Is it possible to set a custom uid and gid for the mount point?

[ruanformigoni]

Greetings,

I've used something similar with squashfuse, squashfuse -o uid=1001,gid=1001 fs.sqfs mount , is it possible to do something similar here?

Thanks

[mhx]

uid and gid are actually options provided by libfuse (not squashfuse). However, the options are only provided for file systems implemented using the high-level API. DwarFS uses the low-level API (at least on Linux), so these options are not available.

That being said, it should be trivial to provide these options if there's a use case.

[ruanformigoni]

Thanks for the info, for the use case, recently bubblewrap merged --overlay related options, now it is possible to use the kernel overlayfs with dwarfs without superuser privileges, however, compared to fuse-overlayfs, this does not offer an option to modify the uid and gid of the mount point. This leads to a mismatch between the uid and gid of the dwarfs filesystems and the host, which breaks things with permission issues if they do not match. In squashfuse this is resolved with the uid and gid parameters, configured to match the host's.

[ruanformigoni]

I've modified the filesystem to always use the current uid and gid in this patch ruanformigoni@84e4b83 , seems to work so far.

[VHSgunzo]

I also think it would be great to have this functionality. This would speed up the operation of portable unprivileged containers based on bubblewrap and DWARFS rootfs image by using bubblewrap overlay, rather than fuse-overlay or union-fuse.

[mhx]

I'm totally fine with adding support for this.

One question, though: @ruanformigoni, When you're saying

[...] option to modify the uid and gid of the mount point [...]

do you mean just the mountpoint itself or rather everything below the mountpoint? I expect you mean everything, as that's what your change is doing, and that's also what libfuse would do according to the manpage:

uid=N  Override the st_uid field set by the filesystem (N is
       numeric).
gid=N  Override the st_gid field set by the filesystem (N is
       numeric).

So I guess I'd add uid and gid options to dwarfs that can be used with (at least) numeric IDs, just as with libfuse.

[ruanformigoni]

Hi @mhx, I do mean everything under it.

[mhx]

Implemented in fb74c44. Feel free to check if this works for you with the binaries from the CI pipeline.

[VHSgunzo]

Thank you so much for adding this functionality! Now the bubblewrap overlay works as it should.

[ruanformigoni]

Thank you for implementing this so quickly 😄