Allow overwriting non-empty rootfs directories via fstab mounts

[nderjung]

Feature request summary

This issue tracks the ability to overwrite an existing non-empty directory via a user-provided fstab mount. Presently, when a preseeded root filesystem is provided to an instance, for example via initramfs, and an additional fstab mount is set to a path within this filesystem to a non-empty directory, the mount is not respected and the existing directory remains. However, when the directory is empty, the contents are correctly mounted.

Potentially it should also be possible to do this same type of operation but for a single file (in the case of 9pfs mount), however, I am not sure if this easily feasible.

Describe alternatives

No response

Related architectures

None

Related platforms

None

Additional context

No response

[AllMight2099]

Hi @nderjung
I'd like to work on this issue, if that's alright? I have an approach in my head, but I would have some questions and doubts as I keep going

[nderjung]

Hi @AllMight2099, that is certainly alright and thank you for considering to contribute to the Unikraft Open Source Project! Let's keep all discussions on this issue; please could write down in a comment what your approach is, the questions and doubts you have, we can work towards a solution for this issue. Thanks!

[AllMight2099]

Hi @nderjung
Sorry about the delay, had a few problems at work. I'm back now and do have a few questions:

1. Does "preseeded filesystem" mean that I create a build with a file system by default or does it mean that I'm mounting it externally using qemu?
2. Also, is there any documentation or link that could help me reproduce this issue? I looked at the documentation on the unikernel website and I couldn't find anything that I could use to mount a file system