Read-Write capabilities

[retpolanne]

Hey!

This project helps me a lot, and I was wondering how could I contribute to adding RW capabilities to ext4fuse.

Here are the things that I mapped - code is in my fork:

• create a test for copying a file to the mounted directory (https://github.com/retpolanne/ext4fuse/blob/master/test/0040-write-file.sh)
• add checks to see if copied file permissions are okay
• get -o rw from ext4fuse cmdline and pass it to macfuse so it mounts with rw permissions
• implement op_create (done, but still testing) (https://github.com/retpolanne/ext4fuse/blob/master/op_create.c)
• implement op_write
• implement op_writedir?

I'm currently having trouble getting -o rw and passing to the mount options, I can't really understand how parsing works.

[GwynethLlewelyn]

Aww. I see that your project didn't go much further, such a pity. I've just taken a quick peek at how exactly those parameters are being passed, but I'm afraid I couldn't understand even the basics — the whole FUSE system is absolutely unknown to me, and, on top of all that, it seems to be different from version to version, so sometimes grabbing an example of how things are done and trying to apply it will catastrophically fail.

Oh well. Perhaps others might pick up on where you got stuck and proceed from there; I'm really sorry that I'm not able to help you out, because I certainly would enjoy havng read/wrte access to my ext4 filesystems...

[retpolanne]

Thanks @GwynethLlewelyn! Life came in the way and I completely forgot about that. I don't know if the work I was doing is in my fork, but please feel free (you and everybody else) to use it and hack it :)

[GwynethLlewelyn]

Thanks!

I believe that your work is, indeed, in your fork — at least, I could see some of the changes you made, and others that you started, then commented out as the compiling step broke. I have no idea if the fork has all your work, though.

Unfortunately, I'm really not a good enough programmer (much less in C, which I haven't done anything serious for many years... uh, decades, to be more precise...), and, as said, I totally lack the knowledge of how FUSE really works. As such, I'd have to take a look at a different example (fortunately, there are plenty of those around) to see how such parameters are passed to the underlying mount system. Currently, it's a mystery to me, since on the few examples I came across, things "just work", which is rather unhelpful — and annoying, because it seems so simple. Oh well. I wish I were more qualified to finish your work. Sure, because I have a certain urgency in writing to an ext4 filesystem, I will take a look at your code and a few other FUSE examples and see if I can cook something together. But I'm afraid I'm overestimating myself; some things don't work despite my sheer stubbornness and sense of urgency pushing me ahead :)

Don't expect miracles, there won't be any.

[retpolanne]

If you want, hit me up on my email (in my profile) or Mastodon (which might be fast) if you want to dig into this rabbit hole and find yourself full of questions :)

Lemme clone this fork and take a look!

[retpolanne]

@GwynethLlewelyn currently working on improving the test suite because I believe the libs used there were renamed at some point. It's compiling now btw, with op_write and op_create.

I'm assuming you use brew for dependency management btw.

[retpolanne]

@GwynethLlewelyn I'm currently using macOS Sequoia, so I can't test FUSE :(

Can you please git pull my fork and:

brew bundle
make
make test

The 0040 test regards op_write, if it passes then we have op_write working :)

I also set up a pipeline for testing this on Github Runners. However, ext4fuse gets stuck :( If I remember correctly, these tests weren't running for me even before my changes, Idk why.

https://github.com/retpolanne/ext4fuse/actions/runs/9653147561/job/26624840445

[ainaracatgirl]

I might test this later today, since I'm trying to get LUKS + ext4 working on macOS and I really don't want to pay €40 for Paragon's extFS.

[ainaracatgirl]

It has been stuck here for quite a while now, macOS 15.2 arm64 using FUSE-T.

$ make test
/opt/homebrew/opt/e2fsprogs/sbin/mke2fs
0000-sanity.sh: 

[retpolanne]

@ainaracatgirl if it's stuck, then it's probably some kernel deadlock :/

I remember having this problem before but I don't recall why, but it was definitely some deadlock.

[xxade]

I made a fork and implemented experimental read-write support, with a lot of the design and implementation done via AI-assisted development (Cursor).

The fork currently has:

• op_create, op_write, op_truncate, op_unlink, op_rename, op_mkdir, op_rmdir, op_symlink (chmod, utimens)
• 48/64-bit block support (superblock, group descriptors, allocator, extents)
• Correct group descriptor table offset for 4096-byte block size (so it mounts and works on real USB sticks)
• Extent tree depth 0–2, directory growth beyond 4 blocks, dcache invalidation after unlink/rmdir/rename (and a fix for the circular list to avoid use-after-free on unlink)
• No journal — not crash-safe; e2fsck after abnormal shutdown is recommended