bis_factory: Add mod directory VFS getter

src/core/CMakeLists.txt

@@ -32,6 +32,8 @@ add_library(core STATIC
     file_sys/control_metadata.h
     file_sys/directory.h
     file_sys/errors.h
+    file_sys/fsmitm_romfsbuild.cpp
+    file_sys/fsmitm_romfsbuild.hpp
     file_sys/mode.h
     file_sys/nca_metadata.cpp
     file_sys/nca_metadata.h
@@ -59,6 +61,8 @@ add_library(core STATIC
     file_sys/vfs.h
     file_sys/vfs_concat.cpp
     file_sys/vfs_concat.h
+    file_sys/vfs_layered.cpp
+    file_sys/vfs_layered.h
     file_sys/vfs_offset.cpp
     file_sys/vfs_offset.h
     file_sys/vfs_real.cpp

src/core/file_sys/bis_factory.cpp

@@ -4,11 +4,12 @@
 
 #include "core/file_sys/bis_factory.h"
 #include "core/file_sys/registered_cache.h"
+#include "fmt/format.h"
 
 namespace FileSys {
 
-BISFactory::BISFactory(VirtualDir nand_root_)
-    : nand_root(std::move(nand_root_)),
+BISFactory::BISFactory(VirtualDir nand_root_, VirtualDir load_root_)
+    : nand_root(std::move(nand_root_)), load_root(std::move(load_root_)),
       sysnand_cache(std::make_shared<RegisteredCache>(
           GetOrCreateDirectoryRelative(nand_root, "/system/Contents/registered"))),
       usrnand_cache(std::make_shared<RegisteredCache>(
@@ -24,4 +25,11 @@ std::shared_ptr<RegisteredCache> BISFactory::GetUserNANDContents() const {
     return usrnand_cache;
 }
 
+VirtualDir BISFactory::GetModificationLoadRoot(u64 title_id) const {
+    // LayeredFS doesn't work on updates and title id-less homebrew
+    if (title_id == 0 || (title_id & 0x800) > 0)
+        return nullptr;
+    return GetOrCreateDirectoryRelative(load_root, fmt::format("/{:016X}", title_id));
+}
+
 } // namespace FileSys

src/core/file_sys/bis_factory.h

@@ -17,14 +17,17 @@ class RegisteredCache;
 /// registered caches.
 class BISFactory {
 public:
-    explicit BISFactory(VirtualDir nand_root);
+    BISFactory(VirtualDir nand_root, VirtualDir load_root);
     ~BISFactory();
 
     std::shared_ptr<RegisteredCache> GetSystemNANDContents() const;
     std::shared_ptr<RegisteredCache> GetUserNANDContents() const;
 
+    VirtualDir GetModificationLoadRoot(u64 title_id) const;
+
 private:
     VirtualDir nand_root;
+    VirtualDir load_root;
 
     std::shared_ptr<RegisteredCache> sysnand_cache;
     std::shared_ptr<RegisteredCache> usrnand_cache;