Re: [PATCH net-next v5] bridge: multicast to unicast

[Nikolay Aleksandrov <nikolay@cumulusnetworks.com>]

On 21/01/17 21:01, Linus Lüssing wrote:
> From: Felix Fietkau <nbd@nbd.name>
> 
> Implements an optional, per bridge port flag and feature to deliver
> multicast packets to any host on the according port via unicast
> individually. This is done by copying the packet per host and
> changing the multicast destination MAC to a unicast one accordingly.
> 
> multicast-to-unicast works on top of the multicast snooping feature of
> the bridge. Which means unicast copies are only delivered to hosts which
> are interested in it and signalized this via IGMP/MLD reports
> previously.
> 
> This feature is intended for interface types which have a more reliable
> and/or efficient way to deliver unicast packets than broadcast ones
> (e.g. wifi).
> 
> However, it should only be enabled on interfaces where no IGMPv2/MLDv1
> report suppression takes place. This feature is disabled by default.
> 
> The initial patch and idea is from Felix Fietkau.
> 
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> [linus.luessing@c0d3.blue: various bug + style fixes, commit message]
> Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
> 
> ---
> 
> This feature is used and enabled by default in OpenWRT and LEDE for AP
> interfaces for more than a year now to allow both a more robust multicast
> delivery and multicast at higher rates (e.g. multicast streaming).
> 
> In OpenWRT/LEDE the IGMP/MLD report suppression issue is overcome by
> the network daemon enabling AP isolation and by that separating all STAs.
> Delivery of STA-to-STA IP mulitcast is made possible again by
> enabling and utilizing the bridge hairpin mode, which considers the
> incoming port as a potential outgoing port, too.
> 
> Hairpin-mode is performed after multicast snooping, therefore leading to
> only deliver reports to STAs running a multicast router.
> 
> Changes in v5:
> * fix a potential pagefault in br_ip6_multicast_mld2_report():
>   -> a pskb_may_pull() might reallocate skb->data, therefore perform
>      the "src = eth_hdr(skb)->h_source" only afterwards
> * simplify code by always adding ether source address to a port group
>   and checking the per-port multicast-to-unicast flag instead of a
>   per-port-group one (thanks Stephen!)
> 
> Changes in v4:
> * readd "From: Felix Fietkau [...]" (missed it again in v3)
> 
> Changes in v3:
> * fix an uninitialized variable bug introduced in br_multicast_flood()
>   in v2, found by kbuild test bot
> 
> Changes in v2:
> * netlink support (thanks Nik!)
> * fixed switching between multicast_to_unicast on/off
>   -> even after toggling an already existing entry would
>      stale in its mode and would never be replaced
>   -> new extra check in br_port_group_equal)
> * reduced checks in br_multicast_flood() from two to one
>   to address fast-path concerns (thanks Nik!)
> * rev-christmas tree ordering (thanks Nik!)
> * removed "net_bridge_port_group::unicast", using
>   ::flags instead (thanks Nik!)
> * BR_MULTICAST_TO_UCAST -> BR_MULTICAST_TO_UNICAST
>   (BR_MULTICAST_FLAST_LEAVE has the same length anyway)
> * simplified maybe_deliver_addr()
>   (no return, no "prev" paramater -> was a NOP anyway)
> * added "From: Felix Fietkau [...]"
> * added "Signed-off-by: Felix Fietkau [...]"
> ---
>  include/linux/if_bridge.h    |  1 +
>  include/uapi/linux/if_link.h |  1 +
>  net/bridge/br_forward.c      | 39 ++++++++++++++++++-
>  net/bridge/br_mdb.c          |  2 +-
>  net/bridge/br_multicast.c    | 90 ++++++++++++++++++++++++++++++++------------
>  net/bridge/br_netlink.c      |  5 +++
>  net/bridge/br_private.h      |  3 +-
>  net/bridge/br_sysfs_if.c     |  2 +
>  8 files changed, 114 insertions(+), 29 deletions(-)
> 

Reviewed-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>