feat:添加symlink系统调用 (#984)

* 添加symlink系统调用

* 修改FATInode的dname的获取逻辑

* 修改fat对Dname的处理，分离dname和inode缓存的key

---------

Co-authored-by: sparkzky <sparkhhhhhhhhh@outlook.com>
Co-authored-by: longjin <longjin@DragonOS.org>

user/apps/test-symlink/src/main.rs

@@ -0,0 +1,78 @@
+extern crate libc;
+use core::ffi::{c_char, c_void};
+use libc::{mount, umount};
+use nix::errno::Errno;
+use std::fs;
+use std::os::unix::fs::symlink;
+use std::path::Path;
+
+fn main() {
+    mount_test_ramfs();
+
+    let target = "/mnt/myramfs/target_file.txt";
+    let symlink_path = "/mnt/myramfs/another/symlink_file.txt";
+    let dir = "/mnt/myramfs/another";
+
+    fs::write(target, "This is the content of the target file.")
+        .expect("Failed to create target file");
+    fs::create_dir(dir).expect("Failed to create target dir");
+
+    assert!(Path::new(target).exists(), "Target file was not created");
+    assert!(Path::new(dir).exists(), "Target dir was not created");
+
+    symlink(target, symlink_path).expect("Failed to create symlink");
+
+    assert!(Path::new(symlink_path).exists(), "Symlink was not created");
+
+    let symlink_content = fs::read_link(symlink_path).expect("Failed to read symlink");
+    assert_eq!(
+        symlink_content.display().to_string(),
+        target,
+        "Symlink points to the wrong target"
+    );
+
+    fs::remove_file(symlink_path).expect("Failed to remove symlink");
+    fs::remove_file(target).expect("Failed to remove target file");
+    fs::remove_dir(dir).expect("Failed to remove test_dir");
+
+    assert!(!Path::new(symlink_path).exists(), "Symlink was not deleted");
+    assert!(!Path::new(target).exists(), "Target file was not deleted");
+    assert!(!Path::new(dir).exists(), "Directory was not deleted");
+
+    umount_test_ramfs();
+
+    println!("All tests passed!");
+}
+
+fn mount_test_ramfs() {
+    let path = Path::new("mnt/myramfs");
+    let dir = fs::create_dir_all(path);
+    assert!(dir.is_ok(), "mkdir /mnt/myramfs failed");
+
+    let source = b"\0".as_ptr() as *const c_char;
+    let target = b"/mnt/myramfs\0".as_ptr() as *const c_char;
+    let fstype = b"ramfs\0".as_ptr() as *const c_char;
+    // let flags = MS_BIND;
+    let flags = 0;
+    let data = std::ptr::null() as *const c_void;
+    let result = unsafe { mount(source, target, fstype, flags, data) };
+
+    assert_eq!(
+        result,
+        0,
+        "Mount myramfs failed, errno: {}",
+        Errno::last().desc()
+    );
+    println!("Mount myramfs success!");
+}
+
+fn umount_test_ramfs() {
+    let path = b"/mnt/myramfs\0".as_ptr() as *const c_char;
+    let result = unsafe { umount(path) };
+    if result != 0 {
+        let err = Errno::last();
+        println!("Errno: {}", err);
+        println!("Infomation: {}", err.desc());
+    }
+    assert_eq!(result, 0, "Umount myramfs failed");
+}