T4825: Add interface type veth

Add interface type veth (Virtual ethernet)
One of the usecases it's interconnect different vrf's and
default vrf via bridge

set interfaces virtual-ethernet veth0 peer-name 'veth1010'
set interfaces virtual-ethernet veth1010 address '10.0.0.10/24'
set interfaces virtual-ethernet veth1010 peer-name 'veth0'
set interfaces virtual-ethernet veth1010 vrf 'foo'
set interfaces bridge br0 address '10.0.0.1/24'
set interfaces bridge br0 member interface veth0

vyos@r1:~$ ping 10.0.0.10 count 1
PING 10.0.0.10 (10.0.0.10) 56(84) bytes of data.
64 bytes from 10.0.0.10: icmp_seq=1 ttl=64 time=0.082 ms

1 files changed, 117 insertions, 0 deletions

diff --git a/src/conf_mode/interfaces-virtual-ethernet.py b/src/conf_mode/interfaces-virtual-ethernet.py
new file mode 100755
index 000000000..21f8cdad3
--- /dev/null
+++ b/src/conf_mode/interfaces-virtual-ethernet.py
@@ -0,0 +1,117 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2023 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from sys import exit
+
+from netifaces import interfaces
+from vyos import ConfigError
+from vyos import airbag
+from vyos.config import Config
+from vyos.configdict import get_interface_dict
+from vyos.configverify import verify_address
+from vyos.configverify import verify_bridge_delete
+from vyos.configverify import verify_vrf
+from vyos.ifconfig import VethIf
+
+airbag.enable()
+
+def get_config(config=None):
+    """
+    Retrive CLI config as dictionary. Dictionary can never be empty, as at
+    least the interface name will be added or a deleted flag
+    """
+    if config:
+        conf = config
+    else:
+        conf = Config()
+    base = ['interfaces', 'virtual-ethernet']
+    veth = get_interface_dict(conf, base)
+
+    # We need to know all other veth related interfaces as veth requires a 1:1
+    # mapping for the peer-names. The Linux kernel automatically creates both
+    # interfaces, the local one and the peer-name, but VyOS also needs a peer
+    # interfaces configrued on the CLI so we can assign proper IP addresses etc.
+    conf.set_level(base)
+    veth['other_interfaces'] = conf.get_config_dict([], key_mangling=('-', '_'),
+                                                    get_first_key=True,
+                                                    no_tag_node_value_mangle=True)
+
+    return veth
+
+
+def verify(veth):
+    if 'deleted' in veth:
+        verify_bridge_delete(veth)
+        # Prevent to delete veth interface which used for another "vethX peer-name"
+        for iface, iface_config in veth['other_interfaces'].items():
+            if veth['ifname'] in iface_config['peer_name']:
+                ifname = veth['ifname']
+                raise ConfigError(
+                    f'Cannot delete "{ifname}" used for "interface {iface} peer-name"'
+                )
+        return None
+
+    verify_vrf(veth)
+    verify_address(veth)
+
+    if 'peer_name' not in veth:
+        raise ConfigError(f'Remote peer name must be set for "{veth["ifname"]}"!')
+
+    peer_name = veth['peer_name']
+    ifname = veth['ifname']
+
+    if veth['peer_name'] not in veth['other_interfaces']:
+        raise ConfigError(f'Used peer-name "{peer_name}" on interface "{ifname}" ' \
+                          'is not configured!')
+
+    if veth['other_interfaces'][peer_name]['peer_name'] != ifname:
+        raise ConfigError(
+            f'Configuration mismatch between "{ifname}" and "{peer_name}"!')
+
+    if peer_name == ifname:
+        raise ConfigError(
+            f'Peer-name "{peer_name}" cannot be the same as interface "{ifname}"!')
+
+    return None
+
+
+def generate(peth):
+    return None
+
+
+def apply(veth):
+    # Check if the Veth interface already exists
+    if 'rebuild_required' in veth or 'deleted' in veth:
+        if veth['ifname'] in interfaces():
+            p = VethIf(veth['ifname'])
+            p.remove()
+
+    if 'deleted' not in veth:
+        p = VethIf(**veth)
+        p.update(veth)
+
+    return None
+
+
+if __name__ == '__main__':
+    try:
+        c = get_config()
+        verify(c)
+        generate(c)
+        apply(c)
+    except ConfigError as e:
+        print(e)
+        exit(1)