kernel/ext2: Allow reading up to 4 MB of data from files

This is done by scanning the singly indirect pointer of the inode.

kernel/src/fs/ext2/Inode.cpp

@@ -28,7 +28,7 @@ namespace Ext2
         if (offset % block_size)
         {
             usize block_offset = (offset % block_size);
-            usize block = find_block(offset / block_size);
+            usize block = TRY(find_block(offset / block_size));
             usize size_to_read = block_size - block_offset;
             if (size_to_read > to_read) size_to_read = to_read;
 
@@ -44,7 +44,7 @@ namespace Ext2
 
         while (to_read >= block_size)
         {
-            usize block = find_block(offset / block_size);
+            usize block = TRY(find_block(offset / block_size));
 
             usize host_offset = block * block_size;
 
@@ -58,7 +58,7 @@ namespace Ext2
 
         if (to_read > 0)
         {
-            usize block = find_block(offset / block_size);
+            usize block = TRY(find_block(offset / block_size));
 
             usize host_offset = block * block_size;
 
@@ -69,11 +69,26 @@ namespace Ext2
         return length;
     }
 
-    usize Inode::find_block(usize index) const
+    Result<usize> Inode::find_block(usize index) const
     {
-        expect(index < 12, "ext2: Finding blocks in the indirect pointers is not yet supported");
+        if (index < 12) return m_raw_inode.direct_pointers[index];
 
-        return m_raw_inode.direct_pointers[index];
+        usize block_index = (index - 12) * sizeof(u32);
+        if (block_index >= m_fs->m_block_size)
+        {
+            fail("ext2: Finding blocks beyond the singly indirect pointer block is not yet supported");
+        }
+
+        usize block_size = m_fs->m_block_size;
+
+        if (m_singly_indirect_block.is_empty())
+        {
+            TRY(m_singly_indirect_block.try_resize(block_size));
+            TRY(m_fs->m_host_device->read(m_singly_indirect_block.data(), m_raw_inode.singly_indirect_ptr * block_size,
+                                          block_size));
+        }
+
+        return *reinterpret_cast<u32*>(&m_singly_indirect_block.data()[block_index]);
     }
 
     Result<void> Inode::lazy_initialize_dir() const

kernel/src/fs/ext2/Inode.h

@@ -1,5 +1,6 @@
 #pragma once
 #include "fs/ext2/FileSystem.h"
+#include <luna/Buffer.h>
 #include <luna/String.h>
 
 #define EXT2_FIFO 0x1000
@@ -141,12 +142,14 @@ namespace Ext2
         FileSystem* m_fs;
         ino_t m_inum;
 
+        mutable Buffer m_singly_indirect_block;
+
         String m_link;
 
         mutable Vector<VFS::DirectoryEntry> m_entries;
         mutable bool m_dir_already_lazily_initialized { false };
 
-        usize find_block(usize index) const;
+        Result<usize> find_block(usize index) const;
 
         friend class FileSystem;
     };