Add read_at and write_at for FileLike and InodeHandle

kernel/aster-nix/src/fs/file_handle.rs

@@ -23,6 +23,23 @@ pub trait FileLike: Send + Sync + Any {
         return_errno_with_message!(Errno::EINVAL, "write is not supported");
     }
 
+    /// Read at the given file offset.
+    ///
+    /// The file must be seekable to support `read_at`.
+    /// Unlike [`read`], `read_at` will not change the file offset.
+    fn read_at(&self, offset: usize, buf: &mut [u8]) -> Result<usize> {
+        return_errno_with_message!(Errno::EINVAL, "read_at is not supported");
+    }
+
+    /// Write at the given file offset.
+    ///
+    /// The file must be seekable to support `write_at`.
+    /// Unlike [`write`], `write_at` will not change the file offset.
+    /// If the file is append-only, the `offset` will be ignored.
+    fn write_at(&self, offset: usize, buf: &[u8]) -> Result<usize> {
+        return_errno_with_message!(Errno::EINVAL, "write_at is not supported");
+    }
+
     fn ioctl(&self, cmd: IoctlCmd, arg: usize) -> Result<i32> {
         return_errno_with_message!(Errno::EINVAL, "ioctl is not supported");
     }

kernel/aster-nix/src/fs/inode_handle/dyn_cap.rs

@@ -98,6 +98,20 @@ impl FileLike for InodeHandle<Rights> {
         self.0.write(buf)
     }
 
+    fn read_at(&self, offset: usize, buf: &mut [u8]) -> Result<usize> {
+        if !self.1.contains(Rights::READ) {
+            return_errno_with_message!(Errno::EBADF, "file is not readable");
+        }
+        self.0.read_at(offset, buf)
+    }
+
+    fn write_at(&self, offset: usize, buf: &[u8]) -> Result<usize> {
+        if !self.1.contains(Rights::WRITE) {
+            return_errno_with_message!(Errno::EBADF, "file is not writable");
+        }
+        self.0.write_at(offset, buf)
+    }
+
     fn resize(&self, new_size: usize) -> Result<()> {
         if !self.1.contains(Rights::WRITE) {
             return_errno_with_message!(Errno::EINVAL, "File is not writable");

kernel/aster-nix/src/fs/inode_handle/mod.rs

@@ -41,42 +41,64 @@ struct InodeHandle_ {
 
 impl InodeHandle_ {
     pub fn read(&self, buf: &mut [u8]) -> Result<usize> {
-        let mut offset = self.offset.lock();
-
         if let Some(ref file_io) = self.file_io {
             return file_io.read(buf);
         }
 
-        let len = if self.status_flags().contains(StatusFlags::O_DIRECT) {
-            self.dentry.inode().read_direct_at(*offset, buf)?
-        } else {
-            self.dentry.inode().read_at(*offset, buf)?
-        };
+        let mut offset = self.offset.lock();
+
+        let len = self.read_at(*offset, buf)?;
 
         *offset += len;
         Ok(len)
     }
 
     pub fn write(&self, buf: &[u8]) -> Result<usize> {
-        let mut offset = self.offset.lock();
-
         if let Some(ref file_io) = self.file_io {
             return file_io.write(buf);
         }
 
+        let mut offset = self.offset.lock();
+
         if self.status_flags().contains(StatusFlags::O_APPEND) {
             *offset = self.dentry.size();
         }
-        let len = if self.status_flags().contains(StatusFlags::O_DIRECT) {
-            self.dentry.inode().write_direct_at(*offset, buf)?
-        } else {
-            self.dentry.inode().write_at(*offset, buf)?
-        };
+
+        let len = self.write_at(*offset, buf)?;
 
         *offset += len;
         Ok(len)
     }
 
+    pub fn read_at(&self, offset: usize, buf: &mut [u8]) -> Result<usize> {
+        if let Some(ref file_io) = self.file_io {
+            todo!("support read_at for FileIo");
+        }
+
+        if self.status_flags().contains(StatusFlags::O_DIRECT) {
+            self.dentry.inode().read_direct_at(offset, buf)
+        } else {
+            self.dentry.inode().read_at(offset, buf)
+        }
+    }
+
+    pub fn write_at(&self, mut offset: usize, buf: &[u8]) -> Result<usize> {
+        if let Some(ref file_io) = self.file_io {
+            todo!("support write_at for FileIo");
+        }
+
+        if self.status_flags().contains(StatusFlags::O_APPEND) {
+            // If the file has the O_APPEND flag, the offset is ignored
+            offset = self.dentry.size();
+        }
+
+        if self.status_flags().contains(StatusFlags::O_DIRECT) {
+            self.dentry.inode().write_direct_at(offset, buf)
+        } else {
+            self.dentry.inode().write_at(offset, buf)
+        }
+    }
+
     pub fn read_to_end(&self, buf: &mut Vec<u8>) -> Result<usize> {
         if self.file_io.is_some() {
             return_errno_with_message!(Errno::EINVAL, "file io does not support read to end");