[Galaxy S III General] Mike Green:
Mounting ext3 external SD "despite" ROM?

What are my options here that aren't prohibitive in terms of risk and/or rip up, to get external SD mounted as ext4?

I see the following choices:

Custom ROM:

Use a different ROM. Not sure I want to venture there just yet - this is for my 12 year old daughter, so ease of use and user-experience beats flexibility, and don't want her to have to deal with breakage, work arounds, and things that just are work in progress. (Both parents are using and have been using various custom ROMs. Not sure thta LG Vilt has a rich stable of choice for custom ROMs either...)

New rootfs:

see if the current ROM can be modified. In principle, it may be fairly easy (modify fstab.x5) in rootfs ? But requires a way to modify rootfs, which is substantially turning the stock ROM into a custom ROM, with an additional requirement of needing to obtain, modify and in the process not screw up a proprietary ROM which doesn't have a clean rebuild path.

Look into a modfiable daisy-chained init file:

One could bypass fstab.x5 in / and modifiy an init file executed at boot time. Alas, the basic init scripts are in / -- however, it appears as if one of these calls another init in /system/etc - whicle it related to something non-filesystem-related, I can't see why one might not just add mount -t ext4 /dev/blk/<SD-ext4-partition>. /storage/external_SD

Once this is done, the question is whether everything else will fall in place. (For example, /etc/vold.fstab lists ext4 - how will vold react?)

A variant of this, that might fit better in the Android architecture may be to mount the external sd as an internal SD, /storage/sdcard/1 and treat it like a secondary built in Maybe this mucks less with the basic architectural notions of where an ext4 file system might go? (There is no intent here to actually remove the external SD, so it's really just a seocndary storage...)

Maybe that would also make it easier to place files that don't want to be installed on an external SD on the external SD? (On the other hand, this file system would be mounted "lateish" in an init script, so maybe it is not available timely enough to move an app that has an "On Boot" action?)

Thanks

Mike

PS: Stepping back, this all started with my daughter filling up her internal storage with Manga because the "Webtoons" application won't let itself move to external storage. I was able to force the move after setting the install location with set-install-location using adb

So, I was able to move the application, but the data which fill up internal storage was still in its original location. So, I moved that with File Manager - whereupon Webtoon no longer found the data.

So I tried to make a symbolic link, from the original location to the new location. Alas, that didn't work - I know that FAT doesn't support ln -s symbolic links, but... this would be a link into vfat, not in vfat. Maybe it's a way to avoid dangling links, or avoid subverting the security offered by native file systems with permissions...

So, I decided to move external SD to ext4...

Other paths forward might be to create the symbolic link now with the ext4 mounted, and then switch back to vfat. Unless the kernel also includes code the refuses to honor symbolic links from a Unix file system into a vfat, this should still work, even when the standard ln -s command doesn't let me make them?

Or, since starting on this, I've come across mount -o bind to "mount" a directory in anotherplace... really similar to a hard link, butusing the mount machinery because a link can't go across file system boundaries? (Folder mount and king root seem to both offer these capability, I assume using the same mount -o bind mechanism?)

That being said, ext4 is a better file system, so I had been persisiting in trying to make that work in lieu of what might seem like easier paths... will appreciate everybody's feedback, suggestons, experiences.