/*
This is a helper function for find_paths and is invoked when we are interested in just the shortest
path between two switches. It will find the shortest path, and then build a path structure which
represents it. ssw is the starting switch and h2nm is the endpoint "name" (probably a mac that we
are looking for.
The usr_max value is the percentage (1-100) that indicates the maximum percentage of a link that the
user may reserve.
This function assumes that the switches have all been initialised with a reset of the visited flag,
setting of inital cost, etc.
*/
func (n *Network) find_shortest_path(ssw *gizmos.Switch, h1 *gizmos.Host, h2 *gizmos.Host, usr *string, commence int64, conclude int64, inc_cap int64, usr_max int64) (path *gizmos.Path, cap_trip bool) {
h1nm := h1.Get_mac()
h2nm := h2.Get_mac()
path = nil
if usr_max <= 0 {
i41, _ := h1.Get_addresses()
i42, _ := h2.Get_addresses()
net_sheep.Baa(1, "no path generated: user link capacity set to 0: attempt %s -> %s", *i41, *i42)
return
}
ssw.Cost = 0 // seed the cost in the source switch
tsw, cap_trip := ssw.Path_to(h2nm, commence, conclude, inc_cap, usr, usr_max) // discover the shortest path to terminating switch that has enough bandwidth
if tsw != nil { // must walk from the term switch backwards collecting the links to set the path
path = gizmos.Mk_path(h1, h2)
path.Set_reverse(true) // indicate that the path is saved in reverse order
path.Set_bandwidth(inc_cap)
net_sheep.Baa(2, "find_spath: found target on %s", tsw.To_str())
lnk := n.find_vlink(*(tsw.Get_id()), h2.Get_port(tsw), -1, nil, nil) // add endpoint -- a virtual link out from switch to h2
lnk.Add_lbp(*h2nm)
lnk.Set_forward(tsw) // endpoints have only a forward link
path.Add_endpoint(lnk)
for tsw != nil {
if tsw.Prev != nil { // last node won't have a prev pointer so no link
lnk = tsw.Prev.Get_link(tsw.Plink)
path.Add_link(lnk)
}
path.Add_switch(tsw)
net_sheep.Baa(3, "\t%s using link %d", tsw.Prev.To_str(), tsw.Plink)
if tsw.Prev == nil { // last switch in the path, add endpoint
lnk = n.find_vlink(*(tsw.Get_id()), h1.Get_port(tsw), -1, nil, nil) // endpoint is a virt link from switch to h1
lnk.Add_lbp(*h1nm)
lnk.Set_forward(tsw) // endpoints have only a forward link
path.Add_endpoint(lnk)
}
tsw = tsw.Prev
}
path.Flip_endpoints() // path expects them to be in h1,h2 order; we added them backwards so must flip
}
return
}