[bpf-next,v3,5/8] bpftool: support dumping metadata

Message ID 20200828193603.335512-6-sdf@google.com
State New
Headers show
Series
  • [bpf-next,v3,1/8] bpf: Mutex protect used_maps array and count
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Commit Message

Stanislav Fomichev Aug. 28, 2020, 7:36 p.m.
From: YiFei Zhu <zhuyifei@google.com>

Added a flag "--metadata" to `bpftool prog list` to dump the metadata
contents. For some formatting some BTF code is put directly in the
metadata dumping. Sanity checks on the map and the kind of the btf_type
to make sure we are actually dumping what we are expecting.

A helper jsonw_reset is added to json writer so we can reuse the same
json writer without having extraneous commas.

Sample output:

  $ bpftool prog --metadata
  6: cgroup_skb  name prog  tag bcf7977d3b93787c  gpl
  [...]
  	btf_id 4
  	metadata:
  		metadata_a = "foo"
  		metadata_b = 1

  $ bpftool prog --metadata --json --pretty
  [{
          "id": 6,
  [...]
          "btf_id": 4,
          "metadata": {
              "metadata_a": "foo",
              "metadata_b": 1
          }
      }
  ]

Cc: YiFei Zhu <zhuyifei1999@gmail.com>
Signed-off-by: YiFei Zhu <zhuyifei@google.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 tools/bpf/bpftool/json_writer.c |   6 ++
 tools/bpf/bpftool/json_writer.h |   3 +
 tools/bpf/bpftool/main.c        |  10 +++
 tools/bpf/bpftool/main.h        |   1 +
 tools/bpf/bpftool/prog.c        | 130 ++++++++++++++++++++++++++++++++
 5 files changed, 150 insertions(+)

Comments

Andrii Nakryiko Sept. 3, 2020, 5 a.m. | #1
On Fri, Aug 28, 2020 at 12:37 PM Stanislav Fomichev <sdf@google.com> wrote:
>
> From: YiFei Zhu <zhuyifei@google.com>
>
> Added a flag "--metadata" to `bpftool prog list` to dump the metadata
> contents. For some formatting some BTF code is put directly in the
> metadata dumping. Sanity checks on the map and the kind of the btf_type
> to make sure we are actually dumping what we are expecting.
>
> A helper jsonw_reset is added to json writer so we can reuse the same
> json writer without having extraneous commas.
>
> Sample output:
>
>   $ bpftool prog --metadata
>   6: cgroup_skb  name prog  tag bcf7977d3b93787c  gpl
>   [...]
>         btf_id 4
>         metadata:
>                 metadata_a = "foo"
>                 metadata_b = 1
>
>   $ bpftool prog --metadata --json --pretty
>   [{
>           "id": 6,
>   [...]
>           "btf_id": 4,
>           "metadata": {
>               "metadata_a": "foo",
>               "metadata_b": 1
>           }
>       }
>   ]
>
> Cc: YiFei Zhu <zhuyifei1999@gmail.com>
> Signed-off-by: YiFei Zhu <zhuyifei@google.com>
> Signed-off-by: Stanislav Fomichev <sdf@google.com>
> ---
>  tools/bpf/bpftool/json_writer.c |   6 ++
>  tools/bpf/bpftool/json_writer.h |   3 +
>  tools/bpf/bpftool/main.c        |  10 +++
>  tools/bpf/bpftool/main.h        |   1 +
>  tools/bpf/bpftool/prog.c        | 130 ++++++++++++++++++++++++++++++++
>  5 files changed, 150 insertions(+)
>

[...]

> +
> +       if (bpf_map_lookup_elem(map_fd, &key, value)) {
> +               p_err("metadata map lookup failed: %s", strerror(errno));
> +               goto out_free;
> +       }
> +
> +       err = btf__get_from_id(map_info.btf_id, &btf);

what if the map has no btf_id associated (e.g., because of an old
kernel?); why fail in this case?

