Replacing files in built filesystem image

[David Smith]

I'm reviewing the OSv documentation and scripts to see if I can find an existing solution which would allow the addition/replacement/deletion of files in an already built filesystem image, without needing the entire OSv build environment and performing a rebuild. In my case, the filesystem type used to build the .raw image file is ROFS (selected primarily to reduce startup time).

I can see the script being used to generate this filesystem image (gen-rofs-img.py), but I haven't yet seen any way in which I can unpack/mount an existing filesystem image, make changes to the content and re-pack/unmount the image.

Is this a facility that is already available in some form?

If not, any suggestions on the best approach would be welcome.

[Fotis Xenakis]

Hello David,

Virtio-fs sounds like a natural fit for your situation. Please see this wiki page for details: https://github.com/cloudius-systems/osv/wiki/virtio-fs

In short, virtio-fs lets you mount a host directory on the guest. The OSv implementation is read-only but that shouldn't be a problem since you are using rofs currently.

Feel free to check it out and of course come back if you run into any issues or have any feedback!

Fotis

---

From: osv...@googlegroups.com <osv...@googlegroups.com> on behalf of David Smith <d787...@gmail.com>
Sent: Tuesday, April 6, 2021 4:08:31 PM
To: OSv Development <osv...@googlegroups.com>
Subject: [osv-dev] Replacing files in built filesystem image

 

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[David Smith]

Thanks Fotis. I'll take a look.

[David Smith]

Unfortunately my environment is Firecracker, which it seems has no virtio-fs support, but thanks for the suggestion. I think my simplest option is to rebuild the disk image from the original build artefacts, inserting any changed files as needed. It looks like the gen-rofs-img.py script is reasonably self-contained, so I'm experimenting using this with a customised usr.manifest.