实现SYS_LINK和SYS_LINKAT

kernel/src/filesystem/vfs/syscall.rs

@@ -538,6 +538,93 @@ impl Syscall {
         return do_mkdir(path, FileMode::from_bits_truncate(mode as u32)).map(|x| x as usize);
     }
 
+    /// **创建硬连接的系统调用**
+    ///    
+    /// ## 参数
+    ///
+    /// - 'oldfd': 用于解析源文件路径的文件描述符
+    /// - 'old': 源文件路径
+    /// - 'newfd': 用于解析新文件路径的文件描述符
+    /// - 'new': 新文件将创建的路径
+    /// - 'flags': 标志位，仅以位或方式包含AT_EMPTY_PATH和AT_SYMLINK_FOLLOW
+    ///
+    ///
+    pub fn do_linkat(
+        oldfd: i32,
+        old: &str,
+        newfd: i32,
+        new: &str,
+        flags: i32,
+    ) -> Result<usize, SystemError> {
+        // flag错误时返回EINVAL
+        if flags & ((!(AtFlags::AT_EMPTY_PATH | AtFlags::AT_SYMLINK_FOLLOW)).bits()) != 0 {
+            return Err(SystemError::EINVAL);
+        }
+        // TODO AT_EMPTY_PATH标志启用时，进行调用者CAP_DAC_READ_SEARCH或相似的检查
+        let symlink_times = match flags & AtFlags::AT_SYMLINK_FOLLOW.bits() {
+            0 => 0,
+            _ => VFS_MAX_FOLLOW_SYMLINK_TIMES,
+        };
+        let pcb = ProcessManager::current_pcb();
+
+        // AT_EMPTY_PATH标志不启用时得到源路径的inode的闭包
+        let get_old_inode_without_empty_flag = || {
+            let (old_begin_inode, old_remain_path) = user_path_at(&pcb, oldfd, old)?;
+            old_begin_inode.lookup_follow_symlink(&old_remain_path, symlink_times)
+        };
+
+        // 得到源路径的inode
+        let old_inode: Arc<dyn IndexNode> = match flags & AtFlags::AT_EMPTY_PATH.bits() {
+            0 => get_old_inode_without_empty_flag()?,
+            _ => {
+                if old.len() == 0 {
+                    // 在AT_EMPTY_PATH启用时，old可以为空，old_inode实际为oldfd所指文件，但该文件不能为目录。
+                    let binding = pcb.fd_table();
+                    let fd_table_guard = binding.read();
+                    let file = fd_table_guard
+                        .get_file_by_fd(oldfd)
+                        .ok_or(SystemError::EBADF)?;
+                    let old_inode = file.lock().inode();
+                    if old_inode.metadata().unwrap().file_type == FileType::Dir {
+                        return Err(SystemError::EPERM);
+                    }
+                    old_inode
+                } else {
+                    get_old_inode_without_empty_flag()?
+                }
+            }
+        };
+
+        // 得到新创建节点的父节点
+        let (new_begin_inode, new_remain_path) = user_path_at(&pcb, newfd, new)?;
+        let (new_name, new_parent_path) = rsplit_path(&new_remain_path);
+        let new_parent = new_begin_inode
+            .lookup_follow_symlink(&new_parent_path.unwrap_or("/"), symlink_times)?;
+
+        // 在下层检查是否处于同一文件系统
+        return new_parent.link(&new_name, &old_inode).map(|_| 0);
+    }
+
+    pub fn link(old: &str, new: &str) -> Result<usize, SystemError> {
+        Self::do_linkat(
+            AtFlags::AT_FDCWD.bits() as i32,
+            old,
+            AtFlags::AT_FDCWD.bits() as i32,
+            new,
+            0,
+        )
+    }
+
+    pub fn linkat(
+        oldfd: i32,
+        old: &str,
+        newfd: i32,
+        new: &str,
+        flags: i32,
+    ) -> Result<usize, SystemError> {
+        Self::do_linkat(oldfd, old, newfd, new, flags)
+    }
+
     /// **删除文件夹、取消文件的链接、删除文件的系统调用**
     ///
     /// ## 参数
@@ -579,6 +666,9 @@ impl Syscall {
         if pathname.len() >= MAX_PATHLEN {
             return Err(SystemError::ENAMETOOLONG);
         }
+        if pathname.len() <= 0 {
+            return Err(SystemError::ENOENT);
+        }
         let pathname = pathname.as_str().trim();
         return do_remove_dir(AtFlags::AT_FDCWD.bits(), pathname).map(|v| v as usize);
     }

kernel/src/syscall/mod.rs

@@ -6,6 +6,7 @@ use core::{
 use crate::{
     arch::{ipc::signal::SigSet, syscall::nr::*},
     driver::base::device::device_number::DeviceNumber,
+    filesystem::vfs::fcntl::AtFlags,
     libs::{futex::constant::FutexFlag, rand::GRandFlags},
     mm::syscall::MremapFlags,
     net::syscall::MsgHdr,
@@ -411,6 +412,43 @@ impl Syscall {
                 Self::rmdir(pathname)
             }
 
+            #[cfg(target_arch = "x86_64")]
+            SYS_LINK => {
+                let old_cstr = args[0] as *const u8;
+                let new_cstr = args[1] as *const u8;
+
+                let old = check_and_clone_cstr(old_cstr, Some(MAX_PATHLEN))?;
+                let new = check_and_clone_cstr(new_cstr, Some(MAX_PATHLEN))?;
+                if old.len() >= MAX_PATHLEN || new.len() >= MAX_PATHLEN {
+                    return Err(SystemError::ENAMETOOLONG);
+                }
+                if old.len() <= 0 || new.len() <= 0 {
+                    return Err(SystemError::ENOENT);
+                }
+                return Self::link(&old, &new);
+            }
+
+            #[cfg(target_arch = "x86_64")]
+            SYS_LINKAT => {
+                let oldfd = args[0] as i32;
+                let old_cstr = args[1] as *const u8;
+                let newfd = args[2] as i32;
+                let new_cstr = args[3] as *const u8;
+                let flags = args[4] as i32;
+
+                let old = check_and_clone_cstr(old_cstr, Some(MAX_PATHLEN))?;
+                let new = check_and_clone_cstr(new_cstr, Some(MAX_PATHLEN))?;
+                if old.len() >= MAX_PATHLEN || new.len() >= MAX_PATHLEN {
+                    return Err(SystemError::ENAMETOOLONG);
+                }
+                // old.len() 根据flags & AtFlags::AT_EMPTY_PATH判空
+                if new.len() <= 0 || (old.len() <= 0 && flags & AtFlags::AT_EMPTY_PATH.bits() == 0)
+                {
+                    return Err(SystemError::ENOENT);
+                }
+                return Self::linkat(oldfd, &old, newfd, &new, flags);
+            }
+
             #[cfg(target_arch = "x86_64")]
             SYS_UNLINK => {
                 let pathname = args[0] as *const u8;

kernel/src/syscall/syscall_num.h

@@ -64,9 +64,10 @@
 #define SYS_CHDIR 80
 
 #define SYS_MKDIR 83
-
 #define SYS_RMDIR 84
 
+#define SYS_LINK 86
+
 #define SYS_GETTIMEOFDAY 96
 
 #define SYS_ARCH_PRCTL 158
@@ -84,6 +85,8 @@
 
 #define SYS_UNLINK_AT 263
 
+#define SYS_LINKAT 265
+
 #define SYS_PIPE 293
 
 #define SYS_WRITEV 20