kernel/ext2: Implement Inode::read()

kernel/src/fs/ext2/FileSystem.h

@@ -81,6 +81,8 @@ namespace Ext2
     static_assert(sizeof(BlockGroupDescriptor) == 32);
     static_assert(sizeof(RawInode) == 128);
 
+    class Inode;
+
     class FileSystem : public VFS::FileSystem
     {
       public:
@@ -149,5 +151,7 @@ namespace Ext2
         HashMap<ino_t, SharedPtr<VFS::Inode>> m_inode_cache;
 
         HashMap<u32, BlockGroupDescriptor> m_block_group_descriptor_cache;
+
+        friend class Inode;
     };
 }

kernel/src/fs/ext2/Inode.cpp

@@ -6,8 +6,64 @@ namespace Ext2
     {
     }
 
-    Result<usize> Inode::read(u8* /*buf*/, usize /*offset*/, usize /*length*/) const
+    Result<usize> Inode::read(u8* buf, usize offset, usize length) const
     {
-        fail("FIXME: Ext2::Inode::read()");
+        if (length == 0) return 0;
+
+        if (offset > size()) return 0;
+        if (offset + length > size()) length = size() - offset;
+
+        const usize block_size = m_fs->m_block_size;
+
+        usize to_read = length;
+
+        if (offset % block_size)
+        {
+            usize block_offset = (offset % block_size);
+            usize block = find_block(offset / block_size);
+            usize size_to_read = block_size - block_offset;
+
+            usize host_offset = (block * block_size) + block_offset;
+
+            // FIXME: Cache this data.
+            TRY(m_fs->m_host_device->read(buf, host_offset, size_to_read));
+
+            to_read -= size_to_read;
+            buf += size_to_read;
+            offset += size_to_read;
+        }
+
+        while (to_read >= block_size)
+        {
+            usize block = find_block(offset / block_size);
+
+            usize host_offset = block * block_size;
+
+            // FIXME: Cache this data.
+            TRY(m_fs->m_host_device->read(buf, host_offset, block_size));
+
+            to_read -= block_size;
+            buf += block_size;
+            offset += block_size;
+        }
+
+        if (to_read > 0)
+        {
+            usize block = find_block(offset / block_size);
+
+            usize host_offset = block * block_size;
+
+            // FIXME: Cache this data.
+            TRY(m_fs->m_host_device->read(buf, host_offset, to_read));
+        }
+
+        return length;
+    }
+
+    usize Inode::find_block(usize index) const
+    {
+        expect(index < 12, "ext2: Finding blocks in the indirect pointers is not yet supported");
+
+        return m_raw_inode.direct_pointers[index];
     }
 }

kernel/src/fs/ext2/Inode.h

@@ -94,6 +94,8 @@ namespace Ext2
         FileSystem* m_fs;
         ino_t m_inum;
 
+        usize find_block(usize index) const;
+
         friend class FileSystem;
     };
 }