Split VFS implementations from API

This allows better validation and simplified default argument handling.
Could also be useful in the future when we switch to proper VFS error
reporting.

app/src/main/cpp/skyline/vfs/backing.h

@@ -10,6 +10,17 @@ namespace skyline::vfs {
      * @brief The Backing class provides abstract access to a storage device, all access can be done without using a specific backing
      */
     class Backing {
+      protected:
+        virtual size_t ReadImpl(span <u8> output, size_t offset) = 0;
+
+        virtual size_t WriteImpl(span <u8> input, size_t offset) {
+            throw exception("This backing does not support being written to");
+        }
+
+        virtual void ResizeImpl(size_t pSize) {
+            throw exception("This backing does not support being resized");
+        }
+
       public:
         union Mode {
             struct {
@@ -42,7 +53,15 @@ namespace skyline::vfs {
          * @param offset The offset to start reading from
          * @return The amount of bytes read
          */
-        virtual size_t Read(span <u8> output, size_t offset = 0) = 0;
+        size_t Read(span <u8> output, size_t offset = 0) {
+            if (!mode.read)
+                throw exception("Attempting to read a backing that is not readable");
+
+            if ((static_cast<ssize_t>(size) - offset) < output.size())
+                throw exception("Trying to read past the end of a backing: 0x{:X}/0x{:X} (Offset: 0x{:X})", output.size(), size, offset);
+
+            return ReadImpl(output, offset);
+        };
 
         /**
          * @brief Implicit casting for reading into spans of different types
@@ -70,8 +89,18 @@ namespace skyline::vfs {
          * @param offset The offset where the input buffer should be written
          * @return The amount of bytes written
          */
-        virtual size_t Write(span <u8> input, size_t offset = 0) {
+        size_t Write(span <u8> input, size_t offset = 0) {
-            throw exception("This backing does not support being written to");
+            if (!mode.write)
+                throw exception("Attempting to write to a backing that is not writable");
+
+            if (input.size() > (static_cast<ssize_t>(size) - offset)) {
+                if (mode.append)
+                    Resize(offset + input.size());
+                else
+                    throw exception("Trying to write past the end of a non-appendable backing: 0x{:X}/0x{:X} (Offset: 0x{:X})", input.size(), size, offset);
+            }
+
+            return WriteImpl(input, offset);
         }
 
         /**
@@ -81,17 +110,17 @@ namespace skyline::vfs {
          */
         template<typename T>
         void WriteObject(const T &object, size_t offset = 0) {
-            size_t size;
+            size_t lSize;
-            if ((size = Write(span(reinterpret_cast<u8 *>(&object), sizeof(T)), offset)) != sizeof(T))
+            if ((lSize = Write(span(reinterpret_cast<u8 *>(&object), sizeof(T)), offset)) != sizeof(T))
-                throw exception("Object wasn't written fully into output backing: {}/{}", size, sizeof(T));
+                throw exception("Object wasn't written fully into output backing: {}/{}", lSize, sizeof(T));
         }
 
         /**
          * @brief Resizes a backing to the given size
-         * @param size The new size for the backing
+         * @param pSize The new size for the backing
          */
-        virtual void Resize(size_t size) {
+        void Resize(size_t pSize) {
-            throw exception("This backing does not support being resized");
+            ResizeImpl(pSize);
         }
     };
 }

app/src/main/cpp/skyline/vfs/ctr_encrypted_backing.cpp

@@ -6,7 +6,10 @@
 namespace skyline::vfs {
     constexpr size_t SectorSize{0x10};
 
-    CtrEncryptedBacking::CtrEncryptedBacking(crypto::KeyStore::Key128 ctr, crypto::KeyStore::Key128 key, std::shared_ptr<Backing> backing, size_t baseOffset) : Backing({true, false, false}), ctr(ctr), cipher(key, MBEDTLS_CIPHER_AES_128_CTR), backing(std::move(backing)), baseOffset(baseOffset) {}
+    CtrEncryptedBacking::CtrEncryptedBacking(crypto::KeyStore::Key128 ctr, crypto::KeyStore::Key128 key, std::shared_ptr<Backing> backing, size_t baseOffset) : Backing({true, false, false}), ctr(ctr), cipher(key, MBEDTLS_CIPHER_AES_128_CTR), backing(std::move(backing)), baseOffset(baseOffset) {
+        if (mode.write || mode.append)
+            throw exception("Cannot open a CtrEncryptedBacking as writable");
+    }
 
     void CtrEncryptedBacking::UpdateCtr(u64 offset) {
         offset >>= 4;
@@ -15,7 +18,7 @@ namespace skyline::vfs {
         cipher.SetIV(ctr);
     }
 
