Alright guys, here is an update to the library.
I added DISC_INTERFACE devices for sd and usb to the library. Those disc interfaces can be used in combination with libfat, libntfs or libext2fs to mount varios devices with different filesystems on the wii u homebrews.
One of a great improvements is that the SD speed is way faster than using the original FS library of nintendo. Another bonus is that mounting USB with other filesystems than the original nintendo WFS filesystem is now also possible. This could theoritically be used to mount the USB inside the MCP iosuhax module (aka wupserver) before the original MCP module starts to search for titles on the USB. Then force it to search on an NTFS/FAT32 formatted USB device through a hook. This is not done yet but it would be quite possible. Maybe with this some people that were sceptical above see some light in this now.
What's done for now as a demonstration on how it works is a version of ftpiiu everywhere that uses libfat for SD and USB mounting. You can just insert a FAT32 formatted USB device either as first or 2nd usb device and it will be mounted by ftpiiu everywhere. It first tries the first device and if that fails then the second. Be aware hat if you attach the 2nd usb drive inside the WiiU Menu it will tell you to remove it and reboot. So only attach the 2nd device once you are inside HBL. If you only use one device as FAT32 you can attach it at any time. ftpiiu everywhere will automatically mount FAT32 usb devices to "usb" and WFS usb devices to "storage_usb".
Where to find the new stuff?
You can find the new update of libiosuhax on my github here:
https://github.com/dimok789/libiosuhax/commit/918491b2db486dd3c6ddb45c009b14a9fefc3561
I adapted libfat a bit to use the new disc interfaces as defaults. With that you can simply use fatInitDefault(); and it will mount the SD card and any FAT32 usb devices. Of course you can also just use the manual libfat mount functions. You can find it here:
https://github.com/dimok789/libfat
The new ftpiiu everywhere version that makes use of the new changes can be found here:
https://github.com/dimok789/ftpiiu/tree/ftpiiu_everywhere
Here a compiled version:
http://www81.zippyshare.com/v/2wnWV6Xd/file.html
Have fun with it