• David S. Miller's avatar
    inet: Create a mechanism for upward inetpeer propagation into routes. · 6431cbc2
    David S. Miller authored
    If we didn't have a routing cache, we would not be able to properly
    propagate certain kinds of dynamic path attributes, for example
    PMTU information and redirects.
    
    The reason is that if we didn't have a routing cache, then there would
    be no way to lookup all of the active cached routes hanging off of
    sockets, tunnels, IPSEC bundles, etc.
    
    Consider the case where we created a cached route, but no inetpeer
    entry existed and also we were not asked to pre-COW the route metrics
    and therefore did not force the creation a new inetpeer entry.
    
    If we later get a PMTU message, or a redirect, and store this
    information in a new inetpeer entry, there is no way to teach that
    cached route about the newly existing inetpeer entry.
    
    The facilities implemented here handle this problem.
    
    First we create a generation ID.  When we create a cached route of any
    kind, we remember the generation ID at the time of attachment.  Any
    time we force-create an inetpeer entry in response to new path
    information, we bump that generation ID.
    
    The dst_ops->check() callback is where the knowledge of this event
    is propagated.  If the global generation ID does not equal the one
    stored in the cached route, and the cached route has not attached
    to an inetpeer yet, we look it up and attach if one is found.  Now
    that we've updated the cached route's information, we update the
    route's generation ID too.
    
    This clears the way for implementing PMTU and redirects directly in
    the inetpeer cache.  There is absolutely no need to consult cached
    route information in order to maintain this information.
    
    At this point nothing bumps the inetpeer genids, that comes in the
    later changes which handle PMTUs and redirects using inetpeers.
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    6431cbc2
ip6_fib.h 5.17 KB