-    size_t CtrEncryptedBacking::Read(span<u8> output, size_t offset) {
+    size_t CtrEncryptedBacking::ReadImpl(span<u8> output, size_t offset) {
         size_t size{output.size()};
         if (size == 0)
             return 0;

app/src/main/cpp/skyline/vfs/ctr_encrypted_backing.h

@@ -24,9 +24,10 @@ namespace skyline::vfs {
          */
         void UpdateCtr(u64 offset);
 
+      protected:
+        size_t ReadImpl(span<u8> output, size_t offset) override;
+
       public:
         CtrEncryptedBacking(crypto::KeyStore::Key128 ctr, crypto::KeyStore::Key128 key, std::shared_ptr<Backing> backing, size_t baseOffset);
-
-        size_t Read(span<u8> output, size_t offset = 0) override;
     };
 }

app/src/main/cpp/skyline/vfs/filesystem.h

@@ -11,6 +11,23 @@ namespace skyline::vfs {
      * @brief The FileSystem class represents an abstract filesystem with child files and folders
      */
     class FileSystem {
+      protected:
+        virtual bool CreateFileImpl(const std::string &path, size_t size) {
+            throw exception("This filesystem does not support creating files");
+        };
+
+        virtual bool CreateDirectoryImpl(const std::string &path, bool parents) {
+            throw exception("This filesystem does not support creating directories");
+        };
+
+        virtual std::shared_ptr<Backing> OpenFileImpl(const std::string &path, Backing::Mode mode) = 0;
+
+        virtual std::optional<Directory::EntryType> GetEntryTypeImpl(const std::string &path) = 0;
+
+        virtual std::shared_ptr<Directory> OpenDirectoryImpl(const std::string &path, Directory::ListMode listMode) {
+            throw exception("This filesystem does not support opening directories");
+        };
+
       public:
         FileSystem() = default;
 
@@ -27,8 +44,8 @@ namespace skyline::vfs {
          * @param size The size of the file to create
          * @return Whether creating the file succeeded
          */
-        virtual bool CreateFile(const std::string &path, size_t size) {
+        bool CreateFile(const std::string &path, size_t size) {
-            throw exception("This filesystem does not support creating files");
+            return CreateFileImpl(path, size);
         };
 
         /**
@@ -37,8 +54,8 @@ namespace skyline::vfs {
          * @param parents Whether all parent directories in the given path should be created
          * @return Whether creating the directory succeeded
          */
-        virtual bool CreateDirectory(const std::string &path, bool parents) {
+        bool CreateDirectory(const std::string &path, bool parents) {
-            throw exception("This filesystem does not support creating directories");
+            return CreateDirectoryImpl(path, parents);
         };
 
         /**
@@ -47,14 +64,21 @@ namespace skyline::vfs {
          * @param mode The mode to open the file with
          * @return A shared pointer to a Backing object of the file
          */
-        virtual std::shared_ptr<Backing> OpenFile(const std::string &path, Backing::Mode mode = {true, false, false}) = 0;
+        std::shared_ptr<Backing> OpenFile(const std::string &path, Backing::Mode mode = {true, false, false}) {
+            if (!mode.write && !mode.read)
+                throw exception("Cannot open a file with a mode that is neither readable nor writable");
+
+            return OpenFileImpl(path, mode);
+        }
 
         /**
          * @brief Queries the type of the entry given by path
          * @param path The path to the entry
          * @return The type of the entry, if present
          */
-        virtual std::optional<Directory::EntryType> GetEntryType(const std::string &path) = 0;
+        std::optional<Directory::EntryType> GetEntryType(const std::string &path) {
+            return GetEntryTypeImpl(path);
+        }
 
