dev: Use the new Port role mechanism to make an EtherInt Port type.

This type always uses the same "ETHERNET" role, and all connections are
symmetric and self compatible.

Change-Id: I1d060f8c098d52ae9f65c052f816bc813590ff9c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18171
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch, cpu, dev, gpu, mem, sim, python: start using getPort.

Replace the getMasterPort, getSlavePort, and getEthPort functions
with getPort, and remove extraneous mechanisms that are no longer
necessary.

Change-Id: Iab7e3c02d2f3a0cf33e7e824e18c28646b5bc318
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17040
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

dev: Make the EtherDevice class inherit EtherObject.

This avoids having to define two parallel versions of the getEthPort
function, and the complex dynamic_cast macrame in connectPorts().

Change-Id: I24c09864005ff39a049e50d7245ff17e9480edea
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17029
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

dev: Turn EtherObject into an interface class.

This class used to drive from SimObject so that it could be derived
from to get both the interface and SimObject while still using single
inheritance.

With this change, EtherObject is now just an interface class with only
one pure virtual function which can be inherited alongside SimObject.
This makes it more flexible so that it can be used in places where you
might want a different inheritance hierarchy, for instance to inherit
from MemObject.

Change-Id: I0f07664d104eed012cf4ce6e30c416ada19505a7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17028
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

python: Don't assume SimObjects live in the global namespace

The importer in Python 3 doesn't like the way we import SimObjects
from the global namespace. Convert the existing SimObject declarations
to import from m5.objects. As a side-effect, this makes these files
consistent with configuration files.

Change-Id: I11153502b430822130722839e1fa767b82a027aa
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15981
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

dev: Add a version of EtherTap which uses the tap driver.

The object is called EtherTap (as opposed to EtherTapStub, what the former
EtherTap was renamed to), and its existance is gated on the linux/if_tun.h
header file existing. That's probably overly strict, but it will hopefully
be minimally likely to break the build for other systems.

Change-Id: Ie03507fadf0d843a4d4d52f283c44a416c6f2a74
Reviewed-on: https://gem5-review.googlesource.com/3646
Reviewed-by: Nathan Binkert <nate@binkert.org>
Maintainer: Nathan Binkert <nate@binkert.org>

dev: Refactor the EtherTapStub to make room for using tap.

A lot of the implementation of EtherTapStub can be shared with a version
which uses a tap device directly. This change factors out those parts to
accommodate that.

Change-Id: I9c2e31f1be139ca73859a83f05457cef90101006
Reviewed-on: https://gem5-review.googlesource.com/3645
Reviewed-by: Nathan Binkert <nate@binkert.org>
Maintainer: Nathan Binkert <nate@binkert.org>

dev: Rename EtherTap to be EtherTapStub.

The EtherTap object is going to be reworked so that it connects to a tap
device directly, but it's worthwhile to still be able to use the m5tap
utility (util/tap) to send/receive packets on systems which don't support
tap but do support the pcap API. It can also be used to replay ethernet
frames, to capture the ethernet frames coming from gem5 for analysis, to
programmatically consume and/or generate the frames, or even to forward
them to/from a remote system.

Change-Id: Ic7bd763d86cd913ac373dd10a8d6d1fc6b35f95a
Reviewed-on: https://gem5-review.googlesource.com/3644
Reviewed-by: Nathan Binkert <nate@binkert.org>
Maintainer: Nathan Binkert <nate@binkert.org>

dev: Add a missing parameter to the EtherTap device.

There needs to be a SlavePort called "tap" for the ethertap device to be
able to connect to the gem5 network successfully.

Change-Id: I1ad81219f612fd1ec278c6148af728d20bc916da
Reviewed-on: https://gem5-review.googlesource.com/3580
Reviewed-by: Nathan Binkert <nate@binkert.org>
Maintainer: Nathan Binkert <nate@binkert.org>

dev: Add m5 op to toggle synchronization for dist-gem5.
This patch adds the ability for an application to request dist-gem5 to begin/
end synchronization using an m5 op. When toggling on sync, all nodes agree
on the next sync point based on the maximum of all nodes' ticks. CPUs are
suspended until the sync point to avoid sending network messages until sync has
been enabled. Toggling off sync acts like a global execution barrier, where
all CPUs are disabled until every node reaches the toggle off point. This
avoids tricky situations such as one node hitting a toggle off followed by a
toggle on before the other nodes hit the first toggle off.

dist, dev: add an ethernet switch model

dev: Distributed Ethernet link for distributed gem5 simulations

Distributed gem5 (abbreviated dist-gem5) is the result of the
convergence effort between multi-gem5 and pd-gem5 (from Univ. of
Wisconsin). It relies on the base multi-gem5 infrastructure for packet
forwarding, synchronisation and checkpointing but combines those with
the elaborated network switch model from pd-gem5.

dev: Move network devices to src/dev/net/