virtq: use a struct with the actual layout rather than a struct of references

[cagatay-y]

The code is not ready as I haven't yet figured out how the existing code ensures that the whole allocation is on the same page. This PR needs to be modified to ensure that as well. It is also based on #1141.

[cagatay-y]

I am not sure if the use of Pin here is correct and I need to check it but I think the PR can be reviewed since any changes related to Pin should not have a big effect for the majority of the changes.

[mkroening]

Thanks!

Apart from one comment, this looks excellent! :)

[cagatay-y]

FYI, in addition to the deprecation change, I also switched a ptr::from_mut call to ptr::from_ref and changed the mutability of the variable declaration accordingly. It is not easily visible because I amended the last commit, so I am noting it here.

kernel/src/drivers/virtio/virtqueue/split.rs

Lines 477 to 485 in 8e446e2

	vq_handler.set_ring_addr(paging::virt_to_phys(VirtAddr::from(
	ptr::from_ref(descr_table_cell.as_ref()).expose_provenance(),
	)));
	// As usize is safe here, as the *mut EventSuppr raw pointer is a thin pointer of size usize
	vq_handler.set_drv_ctrl_addr(paging::virt_to_phys(VirtAddr::from(
	ptr::from_ref(avail_ring_cell.as_ref()).expose_provenance(),
	)));
	vq_handler.set_dev_ctrl_addr(paging::virt_to_phys(VirtAddr::from(
	ptr::from_ref(used_ring_cell.as_ref()).expose_provenance(),

[mkroening]

Thanks! :)