Messages in this thread | | | Date | Sat, 17 Oct 2020 03:48:16 +0300 | From | Vladimir Oltean <> | Subject | Re: [PATCH net-next 1/3] net: dsa: don't pass cloned skb's to drivers xmit function |
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On Fri, Oct 16, 2020 at 10:02:24PM +0200, Christian Eggers wrote: > Ensure that the skb is not cloned and has enough tail room for the tail > tag. This code will be removed from the drivers in the next commits. > > Signed-off-by: Christian Eggers <ceggers@arri.de> > ---
Does 1588 work for you using this change, or you haven't finished implementing it yet? If you haven't, I would suggest finishing that part first.
The post-reallocation skb looks nothing like the one before.
Before: skb len=68 headroom=2 headlen=68 tailroom=186 mac=(2,14) net=(16,-1) trans=-1 shinfo(txflags=1 nr_frags=0 gso(size=0 type=0 segs=0)) csum(0x0 ip_summed=0 complete_sw=0 valid=0 level=0) hash(0x9d6927ec sw=1 l4=0) proto=0x88f7 pkttype=0 iif=0 dev name=swp2 feat=0x0x0002000000005020 sk family=17 type=3 proto=0
After: skb len=68 headroom=2 headlen=68 tailroom=186 mac=(2,16) net=(18,-17) trans=1 shinfo(txflags=0 nr_frags=0 gso(size=0 type=0 segs=0)) csum(0x0 ip_summed=0 complete_sw=0 valid=0 level=0) hash(0x0 sw=0 l4=0) proto=0x0000 pkttype=0 iif=0
Notice how you've changed shinfo(txflags), among other things.
Which proves that you can't just copy&paste whatever you found in tag_trailer.c.
I am not yet sure whether there is any helper that can be used instead of this crazy open-coding. Right now, not having tested anything yet, my candidates of choice would be pskb_expand_head or __pskb_pull_tail. You should probably also try to cater here for the potential reallocation done in the skb_cow_head() of non-tail taggers. Which would lean the balance towards pskb_expand_head(), I believe.
Also, if the result is going to be longer than ~20 lines of code, I strongly suggest moving the reallocation to a separate function so you don't clutter dsa_slave_xmit.
Also, please don't redeclare struct sk_buff *nskb, you don't need to.
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