         /**
          * @brief Checks if a given file exists in a filesystem
@@ -82,8 +106,11 @@ namespace skyline::vfs {
          * @param listMode The list mode for the directory
          * @return A shared pointer to a Directory object of the directory
          */
-        virtual std::shared_ptr<Directory> OpenDirectory(const std::string &path, Directory::ListMode listMode) {
+        std::shared_ptr<Directory> OpenDirectory(const std::string &path, Directory::ListMode listMode = {true, true}) {
-            throw exception("This filesystem does not support opening directories");
+            if (!listMode.raw)
+                throw exception("Cannot open a directory with an empty listMode");
+
+            return OpenDirectoryImpl(path, listMode);
         };
     };
 }

app/src/main/cpp/skyline/vfs/os_backing.cpp

@@ -20,10 +20,7 @@ namespace skyline::vfs {
             close(fd);
     }
 
-    size_t OsBacking::Read(span<u8> output, size_t offset) {
+    size_t OsBacking::ReadImpl(span<u8> output, size_t offset) {
-        if (!mode.read)
-            throw exception("Attempting to read a backing that is not readable");
-
         auto ret{pread64(fd, output.data(), output.size(), offset)};
         if (ret < 0)
             throw exception("Failed to read from fd: {}", strerror(errno));
@@ -31,10 +28,7 @@ namespace skyline::vfs {
         return static_cast<size_t>(ret);
     }
 
-    size_t OsBacking::Write(span<u8> input, size_t offset) {
+    size_t OsBacking::WriteImpl(span<u8> input, size_t offset) {
-        if (!mode.write)
-            throw exception("Attempting to write to a backing that is not writable");
-
         auto ret{pwrite64(fd, input.data(), input.size(), offset)};
         if (ret < 0)
             throw exception("Failed to write to fd: {}", strerror(errno));
@@ -42,7 +36,7 @@ namespace skyline::vfs {
         return static_cast<size_t>(ret);
     }
 
-    void OsBacking::Resize(size_t pSize) {
+    void OsBacking::ResizeImpl(size_t pSize) {
         int ret{ftruncate(fd, pSize)};
         if (ret < 0)
             throw exception("Failed to resize file: {}", strerror(errno));

app/src/main/cpp/skyline/vfs/os_backing.h

@@ -14,6 +14,13 @@ namespace skyline::vfs {
         int fd; //!< An FD to the backing
         bool closable; //!< Whether the FD can be closed when the backing is destroyed
 
+      protected:
+        size_t ReadImpl(span<u8> output, size_t offset) override;
+
+        size_t WriteImpl(span<u8> input, size_t offset) override;
+
+        void ResizeImpl(size_t size) override;
+
       public:
         /**
          * @param fd The file descriptor of the backing
@@ -21,11 +28,5 @@ namespace skyline::vfs {
         OsBacking(int fd, bool closable = false, Mode = {true, false, false});
 
         ~OsBacking();
-
-        size_t Read(span<u8> output, size_t offset = 0);
-
-        size_t Write(span<u8> input, size_t offset = 0);
-
-        void Resize(size_t size);
     };
 }

app/src/main/cpp/skyline/vfs/os_filesystem.cpp

@@ -15,7 +15,7 @@ namespace skyline::vfs {
                 throw exception("Error creating the OS filesystem backing directory");
     }
 
-    bool OsFileSystem::CreateFile(const std::string &path, size_t size) {
+    bool OsFileSystem::CreateFileImpl(const std::string &path, size_t size) {
         auto fullPath{basePath + path};
 
         // Create a directory that will hold the file
@@ -38,7 +38,7 @@ namespace skyline::vfs {
         return true;
     }
 
-    bool OsFileSystem::CreateDirectory(const std::string &path, bool parents) {
+    bool OsFileSystem::CreateDirectoryImpl(const std::string &path, bool parents) {
         if (!parents) {
             int ret{mkdir(path.c_str(), S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH)};
             return ret == 0 || errno == EEXIST;
@@ -58,10 +58,7 @@ namespace skyline::vfs {
         return true;
     }
 
-    std::shared_ptr<Backing> OsFileSystem::OpenFile(const std::string &path, Backing::Mode mode) {
+    std::shared_ptr<Backing> OsFileSystem::OpenFileImpl(const std::string &path, Backing::Mode mode) {
-        if (!(mode.read || mode.write))
-            throw exception("Cannot open a file that is neither readable or writable");
-
         int fd{open((basePath + path).c_str(), (mode.read && mode.write) ? O_RDWR : (mode.write ? O_WRONLY : O_RDONLY))};
         if (fd < 0)
             throw exception("Failed to open file at '{}': {}", path, strerror(errno));
@@ -69,7 +66,7 @@ namespace skyline::vfs {
         return std::make_shared<OsBacking>(fd, true, mode);
     }
 
