/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.

ioctlv() interface

0x0F - FSReadFile()

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()

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.

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		X
0x01	FSMountAsync		X
0x01	FSBindMount		X
0x02	FSUnmount	X
0x02	FSAUnmount		X
0x02	FSUnmountAsync		X
0x02	FSBindUnmount	X
0x02	FSBindUnmountAsync	X	X
0x03	FSGetVolumeInfo	X
0x03	FSAGetVolumeInfo		X
0x03	FSGetVolumeInfoAsync		X
0x04	FSInit			X
0x04	FSAInit			X
0x05	FSChangeDir	X
0x05	FSAChangeDir		X
0x05	FSChangeDirAsync		X
0x06	FSGetCwd	X
0x06	FSAGetCwd	X
0x06	FSGetCwd Async	X
0x07	FSMakeDir	X	X
0x08	FSRemove	X	X
0x09	FSRename		X
0x0A	FSOpenDir	X	X
0x0B	FSReadDir	X
0x0C	FSRewindDir	X
0x0D	FSCloseDir	X
0x0E	FSOpenFile		X
0x0E	FSOpenFileEx		X
0x0F	FSReadFile		X
0x0F	FSReadFileWith Pos		X
0x10	FSWriteFile		X
0x10	FSWriteFileWithPos		X
0x11	FSGetPosFile	X
0x12	FSSetPosFile	X
0x13	FSIsEof	X
0x14	FSGetStatFile	X
0x15	FSCloseFile	X
0x16	FSAGetError		X
0x17	FSFlushFile	X
0x18	FSGetStat	X	X
0x18	FSGetFreeSpaceSize	X	X
0x18	FSGetEntryNum	X	X
0x18	FSGetFileSystemInfo	X	X
0x19	FSAppendFile	X
0x19	FSAppendFileEx	X
0x1A	FSTruncateFile	X
0x1B	FSAFlushVolume	X	X
0x1C	FSARollbackVolume	X	X
0x1D	FSMakeQuota	X	X
0x1E	FSFlushQuota	X	X
0x1F	FSRollbackQuota	X	X
0x1F	FSARollbackQuotaForce	X	X
0x20	FSChangeMode	X	X
0x21	FSOpenFileByStat		X
0x21	FSAOpenFileByStat		X
0x21	FSOpenFileByStatAsync		X
0x22	FSRegisterFlushQuota	X	X
0x23	FSFlushMultiQuota	X	X
0x25	FSGetFileBlockAddress		X
0x6E	Unknown	X
0x6F	Unknown		X
0x72	FSRemoveQuota	X	X
0x75	FSMakeLinkAsync	X	X
0x76	HIOInit	?	?	?	Not FS Command?
0x??	FSAddClientEx			X	Used with 0x01 and 0x02