NETIF_F_(SG|FRAGLIST|HIGHDMA) docs anywhere?

[Daniel Stodden <stodden@in.tum.de>]

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hi.

software-only network device, currently implementing none of the
dev->features flags.

the driver transmits packets via pci dma to other processors residing on
a shared PCI bus segment. so i guess supporting at least scatter/gather
should give some performance improvements in order to get rid of
skb_linearize() on xmit? since transmission is done completely by the
local cpu, all of F_SG/FRAGLIST/HIGHDMA look relatively easy to
implemement to me. 

my major problem is test cases and getting the picture behind these
structures. is there any documentation around on the
skb_shinfo(skb)->frags and skb_shinfo(skb)->frag_list stuff? i've spend
quite some time now trying to figure out exactly under which
circumstances which of both applies. not too successful i must admit :)

frag_list seems to be the list involved with keeping track of ip
fragmentation. so dev->hard_start_xmit() with frag_list set would only
happen on routers or when??

when is nr_frags>0? i've found some postings indicating sendfile(2) will
benefit here. is this the only case? need some test code..

any hint appreciated,
dns

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