> -----Original Message----- > From: Tobias Waldekranz <tobias@xxxxxxxxxxxxxx> > Sent: 2021年4月29日 4:30 > To: Y.b. Lu <yangbo.lu@xxxxxxx>; netdev@xxxxxxxxxxxxxxx > Cc: Y.b. Lu <yangbo.lu@xxxxxxx>; Richard Cochran > <richardcochran@xxxxxxxxx>; Vladimir Oltean <vladimir.oltean@xxxxxxx>; > David S . Miller <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; > Jonathan Corbet <corbet@xxxxxxx>; Kurt Kanzenbach <kurt@xxxxxxxxxxxxx>; > Andrew Lunn <andrew@xxxxxxx>; Vivien Didelot <vivien.didelot@xxxxxxxxx>; > Florian Fainelli <f.fainelli@xxxxxxxxx>; Claudiu Manoil > <claudiu.manoil@xxxxxxx>; Alexandre Belloni > <alexandre.belloni@xxxxxxxxxxx>; UNGLinuxDriver@xxxxxxxxxxxxx; > linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [net-next, v2, 3/7] net: dsa: free skb->cb usage in core driver > > On Mon, Apr 26, 2021 at 17:37, Yangbo Lu <yangbo.lu@xxxxxxx> wrote: > > Free skb->cb usage in core driver and let device drivers decide to use > > or not. The reason having a DSA_SKB_CB(skb)->clone was because > > dsa_skb_tx_timestamp() which may set the clone pointer was called > > before p->xmit() which would use the clone if any, and the device > > driver has no way to initialize the clone pointer. > > > > Although for now putting memset(skb->cb, 0, 48) at beginning of > > dsa_slave_xmit() by this patch is not very good, there is still way to > > improve this. Otherwise, some other new features, like one-step > > Could you please expand on this improvement? > > This memset makes it impossible to carry control buffer information from > driver callbacks that run before .ndo_start_xmit, for > example .ndo_select_queue, to a tagger's .xmit. > > It seems to me that if the drivers are to handle the CB internally from now on, > that should go for both setting and clearing of the required fields. > For the timestamping case, dsa_skb_tx_timestamp may not touch .port_txtstamp callback, so we had to put skb->cb initialization at beginning of dsa_slave_xmit. To avoid breaking future skb->cb usage you mentioned, do you think we can back to Vladimir's idea initializing only field required, or even just add a callback for cb initialization for timestamping? Thanks. > > timestamp which needs a flag of skb marked in dsa_skb_tx_timestamp(), > > and handles as one-step timestamp in p->xmit() will face same > > situation. > > > > Signed-off-by: Yangbo Lu <yangbo.lu@xxxxxxx>
