diff --git a/stratosphere/ams_mitm/source/bpc_mitm/bpcmitm_reboot_manager.cpp b/stratosphere/ams_mitm/source/bpc_mitm/bpcmitm_reboot_manager.cpp
index 98f37bcf1..a7701ccd8 100644
--- a/stratosphere/ams_mitm/source/bpc_mitm/bpcmitm_reboot_manager.cpp
+++ b/stratosphere/ams_mitm/source/bpc_mitm/bpcmitm_reboot_manager.cpp
@@ -39,7 +39,7 @@ void BpcRebootManager::Initialize() {
     
     /* Read payload file. */
     size_t actual_size;
-    fsFileRead(&payload_file, 0, g_reboot_payload, IRAM_PAYLOAD_MAX_SIZE, &actual_size);
+    fsFileRead(&payload_file, 0, g_reboot_payload, IRAM_PAYLOAD_MAX_SIZE, FS_READOPTION_NONE, &actual_size);
     
     g_payload_loaded = true;
     
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.cpp b/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.cpp
index e7ec6596a..5ba3747ae 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.cpp
@@ -48,13 +48,13 @@ class DirectorySaveDataFile : public IFile {
         virtual Result FlushImpl() override {
             return this->base_file->Flush();
         }
-        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, bool flush) override {
-            return this->base_file->Write(offset, buffer, size, flush);
+        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, u32 option) override {
+            return this->base_file->Write(offset, buffer, size, option);
         }
         virtual Result SetSizeImpl(u64 size) override {
             return this->base_file->SetSize(size);
         }
-        virtual Result OperateRangeImpl(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
+        virtual Result OperateRangeImpl(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
             return this->base_file->OperateRange(operation_type, offset, size, out_range_info);
         }
 };
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.cpp b/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.cpp
index f4e154f7d..55fecc95b 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.cpp
@@ -45,7 +45,12 @@ Result FileStorage::Read(void *buffer, size_t size, u64 offset) {
         return ResultFsOutOfRange;
     }
 
-    return this->file->Read(&read_size, offset, buffer, size);
+    /* Nintendo doesn't do check output read size, but we will for safety. */
+    R_TRY(this->file->Read(&read_size, offset, buffer, size));
+    if (read_size != size && read_size) {
+        return this->Read(reinterpret_cast<void *>(reinterpret_cast<uintptr_t>(buffer) + read_size), size - read_size, offset + read_size);
+    }
+    return ResultSuccess;
 }
 
 Result FileStorage::Write(void *buffer, size_t size, u64 offset) {
@@ -85,14 +90,14 @@ Result FileStorage::SetSize(u64 size) {
     return this->file->SetSize(size);
 }
 
-Result FileStorage::OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
+Result FileStorage::OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
     Result rc;
 
     switch (operation_type) {
-        case 2: /* TODO: OperationType_Invalidate */
-        case 3: /* TODO: OperationType_Query */
+        case FsOperationId_InvalidateCache:
+        case FsOperationId_QueryRange:
             if (size == 0) {
-                if (operation_type == 3) {
+                if (operation_type == FsOperationId_QueryRange) {
                     if (out_range_info == nullptr) {
                         return ResultFsNullptrArgument;
                     }
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.hpp
index 6b21383e4..58f4da8f4 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_file_storage.hpp
@@ -50,5 +50,5 @@ class FileStorage : public IStorage {
         virtual Result Flush() override;
         virtual Result GetSize(u64 *out_size) override;
         virtual Result SetSize(u64 size) override;
-        virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override;
+        virtual Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override;
 };
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
index 10f58477d..f07cb0d03 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
@@ -70,8 +70,7 @@ class IFile {
             if (buffer == nullptr) {
                 return ResultFsNullptrArgument;
             }
-            const bool flush = (flags & 1) != 0;
-            return WriteImpl(offset, buffer, size, flush);
+            return WriteImpl(offset, buffer, size, flags);
         }
 
         Result Write(uint64_t offset, void *buffer, uint64_t size, bool flush = false) {
@@ -88,8 +87,8 @@ class IFile {
             return SetSizeImpl(size);
         }
 
-        Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
-            if (operation_type == 3) {
+        Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
+            if (operation_type == FsOperationId_QueryRange) {
                 return OperateRangeImpl(operation_type, offset, size, out_range_info);
             }
             return ResultFsUnsupportedOperation;
@@ -101,9 +100,9 @@ class IFile {
         virtual Result ReadImpl(u64 *out, u64 offset, void *buffer, u64 size) = 0;
         virtual Result GetSizeImpl(u64 *out) = 0;
         virtual Result FlushImpl() = 0;
-        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, bool flush) = 0;
+        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, u32 option) = 0;
         virtual Result SetSizeImpl(u64 size) = 0;
-        virtual Result OperateRangeImpl(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
+        virtual Result OperateRangeImpl(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
 };
 
 class IFileInterface : public IServiceObject {
@@ -135,7 +134,7 @@ class IFileInterface : public IServiceObject {
             return this->base_file->GetSize(size.GetPointer());
         };
         virtual Result OperateRange(Out<FsRangeInfo> range_info, u32 operation_type, u64 offset, u64 size) final {
-            return this->base_file->OperateRange(operation_type, offset, size, range_info.GetPointer());
+            return this->base_file->OperateRange(static_cast<FsOperationId>(operation_type), offset, size, range_info.GetPointer());
         };
     public:
         DEFINE_SERVICE_DISPATCH_TABLE {
@@ -174,7 +173,7 @@ class ProxyFile : public IFile {
         virtual Result ReadImpl(u64 *out, u64 offset, void *buffer, u64 size) override {
             size_t out_sz;
 
