/dev/fsa

/dev/fsa is the IOSU device node for the virtual filesystem API. It exposes a generic interface for accessing various filesystems supported by the Wii U, including the internal storage filesystem (ISFS), game disc filesystems, and SD cards. These filesystems can be mounted on directories under /vol and accessed through a common API. Once opened, ioctl() and ioctlv() requests can be issued to the interface, which are documented below.

Structures

Request Blocks

The parameters to FSA functions are passed in a 0x520-byte request block. While the size is constant, the structure varies by call, as shown below:

/* Read/write request block */
typedef struct
{
    char unknown0[0x4-0x0];
    void *buffer;                  // Not looked at by FSA
    uint32_t size, count;
    char unknown10[0x14-0x10];
    uint32_t handle;
    char unknown18[0x1c-0x18];
    uint32_t unknown1c;            // Always 0x6e000000
    char unknown20[0x284-0x20];
    uint32_t unknown284;           // Always 0x77000000
    char unknown288[0x294-0x288];
    uint32_t unknown294;           // Always 0x660
    char unknown298[0x520-0x298];
} rw_req_t;

Status Blocks

All FSA functions return the status of the call in a 0x293-byte buffer.

Tables

List of Functions (Ioctl/Ioctlv/IoctlAsync)

Command	Function	Ioctl	Ioctlv	IoctlAsync	Notes
0x01	FSMount		X
0x01	FSAMount FSMountAsync FSBindMount		X
0x02	FSAUnmount FSUnmountAsync FSBindUnmount FSBindUnmountAsync	X
0x03	FSAGetVolumeInfo FSGetVolumeInfoAsync	X
0x04	FSAInit			X
0x05	FSAChangeDir FSChangeDirAsync	X
0x06	FSAGetCwd FSGetCwdAsync	X
0x07	FSAMakeDir	X	X
0x08	FSARemove	X	X
0x09	FSARename		X
0x0A	FSOpenDir	X	X
0x0B	FSReadDir	X
0x0C	FSRewindDir	X
0x0D	FSCloseDir	X
0x0E	FSAOpenFile FSAOpenFileEx		X
0x0F	FSAReadFile FSReadFileWithPos		X		This function is used to read data from an open file. It takes 1 input buffer through the ioctlv interface, a read request block, and 2 output buffers, a buffer for file data and a status block.
0x10	FSWriteFile FSWriteFileWithPos		X		This function is used to write data to an open file. It takes 2 input buffers through the ioctlv interface, a read request block and a data buffer, and 1 output buffer, a status block.
0x11	FSGetPosFile	X
0x12	FSSetPosFile	X
0x13	FSIsEof	X
0x14	FSAStatFile	X
0x15	FSACloseFile	X
0x16	FSAGetError		X
0x17	FSFlushFile	X
0x18	FSGetStat FSGetFreeSpaceSize FSGetEntryNum FSGetFileSystemInfo	X	X
0x19	FSAppendFile FSAppendFileEx	X
0x1A	FSTruncateFile	X
0x1B	FSAFlushVolume	X	X
0x1C	FSARollbackVolume	X	X
0x1D	FSMakeQuota	X	X
0x1E	FSFlushQuota	X	X
0x1F	FSRollbackQuota FSARollbackQuotaForce	X	X
0x20	FSChangeMode	X	X
0x21	FSAOpenFileByStat FSOpenFileByStatAsync		X
0x22	FSRegisterFlushQuota	X	X
0x23	FSFlushMultiQuota	X	X
0x25	FSGetFileBlockAddress		X
0x65	AddUserProcess	‎ ‎ ‎ ‎ ‎ X
0x66	DelUserProcess	‎ ‎ ‎ ‎ ‎ X
0x67	FSAMountWithProcess		‎ ‎ ‎ ‎ ‎ X
0x68	FSAUnmountWithProcess	‎ ‎ ‎ ‎ ‎ X
0x69	FSAFormat	‎ ‎ ‎ ‎ ‎ X
0x6A	FSARawOpen	‎ ‎ ‎ ‎ ‎ X
0x6B	FSARawRead		‎ ‎ ‎ ‎ ‎ X
0x6C	FSARawWrite		‎ ‎ ‎ ‎ ‎ X
0x6D	FSARawClose	‎ ‎ ‎ ‎ ‎ X
0x6E	GetLastFailedVolume	‎ ‎ ‎ ‎ ‎ X
0x6F	GetVolumeExistence		‎ ‎ ‎ ‎ ‎ X
0x70	FSAChangeOwner	‎ ‎ ‎ ‎ ‎ X
0x71	CancelGetAttach	‎ ‎ ‎ ‎ ‎ X
0x72	FSARemoveQuota	‎ ‎ ‎ ‎ ‎ X	‎ ‎ ‎ ‎ ‎ X
0x73	SetClientPriority	‎ ‎ ‎ ‎ ‎ X
0x74	ApplyMemoryCache	‎ ‎ ‎ ‎ ‎ X
0x75	FSMakeLinkAsync	‎ ‎ ‎ ‎ ‎ X	‎ ‎ ‎ ‎ ‎ X
0x76	XferParams	‎ ‎ ‎ ‎ ‎ X
0x82	SetProcessConfig		‎ ‎ ‎ ‎ ‎ X		Subcommand Name Notes 0x83 scfmSetMemoryCacheBuffer 0x84 scfmUnsetMemoryCacheBuffer 0x85 Unknown FAT 0x86 scfmSetMemoryCacheArea 0x87 scfmEnableSetMemoryCacheArea 0x88 scfmUnsetMemoryCacheArea 0x89 Unknown 0x8A Unknown Sets an ATFS flag that affects whether a volume will be dropped for having an expired version in its header. 0x8B Unknown SCFM
0x8C	GetProcResourceUsage	‎ ‎ ‎ ‎ ‎ ‎X			Debug/test only
0x8D	GetAllResourceUsage	‎ ‎ ‎ ‎ ‎ ‎X			Debug/test only
0x8E	SendProfileCmd	‎ ‎ ‎ ‎ ‎ ‎‎X			Debug/test only