# VERDICT — DF-3395: reproduced (privileged rename silently wipes all vlan(4) config on the renamed parent)

## Reproduction (DragonFly 6.5-DEVELOPMENT #0, X86_64_GENERIC)
    # ifconfig vlan0 create; ifconfig vlan0 vlan 100 vlandev vtnet0
    vlan0: ... mtu 1500 / vlan: 100 parent interface: vtnet0 / status: active

    # ifconfig vtnet0 name vtnet0r          <- routine SIOCSIFNAME rename
    vlan0: ... mtu 1500 / vlan: 0 parent interface: <none>

    # ifconfig vtnet0r name vtnet0          <- rename back
    vlan0: ... mtu 1500 / vlan: 0 parent interface: <none>   <- NOT restored

Root cause chain:
- SIOCSIFNAME handler (sys/net/if.c:2190-2236) invokes
  `EVENTHANDLER_INVOKE(ifnet_detach_event, ifp)` at if.c:2206 **for a
  rename**, before installing the new name; ifnet_attach_event fires at
  :2232 after.
- vlan registered on ifnet_detach_event (sys/net/vlan/if_vlan.c:377) —
  the event that IS fired (correct per DF-3344's lesson; lagg's bug was
  registering on the never-fired ifnet_departure_event).
- vlan_ifdetach() (if_vlan.c:432) dispatches to netisr0;
  vlan_ifdetach_dispatch() (if_vlan.c:410-429) runs vlan_unconfig() on
  every vlan in the parent's trunk: parent pointer cleared, MTU reset,
  flags cleared, trunk freed.
- Nothing on the vlan side re-attaches when ifnet_attach_event fires:
  the L2 configuration (parent + tag) is permanently destroyed.

## Impact
Every vlan(4) riding the renamed interface is silently disconnected
(traffic blackhole for all tagged subnets) until an administrator
re-runs the full vlan configuration.  Rename is a routine, non-destructive
administrative gesture everywhere else in the system (addresses, routes,
caps and media survive it).  Privileged-only trigger (SIOCSIFNAME is
caps_priv_check'd at if.c:2191), memory-safe teardown — hence Low.

Same collateral applies to other ifnet_detach_event consumers: e.g. a
bridge member would be silently dropped on rename via bridge's detach
handler.

## Recommended fix
A rename is not a detach.  Fire the announcement-only
ifnet_departure_event (the key already exists in eventhandler space and
has no state-tearing subscribers — see DF-3344) instead of
ifnet_detach_event in the SIOCSIFNAME path, keeping ifnet_detach_event
for real interface destruction in if_detach().

## Fix status (batch validation)
Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest `make -j6 nativekernel KERNCONF=X86_64_GENERIC` completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.