vfs+ext2: initial FsNode::read() implementation

The VFS side of things for read() should be done, however due to my
limited ext2 knowledge, I've not implemented partially reading a file,
and in this state only full files can be read.

ableos/src/filesystem/errors.rs

@@ -7,6 +7,8 @@
 pub enum FsError {
     InodeNotFound,
     InvalidDevice,
+    IsDirectory,
+    EndOfFile,
     UnsupportedOperation,
 }
 

ableos/src/filesystem/ext2.rs

@@ -51,11 +51,24 @@ where
         Ok(())
     }
 
-    fn read(&self, _node: &FsNode, _offset: usize, _size: usize) -> Result<Box<[u8]>> {
-        todo!()
+    fn read(&self, node: &FsNode, offset: usize, size: usize, buffer: &mut Vec<u8>) -> Result<()> {
+        let inode = self
+            .fs
+            .inode_nth(node.inode as usize)
+            .ok_or_else(|| FsError::InodeNotFound)?;
+
+        // FIXME: I don't really know how Ext2 works, so for now we don't
+        //        support non-zero offsets and buffer sizes that don't match
+        //        the file length. We always read the whole file.
+        if offset > 0 || size != inode.size() {
+            Err(FsError::UnsupportedOperation)?;
+        }
+
+        inode.read_to_end(buffer).map_err(|e| e.into())?;
+        Ok(())
     }
 
-    fn write(&self, _node: &FsNode, _offset: usize, _buffer: Box<[u8]>) -> Result<()> {
+    fn write(&self, _node: &FsNode, _offset: usize, _buffer: &[u8]) -> Result<()> {
         todo!()
     }
 

ableos/src/filesystem/mod.rs

@@ -7,6 +7,8 @@
 pub mod errors;
 pub mod ext2;
 
+use core::cmp;
+
 use alloc::sync::{Weak, Arc};
 use bitflags::bitflags;
 
@@ -17,14 +19,15 @@ use FsResult as Result;
 
 pub type FsResult<T> = core::result::Result<T, FsError>;
 
+/// The methods on this trait are to be used internally.
 pub trait StorageDevice
 where
     Self: Send,
 {
     fn open(&self, node: Arc<FsNode> /* TODO: flags */) -> Result<FileDescriptor>;
     fn release(&self, node: FsNode) -> Result<()>;
-    fn read(&self, node: &FsNode, offset: usize, size: usize) -> Result<Box<[u8]>>;
-    fn write(&self, node: &FsNode, offset: usize, buffer: Box<[u8]>) -> Result<()>;
+    fn read(&self, node: &FsNode, offset: usize, size: usize, buffer: &mut Vec<u8>) -> Result<()>;
+    fn write(&self, node: &FsNode, offset: usize, buffer: &[u8]) -> Result<()>;
     fn read_dir(&self, node: &FsNode, index: usize) -> Result<DirectoryEntry>;
     fn find_dir(&self, node: &FsNode, name: &str) -> Result<FsNode>;
 }
@@ -94,19 +97,29 @@ impl FsNode {
     /// This method reads from the VFS node without opening a new file
     /// descriptor. This is intended to be used internally, if you're trying to
     /// read a file then you probably want to read from a file descriptor.
-    pub fn read(&self, offset: usize, size: usize) -> Result<Box<[u8]>> {
+    pub fn read(&self, offset: usize, size: usize, buffer: &mut Vec<u8>) -> Result<usize> {
         let state = KERNEL_STATE.lock();
         let device = state
             .get_storage_device(self.device_handle)
             .ok_or_else(|| FsError::InvalidDevice)?;
 
-        device.read(self, offset, size)
+        if self.is_dir() {
+            Err(FsError::IsDirectory)?;
+        }
+
+        if offset > self.length {
+            Err(FsError::EndOfFile)?;
+        }
+
+        let readable_size = cmp::min(size, self.length - offset);
+        device.read(self, offset, readable_size, buffer)?;
+        Ok(readable_size)
     }
 
     /// This method writes to the VFS node without opening a new file
     /// descriptor. This is intended to be used internally, if you're trying to
     /// write to a file then you probably want to write to a file descriptor.
-    pub fn write(&self, offset: usize, buffer: Box<[u8]>) -> Result<()> {
+    pub fn write(&self, offset: usize, buffer: &[u8]) -> Result<()> {
         let state = KERNEL_STATE.lock();
         let device = state
             .get_storage_device(self.device_handle)
@@ -132,6 +145,10 @@ impl FsNode {
 
         device.find_dir(self, name)
     }
+
+    pub fn is_dir(&self) -> bool {
+        (self.flags & FsFlags::DIRECTORY) == FsFlags::DIRECTORY
+    }
 }
 
 impl Drop for FsNode {