[PATCHER][APP] Dual boot any ROM on our OnePlus 3

I'm proud to present the first dual boot project for the Qualcomm-based Samsung Galaxy S4! This project started off as a feature in my ROM, but not anymore. This will allow any two ROMs (soon, three) to be installed at the same time. It works by patching the secondary ROM's installation scripts and boot image to load the ROM files from an alternate location (/system/multiboot, /cache/multiboot, and /data/multiboot). Because of the way this is implemented, no changes to the primary ROM are necessary :D

Donators

A huge thanks goes out to all of the donators for supporting this project! I if forgot to add you (and you want to be added), please send me a quick PM.

See all of our supporters here: http://ift.tt/29aiA2i

It patches...
Custom kernels for dual boot support
ROMs so that they can be installed as secondary
Google Apps packages for AOSP-based ROMs
SuperSU so that it can be used in the secondary ROM

NOTE: If you want to dualboot a TouchWiz ROM, I highly recommend installing TW as the primary ROM. Otherwise, any mods will need to be patched before flashing.

How to use the patcher

Android

Download the patcher apk and run it. Tap "Patch Zip File" from the navigation drawer and choose the file you want to patch.

Windows (GUI)

Double click DualBootPatcher.exe and choose the file you want to patch.

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After patching the zip file, a new file, like some_rom_dual.zip file will be created.

*_dual.zip

Instructions for dual booting

Before doing anything, download the Dual Boot Patcher app and the DualBootUtilities.zip from the download section below.

The patcher offers several locations for installing ROMs:
Primary: This is normally used for installing a zip to the primary ROM. It is not required, but is strongly recommended because it has code to prevent the zip from inadvertently affecting other ROMs.
Dual: Dual/Secondary is the first multiboot installation location. It installs to the system partition. This is a good spot for installing a second ROM because it doesn't take any space away from the internal storage.
Multi-slots: There are 3 multislots: multi-slot-1, multi-slot-2, multi-slot-3. These install to the cache partition. This is specifically for devices, like the Galaxy S4, that have a massive cache partition.
Data-slots: There can be an unlimited number of data slots. These install to the data partition and eat up space on the internal storage. This is useful for devices where the system partition is nearly full and the cache partition is tiny. These slots are named "data-slot-[id]", where "id" is something you provide in the app.
Extsd-slots: There can be an unlimited number of extsd slots. These install to the external SD card, which is useful as it keeps the ROMs off of the internal storage. Note that the ROM's data files are still stored on the data partition.

With that said, let's get to the "how to"!
First, boot into your primary ROM and install the Dual Boot Patcher app
Open the app and go to "Roms" in the navigation drawer. It will ask if you want to set the kernel. Make sure that you do.
Go to "Patch zip file" in the navigation drawer and patch the ROM or zip you want to install. You can select one of the installation locations described above.

There are two ways of flashing the patched zip file. You can either flash it normally from recovery or flash it using the in-app flashing feature. Both methods are explained below.

Flashing from recovery

To flash from recovery, just flash the patched zip file like you would for any other zip. Nice and simple.

In-app flashing

To use in-app flashing, go to "Roms" in the navigation drawer, tap the floating button on the bottom right, and add the zips you want to install. You can queue multiple zips and they will all be flashed in one go. Once you've added all the zips you want to flash, click the check mark in the action bar and they will be flashed right away.

A normal backup from recovery will backup every ROM. If you would like to back up ROMs individually, please see @rlorange's awesome tool: http://ift.tt/1NC2ksG

App and data sharing

DualBootPatcher very recently got support for sharing apps and their data across ROMs. Maybe sharing is somewhat of a misleading term. The feature actually makes Android load the shared apps and data from a centralized location, /data/multiboot/_appsharing. So you're not sharing apps from one ROM to another per se. The ROMs are just loading the apps from one shared location. Let me make this clearer with an analogy.

Think of the people in a company office as ROMs. You want to share with your coworkers some documents (apps). Instead of telling them to come over to your desk to see those documents (sharing apps from one ROM to another), everyone goes to the conference room to look at the documents together (loading apps from a shared location). That's how app and data sharing is implemented.

To use app sharing, follow these steps in every ROM that you want to use app sharing:
Install the app you want to share
Open DualBootPatcher and go to "App Sharing" in the navigation drawer
Enable individual app sharing
Tap "Manage shared applications" and enable APK/data sharing for the app
Reboot

When you uninstall an app that's shared, it simply become unshared for the current ROM. That way, other ROMs are not affected. To continue the analogy above, if you quit your job, you won't shred the documents that everybody else was looking at.

If you unshare an app's data, it will go back to using the data it had before it was shared. In other words, you leave the conference room and go back to work on your own documents at your desk.

(Hope my analogy didn't suck too much :p)

How do I...?

Switch the ROM if something doesn't work properly?
You can flash the DualBootUtilities zip from recovery. It will provide a menu interface that allows switching to the various ROMs.

If you have TWRP, you can also switch manually by tapping Install -> Images (bottom right) -> Go to /sdcard/MultiBoot/[Your ROM]/ -> flash boot.img.

Wipe /cache, /data, /system, or dalvik-cache?
The easiest way is to do it from the app while booted in another ROM. Just go to "Roms" in the navigation drawer, tap the 3 dots options menu for the ROM you want to wipe, and tap "Wipe ROM".

Alternatively, flash the DualBootUtilities zip from recovery, which will also allow you to wipe a ROM.

NOTE: Don't use the recovery's built-in wiping abilities as that may delete non-primary ROMs!

Update the primary ROM?
Patch the zip for primary and flash it. The "primary" installation target is designed so that other ROMs won't be affected when you want to flash something for the primary ROM.

Update a non-primary ROM?
Patch and flash the zip exactly like how you did it the first time.

Flash a mod or custom kernel for the primary ROM?
Patch it for primary before flashing. If the zip does not wipe /cache, it is also safe to flash it directly.

Flash a mod or custom kernel for a non-primary ROM?
Just patch and flash it :)

Downloads:

http://ift.tt/1BvgxMu

Donations:

Donations are not required, but are greatly appreciated :D Donators will have their names listed in a nice big font on this post and will also be listed in the README file of the patcher.

Source code:

DualBootPatcher: http://ift.tt/1N6RFlZ
DualBootUtilities: http://ift.tt/1G6MDpU

Build instructions: http://ift.tt/1G6MAdO

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