From 6065b638011f5f91a80392f2fd4aef81aa3b38ba Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Wed, 6 Sep 2023 09:56:24 +0200
Subject: [PATCH] kernel/ext2: Add support for files larger than 4MB

---
 kernel/src/fs/ext2/Inode.cpp | 52 +++++++++++++++++++++++++++++-------
 kernel/src/fs/ext2/Inode.h   |  3 ++-
 2 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/kernel/src/fs/ext2/Inode.cpp b/kernel/src/fs/ext2/Inode.cpp
index 8c132e79..e1bbd47c 100644
--- a/kernel/src/fs/ext2/Inode.cpp
+++ b/kernel/src/fs/ext2/Inode.cpp
@@ -7,6 +7,13 @@ namespace Ext2
     {
     }
 
+    Result<void> Inode::prepare_buffer() const
+    {
+        if (!m_block_buffer.is_empty()) return {};
+        return m_block_buffer.try_resize(m_fs->m_block_size);
+    }
+
+    // FIXME: This code seems awfully similar to BlockDevice::read(). Can this be merged with it in some way?
     Result<usize> Inode::read(u8* buf, usize offset, usize length) const
     {
         if (length == 0) return 0;
@@ -66,22 +73,47 @@ namespace Ext2
     {
         if (index < 12) 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");
-        }
+        const usize block_size = m_fs->m_block_size;
+        const usize blocks_per_indirect_block = block_size / sizeof(u32);
 
-        usize block_size = m_fs->m_block_size;
+        index -= 12;
 
-        if (m_singly_indirect_block.is_empty())
+        TRY(prepare_buffer());
+
+        // Singly indirect block
+        if (index < blocks_per_indirect_block)
         {
-            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,
+            TRY(m_fs->m_host_device->read(m_block_buffer.data(), m_raw_inode.singly_indirect_ptr * block_size,
                                           block_size));
+            return ((u32*)m_block_buffer.data())[index];
         }
 
-        return *reinterpret_cast<u32*>(&m_singly_indirect_block.data()[block_index]);
+        index -= blocks_per_indirect_block;
+
+        // Doubly indirect block
+        if (index < blocks_per_indirect_block * blocks_per_indirect_block)
+        {
+            TRY(m_fs->m_host_device->read(m_block_buffer.data(), m_raw_inode.doubly_indirect_ptr * block_size,
+                                          block_size));
+            const u32 block = ((u32*)m_block_buffer.data())[index / blocks_per_indirect_block];
+
+            TRY(m_fs->m_host_device->read(m_block_buffer.data(), block * block_size, block_size));
+            return ((u32*)m_block_buffer.data())[index % blocks_per_indirect_block];
+        }
+
+        index -= blocks_per_indirect_block * blocks_per_indirect_block;
+
+        check(index < blocks_per_indirect_block * blocks_per_indirect_block * blocks_per_indirect_block);
+
+        // Triply indirect block
+        TRY(m_fs->m_host_device->read(m_block_buffer.data(), m_raw_inode.triply_indirect_ptr * block_size, block_size));
+        u32 block = ((u32*)m_block_buffer.data())[index / (blocks_per_indirect_block * blocks_per_indirect_block)];
+
+        TRY(m_fs->m_host_device->read(m_block_buffer.data(), block * block_size, block_size));
+        block = ((u32*)m_block_buffer.data())[(index / blocks_per_indirect_block) % blocks_per_indirect_block];
+
+        TRY(m_fs->m_host_device->read(m_block_buffer.data(), block * block_size, block_size));
+        return ((u32*)m_block_buffer.data())[index % blocks_per_indirect_block];
     }
 
     Result<void> Inode::lazy_initialize_dir() const
diff --git a/kernel/src/fs/ext2/Inode.h b/kernel/src/fs/ext2/Inode.h
index fa7211f3..6234f144 100644
--- a/kernel/src/fs/ext2/Inode.h
+++ b/kernel/src/fs/ext2/Inode.h
@@ -115,7 +115,7 @@ namespace Ext2
         FileSystem* m_fs;
         ino_t m_inum;
 
-        mutable Buffer m_singly_indirect_block;
+        mutable Buffer m_block_buffer;
 
         String m_link;
 
@@ -123,6 +123,7 @@ namespace Ext2
         mutable bool m_dir_already_lazily_initialized { false };
 
         Result<usize> find_block(usize index) const;
+        Result<void> prepare_buffer() const;
 
         friend class FileSystem;
     };