> +       if (err || !btf) {
> +               p_err("metadata BTF get failed: %s", strerror(-err));
> +               goto out_free;
> +       }
> +
> +       t_datasec = btf__type_by_id(btf, map_info.btf_value_type_id);
> +       if (BTF_INFO_KIND(t_datasec->info) != BTF_KIND_DATASEC) {

btf_is_datasec(t_datasec)

> +               p_err("bad metadata BTF");
> +               goto out_free;
> +       }
> +
> +       vlen = BTF_INFO_VLEN(t_datasec->info);

btf_vlen(t_datasec)

> +       vsi = (struct btf_var_secinfo *)(t_datasec + 1);

btf_var_secinfos(t_datasec)

> +
> +       /* We don't proceed to check the kinds of the elements of the DATASEC.
> +        * The verifier enforce then to be BTF_KIND_VAR.

typo: then -> them

> +        */
> +
> +       if (json_output) {
> +               struct btf_dumper d = {
> +                       .btf = btf,
> +                       .jw = json_wtr,
> +                       .is_plain_text = false,
> +               };
> +
> +               jsonw_name(json_wtr, "metadata");
> +
> +               jsonw_start_object(json_wtr);
> +               for (i = 0; i < vlen; i++) {

nit: doing ++vsi here


> +                       t_var = btf__type_by_id(btf, vsi[i].type);

and vsi->type here and below would look a bit cleaner

> +
> +                       jsonw_name(json_wtr, btf__name_by_offset(btf, t_var->name_off));
> +                       err = btf_dumper_type(&d, t_var->type, value + vsi[i].offset);
> +                       if (err) {
> +                               p_err("btf dump failed");
> +                               break;
> +                       }
> +               }
> +               jsonw_end_object(json_wtr);

[...]
Stanislav Fomichev Sept. 8, 2020, 8:53 p.m. | #2
On Wed, Sep 2, 2020 at 10:00 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Aug 28, 2020 at 12:37 PM Stanislav Fomichev <sdf@google.com> wrote:
> >
> > From: YiFei Zhu <zhuyifei@google.com>
> >
> > Added a flag "--metadata" to `bpftool prog list` to dump the metadata
> > contents. For some formatting some BTF code is put directly in the
> > metadata dumping. Sanity checks on the map and the kind of the btf_type
> > to make sure we are actually dumping what we are expecting.
> >
> > A helper jsonw_reset is added to json writer so we can reuse the same
> > json writer without having extraneous commas.
> >
> > Sample output:
> >
> >   $ bpftool prog --metadata
> >   6: cgroup_skb  name prog  tag bcf7977d3b93787c  gpl
> >   [...]
> >         btf_id 4
> >         metadata:
> >                 metadata_a = "foo"
> >                 metadata_b = 1
> >
> >   $ bpftool prog --metadata --json --pretty
> >   [{
> >           "id": 6,
> >   [...]
> >           "btf_id": 4,
> >           "metadata": {
> >               "metadata_a": "foo",
> >               "metadata_b": 1
> >           }
> >       }
> >   ]
> >
> > Cc: YiFei Zhu <zhuyifei1999@gmail.com>
> > Signed-off-by: YiFei Zhu <zhuyifei@google.com>
> > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> > ---
> >  tools/bpf/bpftool/json_writer.c |   6 ++
> >  tools/bpf/bpftool/json_writer.h |   3 +
> >  tools/bpf/bpftool/main.c        |  10 +++
> >  tools/bpf/bpftool/main.h        |   1 +
> >  tools/bpf/bpftool/prog.c        | 130 ++++++++++++++++++++++++++++++++
> >  5 files changed, 150 insertions(+)
> >
>
> [...]
>
> > +
> > +       if (bpf_map_lookup_elem(map_fd, &key, value)) {
> > +               p_err("metadata map lookup failed: %s", strerror(errno));
> > +               goto out_free;
> > +       }
> > +
> > +       err = btf__get_from_id(map_info.btf_id, &btf);
>
> what if the map has no btf_id associated (e.g., because of an old
> kernel?); why fail in this case?
Thank you for the review, coming back at it a bit late :-(

This functionality is guarded by --metadata bpftool flag (off by default).
In case of no btf_id, it might be helpful to show why we don't have
the metadata rather than just quietly failing.
WDYT?

