Kernel: Change Ext2FS to be backed by a file instead of a block device

This ensures that we can mount image files as virtual disks without the
need of implementing gross hacks like loopback devices :)

1 files changed, 71 insertions, 0 deletions

diff --git a/Kernel/FileSystem/FileBackedFileSystem.h b/Kernel/FileSystem/FileBackedFileSystem.h
new file mode 100644
index 0000000000..36c89e4af0
--- /dev/null
+++ b/Kernel/FileSystem/FileBackedFileSystem.h
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <Kernel/FileSystem/FileDescription.h>
+#include <Kernel/FileSystem/FileSystem.h>
+#include <Kernel/Forward.h>
+
+namespace Kernel {
+
+class FileBackedFS : public FS {
+public:
+    virtual ~FileBackedFS() override;
+
+    virtual bool is_file_backed() const override { return true; }
+
+    File& file() { return m_file_description->file(); }
+    FileDescription& file_description() { return *m_file_description; }
+    const File& file() const { return m_file_description->file(); }
+    const FileDescription& file_description() const { return *m_file_description; }
+
+    virtual void flush_writes() override;
+
+    void flush_writes_impl();
+
+    size_t logical_block_size() const { return m_logical_block_size; };
+
+protected:
+    explicit FileBackedFS(FileDescription&);
+
+    bool read_block(unsigned index, u8* buffer, FileDescription* = nullptr, bool use_logical_block_size = false, bool cache_disabled = false) const;
+    bool read_blocks(unsigned index, unsigned count, u8* buffer, FileDescription* = nullptr, bool use_logical_block_size = false, bool cache_disabled = false) const;
+
+    bool write_block(unsigned index, const u8*, FileDescription* = nullptr, bool use_logical_block_size = false);
+    bool write_blocks(unsigned index, unsigned count, const u8*, FileDescription* = nullptr, bool use_logical_block_size = false);
+
+    size_t m_logical_block_size { 512 };
+
+private:
+    DiskCache& cache() const;
+    void flush_specific_block_if_needed(unsigned index);
+
+    NonnullRefPtr<FileDescription> m_file_description;
+    mutable OwnPtr<DiskCache> m_cache;
+};
+
+}