-    std::optional<Directory::EntryType> OsFileSystem::GetEntryType(const std::string &path) {
+    std::optional<Directory::EntryType> OsFileSystem::GetEntryTypeImpl(const std::string &path) {
         auto fullPath{basePath + path};
 
         auto directory{opendir(fullPath.c_str())};
@@ -84,7 +81,7 @@ namespace skyline::vfs {
         return std::nullopt;
     }
 
-    std::shared_ptr<Directory> OsFileSystem::OpenDirectory(const std::string &path, Directory::ListMode listMode) {
+    std::shared_ptr<Directory> OsFileSystem::OpenDirectoryImpl(const std::string &path, Directory::ListMode listMode) {
         return std::make_shared<OsFileSystemDirectory>(basePath + path, listMode);
     }
 

app/src/main/cpp/skyline/vfs/os_filesystem.h

@@ -13,18 +13,19 @@ namespace skyline::vfs {
       private:
         std::string basePath; //!< The base path for filesystem operations
 
+      protected:
+        bool CreateFileImpl(const std::string &path, size_t size) override;
+
+        bool CreateDirectoryImpl(const std::string &path, bool parents) override;
+
+        std::shared_ptr<Backing> OpenFileImpl(const std::string &path, Backing::Mode mode) override;
+
+        std::optional<Directory::EntryType> GetEntryTypeImpl(const std::string &path) override;
+
+        std::shared_ptr<Directory> OpenDirectoryImpl(const std::string &path, Directory::ListMode listMode) override;
+
       public:
         OsFileSystem(const std::string &basePath);
-
-        bool CreateFile(const std::string &path, size_t size);
-
-        bool CreateDirectory(const std::string &path, bool parents);
-
-        std::shared_ptr<Backing> OpenFile(const std::string &path, Backing::Mode mode = {true, false, false});
-
-        std::optional<Directory::EntryType> GetEntryType(const std::string &path);
-
-        std::shared_ptr<Directory> OpenDirectory(const std::string &path, Directory::ListMode listMode);
     };
 
     /**

app/src/main/cpp/skyline/vfs/partition_filesystem.cpp

@@ -31,7 +31,7 @@ namespace skyline::vfs {
         }
     }
 
-    std::shared_ptr<Backing> PartitionFileSystem::OpenFile(const std::string &path, Backing::Mode mode) {
+    std::shared_ptr<Backing> PartitionFileSystem::OpenFileImpl(const std::string &path, Backing::Mode mode) {
         try {
             auto &entry{fileMap.at(path)};
             return std::make_shared<RegionBacking>(backing, fileDataOffset + entry.offset, entry.size, mode);
@@ -40,16 +40,16 @@ namespace skyline::vfs {
         }
     }
 
-    std::optional<Directory::EntryType> PartitionFileSystem::GetEntryType(const std::string &path) {
+    std::optional<Directory::EntryType> PartitionFileSystem::GetEntryTypeImpl(const std::string &path) {
         if (fileMap.count(path))
             return Directory::EntryType::File;
 
         return std::nullopt;
     }
 
-    std::shared_ptr<Directory> PartitionFileSystem::OpenDirectory(const std::string &path, Directory::ListMode listMode) {
+    std::shared_ptr<Directory> PartitionFileSystem::OpenDirectoryImpl(const std::string &path, Directory::ListMode listMode) {
         // PFS doesn't have directories
-        if (path != "")
+        if (!path.empty())
             return nullptr;
 
         std::vector<Directory::Entry> fileList;

app/src/main/cpp/skyline/vfs/partition_filesystem.h

@@ -39,14 +39,15 @@ namespace skyline::vfs {
         std::shared_ptr<Backing> backing; //!< The backing file of the filesystem
         std::unordered_map<std::string, PartitionFileEntry> fileMap; //!< A map that maps file names to their corresponding entry
 
+      protected:
+        std::shared_ptr<Backing> OpenFileImpl(const std::string &path, Backing::Mode mode) override;
+
+        std::optional<Directory::EntryType> GetEntryTypeImpl(const std::string &path) override;
+
+        std::shared_ptr<Directory> OpenDirectoryImpl(const std::string &path, Directory::ListMode listMode) override;
+
       public:
         PartitionFileSystem(const std::shared_ptr<Backing> &backing);
-
-        std::shared_ptr<Backing> OpenFile(const std::string &path, Backing::Mode mode = {true, false, false});
-
-        std::optional<Directory::EntryType> GetEntryType(const std::string &path);
-
-        std::shared_ptr<Directory> OpenDirectory(const std::string &path, Directory::ListMode listMode);
     };
 
