Add test_trunc exercising the OVS_ACTION_ATTR_TRUNC action. The test verifies truncation limits in four steps: reject trunc(1) and trunc(13) which are below ETH_HLEN, confirm normal forwarding works, apply trunc(14) which truncates packets to the Ethernet header and verify ping fails, then restore normal forwarding and verify recovery. The kernel requires max_len >= ETH_HLEN (14 bytes). trunc(14) sets OVS_CB(skb)->cutlen so pskb_trim strips the IP payload at output time; the receiver drops the runt frame and no echo reply is generated. Signed-off-by: Minxi Hou <houminxi@gmail.com> Reviewed-by: Aaron Conole <aconole@redhat.com> Link: https://patch.msgid.link/20260702074926.1174810-1-houminxi@gmail.com Signed-off-by: Paolo Abeni <pabeni@redhat.com>