Re: [bpf-next v7 1/3] bpftool: Add auto_attach for bpf prog load|loadall

[wangyufen]

在 2022/10/1 0:26, Quentin Monnet 写道:
> Tue Sep 27 2022 12:21:14 GMT+0100 ~ Wang Yufen <wangyufen@xxxxxxxxxx>
> > Add auto_attach optional to support one-step load-attach-pin_link.
> Nit: Now "autoattach" instead of "auto_attach". Same in commit title.
will change in v8, thanks.
> > For example,
> >     $ bpftool prog loadall test.o /sys/fs/bpf/test autoattach
> >
> >     $ bpftool link
> >     26: tracing  name test1  tag f0da7d0058c00236  gpl
> >     	loaded_at 2022-09-09T21:39:49+0800  uid 0
> >     	xlated 88B  jited 55B  memlock 4096B  map_ids 3
> >     	btf_id 55
> >     28: kprobe  name test3  tag 002ef1bef0723833  gpl
> >     	loaded_at 2022-09-09T21:39:49+0800  uid 0
> >     	xlated 88B  jited 56B  memlock 4096B  map_ids 3
> >     	btf_id 55
> >     57: tracepoint  name oncpu  tag 7aa55dfbdcb78941  gpl
> >     	loaded_at 2022-09-09T21:41:32+0800  uid 0
> >     	xlated 456B  jited 265B  memlock 4096B  map_ids 17,13,14,15
> >     	btf_id 82
> >
> >     $ bpftool link
> >     1: tracing  prog 26
> >     	prog_type tracing  attach_type trace_fentry
> >     3: perf_event  prog 28
> >     10: perf_event  prog 57
> >
> > The autoattach optional can support tracepoints, k(ret)probes,
> > u(ret)probes.
> >
> > Signed-off-by: Wei Yongjun <weiyongjun1@xxxxxxxxxx>
> > Signed-off-by: Wang Yufen <wangyufen@xxxxxxxxxx>
> > ---
> > v6 -> v7: add info msg print and update doc for the skip program
> > v5 -> v6: skip the programs not supporting auto-attach,
> > 	  and change optional name from "auto_attach" to "autoattach"
> > v4 -> v5: some formatting nits of doc
> > v3 -> v4: rename functions, update doc, bash and do_help()
> > v2 -> v3: switch to extend prog load command instead of extend perf
> > v2: https://patchwork.kernel.org/project/netdevbpf/patch/20220824033837.458197-1-weiyongjun1@xxxxxxxxxx/
> > v1: https://patchwork.kernel.org/project/netdevbpf/patch/20220816151725.153343-1-weiyongjun1@xxxxxxxxxx/
> >   tools/bpf/bpftool/prog.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++--
> >   1 file changed, 79 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> > index c81362a..84eced8 100644
> > --- a/tools/bpf/bpftool/prog.c
> > +++ b/tools/bpf/bpftool/prog.c
> > @@ -1453,6 +1453,72 @@ static int do_run(int argc, char **argv)
> >   	return ret;
> >   }
> >   
> > +static int
> > +auto_attach_program(struct bpf_program *prog, const char *path)
> > +{
> > +	struct bpf_link *link;
> > +	int err;
> > +
> > +	link = bpf_program__attach(prog);
> > +	if (!link)
> > +		return -1;
> > +
> > +	err = bpf_link__pin(link, path);
> > +	if (err) {
> > +		bpf_link__destroy(link);
> > +		return err;
> > +	}
> > +	return 0;
> > +}
> > +
> > +static int pathname_concat(const char *path, const char *name, char *buf)
> > +{
> > +	int len;
> > +
> > +	len = snprintf(buf, PATH_MAX, "%s/%s", path, name);
> > +	if (len < 0)
> > +		return -EINVAL;
> > +	if (len >= PATH_MAX)
> > +		return -ENAMETOOLONG;
> > +
> > +	return 0;
> > +}
> > +
> > +static int
> > +auto_attach_programs(struct bpf_object *obj, const char *path)
> > +{
> > +	struct bpf_program *prog;
> > +	char buf[PATH_MAX];
> > +	int err;
> > +
> > +	bpf_object__for_each_program(prog, obj) {
> > +		err = pathname_concat(path, bpf_program__name(prog), buf);
> > +		if (err)
> > +			goto err_unpin_programs;
> > +
> > +		err = auto_attach_program(prog, buf);
> > +		if (!err)
> > +			continue;
> > +		if (errno == EOPNOTSUPP)
> > +			p_info("Program %s does not support autoattach",
> > +			       bpf_program__name(prog));
> > +		else
> > +			goto err_unpin_programs
> With this code, if auto-attach fails, then we skip this program and move
> on to the next. That's an improvement, but in that case the program
> won't remain loaded in the kernel after bpftool exits. My suggestion in
> my previous message (sorry if it was not clear) was to fall back to
> regular pinning in that case (bpf_obj_pin()), along with the p_info()
> message, so we can have the program pinned but not attached and let the
> user know. If regular pinning fails as well, then we should unpin all
> and error out, for consistency with bpf_object__pin_programs().
>
> And in that case, the (errno == EOPNOTSUPP) with fallback to regular
> pinning could maybe be moved into auto_attach_program(), so that
> auto-attaching single programs can use the fallback too?
>
> Thanks,
> Quentin

If I understand correctly, can we just check link?  as following:

--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1460,9 +1460,10 @@ static int do_run(int argc, char **argv)
        int err;
 
        link = bpf_program__attach(prog);
-       if (!link)
-               return -1;
-
+       if (!link) {
+               p_info("Program %s attach failed", bpf_program__name(prog));
+               return bpf_obj_pin(bpf_program__fd(prog), path);
+       }
        err = bpf_link__pin(link, path);
        if (err) {
                bpf_link__destroy(link);
@@ -1499,9 +1500,6 @@ static int pathname_concat(const char *path, const char *name, char *buf)
                err = auto_attach_program(prog, buf);
                if (!err)
                        continue;
-               if (errno == EOPNOTSUPP)
-                       p_info("Program %s does not support autoattach",
-                              bpf_program__name(prog));
                else
                        goto err_unpin_programs;
        }


and the doc is modified as follows:

If the program does not support autoattach, will do regular pin along with an
info message such as "Program %s attach failed". If the *OBJ* contains multiple
programs and **loadall** is used, if the program A in these programs does not
support autoattach, the program A will do regular pin along with an info message,
and continue to autoattach the next program.

Thanks,
Wang