• John Fastabend's avatar
    net: sched: cls_u32 add bit to specify software only rules · 9e8ce79c
    John Fastabend authored
    In the initial implementation the only way to stop a rule from being
    inserted into the hardware table was via the device feature flag.
    However this doesn't work well when working on an end host system
    where packets are expect to hit both the hardware and software
    datapaths.
    
    For example we can imagine a rule that will match an IP address and
    increment a field. If we install this rule in both hardware and
    software we may increment the field twice. To date we have only
    added support for the drop action so we have been able to ignore
    these cases. But as we extend the action support we will hit this
    example plus more such cases. Arguably these are not even corner
    cases in many working systems these cases will be common.
    
    To avoid forcing the driver to always abort (i.e. the above example)
    this patch adds a flag to add a rule in software only. A careful
    user can use this flag to build software and hardware datapaths
    that work together. One example we have found particularly useful
    is to use hardware resources to set the skb->mark on the skb when
    the match may be expensive to run in software but a mark lookup
    in a hash table is cheap. The idea here is hardware can do in one
    lookup what the u32 classifier may need to traverse multiple lists
    and hash tables to compute. The flag is only passed down on inserts.
    On deletion to avoid stale references in hardware we always try
    to remove a rule if it exists.
    
    The flags field is part of the classifier specific options. Although
    it is tempting to lift this into the generic structure doing this
    proves difficult do to how the tc netlink attributes are implemented
    along with how the dump/change routines are called. There is also
    precedence for putting seemingly generic pieces in the specific
    classifier options such as TCA_U32_POLICE, TCA_U32_ACT, etc. So
    although not ideal I've left FLAGS in the u32 options as well as it
    simplifies the code greatly and user space has already learned how
    to manage these bits ala 'tc' tool.
    
    Another thing if trying to update a rule we require the flags to
    be unchanged. This is to force user space, software u32 and
    the hardware u32 to keep in sync. Thanks to Simon Horman for
    catching this case.
    Signed-off-by: default avatarJohn Fastabend <john.r.fastabend@intel.com>
    Acked-by: default avatarJiri Pirko <jiri@mellanox.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9e8ce79c
pkt_cls.h 9.92 KB