> > +       if (err || !btf) {
> > +               p_err("metadata BTF get failed: %s", strerror(-err));
> > +               goto out_free;
> > +       }
> > +
> > +       t_datasec = btf__type_by_id(btf, map_info.btf_value_type_id);
> > +       if (BTF_INFO_KIND(t_datasec->info) != BTF_KIND_DATASEC) {
>
> btf_is_datasec(t_datasec)
>
> > +               p_err("bad metadata BTF");
> > +               goto out_free;
> > +       }
> > +
> > +       vlen = BTF_INFO_VLEN(t_datasec->info);
>
> btf_vlen(t_datasec)
>
> > +       vsi = (struct btf_var_secinfo *)(t_datasec + 1);
>
> btf_var_secinfos(t_datasec)
>
> > +
> > +       /* We don't proceed to check the kinds of the elements of the DATASEC.
> > +        * The verifier enforce then to be BTF_KIND_VAR.
>
> typo: then -> them
>
> > +        */
> > +
> > +       if (json_output) {
> > +               struct btf_dumper d = {
> > +                       .btf = btf,
> > +                       .jw = json_wtr,
> > +                       .is_plain_text = false,
> > +               };
> > +
> > +               jsonw_name(json_wtr, "metadata");
> > +
> > +               jsonw_start_object(json_wtr);
> > +               for (i = 0; i < vlen; i++) {
>
> nit: doing ++vsi here
Agreed with all the above, except this one.
It feels like it's safer to do [i] in case somebody adds a 'continue'
clause later and we miss that '++vsi'.
Let me know if you feel strongly about it.

> > +                       t_var = btf__type_by_id(btf, vsi[i].type);
>
> and vsi->type here and below would look a bit cleaner
>
> > +
> > +                       jsonw_name(json_wtr, btf__name_by_offset(btf, t_var->name_off));
> > +                       err = btf_dumper_type(&d, t_var->type, value + vsi[i].offset);
> > +                       if (err) {
> > +                               p_err("btf dump failed");
> > +                               break;
> > +                       }
> > +               }
> > +               jsonw_end_object(json_wtr);
>
> [...]
Andrii Nakryiko Sept. 8, 2020, 10:35 p.m. | #3
On Tue, Sep 8, 2020 at 1:53 PM Stanislav Fomichev <sdf@google.com> wrote:
>
> On Wed, Sep 2, 2020 at 10:00 PM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Fri, Aug 28, 2020 at 12:37 PM Stanislav Fomichev <sdf@google.com> wrote:
> > >
> > > From: YiFei Zhu <zhuyifei@google.com>
> > >
> > > Added a flag "--metadata" to `bpftool prog list` to dump the metadata
> > > contents. For some formatting some BTF code is put directly in the
> > > metadata dumping. Sanity checks on the map and the kind of the btf_type
> > > to make sure we are actually dumping what we are expecting.
> > >
> > > A helper jsonw_reset is added to json writer so we can reuse the same
> > > json writer without having extraneous commas.
> > >
> > > Sample output:
> > >
> > >   $ bpftool prog --metadata
> > >   6: cgroup_skb  name prog  tag bcf7977d3b93787c  gpl
> > >   [...]
> > >         btf_id 4
> > >         metadata:
> > >                 metadata_a = "foo"
> > >                 metadata_b = 1
> > >
> > >   $ bpftool prog --metadata --json --pretty
> > >   [{
> > >           "id": 6,
> > >   [...]
> > >           "btf_id": 4,
> > >           "metadata": {
> > >               "metadata_a": "foo",
> > >               "metadata_b": 1
> > >           }
> > >       }
> > >   ]
> > >
> > > Cc: YiFei Zhu <zhuyifei1999@gmail.com>
> > > Signed-off-by: YiFei Zhu <zhuyifei@google.com>
> > > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> > > ---
> > >  tools/bpf/bpftool/json_writer.c |   6 ++
> > >  tools/bpf/bpftool/json_writer.h |   3 +
> > >  tools/bpf/bpftool/main.c        |  10 +++
> > >  tools/bpf/bpftool/main.h        |   1 +
> > >  tools/bpf/bpftool/prog.c        | 130 ++++++++++++++++++++++++++++++++
> > >  5 files changed, 150 insertions(+)
> > >
> >
> > [...]
> >
> > > +
> > > +       if (bpf_map_lookup_elem(map_fd, &key, value)) {
> > > +               p_err("metadata map lookup failed: %s", strerror(errno));
> > > +               goto out_free;
> > > +       }
> > > +
> > > +       err = btf__get_from_id(map_info.btf_id, &btf);
> >
> > what if the map has no btf_id associated (e.g., because of an old
> > kernel?); why fail in this case?
> Thank you for the review, coming back at it a bit late :-(
>
> This functionality is guarded by --metadata bpftool flag (off by default).
> In case of no btf_id, it might be helpful to show why we don't have
> the metadata rather than just quietly failing.
> WDYT?

