On Thu, Oct 15, 2020 at 10:04 PM Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote: > > On Tue, Oct 13, 2020 at 12:50 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > > > On Tue, 13 Oct 2020 18:59:28 +0300 Aleksandr Nogikh wrote: > > > On Mon, 12 Oct 2020 at 09:04, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > > > > > > > On Sat, Oct 10, 2020 at 5:14 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > > > > > > > > > On Sat, 10 Oct 2020 09:54:57 +0200 Dmitry Vyukov wrote: > > > > > > On Sat, Oct 10, 2020 at 1:16 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > > [...] > > > > > > > Could you use skb_extensions for this? > > > > > > > > > > > > Why? If for space, this is already under a non-production ifdef. > > > > > > > > > > I understand, but the skb_ext infra is there for uncommon use cases > > > > > like this one. Any particular reason you don't want to use it? > > > > > The slight LoC increase? > > > > > > > > > > Is there any precedent for adding the kcov field to other performance > > > > > critical structures? > > > > > > It would be great to come to some conclusion on where exactly to store > > > kcov_handle. Technically, it is possible to use skb extensions for the > > > purpose, though it will indeed slightly increase the complexity. > > > > > > Jakub, you think that kcov_handle should be added as an skb extension, > > > right? > > > > That'd be preferable. I understand with current use cases it doesn't > > really matter, but history shows people come up with all sort of > > wonderful use cases down the line. And when they do they rarely go back > > and fix such fundamental minutiae. > > > > > Though I do not really object to moving the field, it still seems to > > > me that sk_buff itself is a better place. Right now skb extensions > > > store values that are local to specific protocols and that are only > > > meaningful in the context of these protocols (correct me if I'm > > > wrong). Although this patch only adds remote kcov coverage to the wifi > > > code, kcov_handle can be meaningful for other protocols as well - just > > > like the already existing sk_buff fields. So adding kcov_handle to skb > > > extensions will break this logical separation. > > > > It's not as much protocols as subsystems. The values are meaningful to > > a subsystem which inserts them, that doesn't mean single layer of the > > stack. If it was about storing layer's context we would just use > > skb->cb. > > > > So I think the kcov use matches pretty well. > > skb_extensions was the first thing that came to mind when I read this > patchset too. It is not specific to protocols. > > We have long stopped growing sk_buff size. Thank you all for your comments. I'll use skb extensions in v3 of the series.
