||
|
|
|
|||
|
|
pub struct SyscallHandle {
|
|||
|
|
pub nr: usize, // 系统调用号
|
|||
|
|
pub inner_handle: &'static dyn Syscall, // 处理函数
|
|||
|
|
pub name: &'static str,
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
SyscallTable
|
|||
|
|
~~~~~~~~~~~~
|
|||
|
|
|
|||
|
|
`SyscallTable` 管理所有系统调用：
|
|||
|
|
|
|||
|
|
- 固定大小512项
|
|||
|
|
- 编译时初始化
|
|||
|
|
- 通过系统调用号快速查找处理函数
|
|||
|
|
|
|||
|
|
使用方式
|
|||
|
|
--------
|
|||
|
|
|
|||
|
|
实现系统调用
|
|||
|
|
~~~~~~~~~~~~
|
|||
|
|
|
|||
|
|
1. 定义实现``Syscall`` trait的结构体
|
|||
|
|
2. 实现``handle()``和``entry_format()``方法
|
|||
|
|
3. 使用``declare_syscall!``宏注册
|
|||
|
|
|
|||
|
|
参考实现：`sys_write.rs <sys_write_>`_
|
|||
|
|
|
|||
|
|
.. _sys_write:
|
|||
|
|
https://github.com/DragonOS-Community/DragonOS/blob/master/kernel/src/filesystem/vfs/syscall/sys_write.rs
|
|||
|
|
|
|||
|
|
注册系统调用
|
|||
|
|
~~~~~~~~~~~~
|
|||
|
|
|
|||
|
|
使用``declare_syscall!``宏注册系统调用：
|
|||
|
|
|
|||
|
|
.. code-block:: rust
|
|||
|
|
|
|||
|
|
syscall_table_macros::declare_syscall!(SYS_WRITE, SysWriteHandle);
|
|||
|
|
|
|||
|
|
参数说明：
|
|||
|
|
|
|||
|
|
1. 系统调用名称（用于生成符号）
|
|||
|
|
2. 实现``Syscall`` trait的结构体
|
|||
|
|
|
|||
|
|
初始化流程
|
|||
|
|
----------
|
|||
|
|
|
|||
|
|
1. 内核启动时调用``syscall_table_init()``
|
|||
|
|
2. 从链接器符号``_syscall_table``加载所有注册的系统调用
|
|||
|
|
3. 填充系统调用表
|