• Simon Horman's avatar
    MPLS: Add limited GSO support · 0d89d203
    Simon Horman authored
    In the case where a non-MPLS packet is received and an MPLS stack is
    added it may well be the case that the original skb is GSO but the
    NIC used for transmit does not support GSO of MPLS packets.
    The aim of this code is to provide GSO in software for MPLS packets
    whose skbs are GSO.
    SKB Usage:
    When an implementation adds an MPLS stack to a non-MPLS packet it should do
    the following to skb metadata:
    * Set skb->inner_protocol to the old non-MPLS ethertype of the packet.
      skb->inner_protocol is added by this patch.
    * Set skb->protocol to the new MPLS ethertype of the packet.
    * Set skb->network_header to correspond to the
      end of the L3 header, including the MPLS label stack.
    I have posted a patch, "[PATCH v3.29] datapath: Add basic MPLS support to
    kernel" which adds MPLS support to the kernel datapath of Open vSwtich.
    That patch sets the above requirements in datapath/actions.c:push_mpls()
    and was used to exercise this code.  The datapath patch is against the Open
    vSwtich tree but it is intended that it be added to the Open vSwtich code
    present in the mainline Linux kernel at some point.
    I believe that the approach that I have taken is at least partially
    consistent with the handling of other protocols.  Jesse, I understand that
    you have some ideas here.  I am more than happy to change my implementation.
    This patch adds dev->mpls_features which may be used by devices
    to advertise features supported for MPLS packets.
    A new NETIF_F_MPLS_GSO feature is added for devices which support
    hardware MPLS GSO offload.  Currently no devices support this
    and MPLS GSO always falls back to software.
    Alternate Implementation:
    One possible alternate implementation is to teach netif_skb_features()
    and skb_network_protocol() about MPLS, in a similar way to their
    understanding of VLANs. I believe this would avoid the need
    for net/mpls/mpls_gso.c and in particular the calls to
    __skb_push() and __skb_push() in mpls_gso_segment().
    I have decided on the implementation in this patch as it should
    not introduce any overhead in the case where mpls_gso is not compiled
    into the kernel or inserted as a module.
    MPLS GSO suggested by Jesse Gross.
    Based in part on "v4 GRE: Add TCP segmentation offload for GRE"
    by Pravin B Shelar.
    Cc: Jesse Gross <jesse@nicira.com>
    Cc: Pravin B Shelar <pshelar@nicira.com>
    Signed-off-by: default avatarSimon Horman <horms@verge.net.au>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
netdev_features.h 6.43 KB