On Fri, 2025-05-09 at 01:33 +0200, Kumar Kartikeya Dwivedi wrote:
[...]
> > > -#define ___bpf_pick_printk(...) \
> > > - ___bpf_nth(_, ##__VA_ARGS__, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \
> > > - __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \
> > > - __bpf_vprintk, __bpf_vprintk, __bpf_printk /*3*/, __bpf_printk /*2*/,\
> > > - __bpf_printk /*1*/, __bpf_printk /*0*/)
> > > +#define ___bpf_pick_printk(choice, choice_3, ...) \
> > > + ___bpf_nth(_, ##__VA_ARGS__, choice, choice, choice, \
> > > + choice, choice, choice, choice, \
> > > + choice, choice, choice_3 /*3*/, choice_3 /*2*/, \
> > > + choice_3 /*1*/, choice_3 /*0*/)
> > >
> > > /* Helper macro to print out debug messages */
> > > -#define bpf_printk(fmt, args...) ___bpf_pick_printk(args)(fmt, ##args)
> > > +#define __bpf_trace_printk(fmt, args...) \
> > > + ___bpf_pick_printk(__bpf_vprintk, __bpf_printk, args)(fmt, ##args)
> > > +#define __bpf_stream_printk(stream, fmt, args...) \
> > > + ___bpf_pick_printk(__bpf_stream_vprintk, __bpf_stream_vprintk, args)(stream, fmt, ##args)
> > ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^
> > These two parameters are identical,
> > why is ___bpf_pick_printk is necessary in such case?
>
> In our case choice and choice_3 are the same, but for bpf_printk
> they're different, I was mostly trying to reuse the pick_printk
> machinery for both (which dispatches correctly to the actual macro).
>
But ___bpf_pick_printk is a noop if two identical choices are supplied,
so there is nothing to reuse. E.g. nothing breaks after the following change:
#define __bpf_trace_printk(fmt, args...) \
___bpf_pick_printk(__bpf_vprintk, __bpf_printk, args)(fmt, ##args)
-#define __bpf_stream_printk(stream, fmt, args...) \
- ___bpf_pick_printk(__bpf_stream_vprintk, __bpf_stream_vprintk, args)(stream, fmt, ##args)
-#define bpf_stream_printk(stream, fmt, args...) __bpf_stream_printk(stream, fmt, ##args)
+#define bpf_stream_printk(stream, fmt, args...) __bpf_stream_vprintk(stream, fmt, ##args)
#define bpf_printk(arg, args...) __bpf_trace_printk(arg, ##args)
Which allows to shorten this patch.
Or do I miss something?
[...]