-            Result rc = fsFileRead(this->base_file.get(), offset, buffer, size, &out_sz);
+            Result rc = fsFileRead(this->base_file.get(), offset, buffer, size, FS_READOPTION_NONE, &out_sz);
             if (R_SUCCEEDED(rc)) {
                 *out = out_sz;
             }
@@ -187,18 +186,13 @@ class ProxyFile : public IFile {
         virtual Result FlushImpl() override {
             return fsFileFlush(this->base_file.get());
         }
-        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, bool flush) override {
-            Result rc = fsFileWrite(this->base_file.get(), offset, buffer, size);
-            if (R_SUCCEEDED(rc)) {
-                /* libnx doesn't allow passing the flush flag. */
-                rc = fsFileFlush(this->base_file.get());
-            }
-            return rc;
+        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, u32 option) override {
+            return fsFileWrite(this->base_file.get(), offset, buffer, size, option);
         }
         virtual Result SetSizeImpl(u64 size) override {
             return fsFileSetSize(this->base_file.get(), size);
         }
-        virtual Result OperateRangeImpl(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
+        virtual Result OperateRangeImpl(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
             return fsFileOperateRange(this->base_file.get(), operation_type, offset, size, out_range_info);
         }
 };
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp
index 34ace2eb9..32705292b 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp
@@ -39,7 +39,7 @@ class IStorage {
         virtual Result Flush() = 0;
         virtual Result SetSize(u64 size) = 0;
         virtual Result GetSize(u64 *out_size) = 0;
-        virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
+        virtual Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
 
         static inline bool IsRangeValid(uint64_t offset, uint64_t size, uint64_t total_size) {
             return size <= total_size && offset <= total_size - size;
@@ -76,7 +76,7 @@ class IStorageInterface : public IServiceObject {
             return this->base_storage->GetSize(size.GetPointer());
         };
         virtual Result OperateRange(Out<FsRangeInfo> range_info, u32 operation_type, u64 offset, u64 size) final {
-            return this->base_storage->OperateRange(operation_type, offset, size, range_info.GetPointer());
+            return this->base_storage->OperateRange(static_cast<FsOperationId>(operation_type), offset, size, range_info.GetPointer());
         };
     public:
         DEFINE_SERVICE_DISPATCH_TABLE {
@@ -109,7 +109,7 @@ class IROStorage : public IStorage {
             return ResultFsUnsupportedOperation;
         };
         virtual Result GetSize(u64 *out_size) = 0;
-        virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
+        virtual Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
 };
 
 
@@ -143,33 +143,33 @@ class ProxyStorage : public IStorage {
         virtual Result SetSize(u64 size) override {
             return fsStorageSetSize(this->base_storage, size);
         };
-        virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
+        virtual Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
             return fsStorageOperateRange(this->base_storage, operation_type, offset, size, out_range_info);
         };
 };
 
-class ROProxyStorage : public IROStorage {
+class ReadOnlyStorageAdapter : public IROStorage {
     private:
-        FsStorage *base_storage;
+        std::shared_ptr<IStorage> base_storage;
+        IStorage *storage;
     public:
-        ROProxyStorage(FsStorage *s) : base_storage(s) {
+        ReadOnlyStorageAdapter(IStorage *s) : base_storage(s) {
+            this->storage = this->base_storage.get();
+        }
+        ReadOnlyStorageAdapter(std::shared_ptr<IStorage> s) : base_storage(s) {
+            this->storage = this->base_storage.get();
+        }
+        virtual ~ReadOnlyStorageAdapter() {
             /* ... */
-        };
-        ROProxyStorage(FsStorage s) {
-            this->base_storage = new FsStorage(s);
-        };
-        virtual ~ROProxyStorage() {
-            fsStorageClose(base_storage);
-            delete base_storage;
-        };
+        }
     public:
         virtual Result Read(void *buffer, size_t size, u64 offset) override {
-            return fsStorageRead(this->base_storage, offset, buffer, size);
+            return this->base_storage->Read(buffer, size, offset);
         };
         virtual Result GetSize(u64 *out_size) override {
-            return fsStorageGetSize(this->base_storage, out_size);
+            return this->base_storage->GetSize(out_size);
         };
-        virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
-            return fsStorageOperateRange(this->base_storage, operation_type, offset, size, out_range_info);
+        virtual Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
+            return this->base_storage->OperateRange(operation_type, offset, size, out_range_info);
         };
-};
\ No newline at end of file
+};
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_shim.c b/stratosphere/ams_mitm/source/fs_mitm/fs_shim.c
index 524584b94..02470f76e 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_shim.c
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_shim.c
@@ -19,7 +19,7 @@
 #include "fs_shim.h"
 
