Virtual Filesystem (#597)

* Add VfsFile and VfsDirectory classes

* Finish abstract Vfs classes

* Implement RealVfsFile (computer fs backend)

* Finish RealVfsFile and RealVfsDirectory

* Finished OffsetVfsFile

* More changes

* Fix import paths

* Major refactor

* Remove double const

* Use experimental/filesystem or filesystem depending on compiler

* Port partition_filesystem

* More changes

* More Overhaul

* FSP_SRV fixes

* Fixes and testing

* Try to get filesystem to compile

* Filesystem on linux

* Remove std::filesystem and document/test

* Compile fixes

* Missing include

* Bug fixes

* Fixes

* Rename v_file and v_dir

* clang-format fix

* Rename NGLOG_* to LOG_*

* Most review changes

* Fix TODO

* Guess 'main' to be Directory by filename

src/core/file_sys/vfs_offset.cpp

@@ -0,0 +1,92 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "core/file_sys/vfs_offset.h"
+
+namespace FileSys {
+
+OffsetVfsFile::OffsetVfsFile(std::shared_ptr<VfsFile> file_, size_t size_, size_t offset_,
+                             const std::string& name_)
+    : file(file_), offset(offset_), size(size_), name(name_) {}
+
+std::string OffsetVfsFile::GetName() const {
+    return name.empty() ? file->GetName() : name;
+}
+
+size_t OffsetVfsFile::GetSize() const {
+    return size;
+}
+
+bool OffsetVfsFile::Resize(size_t new_size) {
+    if (offset + new_size < file->GetSize()) {
+        size = new_size;
+    } else {
+        auto res = file->Resize(offset + new_size);
+        if (!res)
+            return false;
+        size = new_size;
+    }
+
+    return true;
+}
+
+std::shared_ptr<VfsDirectory> OffsetVfsFile::GetContainingDirectory() const {
+    return file->GetContainingDirectory();
+}
+
+bool OffsetVfsFile::IsWritable() const {
+    return file->IsWritable();
+}
+
+bool OffsetVfsFile::IsReadable() const {
+    return file->IsReadable();
+}
+
+size_t OffsetVfsFile::Read(u8* data, size_t length, size_t r_offset) const {
+    return file->Read(data, TrimToFit(length, r_offset), offset + r_offset);
+}
+
+size_t OffsetVfsFile::Write(const u8* data, size_t length, size_t r_offset) {
+    return file->Write(data, TrimToFit(length, r_offset), offset + r_offset);
+}
+
+boost::optional<u8> OffsetVfsFile::ReadByte(size_t r_offset) const {
+    if (r_offset < size)
+        return file->ReadByte(offset + r_offset);
+
+    return boost::none;
+}
+
+std::vector<u8> OffsetVfsFile::ReadBytes(size_t r_size, size_t r_offset) const {
+    return file->ReadBytes(TrimToFit(r_size, r_offset), offset + r_offset);
+}
+
+std::vector<u8> OffsetVfsFile::ReadAllBytes() const {
+    return file->ReadBytes(size, offset);
+}
+
+bool OffsetVfsFile::WriteByte(u8 data, size_t r_offset) {
+    if (r_offset < size)
+        return file->WriteByte(data, offset + r_offset);
+
+    return false;
+}
+
+size_t OffsetVfsFile::WriteBytes(std::vector<u8> data, size_t r_offset) {
+    return file->Write(data.data(), TrimToFit(data.size(), r_offset), offset + r_offset);
+}
+
+bool OffsetVfsFile::Rename(const std::string& name) {
+    return file->Rename(name);
+}
+
+size_t OffsetVfsFile::GetOffset() const {
+    return offset;
+}
+
+size_t OffsetVfsFile::TrimToFit(size_t r_size, size_t r_offset) const {
+    return std::max<size_t>(std::min<size_t>(size - r_offset, r_size), 0);
+}
+
+} // namespace FileSys