Re: [PATCHv5 bpf-next 10/28] bpf: Add multi tracing attach types

[Jiri Olsa <olsajiri@gmail.com>]

On Sat, Apr 18, 2026 at 06:49:09AM +0000, bot+bpf-ci@kernel.org wrote:
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -1154,6 +1154,8 @@ enum bpf_attach_type {
> >  	BPF_TRACE_KPROBE_SESSION,
> >  	BPF_TRACE_UPROBE_SESSION,
> >  	BPF_TRACE_FSESSION,
> > +	BPF_TRACE_FENTRY_MULTI,
> > +	BPF_TRACE_FEXIT_MULTI,
> >  	__MAX_BPF_ATTACH_TYPE
> >  };
> 
> In RFC v2 (Feb 4, 2026), Leon Hwang asked whether BPF_TRACE_FSESSION_MULTI
> should be added alongside BPF_TRACE_FENTRY_MULTI and BPF_TRACE_FEXIT_MULTI
> for API consistency, since BPF_TRACE_FSESSION exists and is handled
> similarly to FENTRY/FEXIT. You acknowledged this with 'good catch, will add
> it' but BPF_TRACE_FSESSION_MULTI was never added in any subsequent version
> (v1, v2, v3, v4, or v5).
> 
> Is this attach type intentionally omitted, or should it be included to
> complete the multi tracing API?

ansrewed in the other reply

> 
> Reference: https://lore.kernel.org/bpf/3015991d-2e9b-4bf4-9c17-26e00b5d5926@linux.dev/
> 
> [ ... ]
> 
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> 
> [ ... ]
> 
> > @@ -19368,7 +19379,17 @@
> >  		if (ret < 0)
> >  			return ret;
> >
> > -		if (tgt_prog) {
> > +		/* *.multi programs don't need an address during program
> > +		 * verification, we just take the module ref if needed.
> > +		 */
> > +		if (is_tracing_multi_id(prog, btf_id)) {
> > +			if (btf_is_module(btf)) {
> > +				mod = btf_try_get_module(btf);
> > +				if (!mod)
> > +					return -ENOENT;
> > +			}
> > +			addr = 0;
> > +		} else if (tgt_prog) {
> 
> This isn't a bug, but the new multi-line comment here uses the old kernel
> comment style with text on the same line as the opening '/*'. The BPF
> subsystem guide mandates the modern multi-line style with '/*' on its own
> line for new code under kernel/bpf/, even if surrounding code still uses
> the old style.
> 
> Should the comment be reformatted as:
> 
> 	/*
> 	 * *.multi programs don't need an address during program
> 	 * verification, we just take the module ref if needed.
> 	 */

sure

jirka

> 
> > @@ -19396,6 +19417,12 @@
> >  			ret = -EINVAL;
> >  			switch (prog->type) {
> >  			case BPF_PROG_TYPE_TRACING:
> > +				/* *.multi sleepable programs will pass initial sleepable check,
> > +				 * the actual attached btf ids are checked later during the link
> > +				 * attachment.
> > +				 */
> > +				if (is_tracing_multi_id(prog, btf_id))
> > +					ret = 0;
> 
> The same comment style issue appears here. Should this also use the modern
> style with '/*' on its own line?
> 
> Note that another comment you added in check_attach_btf_id uses the correct
> modern style, making this inconsistency clearly fixable.
> 
> 
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/24598000047