Hi Vladimir, On Saturday, 17 October 2020, 02:48:16 CEST, Vladimir Oltean wrote: > 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 <cegg...@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. Yes it does. Just after finishing this topic, I would to sent the patches for PTP. Maybe I'll do it in parallel, anything but the combination of L2/E2E/SLOB seems to work.
> 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. I get a similar output when placing the two skb_dump() calls in the current ksz_common_xmit() code: [ 5052.662168] old:skb len=58 headroom=2 headlen=58 tailroom=68 [ 5052.662168] mac=(2,14) net=(16,-1) trans=-1 [ 5052.662168] shinfo(txflags=1 nr_frags=0 gso(size=0 type=0 segs=0)) [ 5052.662168] csum(0x0 ip_summed=0 complete_sw=0 valid=0 level=0) [ 5052.662168] hash(0x0 sw=0 l4=0) proto=0x88f7 pkttype=0 iif=0 [ 5052.676360] old:dev name=lan0 feat=0x0x0002000000005220 [ 5052.679001] old:sk family=17 type=3 proto=0 [ 5052.681140] old:skb linear: 00000000: 01 1b 19 00 00 00 52 d9 a9 5d a1 40 88 f7 01 02 [ 5052.685236] old:skb linear: 00000010: 00 2c 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 5052.689342] old:skb linear: 00000020: 00 00 52 d9 a9 ff fe 5d a1 40 00 01 00 00 01 7f [ 5052.693418] old:skb linear: 00000030: 00 00 00 00 00 00 00 00 00 00 [ 5052.696843] new:skb len=65 headroom=2 headlen=65 tailroom=61 [ 5052.696843] mac=(2,16) net=(18,-17) trans=1 [ 5052.696843] shinfo(txflags=0 nr_frags=0 gso(size=0 type=0 segs=0)) [ 5052.696843] csum(0x0 ip_summed=0 complete_sw=0 valid=0 level=0) [ 5052.696843] hash(0x0 sw=0 l4=0) proto=0x0000 pkttype=0 iif=0 [ 5052.711215] new:skb linear: 00000000: 01 1b 19 00 00 00 52 d9 a9 5d a1 40 88 f7 01 02 [ 5052.715305] new:skb linear: 00000010: 00 2c 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 5052.719407] new:skb linear: 00000020: 00 00 52 d9 a9 ff fe 5d a1 40 00 01 00 00 01 7f [ 5052.723484] new:skb linear: 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 5052.727587] new:skb linear: 00000040: 00 Note that whilst some skb members differ, the two hexdumps look correct. > Which proves that you can't just copy&paste whatever you found in > tag_trailer.c. I did. tag_trailer and tag_ksz are quite similar here, so I took a combination of them. > 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. The "open coding" is from the existing code (which doesn't say that it is correct). I will investigate why the copied skb is different and whether psk_expand_head can do better. I don't like to touch the non-tail taggers, this is too much out of the scope of my current work. > 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. As Florian requested I'll likely put the code into a separate function in slave.c and call it from the individual tail-taggers in order not to put extra conditionals in dsa_slave_xmit. regards Christian
