Unionfs, Cramfs And Flash

[speculatrix]

For some time I've felt that the big problem with the Z and having a base OS install is that things can get messy...
There are a lot of symlinks from writable file space to the rom file system, so that all the usual files are in the usual place, but you can patch the OS with new files by replacing the symlink with a real file.

e.g. initially /etc/hosts would symlink to /mnt/rom.cramfs/etc/hosts, but you'd replace it with a real file in /etc/hosts.

As I understand it, Guylhem has done some great work making a clean 6000 ROM without all this clutter, but I don't know how he handled the issue of being able to replace files in ROM with files in regular flash?


Then I came across project-unionfs, which allows you to overlay or stack one FS on top of another, i.e. to add incremental changes. This allows the system to be very flexible because as far as the user is concerned, all the files are real files and you don't have to know where they are.

Does this make sense? How easy would it be to add this support into OE, Cacko or Guylhem's distro?

Paul

[lardman]

As I understand it, Guylhem has done some great work making a clean 6000 ROM without all this clutter, but I don't know how he handled the issue of being able to replace files in ROM with files in regular flash?

Probably by making the 'ROM' writable (it's just flash which can be written to if it's mounted as rw) which is also how things are done with OZ.

Then I came across project-unionfs, which allows you to overlay or stack one FS on top of another, i.e. to add incremental changes. This allows the system to be very flexible because as far as the user is concerned, all the files are real files and you don't have to know where they are.

Does this make sense? How easy would it be to add this support into OE, Cacko or Guylhem's distro?

From what I remember this has been looked at but it still needs some problems ironing out when used on the Zaurus so it hasn't been implemented yet (http://www.openzaurus.org/official/unstable/3.5.3/changelog.txt).


Si

[koen]

To erase doubt: unionfs + unionfs modules are in OE and can be built without effort

[Da_Blitz]

unionsfs is great, what you can do is mount the flash as read only and then mount another directory over the top of that as rw and redirect all writes to the second partion. allowing you to merge a ro and rw partion

it has some uses such as during beta testing, you can make changes to the filesystem and if it dosent work out you can start from scratch by deleteing everything in the second rw part automatically revealing the ro part again

[speculatrix]

I should have explained why I wanted this instead of just having the whole base install on a regular read-write flash: high file compression/optimised storage, which is not amenable to modification.

Da_Blitz also highlighted the reversibility of it too. Anyone remember WORM (write once optical media) which simply added new file and hid the old version(s)? This would be great too. Kind of file-system-wide CVS!

I think once OE 3.5.3 is mature it will be a killer base OS for the Z.

[koen]

I think once OE 3.5.3 is mature it will be a killer base OS for the Z.
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That would be OZ 3.5.4 </knowitall>

[Mickeyl]

Nah, that'd be Ã…ngström, of course  

[koen]

Nah, that'd be Ã…ngström, of course 
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Yeah, with the OE/OZ confusion gone our ReadOnlyMemory building counterparts can finally insult the right project  

[eviLjazz]

If anybody wants to check out unionfs and gzipfs on SharpROM, check out this thread:
https://www.oesf.org/forums/index.php?showtopic=15156

Regards,
Andre