we might do it similarly to PID info I added with bpf_iter: if it's
supported -- emit it, if not -- skip and still succeed. So maybe we
don't really need extra --metadata flag and should do all this always?

>
> > > +       if (err || !btf) {
> > > +               p_err("metadata BTF get failed: %s", strerror(-err));
> > > +               goto out_free;
> > > +       }
> > > +
> > > +       t_datasec = btf__type_by_id(btf, map_info.btf_value_type_id);
> > > +       if (BTF_INFO_KIND(t_datasec->info) != BTF_KIND_DATASEC) {
> >
> > btf_is_datasec(t_datasec)
> >
> > > +               p_err("bad metadata BTF");
> > > +               goto out_free;
> > > +       }
> > > +
> > > +       vlen = BTF_INFO_VLEN(t_datasec->info);
> >
> > btf_vlen(t_datasec)
> >
> > > +       vsi = (struct btf_var_secinfo *)(t_datasec + 1);
> >
> > btf_var_secinfos(t_datasec)
> >
> > > +
> > > +       /* We don't proceed to check the kinds of the elements of the DATASEC.
> > > +        * The verifier enforce then to be BTF_KIND_VAR.
> >
> > typo: then -> them
> >
> > > +        */
> > > +
> > > +       if (json_output) {
> > > +               struct btf_dumper d = {
> > > +                       .btf = btf,
> > > +                       .jw = json_wtr,
> > > +                       .is_plain_text = false,
> > > +               };
> > > +
> > > +               jsonw_name(json_wtr, "metadata");
> > > +
> > > +               jsonw_start_object(json_wtr);
> > > +               for (i = 0; i < vlen; i++) {
> >
> > nit: doing ++vsi here
> Agreed with all the above, except this one.
> It feels like it's safer to do [i] in case somebody adds a 'continue'
> clause later and we miss that '++vsi'.
> Let me know if you feel strongly about it.

I meant to add vsi++ inside the for clause, no way to miss it:

for (i = 0; i < vlen, i++, vsi++) {
  continue/break/whatever you want, except extra i++ or vsi++
}

