Comex – developer of JailbreakMe – popular browser-based jailbreak tool who is expected to release a new version of the tool to jailbreak iPad 2 has revealed that he has reduced the time it will take to jailbreak an iOS device by using a unionfs approach instead of using the stashing approach that has been used by jailbreak tools.
He has also revealed that he plans to use this approach for the iPad 2, thus indicating that iPad 2 users will have to wait for some more time for the eagerly awaited JailbreakMe for iPad 2.
Comex has provided the following information about the performance improvements:
If you don’t know, the stashing approach jailbreaks have been using for years– Cydia’s “Reorganizing Filesystem”– involves moving some large directories from the small / partition into the large /var partition, then creating symlinks from the original to the new location. This both ensures that any additional stuff put in those directories by packages will end up in the /var partition, and frees up space on the / partition for files created outside of those directories. However, the process has some issues, like taking forever to do when you jailbreak (I am a bit fanatical about speed), pretty much requiring the jailbreak to reboot the system to ensure there aren’t any running applications pointing to the old files (ditto about speed, I want a jailbreak to not even require a respring, as in star, but since star used stashing, some obscure things could cause issues before a reboot), and seriously confusing the sandbox code in the kernel (because each application has a sandbox with a list of allowed filenames, but after the symlink has moved files, the filenames no longer match), requiring that code to be patched (it needs to be patched anyway these days because tweaks have to run under the sandboxes of the applications they’re hooking, but depend on accessing various directories; but it still feels good to get rid of a kludge).
With unionfs (which was saurik’s idea originally), new files are created in the /var partition, and merged with files in the corresponding directories in the / partition, so no files need to be moved, no descriptors are invalidated, and I think the sandbox code won’t notice what happened. It also opens the door for upgrading the base operating system without destroying the jailbreak files (although maybe iOS 5 delta updates will already allow this? I haven’t looked at them yet).
I’ve wanted to do this since literally a year ago (that’s the date of the nullfs checkin, since I was dumb and thought I wanted that instead of unionfs), but I never got around to making it work properly.
So, I just hope that I can get rid of the crashes my meddling with unionfs’s code have introduced, and fix it for the iPad 2 (my dumped copies of iPad 2 kernels do not include symbols; I wrote a small BinDiff-like tool to copy over symbols from a kernel for another device, but it’s not perfect) and that there aren’t any performance issues.
Comex has also revealed that the new version of JailbreakMe will support iOS 4.2.1 to iOS 4.3.3 to one of his followers on Twitter and MuscleNerd of iPhone Dev team has indicated it will support all iOS devices with the following tweet:
@itaiyz97 see @comex’s feed tonight for his huge spoilers 🙂 All devices from iPhone3GS through iPad2, iOS 4.2.1 to 4.3.3
That’s good news as JailbreakMe 2.0 for iOS 4.0.x was the mother of all jailbreaking solutions as it allowed users to jailbreak their iOS device using mobile Safari. Based on MuscleNerd’s tweet, we’re assuming that JailbreakMe 3.0 will support iPod touch 3G, iPod touch 4G, iPad 1, iPad 2, iPhone 3GS, iPhone 4 (GSM) and iPhone 4 (CDMA).
Comex hasn’t given any release date, but based on the update above it looks like it will take some more time.