ext2: support reading from files with holes

kernel/driver/fs/ext2/src/access.rs

@@ -2,6 +2,22 @@ use libk::error::Error;
 
 use crate::{BlockGroupDescriptor, Ext2Fs, ExtendedSuperblock, Inode};
 
+pub enum InodeBlock<'a> {
+    Hole,
+    Data(&'a [u8]),
+}
+
+impl InodeBlock<'_> {
+    pub fn copy_to(&self, offset: usize, destination: &mut [u8]) {
+        match self {
+            Self::Hole => destination.fill(0),
+            Self::Data(data) => {
+                destination.copy_from_slice(&data[offset..offset + destination.len()])
+            }
+        }
+    }
+}
+
 impl Ext2Fs {
     pub async fn with_block<T, F: FnOnce(&[u8]) -> Result<T, Error>>(
         &self,
@@ -47,14 +63,19 @@ impl Ext2Fs {
             .await
     }
 
-    pub async fn with_inode_block<T, F: FnOnce(&[u8]) -> Result<T, Error>>(
+    pub async fn with_inode_block<T, F: FnOnce(InodeBlock) -> Result<T, Error>>(
         &self,
         inode: &Inode,
         block: u32,
         mapper: F,
     ) -> Result<T, Error> {
         let block_index = self.inode_block_index(inode, block).await?;
-        self.with_block(block_index, mapper).await
+        if block_index == 0 {
+            mapper(InodeBlock::Hole)
+        } else {
+            self.with_block(block_index, |block| mapper(InodeBlock::Data(block)))
+                .await
+        }
     }
 
     pub async fn with_inode_block_mut<T, F: FnOnce(&mut [u8]) -> Result<T, Error>>(

kernel/driver/fs/ext2/src/dir/walk.rs

@@ -9,7 +9,7 @@ use yggdrasil_abi::{
     util::FixedString,
 };
 
-use crate::{data::FsRequiredFeatures, Dirent, Ext2Fs};
+use crate::{access::InodeBlock, data::FsRequiredFeatures, Dirent, Ext2Fs};
 
 use super::DirentName;
 
@@ -110,8 +110,17 @@ impl<'a, D: DerefMut<Target = [u8]> + 'a> Record<'a, D> {
 }
 
 impl<'a> DirentIter<'a> {
-    pub fn new(fs: &'a Ext2Fs, block: &'a [u8], offset: usize) -> Self {
+    pub fn new(fs: &'a Ext2Fs, block: InodeBlock<'a>, offset: usize) -> Self {
-        Self { fs, block, offset }
+        let data = if let InodeBlock::Data(data) = block {
+            data
+        } else {
+            &[]
+        };
+        Self {
+            fs,
+            block: data,
+            offset,
+        }
     }
 
     pub fn offset(&self) -> usize {

kernel/driver/fs/ext2/src/inode/cache.rs

@@ -15,7 +15,8 @@ use yggdrasil_abi::{
 };
 
 use crate::{
-    data::InodeMode, dir::DirectoryNode, file::RegularNode, symlink::SymlinkNode, Ext2Fs, Inode,
+    access::InodeBlock, data::InodeMode, dir::DirectoryNode, file::RegularNode,
+    symlink::SymlinkNode, Ext2Fs, Inode,
 };
 
 pub struct InodeHolder {
@@ -103,7 +104,7 @@ impl InodeAccess {
         result
     }
 
-    pub async fn map_blocks<T, F: Fn(&Inode, usize, &[u8]) -> Result<Option<T>, Error>>(
+    pub async fn map_blocks<T, F: Fn(&Inode, usize, InodeBlock) -> Result<Option<T>, Error>>(
         &self,
         mapper: F,
     ) -> Result<Option<T>, Error> {

kernel/driver/fs/ext2/src/lib.rs

@@ -390,12 +390,17 @@ impl Ext2Fs {
             let block_offset = (pos % self.block_size as u64) as usize;
             let amount = remaining.min(self.block_size - block_offset);
 
-            self.with_inode_block(inode, block_index as u32, |block| {
+            let block = self.inode_block_index(inode, block_index as u32).await?;
+            if block == 0 {
+                buffer[offset..offset + amount].fill(0);
+            } else {
+                self.with_block(block, |block| {
                     buffer[offset..offset + amount]
                         .copy_from_slice(&block[block_offset..block_offset + amount]);
                     Ok(())
                 })
                 .await?;
+            }
 
             pos += amount as u64;
             offset += amount;

kernel/driver/fs/ext2/src/symlink.rs

@@ -54,8 +54,9 @@ impl SymlinkNode {
                 } else {
                     self.fs
                         .with_inode_block(inode, 0, |block| {
-                            write.extend_from_slice(&block[..len]);
+                            write.resize(len, 0);
-                            buf[..len].copy_from_slice(&block[..len]);
+                            block.copy_to(0, &mut write[..]);
+                            block.copy_to(0, &mut buf[..len]);
                             Ok(())
                         })
                         .await?;