We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace!
This was a slightly tedious refactoring that took a long time, so it's
not unlikely that some bugs crept in.
Nevertheless, it does pass basic functionality testing, and it's just
real nice to finally see the same pattern in all contexts. :^)
This change allows the Kernel to actually construct other interfaces
besides the E1000 type.
This solves a breakage that was introduced recently because of move
semantics.
A couple of points on this patch:
1. In current situation, we can waste time to create a KString and throw
it for nothing. This patch ensures we only create it near construction
point so we know we actually need it.
2. It's very likely to assume that non-x86 machines will expose network
device with a device tree (or with ACPI). The raspberry pi machine is a
good example of that. Therefore, each driver should explicitly ask the
correct interface name generation method, and this patch simplifies this
pattern greatly, especially in a case where the same network device can
appear as a PCI device or as device in another bus type on the same
platform target. For example, the (in)famous ne2000 device can be used
either as a PCI device or as an ISA device, depending on the model.
3. In my opinion, it seems much more readable to construct the name near
calling point of the object constructor than to just pass it with move
semantics.
Instead of initializing network adapters in init.cpp, let's move that
logic into a separate class to handle this.
Also, it seems like a good idea to shift responsiblity on enumeration
of network adapters after the boot process, so this singleton will take
care of finding the appropriate network adapter when asked to with an
IPv4 address or interface name.
With this change being merged, we simplify the creation logic of
NetworkAdapter derived classes, so we enumerate the PCI bus only once,
searching for driver candidates when doing so, and we let each driver
to test if it is resposible for the specified PCI device.
