Support virtio-fs on MMIO

[hcsch]

The non-transport specific parts of the VIRTIO filesystem driver are feature gated on pci, even though they are not transport specific and even contain PCI and non-PCI feature gated types internally.

https://github.com/hermit-os/kernel/blob/70ad8efdbb0245bf0c4d41ec387b2a0e1a00f637/src/drivers/fs/mod.rs#L1-L2 https://github.com/hermit-os/kernel/blob/70ad8efdbb0245bf0c4d41ec387b2a0e1a00f637/src/drivers/fs/virtio_fs.rs#L15-L18

[hcsch]

I might have been a bit too much in an issue opening spree, sorry. It seems this was intentionally done in https://github.com/hermit-os/kernel/commit/b5a45e2619a86c5b10cea85e6918953babe8a848 to hide VIRTIO fs when the PCI feature has not been selected.

[mkroening]

I think that was done to please clippy. Integrating and enabling virtio-fs on MMIO would be good. 👍

[elise-insall]

Hello, I'm a student taking virtualization at UT Austin. Our class requires us to contribute to an open source project. Can my group and I take this one?

[mkroening]

Sure, go ahead!

If you have any questions, feel free to ask them here or chat with us on our Zulip. :)