On Mon, Jul 25, 2022 at 01:15:49PM +0100, Matthew Wilcox wrote: > On Fri, Jul 22, 2022 at 02:23:46PM -0700, Paul E. McKenney wrote: > > On Fri, Jul 22, 2022 at 10:17:57PM +0200, Daniel Borkmann wrote: > > > Otherwise I think this could be a bit misunderstood, e.g. most of the networking > > > programs (e.g. XDP, tc, sock_addr) have a fixed framework around them where > > > attaching programs is part of ABI. > > > > Excellent point, thank you! > > > > Apologies for the newbie question, but does BTF_ID() mark a function as > > ABI from the viewpoing of a BPF program calling that function, attaching > > to that function, or both? Either way, is it worth mentioning this > > in this QA entry? > > Not necessarily. For example, __filemap_add_folio has a BTF_ID(), but > it is not ABI (it's error injection). OK, sounds like something to leave out of the QA, then. Thanx, Paul > > The updated patch below just adds the "arbitrary". > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit 89659e20d11fc1350f5881ff7c9687289806b2ba > > Author: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Date: Fri Jul 22 10:52:05 2022 -0700 > > > > bpf: Update bpf_design_QA.rst to clarify that attaching to functions is not ABI > > > > This patch updates bpf_design_QA.rst to clarify that the ability to > > attach a BPF program to an arbitrary function in the kernel does not > > make that function become part of the Linux kernel's ABI. > > > > [ paulmck: Apply Daniel Borkmann feedback. ] > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > > diff --git a/Documentation/bpf/bpf_design_QA.rst b/Documentation/bpf/bpf_design_QA.rst > > index 2ed9128cfbec8..a06ae8a828e3d 100644 > > --- a/Documentation/bpf/bpf_design_QA.rst > > +++ b/Documentation/bpf/bpf_design_QA.rst > > @@ -279,3 +279,15 @@ cc (congestion-control) implementations. If any of these kernel > > functions has changed, both the in-tree and out-of-tree kernel tcp cc > > implementations have to be changed. The same goes for the bpf > > programs and they have to be adjusted accordingly. > > + > > +Q: Attaching to arbitrary kernel functions is an ABI? > > +----------------------------------------------------- > > +Q: BPF programs can be attached to many kernel functions. Do these > > +kernel functions become part of the ABI? > > + > > +A: NO. > > + > > +The kernel function prototypes will change, and BPF programs attaching to > > +them will need to change. The BPF compile-once-run-everywhere (CO-RE) > > +should be used in order to make it easier to adapt your BPF programs to > > +different versions of the kernel.
