On Thu, Jan 19, 2023 at 09:59:06PM -0800, Alexei Starovoitov wrote:
> On Thu, Jan 19, 2023 at 05:58:32PM -0600, David Vernet wrote:
> > +
> > +For example:
> > +
> > +.. code-block:: c
> > +
> > + /**
> > + * A trivial example tracepoint program that shows how to
> > + * acquire and release a struct bpf_cpumask *.
> > + */
> > + SEC("tp_btf/task_newtask")
> > + int BPF_PROG(task_acquire_release_example, struct task_struct *task, u64 clone_flags)
> > + {
> > + struct bpf_cpumask *cpumask, *acquired;
> > +
> > + cpumask = bpf_cpumask_create();
> > + if (!cpumask)
> > + return 1;
> > +
> > + acquired = bpf_cpumask_acquire(cpumask);
> > + bpf_cpumask_release(cpumask);
> > + bpf_cpumask_acquire(acquired);
> > +
> > + return 0;
> > + }
>
> As the first example in the doc it was... alarming :)
> I've read it as it says that bpf_cpumask_acquire has to be called on
> freshly created cpumask before it can be used.
That's fair, I treated this example like a testcase :-)
> I've started to doubt by code reading skills of the previous patches :)
> A basic example is probably necessary to introduce the concept.
> Or this example should have bpf_cpumask_set_cpu right after create and
> more alu ops after release with comments to demonstrate the point.
Makes sense. I'll update the examples to be more clear and reflect
realistic use cases.
