On Thu, 24 Mar 2022 09:50:06 +0100 Paolo Abeni wrote: > > +/** > > + * DOC: dataref and headerless skbs > > + * > > + * Transport layers send out clones of data skbs they hold for retransmissions. > > + * To allow lower layers of the stack to prepend their headers > > + * we split &skb_shared_info.dataref into two halves. > > + * The lower 16 bits count the overall number of references. > > + * The higher 16 bits indicate number of data-only references. > > + * skb_header_cloned() checks if skb is allowed to add / write the headers. > > Thank you very much for the IMHO much needed documentation! > > Please allow me to do some non-native-english-speaker biased comments;) > > The previous patch uses the form "payload data" instead of data-only, > I think it would be clearer using consistently one or the other. I > personally would go for "payload-data-only" (which is probably a good > reason to pick a different option). That starts to get long. Let me go for payload everywhere. > > - * All users must obey the rule that the skb->data reference count must be > > - * greater than or equal to the payload reference count. > > + * The creator of the skb (e.g. TCP) marks its data-only skb as &sk_buff.nohdr > > + * (via __skb_header_release()). Any clone created from marked skb will get > > + * &sk_buff.hdr_len populated with the available headroom. > > + * If it's the only clone in existence it's able to modify the headroom at will. > > I think it would be great if we explicitly list the expected sequence, > e.g. > <alloc skb> > skb_reserve > __skb_header_release > skb_clone Will do!
