File Management

The PS Vita has a multi-layered file management system that is similar (and may be based off of) the BSD vnode structure. Different kernel modules handle each layer. All information can be found at VFS Implementation.

Hardware

At the lowest level, we have the device drivers for the various virtual and real devices on the system. For example SceSdif interacts with the SDIO interface for speaking to the eMMC and any other SD interfaces.

Block

Next is the block level. This is device blocks, not file system blocks (which is at a higher level). SceSdstor manages the blocks and also exports block level devices to system applications. Block level encryption and decryption also takes place at this level. All user-facing devices including eMMC, Memory Card, and Game Card are encrypted at the block level. Partitions are also managed at this level. One device can export multiple partitions. Partitions tables are a proprietary format.

File System

The file system is implemented on top of the block drivers. SceExfatfs is used to recognize FAT16, FAT32, and exFAT partitions.

Caching

Next is a layer of caching implemented by SceFios2Kernel. SceExfatfs also has two caches as follows:

cache_all_fat_data

 sa0:

cluster_cache

 sd0:
 os0:
 tm0:
 sa0:
 pd0:

However it is unclear how these caches work.

API

Finally, there is SceIofilemgr which exposes IO APIs such as sceIoOpen for applications to use to access files. Different application may deal with different encrypted format files.

Implementation: Mainly vfs only. Lookup the `File System` to create a new vfs node and connect it to the vfs link. This works like a kind of cache.

For example, sceIoOpen first looks for a vfs link from path. If any vfs node is not found in the middle, use "File System"'s lookup to create a new vfs node and continue the search.

If the final vfs node is found, create a uid object and return uid as fd to the user.

For sceIoRead, get the object from uid and convert it to vfs node. Then call sceVopRead with that vfs node as an argument. sceVopRead calls "File System"'s vop_read.

Name	Dependence	Description
ncache	-	name cache per vnode. SceIofilemgr uses this to search for entries in file system. If it is not found in ncache, execute sceVopLookup on the target mnt. If the entry is still not found, it will be an api error.
vfs	ncache	base vfs. like exfat/tty/host/md.
mnt	vfs	moint point. like ux0: / sdstor0: / tty0:.
vnode	mnt	The vnode per entry.
VfsFile (fd)	vnode	-