it's the safest way, imo

>
> > > +                       t_var = btf__type_by_id(btf, vsi[i].type);
> >
> > and vsi->type here and below would look a bit cleaner
> >
> > > +
> > > +                       jsonw_name(json_wtr, btf__name_by_offset(btf, t_var->name_off));
> > > +                       err = btf_dumper_type(&d, t_var->type, value + vsi[i].offset);
> > > +                       if (err) {
> > > +                               p_err("btf dump failed");
> > > +                               break;
> > > +                       }
> > > +               }
> > > +               jsonw_end_object(json_wtr);
> >
> > [...]
Stanislav Fomichev Sept. 8, 2020, 10:49 p.m. | #4
On Tue, Sep 8, 2020 at 3:35 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Tue, Sep 8, 2020 at 1:53 PM Stanislav Fomichev <sdf@google.com> wrote:
> >
> > On Wed, Sep 2, 2020 at 10:00 PM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> > >
> > > On Fri, Aug 28, 2020 at 12:37 PM Stanislav Fomichev <sdf@google.com> wrote:
> > > >
> > > > From: YiFei Zhu <zhuyifei@google.com>
> > > >
> > > > Added a flag "--metadata" to `bpftool prog list` to dump the metadata
> > > > contents. For some formatting some BTF code is put directly in the
> > > > metadata dumping. Sanity checks on the map and the kind of the btf_type
> > > > to make sure we are actually dumping what we are expecting.
> > > >
> > > > A helper jsonw_reset is added to json writer so we can reuse the same
> > > > json writer without having extraneous commas.
> > > >
> > > > Sample output:
> > > >
> > > >   $ bpftool prog --metadata
> > > >   6: cgroup_skb  name prog  tag bcf7977d3b93787c  gpl
> > > >   [...]
> > > >         btf_id 4
> > > >         metadata:
> > > >                 metadata_a = "foo"
> > > >                 metadata_b = 1
> > > >
> > > >   $ bpftool prog --metadata --json --pretty
> > > >   [{
> > > >           "id": 6,
> > > >   [...]
> > > >           "btf_id": 4,
> > > >           "metadata": {
> > > >               "metadata_a": "foo",
> > > >               "metadata_b": 1
> > > >           }
> > > >       }
> > > >   ]
> > > >
> > > > Cc: YiFei Zhu <zhuyifei1999@gmail.com>
> > > > Signed-off-by: YiFei Zhu <zhuyifei@google.com>
> > > > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> > > > ---
> > > >  tools/bpf/bpftool/json_writer.c |   6 ++
> > > >  tools/bpf/bpftool/json_writer.h |   3 +
> > > >  tools/bpf/bpftool/main.c        |  10 +++
> > > >  tools/bpf/bpftool/main.h        |   1 +
> > > >  tools/bpf/bpftool/prog.c        | 130 ++++++++++++++++++++++++++++++++
> > > >  5 files changed, 150 insertions(+)
> > > >
> > >
> > > [...]
> > >
> > > > +
> > > > +       if (bpf_map_lookup_elem(map_fd, &key, value)) {
> > > > +               p_err("metadata map lookup failed: %s", strerror(errno));
> > > > +               goto out_free;
> > > > +       }
> > > > +
> > > > +       err = btf__get_from_id(map_info.btf_id, &btf);
> > >
> > > what if the map has no btf_id associated (e.g., because of an old
> > > kernel?); why fail in this case?
> > Thank you for the review, coming back at it a bit late :-(
> >
> > This functionality is guarded by --metadata bpftool flag (off by default).
> > In case of no btf_id, it might be helpful to show why we don't have
> > the metadata rather than just quietly failing.
> > WDYT?
>
> we might do it similarly to PID info I added with bpf_iter: if it's
> supported -- emit it, if not -- skip and still succeed. So maybe we
> don't really need extra --metadata flag and should do all this always?
Sounds reasonable, especially if there is an existing precedent.
Let me explore that option.

> > > > +       if (err || !btf) {
> > > > +               p_err("metadata BTF get failed: %s", strerror(-err));
> > > > +               goto out_free;
> > > > +       }
> > > > +
> > > > +       t_datasec = btf__type_by_id(btf, map_info.btf_value_type_id);
> > > > +       if (BTF_INFO_KIND(t_datasec->info) != BTF_KIND_DATASEC) {
> > >
> > > btf_is_datasec(t_datasec)
> > >
> > > > +               p_err("bad metadata BTF");
> > > > +               goto out_free;
> > > > +       }
> > > > +
> > > > +       vlen = BTF_INFO_VLEN(t_datasec->info);
> > >
> > > btf_vlen(t_datasec)
> > >
> > > > +       vsi = (struct btf_var_secinfo *)(t_datasec + 1);
> > >
> > > btf_var_secinfos(t_datasec)
> > >
> > > > +
> > > > +       /* We don't proceed to check the kinds of the elements of the DATASEC.
> > > > +        * The verifier enforce then to be BTF_KIND_VAR.
> > >
> > > typo: then -> them
> > >
> > > > +        */
> > > > +
> > > > +       if (json_output) {
> > > > +               struct btf_dumper d = {
> > > > +                       .btf = btf,
> > > > +                       .jw = json_wtr,
> > > > +                       .is_plain_text = false,
> > > > +               };
> > > > +
> > > > +               jsonw_name(json_wtr, "metadata");
> > > > +
> > > > +               jsonw_start_object(json_wtr);
> > > > +               for (i = 0; i < vlen; i++) {
> > >
> > > nit: doing ++vsi here
> > Agreed with all the above, except this one.
> > It feels like it's safer to do [i] in case somebody adds a 'continue'
> > clause later and we miss that '++vsi'.
> > Let me know if you feel strongly about it.
>
> I meant to add vsi++ inside the for clause, no way to miss it:
>
> for (i = 0; i < vlen, i++, vsi++) {
>   continue/break/whatever you want, except extra i++ or vsi++
> }
>
> it's the safest way, imo
Ack, I can do that, thanks!

