On Thu, Aug 25, 2016 at 09:31:26AM +0200, Steffen Klassert wrote: > On Wed, Aug 24, 2016 at 02:25:29PM -0300, Marcelo Ricardo Leitner wrote: > > Em 24-08-2016 13:27, Alexander Duyck escreveu: > > > > > >I'm adding Marcelo as he could probably explain the GSO_BY_FRAGS > > >functionality better than I could since he is the original author. > > > > > >If I recall GSO_BY_FRAGS does something similar to what you are doing, > > >although I believe it doesn't carry any data in the first buffer other > > >than just a header. I believe the idea behind GSO_BY_FRAGS was to > > >allow for segmenting a frame at the frag_list level instead of having > > >it done just based on MSS. That was the only reason why I brought it > > >up. > > > > > > > That's exactly it. > > > > On this no data in the first buffer limitation, we probably can > > allow it have some data in there. It was done this way just because > > sctp is using skb_gro_receive() to build such skb and this was the > > way I found to get such frag_list skb generated by it, thus > > preserving frame boundaries. > > Just to understand what you are doing. You generate MTU sized linear > buffers in sctp and then, skb_gro_receive() chains up these buffers > at the frag_list pointer. skb_gro_receive() does this because > skb_gro_offset is null and skb->head_frag is not set in your case. > > At segmentation, you just need to split at the frag_list pointer > because you know that the chained buffers fit the MTU, right? >
Correct. Just note that these buffers fit the MTU, but not necessary uses all of it. That is main point in here, variable segmentation size.
