/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.

ioctl() interface

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.

List of functions (Ioctl/Ioctlv/IoctlAsync)

Command	Function	Ioctl	Ioctlv	IoctlAsync	Notes
0x01	FSMount	No	Yes	No
0x01	FSAMount	No	Yes	No
0x01	FSMountAsync	No	Yes	No
0x01	FSBindMount	No	Yes	No
0x02	FSUnmount	Yes	No	No
0x02	FSAUnmount	No	Yes	No
0x02	FSUnmountAsync	No	Yes	No
0x02	FSBindUnmount	Yes	No	No
0x02	FSBindUnmountAsync	Yes	Yes	No
0x03	FSGetVolumeInfo	Yes	No	No
0x03	FSAGetVolumeInfo	No	Yes	No
0x03	FSGetVolumeInfoAsync	No	Yes	No
0x04	FSInit	No	No	Yes
0x04	FSAInit	No	No	Yes
0x05	FSChangeDir	Yes	No	No
0x05	FSAChangeDir	No	Yes	No
0x05	FSChangeDirAsync	No	Yes	No
0x06	FSGetCwd	Yes	No	No
0x06	FSAGetCwd	Yes	No	No
0x06	FSGetCwd Async	Yes	No	No
0x07	FSMakeDir	Yes	Yes	No
0x08	FSRemove	Yes	Yes	No
0x09	FSRename	No	Yes	No
0x0A	FSOpenDir	Yes	Yes	No
0x0B	FSReadDir	Yes	No	No
0x0C	FSRewindDir	Yes	No	No
0x0D	FSCloseDir	Yes	No	No
0x0E	FSOpenFile	No	Yes	No
0x0E	FSOpenFileEx	No	Yes	No
0x0F	FSReadFile	No	Yes	No
0x0F	FSReadFileWith Pos	No	Yes	No
0x10	FSWriteFile	No	Yes	No
0x10	FSWriteFileWithPos	No	Yes	No
0x11	FSGetPosFile	Yes	No	No
0x12	FSSetPosFile	Yes	No	No
0x13	FSIsEof	Yes	No	No
0x14	FSGetStatFile	Yes	No	No
0x15	FSCloseFile	Yes	No	No
0x16	FSAGetError	No	Yes	No
0x17	FSFlushFile	Yes	No	No
0x18	FSGetStat	Yes	Yes	No
0x18	FSGetFreeSpaceSize	Yes	Yes	No
0x18	FSGetEntryNum	Yes	Yes	No
0x18	FSGetFileSystemInfo	Yes	Yes	No
0x19	FSAppendFile	Yes	No	No
0x19	FSAppendFileEx	Yes	No	No
0x1A	FSTruncateFile	Yes	No	No
0x1B	FSAFlushVolume	Yes	Yes	No
0x1C	FSARollbackVolume	Yes	Yes	No
0x1D	FSMakeQuota	Yes	Yes	No
0x1E	FSFlushQuota	Yes	Yes	No
0x1F	FSRollbackQuota	Yes	Yes	No
0x1F	FSARollbackQuotaForce	Yes	Yes	No
0x20	FSChangeMode	Yes	Yes	No
0x21	FSOpenFileByStat	No	Yes	No
0x22	FSRegisterFlushQuota	Yes	Yes	No
0x23	FSFlushMultiQuota	Yes	Yes	No
0x25	FSGetFileBlockAddress	No	Yes	No
0x6E	Unknowm	Yes	No	No
0x6F	Unknown	No	Yes	No
0x72	FSRemoveQuota	Yes	Yes	No
0x75	FSMakeLinkAsync	Yes	Yes	No
0x76	HIOInit (Not FS Command??)	??	??	??
0x??	FSAddClientEx	No	No	Yes	Used with 0x01 and 0x02 ?? (maybe)