ethernet: T3871: an ethernet interface belongs to the Kernel and can not be deleted

Every NIC used to carry a hw-id, which was enough to make its node exist.
Without it a bare node is empty and never reaches the running configuration,
so releasing a bond member looked exactly like a deletion: the port was torn
down and left admin-down, with nothing left to bring it back.

An ethernet interface is owned by the Kernel and - like 'lo' - outlives its
configuration. Removing it now resets the port to the Kernel defaults and
leaves the link up.

1 files changed, 36 insertions, 7 deletions

diff --git a/python/vyos/ifconfig/ethernet.py b/python/vyos/ifconfig/ethernet.py
index 41fd6a0b9..8360c4654 100644
--- a/python/vyos/ifconfig/ethernet.py
+++ b/python/vyos/ifconfig/ethernet.py
@@ -19,9 +19,11 @@ from glob import glob
 
 from vyos.base import Warning
 from vyos.ethtool import Ethtool
+from vyos.ifconfig.ifname_store import permanent_mac
 from vyos.ifconfig.interface import Interface
 from vyos.utils.dict import dict_search
 from vyos.utils.file import read_file
+from vyos.utils.network import get_interface_config
 from vyos.utils.process import run
 from vyos.utils.assertion import assert_list
 
@@ -83,6 +85,9 @@ class EthernetIf(Interface):
         },
     }
 
+    # T5862: clamped against the adapter maximum wherever it is used
+    DEFAULT_MTU = '1500'
+
     @staticmethod
     def get_bond_member_allowed_options() -> list:
         """
@@ -122,14 +127,22 @@ class EthernetIf(Interface):
         self.ethtool = Ethtool(ifname)
 
     def _create(self):
+        # we cannot create this interface as it is managed by the Kernel
         pass
 
     def remove(self):
         """
-        Remove interface from config. Removing the interface deconfigures all
-        assigned IP addresses.
+        Return the interface to the state the Kernel gave it.
+
+        An ethernet interface is owned by the Kernel and - like 'lo' - can not
+        be removed, so deleting its configuration means resetting the port
+        rather than tearing it down: addresses flushed, MTU and hardware
+        address back to the Kernel default and the link left up. Leaving it
+        admin-down stranded a port with nothing left to bring it back, a
+        released bond member included.
+
         Example:
-        >>> from vyos.ifconfig import WWANIf
+        >>> from vyos.ifconfig import EthernetIf
         >>> i = EthernetIf('eth0')
         >>> i.remove()
         """
@@ -140,10 +153,26 @@ class EthernetIf(Interface):
         # and thus survives this call.
         super().remove()
 
-        if self.exists(self.ifname):
-            # interface is placed in A/D state when removed from config! It
-            # will remain visible for the operating system.
-            self.set_admin_state('down')
+        if not self.exists(self.ifname):
+            return
+
+        # undo what the configuration changed about the hardware itself.
+        #
+        # While the port is still enslaved its address belongs to the bond -
+        # most modes need every member to carry the bond's one, and set_mac()
+        # would bounce the link underneath it. BondIf.update() releases the
+        # member and then runs this cleanup again, which is where the address
+        # is put back.
+        tmp = get_interface_config(self.ifname)
+        if dict_search('linkinfo.info_slave_kind', tmp) != 'bond':
+            mac = permanent_mac(self.ifname)
+            if mac:
+                self.set_mac(mac)
+
+        mtu = min(int(EthernetIf.DEFAULT_MTU), int(self.get_max_mtu()))
+        self.set_mtu(str(mtu))
+
+        self.set_admin_state('up')
 
     def set_flow_control(self, enable, warn=True):
         """