 /* Missing fsp-srv commands. */
-Result fsOpenBisStorageFwd(Service* s, FsStorage* out, u32 PartitionId) {
+Result fsOpenBisStorageFwd(Service* s, FsStorage* out, FsBisStorageId PartitionId) {
     IpcCommand c;
     ipcInitialize(&c);
 
@@ -264,85 +264,3 @@ Result fsOpenSaveDataFileSystemFwd(Service *s, FsFileSystem* out, u8 inval, FsSa
 
     return rc;
 }
-
-/* Missing FS File commands. */
-Result fsFileOperateRange(FsFile* f, u32 op_id, u64 off, u64 len, FsRangeInfo *out) {
-    IpcCommand c;
-    ipcInitialize(&c);
-
-    struct {
-        u64 magic;
-        u64 cmd_id;
-        u32 op_id;
-        u64 off;
-        u64 len;
-    } *raw;
-
-    raw = serviceIpcPrepareHeader(&f->s, &c, sizeof(*raw));
-
-    raw->magic = SFCI_MAGIC;
-    raw->cmd_id = 5;
-    raw->op_id = op_id;
-    raw->off = off;
-    raw->len = len;
-
-    Result rc = serviceIpcDispatch(&f->s);
-
-    if (R_SUCCEEDED(rc)) {
-        IpcParsedCommand r;
-        struct {
-            u64 magic;
-            u64 result;
-            FsRangeInfo range_info;
-        } *resp;
-        
-        serviceIpcParse(&f->s, &r, sizeof(*resp));
-        resp = r.Raw;
-
-        rc = resp->result;
-        if (R_SUCCEEDED(rc) && out) *out = resp->range_info;
-    }
-
-    return rc;
-}
-
-/* Missing FS Storage commands. */
-Result fsStorageOperateRange(FsStorage* s, u32 op_id, u64 off, u64 len, FsRangeInfo *out) {
-    IpcCommand c;
-    ipcInitialize(&c);
-
-    struct {
-        u64 magic;
-        u64 cmd_id;
-        u32 op_id;
-        u64 off;
-        u64 len;
-    } *raw;
-
-    raw = serviceIpcPrepareHeader(&s->s, &c, sizeof(*raw));
-
-    raw->magic = SFCI_MAGIC;
-    raw->cmd_id = 5;
-    raw->op_id = op_id;
-    raw->off = off;
-    raw->len = len;
-
-    Result rc = serviceIpcDispatch(&s->s);
-
-    if (R_SUCCEEDED(rc)) {
-        IpcParsedCommand r;
-        struct {
-            u64 magic;
-            u64 result;
-            FsRangeInfo range_info;
-        } *resp;
-        
-        serviceIpcParse(&s->s, &r, sizeof(*resp));
-        resp = r.Raw;
-
-        rc = resp->result;
-        if (R_SUCCEEDED(rc) && out) *out = resp->range_info;
-    }
-
-    return rc;
-}
\ No newline at end of file
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_shim.h b/stratosphere/ams_mitm/source/fs_mitm/fs_shim.h
index fa163fe7e..96b0fc0fc 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_shim.h
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_shim.h
@@ -11,25 +11,14 @@
 extern "C" {
 #endif
 
-/* TODO: Reverse this more. */
-typedef struct {
-    u32 flags[0x40/sizeof(u32)];
-} FsRangeInfo;
-
 /* Missing fsp-srv commands. */
-Result fsOpenBisStorageFwd(Service* s, FsStorage* out, u32 PartitionId);
+Result fsOpenBisStorageFwd(Service* s, FsStorage* out, FsBisStorageId PartitionId);
 Result fsOpenDataStorageByCurrentProcessFwd(Service* s, FsStorage* out);
 Result fsOpenDataStorageByDataIdFwd(Service* s, FsStorageId storage_id, u64 data_id, FsStorage* out);
 Result fsOpenFileSystemWithPatchFwd(Service* s, FsFileSystem* out, u64 titleId, FsFileSystemType fsType);
 Result fsOpenFileSystemWithIdFwd(Service* s, FsFileSystem* out, u64 titleId, FsFileSystemType fsType, const char* contentPath);
 Result fsOpenSaveDataFileSystemFwd(Service* s, FsFileSystem* out, u8 inval, FsSave *save);
 
-/* Missing FS File commands. */
-Result fsFileOperateRange(FsFile* f, u32 op_id, u64 off, u64 len, FsRangeInfo *out);
-
-/* Missing FS Storage commands. */
-Result fsStorageOperateRange(FsStorage* s, u32 op_id, u64 off, u64 len, FsRangeInfo *out);
-
 #ifdef __cplusplus
 }
 #endif
\ No newline at end of file
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp
index 95fd7e687..c57738971 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp
@@ -23,7 +23,7 @@
 
 IStorage::~IStorage() = default;
 