     /**

app/src/main/cpp/skyline/vfs/region_backing.h

@@ -14,20 +14,20 @@ namespace skyline::vfs {
         std::shared_ptr<vfs::Backing> backing; //!< The parent backing
         size_t baseOffset; //!< The offset of the region in the parent backing
 
+      protected:
+        size_t ReadImpl(span <u8> output, size_t offset) override {
+            return backing->Read(output, baseOffset + offset);
+        }
+
       public:
         /**
          * @param file The backing to create the RegionBacking from
          * @param offset The offset of the region start within the parent backing
          * @param size The size of the region in the parent backing
          */
-        RegionBacking(const std::shared_ptr<vfs::Backing> &backing, size_t offset, size_t size, Mode mode = {true, false, false}) : Backing(mode, size), backing(backing), baseOffset(offset) {};
+        RegionBacking(const std::shared_ptr<vfs::Backing> &backing, size_t offset, size_t size, Mode mode = {true, false, false}) : Backing(mode, size), backing(backing), baseOffset(offset) {
-
+            if (mode.write || mode.append)
-        size_t Read(span <u8> output, size_t offset = 0) {
+                throw exception("Cannot open a RegionBacking as writable");
-            if (!mode.read)
+        };
-                throw exception("Attempting to read a backing that is not readable");
-            if (size - offset < output.size())
-                throw exception("Trying to read past the end of a region backing: 0x{:X}/0x{:X} (Offset: 0x{:X})", output.size(), size, offset);
-            return backing->Read(output, baseOffset + offset);
-        }
     };
 }

app/src/main/cpp/skyline/vfs/rom_filesystem.cpp

@@ -49,7 +49,7 @@ namespace skyline::vfs {
             TraverseDirectory(entry.siblingOffset, path);
     }
 
-    std::shared_ptr<Backing> RomFileSystem::OpenFile(const std::string &path, Backing::Mode mode) {
+    std::shared_ptr<Backing> RomFileSystem::OpenFileImpl(const std::string &path, Backing::Mode mode) {
         try {
             const auto &entry{fileMap.at(path)};
             return std::make_shared<RegionBacking>(backing, header.dataOffset + entry.offset, entry.size, mode);
@@ -58,7 +58,7 @@ namespace skyline::vfs {
         }
     }
 
-    std::optional<Directory::EntryType> RomFileSystem::GetEntryType(const std::string &path) {
+    std::optional<Directory::EntryType> RomFileSystem::GetEntryTypeImpl(const std::string &path) {
         if (fileMap.count(path))
             return Directory::EntryType::File;
         else if (directoryMap.count(path))
@@ -67,7 +67,7 @@ namespace skyline::vfs {
         return std::nullopt;
     }
 
-    std::shared_ptr<Directory> RomFileSystem::OpenDirectory(const std::string &path, Directory::ListMode listMode) {
+    std::shared_ptr<Directory> RomFileSystem::OpenDirectoryImpl(const std::string &path, Directory::ListMode listMode) {
         try {
             auto &entry{directoryMap.at(path)};
             return std::make_shared<RomFileSystemDirectory>(backing, header, entry, listMode);

app/src/main/cpp/skyline/vfs/rom_filesystem.h

@@ -32,6 +32,13 @@ namespace skyline {
              */
             void TraverseDirectory(u32 offset, const std::string &path);
 
+          protected:
+            std::shared_ptr<Backing> OpenFileImpl(const std::string &path, Backing::Mode mode) override;
+
+            std::optional<Directory::EntryType> GetEntryTypeImpl(const std::string &path) override;
+
+            std::shared_ptr<Directory> OpenDirectoryImpl(const std::string &path, Directory::ListMode listMode) override;
+
           public:
             struct RomFsHeader {
                 u64 headerSize; //!< The size of the header
@@ -69,12 +76,6 @@ namespace skyline {
             std::unordered_map<std::string, RomFsDirectoryEntry> directoryMap; //!< A map that maps directory names to their corresponding entry
 
             RomFileSystem(std::shared_ptr<Backing> backing);
-
-            std::shared_ptr<Backing> OpenFile(const std::string &path, Backing::Mode mode = {true, false, false});
-
-            std::optional<Directory::EntryType> GetEntryType(const std::string &path);
-
-            std::shared_ptr<Directory> OpenDirectory(const std::string &path, Directory::ListMode listMode);
         };
 
         /**