Added a comment in fs_dev.h. Adjusted fs.h formatting, etc. Added support for mounting SaveData.

nx/include/switch/devices/fs_dev.h

@@ -25,6 +25,7 @@ Result fsdevInit(void);
 Result fsdevExit(void);
 
 /// Mounts the input fs with the specified device name. fsdev will handle closing the fs when required, including when fsdevMountDevice() fails.
+/// Returns -1 when any errors occur.
 int fsdevMountDevice(const char *name, FsFileSystem fs);
 
 /// Unmounts the specified device.

nx/include/switch/services/fs.h

@@ -4,6 +4,15 @@
 
 #define FS_MAX_PATH 0x301
 
+/// For use with fsMountSaveData().
+#define FS_MOUNTSAVEDATA_INVAL_DEFAULT 0x1
+
+/// For use with FsSave.
+#define FS_SAVEDATA_CURRENT_TITLEID 0
+
+/// For use with FsSave.
+#define FS_SAVEDATA_USERID_COMMONSAVE 0
+
 typedef struct {
     Handle  h;
 } FsFileSystem;
@@ -23,13 +32,25 @@ typedef struct {
 /// Directory entry.
 typedef struct
 {
-	char name[FS_MAX_PATH];      ///< Entry name.
-	u8 pad[3];
-	s8 type;       ///< See FsEntryType.
-        u8 pad2[3];     ///< ?
-	u64 fileSize;         ///< File size.
+    char name[FS_MAX_PATH];      ///< Entry name.
+    u8 pad[3];
+    s8 type;       ///< See FsEntryType.
+    u8 pad2[3];     ///< ?
+    u64 fileSize;         ///< File size.
 } FsDirectoryEntry;
 
+/// Save Struct
+typedef struct
+{
+    u64 titleID;          ///< titleID of the savedata to access when accessing other titles' savedata via SaveData, otherwise FS_SAVEDATA_CURRENT_TITLEID.
+    u128 userID;          ///< userID of the user-specific savedata to access, otherwise FS_SAVEDATA_USERID_COMMONSAVE. See account.h.
+    u64 saveID;           ///< saveID, 0 for SaveData.
+    u64 ContentStorageId; ///< ContentStorageId? See FsContentStorageId.
+    u64 unk_x28;          ///< 0 for SystemSaveData/SaveData.
+    u64 unk_x30;          ///< 0 for SystemSaveData/SaveData.
+    u64 unk_x38;          ///< 0 for SystemSaveData/SaveData.
+} PACKED FsSave;
+
 typedef enum {
     ENTRYTYPE_DIR = 0,
     ENTRYTYPE_FILE = 1
@@ -37,26 +58,40 @@ typedef enum {
 
 typedef enum
 {
-	FS_OPEN_READ   = BIT(0), ///< Open for reading.
-	FS_OPEN_WRITE  = BIT(1), ///< Open for writing.
-	FS_OPEN_APPEND = BIT(2), ///< Append file.
+    FS_OPEN_READ   = BIT(0), ///< Open for reading.
+    FS_OPEN_WRITE  = BIT(1), ///< Open for writing.
+    FS_OPEN_APPEND = BIT(2), ///< Append file.
 } FsFileFlags;
 
 /// For use with fsFsOpenDirectory.
 typedef enum
 {
-	FS_DIROPEN_DIRECTORY   = BIT(0), ///< Enable reading directory entries.
-	FS_DIROPEN_FILE  = BIT(1),       ///< Enable reading file entries.
+    FS_DIROPEN_DIRECTORY   = BIT(0), ///< Enable reading directory entries.
+    FS_DIROPEN_FILE  = BIT(1),       ///< Enable reading file entries.
 } FsDirectoryFlags;
 
+typedef enum
+{
+    FS_CONTENTSTORAGEID_NandSystem = 0,
+    FS_CONTENTSTORAGEID_NandUser   = 1,
+    FS_CONTENTSTORAGEID_SdCard     = 2,
+} FsContentStorageId;
+
 Result fsInitialize();
 void fsExit(void);
 
 Handle fsGetServiceSession(void);
 
 Result fsMountSdcard(FsFileSystem* out);
+Result fsMountSaveData(FsFileSystem* out, u8 inval, FsSave *save);
 // todo: Rest of commands here
 
+/// FsFileSystem can be mounted with fs_dev for use with stdio, see fs_dev.h.
+
+/// Wrapper(s) for fsMountSaveData.
+/// See FsSave for titleID and userID.
+Result fsMount_SaveData(FsFileSystem* out, u64 titleID, u128 userID);
+
 // IFileSystem
 Result fsFsCreateFile(FsFileSystem* fs, const char* path, size_t size, int flags);
 Result fsFsDeleteFile(FsFileSystem* fs, const char* path);

nx/source/devices/fs_dev.c

@@ -308,6 +308,7 @@ static int _fsdevMountDevice(const char *name, FsFileSystem fs, fsdev_fsdevice *
 
   return dev;
 }
+
 int fsdevMountDevice(const char *name, FsFileSystem fs)
 {
   return _fsdevMountDevice(name, fs, NULL);

nx/source/services/fs.c

@@ -87,6 +87,57 @@ Result fsMountSdcard(FsFileSystem* out) {
     return rc;
 }
 
+Result fsMountSaveData(FsFileSystem* out, u8 inval, FsSave *save) {
+    IpcCommand c;
+    ipcInitialize(&c);
+
+    struct {
+        u64 magic;
+        u64 cmd_id;
+        u64 inval;//Actually u8.
+        FsSave save;
+    } PACKED *raw;
+
+    raw = ipcPrepareHeader(&c, sizeof(*raw));
+
+    raw->magic = SFCI_MAGIC;
+    raw->cmd_id = 51;
+    raw->inval = (u64)inval;
+    memcpy(&raw->save, save, sizeof(FsSave));
+
+    Result rc = ipcDispatch(g_fsHandle);
+
+    if (R_SUCCEEDED(rc)) {
+        IpcCommandResponse r;
+        ipcParseResponse(&r);
+
+        struct {
+            u64 magic;
+            u64 result;
+        } *resp = r.Raw;
+
+        rc = resp->result;
+
+        if (R_SUCCEEDED(rc)) {
+            out->h = r.Handles[0];
+        }
+    }
+
+    return rc;
+}
+
+// Wrapper(s) for fsMountSaveData.
+Result fsMount_SaveData(FsFileSystem* out, u64 titleID, u128 userID) {
+    FsSave save;
+
+    memset(&save, 0, sizeof(save));
+    save.titleID = titleID;
+    save.userID = userID;
+    save.ContentStorageId = FS_CONTENTSTORAGEID_NandUser;
+
+    return fsMountSaveData(out, FS_MOUNTSAVEDATA_INVAL_DEFAULT, &save);
+}
+
 // IFileSystem impl
 Result fsFsCreateFile(FsFileSystem* fs, const char* path, size_t size, int flags) {
     IpcCommand c;