-LayeredRomFS::LayeredRomFS(std::shared_ptr<RomInterfaceStorage> s_r, std::shared_ptr<RomFileStorage> f_r, u64 tid) : storage_romfs(s_r), file_romfs(f_r), title_id(tid) {
+LayeredRomFS::LayeredRomFS(std::shared_ptr<IROStorage> s_r, std::shared_ptr<IROStorage> f_r, u64 tid) : storage_romfs(s_r), file_romfs(f_r), title_id(tid) {
     /* Start building the new virtual romfs. */
     RomFSBuildContext build_ctx(this->title_id);
     this->p_source_infos = std::shared_ptr<std::vector<RomFSSourceInfo>>(new std::vector<RomFSSourceInfo>(), [](std::vector<RomFSSourceInfo> *to_delete) {
@@ -95,7 +95,7 @@ Result LayeredRomFS::Read(void *buffer, size_t size, u64 offset)  {
                             fatalSimple(rc);
                         }
                         size_t out_read;
-                        if (R_FAILED((rc = fsFileRead(&file, (offset - cur_source->virtual_offset), (void *)((uintptr_t)buffer + read_so_far), cur_read_size, &out_read)))) {
+                        if (R_FAILED((rc = fsFileRead(&file, (offset - cur_source->virtual_offset), (void *)((uintptr_t)buffer + read_so_far), cur_read_size, FS_READOPTION_NONE, &out_read)))) {
                             fatalSimple(rc);
                         }
                         if (out_read != cur_read_size) {
@@ -111,7 +111,7 @@ Result LayeredRomFS::Read(void *buffer, size_t size, u64 offset)  {
                             fatalSimple(rc);
                         }
                         size_t out_read;
-                        if (R_FAILED((rc = fsFileRead(&file, (offset - cur_source->virtual_offset), (void *)((uintptr_t)buffer + read_so_far), cur_read_size, &out_read)))) {
+                        if (R_FAILED((rc = fsFileRead(&file, (offset - cur_source->virtual_offset), (void *)((uintptr_t)buffer + read_so_far), cur_read_size, FS_READOPTION_NONE, &out_read)))) {
                             fatalSimple(rc);
                         }
                         if (out_read != cur_read_size) {
@@ -164,9 +164,9 @@ Result LayeredRomFS::GetSize(u64 *out_size)  {
     *out_size = (*this->p_source_infos)[this->p_source_infos->size() - 1].virtual_offset + (*this->p_source_infos)[this->p_source_infos->size() - 1].size;
     return ResultSuccess;
 }
-Result LayeredRomFS::OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
+Result LayeredRomFS::OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
     /* TODO: How should I implement this for a virtual romfs? */
-    if (operation_type == 3) {
+    if (operation_type == FsOperationId_QueryRange) {
         *out_range_info = {0};
     }
     return ResultSuccess;
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.hpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.hpp
index cebf07a89..e06de07d4 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.hpp
@@ -18,7 +18,7 @@
 #include <switch.h>
 #include <stratosphere.hpp>
 
-#include "fsmitm_romstorage.hpp"
+#include "fs_istorage.hpp"
 #include "fsmitm_romfsbuild.hpp"
 #include "../utils.hpp"
 
@@ -27,17 +27,17 @@
 class LayeredRomFS : public IROStorage {
     private:
         /* Data Sources. */
-        std::shared_ptr<RomInterfaceStorage> storage_romfs;
-        std::shared_ptr<RomFileStorage> file_romfs;
+        std::shared_ptr<IROStorage> storage_romfs;
+        std::shared_ptr<IROStorage> file_romfs;
         /* Information about the merged RomFS. */
         u64 title_id;
         std::shared_ptr<std::vector<RomFSSourceInfo>> p_source_infos;
                 
     public:
-        LayeredRomFS(std::shared_ptr<RomInterfaceStorage> s_r, std::shared_ptr<RomFileStorage> f_r, u64 tid);
+        LayeredRomFS(std::shared_ptr<IROStorage> s_r, std::shared_ptr<IROStorage> f_r, u64 tid);
         virtual ~LayeredRomFS() = default;
         
         virtual Result Read(void *buffer, size_t size, u64 offset) override;
         virtual Result GetSize(u64 *out_size) override;
-        virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override;
+        virtual Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override;
 };
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romfsbuild.hpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romfsbuild.hpp
index 2079ebcfe..d59ebe583 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romfsbuild.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romfsbuild.hpp
@@ -19,9 +19,8 @@
 #include <switch.h>
 #include <map>
 
-#include "fsmitm_romstorage.hpp"
-
 #include "../debug.hpp"
+#include "fs_istorage.hpp"
 
 #define ROMFS_ENTRY_EMPTY 0xFFFFFFFF
 #define ROMFS_FILEPARTITION_OFS 0x200
@@ -65,7 +64,7 @@ struct RomFSSourceInfo {
         RomFSFileSourceInfo file_source_info;
         RomFSLooseSourceInfo loose_source_info;
         RomFSMemorySourceInfo memory_source_info;
-        RomFSMemorySourceInfo metadata_source_info;
+        RomFSMetaDataSourceInfo metadata_source_info;
     };
     RomFSDataSource type;
     
