How does the net interface name in guest be determined from iface_id parameter?

[huang-jl]

Hello, I found the following statement in the docs of firecracker:

Once you have booted the guest, it will have its networking interface with the name specified by iface_id in the Firecracker configuration.

I am curious about how does this implement in firecracker? I briefly look through the source code of firecracker, but still cannot tell how does this feature implement. It looks like a new feature added recently. Currently, I am still using firecracker v1.9.0. The docs (and also implementation) in v1.9.0 does not promise any relationship between the iface_id and the network interface name in guest.

Can any one just point some hint on how does this implement in firecracker? (high-level ideas or related source code links are both fine). Thanks a lot!