On Sat, 21 Mar 2026 15:48:40 +0100 Robin Jarry <[email protected]> wrote:
> Linux TAP devices deliver all packets to userspace regardless of the > PROMISC/ALLMULTI flags on the interface. When promiscuous mode is > disabled, drop received packets whose destination MAC does not match > any configured unicast or multicast address. > > The receive path checks the destination MAC against the device's > unicast address table (managed by the ethdev layer), the multicast > address list (stored by the driver since the ethdev layer does not keep > a copy), and accepts broadcast unconditionally. Promiscuous and > all-multicast modes bypass the respective checks. > > To support multiple unicast addresses via rte_eth_dev_mac_addr_add(), > allocate mac_addrs with rte_zmalloc (TAP_MAX_MAC_ADDRS=16) instead of > pointing into dev_private, and advertise the new limit in dev_infos_get. > > Dropped packets are reported via per-queue xstats > (rx_q<N>_mac_filter_drops). > > Signed-off-by: Robin Jarry <[email protected]> Not sure the xstat for mac_filter_drops is needed, since it is what other devices do as normal operation. AI review found: Two issues worth addressing in this patch. The rte_realloc call in tap_set_mc_addr_list assigns directly back to pmd->mc_addrs. When realloc fails it returns NULL but leaves the original allocation intact, so the old pointer is lost and the memory leaks. Use a temporary variable for the realloc result. The ops table sets .xstats_reset = tap_stats_reset, but that function only zeroes the base counters. The new mac_drops xstat is never reset. Either extend the existing reset or add a dedicated xstats reset function.