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romstorage.hpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romstorage.hpp
index 779f4db4e..b3c531d64 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romstorage.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_romstorage.hpp
@@ -38,7 +38,7 @@ class RomFileStorage : public IROStorage {
     public:
         Result Read(void *buffer, size_t size, u64 offset) override {
             size_t out_sz = 0;
-            Result rc = fsFileRead(this->base_file, offset, buffer, size, &out_sz);
+            Result rc = fsFileRead(this->base_file, offset, buffer, size, FS_READOPTION_NONE, &out_sz);
             if (R_SUCCEEDED(rc) && out_sz != size && out_sz) {
                 return this->Read((void *)((uintptr_t)buffer + out_sz), size - out_sz, offset + out_sz);
             }
@@ -47,7 +47,7 @@ class RomFileStorage : public IROStorage {
         Result GetSize(u64 *out_size) override {
             return fsFileGetSize(this->base_file, out_size);
         };
-        Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
+        Result OperateRange(FsOperationId operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
             /* TODO: Merge into libnx? */
             return fsFileOperateRange(this->base_file, operation_type, offset, size, out_range_info);
         };
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
index 991d4113f..fb47fb79d 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
@@ -25,11 +25,11 @@
 
 #include "../utils.hpp"
 #include "fsmitm_boot0storage.hpp"
-#include "fsmitm_romstorage.hpp"
 #include "fsmitm_layeredrom.hpp"
 
 #include "fs_dir_utils.hpp"
 #include "fs_save_utils.hpp"
+#include "fs_file_storage.hpp"
 #include "fs_subdirectory_filesystem.hpp"
 #include "fs_directory_redirection_filesystem.hpp"
 #include "fs_directory_savedata_filesystem.hpp"
@@ -279,10 +279,11 @@ Result FsMitmService::OpenSaveDataFileSystem(Out<std::shared_ptr<IFileSystemInte
 }
 
 /* Gate access to the BIS partitions. */
-Result FsMitmService::OpenBisStorage(Out<std::shared_ptr<IStorageInterface>> out_storage, u32 bis_partition_id) {
+Result FsMitmService::OpenBisStorage(Out<std::shared_ptr<IStorageInterface>> out_storage, u32 _bis_partition_id) {
     std::shared_ptr<IStorageInterface> storage = nullptr;
     u32 out_domain_id = 0;
     Result rc = ResultSuccess;
+    const FsBisStorageId bis_partition_id = static_cast<FsBisStorageId>(_bis_partition_id);
 
     ON_SCOPE_EXIT {
         if (R_SUCCEEDED(rc)) {
@@ -300,12 +301,12 @@ Result FsMitmService::OpenBisStorage(Out<std::shared_ptr<IStorageInterface>> out
             const bool is_sysmodule = TitleIdIsSystem(this->title_id);
             const bool has_bis_write_flag = Utils::HasFlag(this->title_id, "bis_write");
             const bool has_cal0_read_flag = Utils::HasFlag(this->title_id, "cal_read");
-            if (bis_partition_id == BisStorageId_Boot0) {
+            if (bis_partition_id == FsBisStorageId_Boot0) {
                 storage = std::make_shared<IStorageInterface>(new Boot0Storage(bis_storage, this->title_id));
-            } else if (bis_partition_id == BisStorageId_Prodinfo) {
+            } else if (bis_partition_id == FsBisStorageId_CalibrationBinary) {
                 /* PRODINFO should *never* be writable. */
                 if (is_sysmodule || has_cal0_read_flag) {
-                    storage = std::make_shared<IStorageInterface>(new ROProxyStorage(bis_storage));
+                    storage = std::make_shared<IStorageInterface>(new ReadOnlyStorageAdapter(new ProxyStorage(bis_storage)));
                 } else {
                     /* Do not allow non-sysmodules to read *or* write CAL0. */
                     fsStorageClose(&bis_storage);
@@ -317,14 +318,15 @@ Result FsMitmService::OpenBisStorage(Out<std::shared_ptr<IStorageInterface>> out
                     /* Sysmodules should still be allowed to read and write. */
                     storage = std::make_shared<IStorageInterface>(new ProxyStorage(bis_storage));
                 } else if (Utils::IsHblTid(this->title_id) &&
-                    ((BisStorageId_BcPkg2_1 <= bis_partition_id && bis_partition_id <= BisStorageId_BcPkg2_6) || bis_partition_id == BisStorageId_Boot1)) {
+                    ((FsBisStorageId_BootConfigAndPackage2NormalMain <= bis_partition_id && bis_partition_id <= FsBisStorageId_BootConfigAndPackage2RepairSub) ||
+                    bis_partition_id == FsBisStorageId_Boot1)) {
                     /* Allow HBL to write to boot1 (safe firm) + package2. */
                     /* This is needed to not break compatibility with ChoiDujourNX, which does not check for write access before beginning an update. */
                     /* TODO: get fixed so that this can be turned off without causing bricks :/ */
                     storage = std::make_shared<IStorageInterface>(new ProxyStorage(bis_storage));
                 } else {
                     /* Non-sysmodules should be allowed to read. */
-                    storage = std::make_shared<IStorageInterface>(new ROProxyStorage(bis_storage));
+                    storage = std::make_shared<IStorageInterface>(new ReadOnlyStorageAdapter(new ProxyStorage(bis_storage)));
                 }
             }
             if (out_storage.IsDomain()) {
@@ -386,9 +388,9 @@ Result FsMitmService::OpenDataStorageByCurrentProcess(Out<std::shared_ptr<IStora
             if (Utils::HasSdRomfsContent(this->title_id)) {
                 /* TODO: Is there a sensible path that ends in ".romfs" we can use?" */
                 if (R_SUCCEEDED(Utils::OpenSdFileForAtmosphere(this->title_id, "romfs.bin", FS_OPEN_READ, &data_file))) {
-                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<RomInterfaceStorage>(data_storage), std::make_shared<RomFileStorage>(data_file), this->title_id));
+                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<ReadOnlyStorageAdapter>(new ProxyStorage(data_storage)), std::make_shared<ReadOnlyStorageAdapter>(new FileStorage(new ProxyFile(data_file))), this->title_id));
                 } else {
-                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<RomInterfaceStorage>(data_storage), nullptr, this->title_id));
+                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<ReadOnlyStorageAdapter>(new ProxyStorage(data_storage)), nullptr, this->title_id));
                 }
                 if (out_storage.IsDomain()) {
                     out_domain_id = data_storage.s.object_id;
@@ -453,9 +455,9 @@ Result FsMitmService::OpenDataStorageByDataId(Out<std::shared_ptr<IStorageInterf
             if (Utils::HasSdRomfsContent(data_id)) {
                 /* TODO: Is there a sensible path that ends in ".romfs" we can use?" */
                 if (R_SUCCEEDED(Utils::OpenSdFileForAtmosphere(data_id, "romfs.bin", FS_OPEN_READ, &data_file))) {
-                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<RomInterfaceStorage>(data_storage), std::make_shared<RomFileStorage>(data_file), data_id));
+                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<ReadOnlyStorageAdapter>(new ProxyStorage(data_storage)), std::make_shared<ReadOnlyStorageAdapter>(new FileStorage(new ProxyFile(data_file))), data_id));
                 } else {
-                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<RomInterfaceStorage>(data_storage), nullptr, data_id));
+                    storage = std::make_shared<IStorageInterface>(new LayeredRomFS(std::make_shared<ReadOnlyStorageAdapter>(new ProxyStorage(data_storage)), nullptr, data_id));
                 }
                 if (out_storage.IsDomain()) {
                     out_domain_id = data_storage.s.object_id;
diff --git a/stratosphere/ams_mitm/source/set_mitm/setsys_settings_items.cpp b/stratosphere/ams_mitm/source/set_mitm/setsys_settings_items.cpp
index 2fc433e4e..ef483d696 100644
--- a/stratosphere/ams_mitm/source/set_mitm/setsys_settings_items.cpp
+++ b/stratosphere/ams_mitm/source/set_mitm/setsys_settings_items.cpp
@@ -263,7 +263,7 @@ void SettingsItemManager::LoadConfiguration() {
     /* Read from file. */
     if (R_SUCCEEDED(rc)) {
         size_t actual_size;
-        rc = fsFileRead(&config_file, 0, config_buf, 0xFFFF, &actual_size);
+        rc = fsFileRead(&config_file, 0, config_buf, 0xFFFF, FS_READOPTION_NONE, &actual_size);
     }
     
     if (R_SUCCEEDED(rc)) {
diff --git a/stratosphere/ams_mitm/source/utils.cpp b/stratosphere/ams_mitm/source/utils.cpp
index 1304c31a7..d208d7829 100644
--- a/stratosphere/ams_mitm/source/utils.cpp
+++ b/stratosphere/ams_mitm/source/utils.cpp
@@ -99,7 +99,7 @@ void Utils::InitializeThreadFunc(void *args) {
     fsFsCreateDirectory(&g_sd_filesystem, "/atmosphere/automatic_backups");
     {
         FsStorage cal0_storage;
-        if (R_FAILED(fsOpenBisStorage(&cal0_storage, BisStorageId_Prodinfo)) || R_FAILED(fsStorageRead(&cal0_storage, 0, g_cal0_storage_backup, ProdinfoSize))) {
+        if (R_FAILED(fsOpenBisStorage(&cal0_storage, FsBisStorageId_CalibrationBinary)) || R_FAILED(fsStorageRead(&cal0_storage, 0, g_cal0_storage_backup, ProdinfoSize))) {
             std::abort();
         }
         fsStorageClose(&cal0_storage);
@@ -119,7 +119,7 @@ void Utils::InitializeThreadFunc(void *args) {
         if (R_SUCCEEDED(fsFsOpenFile(&g_sd_filesystem, prodinfo_backup_path, FS_OPEN_READ | FS_OPEN_WRITE, &g_cal0_file))) {
             bool has_auto_backup = false;
             size_t read = 0;
-            if (R_SUCCEEDED(fsFileRead(&g_cal0_file, 0, g_cal0_backup, sizeof(g_cal0_backup), &read)) && read == sizeof(g_cal0_backup)) {
+            if (R_SUCCEEDED(fsFileRead(&g_cal0_file, 0, g_cal0_backup, sizeof(g_cal0_backup), FS_READOPTION_NONE, &read)) && read == sizeof(g_cal0_backup)) {
                 bool is_cal0_valid = true;
                 is_cal0_valid &= memcmp(g_cal0_backup, "CAL0", 4) == 0;
                 is_cal0_valid &= memcmp(g_cal0_backup + 0x250, serial_number, 0x18) == 0;
@@ -135,8 +135,7 @@ void Utils::InitializeThreadFunc(void *args) {
 
             if (!has_auto_backup) {
                 fsFileSetSize(&g_cal0_file, ProdinfoSize);
-                fsFileWrite(&g_cal0_file, 0, g_cal0_storage_backup, ProdinfoSize);
-                fsFileFlush(&g_cal0_file);
+                fsFileWrite(&g_cal0_file, 0, g_cal0_storage_backup, ProdinfoSize, FS_WRITEOPTION_FLUSH);
             }
 
             /* NOTE: g_cal0_file is intentionally not closed here. This prevents any other process from opening it. */
@@ -378,7 +377,7 @@ Result Utils::SaveSdFileForAtmosphere(u64 title_id, const char *fn, void *data,
     }
 
     /* Try to write the data. */
-    rc = fsFileWrite(&f, 0, data, size);
+    rc = fsFileWrite(&f, 0, data, size, FS_WRITEOPTION_FLUSH);
 
     return rc;
 }
@@ -614,7 +613,7 @@ OverrideKey Utils::GetTitleOverrideKey(u64 tid) {
             ON_SCOPE_EXIT { free(config_buf); };
 
             /* Read title ini contents. */
-            fsFileRead(&cfg_file, 0, config_buf, config_file_size, &config_file_size);
+            fsFileRead(&cfg_file, 0, config_buf, config_file_size, FS_READOPTION_NONE, &config_file_size);
 
             /* Parse title ini. */
             ini_parse_string(config_buf, FsMitmTitleSpecificIniHandler, &cfg);
@@ -672,7 +671,7 @@ OverrideLocale Utils::GetTitleOverrideLocale(u64 tid) {
             ON_SCOPE_EXIT { free(config_buf); };
 
             /* Read title ini contents. */
-            fsFileRead(&cfg_file, 0, config_buf, config_file_size, &config_file_size);
+            fsFileRead(&cfg_file, 0, config_buf, config_file_size, FS_READOPTION_NONE, &config_file_size);
 
             /* Parse title ini. */
             ini_parse_string(config_buf, FsMitmTitleSpecificLocaleIniHandler, &locale);
@@ -698,7 +697,7 @@ void Utils::RefreshConfiguration() {
     /* Read in string. */
     std::fill(g_config_ini_data, g_config_ini_data + 0x800, 0);
     size_t r_s;
-    fsFileRead(&config_file, 0, g_config_ini_data, size, &r_s);
+    fsFileRead(&config_file, 0, g_config_ini_data, size, FS_READOPTION_NONE, &r_s);
     fsFileClose(&config_file);
 
     ini_parse_string(g_config_ini_data, FsMitmIniHandler, NULL);
diff --git a/stratosphere/ams_mitm/source/utils.hpp b/stratosphere/ams_mitm/source/utils.hpp
index a3e9ce4ab..02c300dc4 100644
--- a/stratosphere/ams_mitm/source/utils.hpp
+++ b/stratosphere/ams_mitm/source/utils.hpp
@@ -18,25 +18,6 @@
 #include <switch.h>
 #include <stratosphere.hpp>
 
-enum BisStorageId : u32 {
-    BisStorageId_Boot0 = 0,
-    BisStorageId_Boot1 = 10,
-    BisStorageId_RawNand = 20,
-    BisStorageId_BcPkg2_1 = 21,
-    BisStorageId_BcPkg2_2 = 22,
-    BisStorageId_BcPkg2_3 = 23,
-    BisStorageId_BcPkg2_4 = 24,
-    BisStorageId_BcPkg2_5 = 25,
-    BisStorageId_BcPkg2_6 = 26,
-    BisStorageId_Prodinfo = 27,
-    BisStorageId_ProdinfoF = 28,
-    BisStorageId_Safe = 29,
-    BisStorageId_User = 30,
-    BisStorageId_System = 31,
-    BisStorageId_SystemProperEncryption = 32,
-    BisStorageId_SystemProperPartition = 33,
-};
-
 struct OverrideKey {
     u64 key_combination;
     bool override_by_default;
diff --git a/stratosphere/boot/source/boot_calibration.cpp b/stratosphere/boot/source/boot_calibration.cpp
index 67bfadab4..9971b255b 100644
--- a/stratosphere/boot/source/boot_calibration.cpp
+++ b/stratosphere/boot/source/boot_calibration.cpp
@@ -21,8 +21,6 @@ static constexpr size_t BatteryLotSize = 0x20;
 static constexpr size_t BatteryVersionOffset = 0x4310;
 static constexpr size_t BatteryVersionSize = 0x10;
 
-static constexpr u32 BisStorageId_Prodinfo = 27;
-
 static constexpr u32 DefaultBatteryVendor = static_cast<u32>('A');
 static constexpr u32 DefaultBatteryVersion = 0;
 
@@ -57,7 +55,7 @@ static Result ValidateCalibrationCrc16(const void *data, size_t size) {
 
 static Result GetBatteryVendorImpl(u32 *vendor) {
     FsStorage s;
-    Result rc = fsOpenBisStorage(&s, BisStorageId_Prodinfo);
+    Result rc = fsOpenBisStorage(&s, FsBisStorageId_CalibrationBinary);
     if (R_FAILED(rc)) {
         return rc;
     }
@@ -78,7 +76,7 @@ static Result GetBatteryVendorImpl(u32 *vendor) {
 
 static Result GetBatteryVersionImpl(u32 *version) {
     FsStorage s;
-    Result rc = fsOpenBisStorage(&s, BisStorageId_Prodinfo);
+    Result rc = fsOpenBisStorage(&s, FsBisStorageId_CalibrationBinary);
     if (R_FAILED(rc)) {
         return rc;
     }
diff --git a/stratosphere/boot/source/updater/updater_bis_management.hpp b/stratosphere/boot/source/updater/updater_bis_management.hpp
index b4260c8c0..299109eab 100644
--- a/stratosphere/boot/source/updater/updater_bis_management.hpp
+++ b/stratosphere/boot/source/updater/updater_bis_management.hpp
@@ -25,10 +25,10 @@ class BisAccessor {
         static constexpr size_t SectorAlignment = 0x200;
     private:
         FsStorage storage = {};
-        u32 partition_id;
+        FsBisStorageId partition_id;
         bool active;
     public:
-        BisAccessor(u32 id) : partition_id(id), active(false) { }
+        BisAccessor(FsBisStorageId id) : partition_id(id), active(false) { }
         ~BisAccessor() {
             if (this->active) {
                 fsStorageClose(&storage);
@@ -126,7 +126,7 @@ class PartitionAccessor : public BisAccessor {
         using EnumType = typename Meta::EnumType;
         using OffsetSizeType = typename Meta::OffsetSizeType;
     public:
-        PartitionAccessor(u32 id) : BisAccessor(id) { }
+        PartitionAccessor(FsBisStorageId id) : BisAccessor(id) { }
     private:
         constexpr const OffsetSizeType *FindEntry(EnumType which) {
             for (size_t i = 0; i < Meta::NumEntries; i++) {
@@ -177,9 +177,6 @@ class PartitionAccessor : public BisAccessor {
         }
 };
 
-static constexpr u32 BisStorageId_Boot0 = 0;
-static constexpr u32 BisStorageId_Boot1 = 10;
-
 enum class Package2Type {
     NormalMain,
     NormalSub,
@@ -189,20 +186,20 @@ enum class Package2Type {
     RepairSub,
 };
 
-static constexpr u32 GetPackage2StorageId(Package2Type which) {
+static constexpr FsBisStorageId GetPackage2StorageId(Package2Type which) {
     switch (which) {
         case Package2Type::NormalMain:
-            return 21;
+            return FsBisStorageId_BootConfigAndPackage2NormalMain;
         case Package2Type::NormalSub:
-            return 22;
+            return FsBisStorageId_BootConfigAndPackage2NormalSub;
         case Package2Type::SafeMain:
-            return 23;
+            return FsBisStorageId_BootConfigAndPackage2SafeMain;
         case Package2Type::SafeSub:
-            return 24;
+            return FsBisStorageId_BootConfigAndPackage2SafeSub;
         case Package2Type::RepairMain:
-            return 25;
+            return FsBisStorageId_BootConfigAndPackage2RepairMain;
         case Package2Type::RepairSub:
-            return 26;
+            return FsBisStorageId_BootConfigAndPackage2RepairSub;
         default:
             std::abort();
     }
@@ -210,7 +207,7 @@ static constexpr u32 GetPackage2StorageId(Package2Type which) {
 
 class Boot0Accessor : public PartitionAccessor<Boot0Meta> {
     public:
-        static constexpr u32 PartitionId = 0;
+        static constexpr FsBisStorageId PartitionId = FsBisStorageId_Boot0;
         static constexpr size_t BctPubkOffset = 0x210;
         static constexpr size_t BctPubkSize = 0x100;
         static constexpr size_t BctEksOffset = 0x450;
@@ -230,7 +227,7 @@ class Boot0Accessor : public PartitionAccessor<Boot0Meta> {
 
 class Boot1Accessor : public PartitionAccessor<Boot1Meta> {
     public:
-        static constexpr u32 PartitionId = 10;
+        static constexpr FsBisStorageId PartitionId = FsBisStorageId_Boot1;
     public:
         Boot1Accessor() : PartitionAccessor<Boot1Meta>(PartitionId) { }
 };
diff --git a/stratosphere/libstratosphere b/stratosphere/libstratosphere
index 44f52b445..05c58ef00 160000
--- a/stratosphere/libstratosphere
+++ b/stratosphere/libstratosphere
@@ -1 +1 @@
-Subproject commit 44f52b445e9154a18fc0e99b9efc6be78b859495
+Subproject commit 05c58ef00263552d4925ed29ac0828cacdfc2ed1