> > > > +                       t_var = btf__type_by_id(btf, vsi[i].type);
> > >
> > > and vsi->type here and below would look a bit cleaner
> > >
> > > > +
> > > > +                       jsonw_name(json_wtr, btf__name_by_offset(btf, t_var->name_off));
> > > > +                       err = btf_dumper_type(&d, t_var->type, value + vsi[i].offset);
> > > > +                       if (err) {
> > > > +                               p_err("btf dump failed");
> > > > +                               break;
> > > > +                       }
> > > > +               }
> > > > +               jsonw_end_object(json_wtr);
> > >
> > > [...]

Patch

diff --git a/tools/bpf/bpftool/json_writer.c b/tools/bpf/bpftool/json_writer.c
index 86501cd3c763..7fea83bedf48 100644
--- a/tools/bpf/bpftool/json_writer.c
+++ b/tools/bpf/bpftool/json_writer.c
@@ -119,6 +119,12 @@  void jsonw_pretty(json_writer_t *self, bool on)
 	self->pretty = on;
 }
 
+void jsonw_reset(json_writer_t *self)
+{
+	assert(self->depth == 0);
+	self->sep = '\0';
+}
+
 /* Basic blocks */
 static void jsonw_begin(json_writer_t *self, int c)
 {
diff --git a/tools/bpf/bpftool/json_writer.h b/tools/bpf/bpftool/json_writer.h
index 35cf1f00f96c..8ace65cdb92f 100644
--- a/tools/bpf/bpftool/json_writer.h
+++ b/tools/bpf/bpftool/json_writer.h
@@ -27,6 +27,9 @@  void jsonw_destroy(json_writer_t **self_p);
 /* Cause output to have pretty whitespace */
 void jsonw_pretty(json_writer_t *self, bool on);
 
+/* Reset separator to create new JSON */
+void jsonw_reset(json_writer_t *self);
+
 /* Add property name */
 void jsonw_name(json_writer_t *self, const char *name);
 
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 4a191fcbeb82..a681d568cfa7 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -28,6 +28,7 @@  bool show_pinned;
 bool block_mount;
 bool verifier_logs;
 bool relaxed_maps;
+bool dump_metadata;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
 struct pinned_obj_table link_table;
@@ -351,6 +352,10 @@  static int do_batch(int argc, char **argv)
 	return err;
 }
 
+enum bpftool_longonly_opts {
+	OPT_METADATA = 256,
+};
+
 int main(int argc, char **argv)
 {
 	static const struct option options[] = {
@@ -362,6 +367,7 @@  int main(int argc, char **argv)
 		{ "mapcompat",	no_argument,	NULL,	'm' },
 		{ "nomount",	no_argument,	NULL,	'n' },
 		{ "debug",	no_argument,	NULL,	'd' },
+		{ "metadata",	no_argument,	NULL,	OPT_METADATA },
 		{ 0 }
 	};
 	int opt, ret;
@@ -371,6 +377,7 @@  int main(int argc, char **argv)
 	json_output = false;
 	show_pinned = false;
 	block_mount = false;
+	dump_metadata = false;
 	bin_name = argv[0];
 
 	hash_init(prog_table.table);
@@ -412,6 +419,9 @@  int main(int argc, char **argv)
 			libbpf_set_print(print_all_levels);
 			verifier_logs = true;
 			break;
+		case OPT_METADATA:
+			dump_metadata = true;
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index c46e52137b87..8750758e9150 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -90,6 +90,7 @@  extern bool show_pids;
 extern bool block_mount;
 extern bool verifier_logs;
 extern bool relaxed_maps;
+extern bool dump_metadata;
 extern struct pinned_obj_table prog_table;
 extern struct pinned_obj_table map_table;
 extern struct pinned_obj_table link_table;
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index d393eb8263a6..5d626c134e7d 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -151,6 +151,130 @@  static void show_prog_maps(int fd, __u32 num_maps)
 	}
 }
 
+static void show_prog_metadata(int fd, __u32 num_maps)
+{
+	const struct btf_type *t_datasec, *t_var;
+	struct bpf_map_info map_info = {};
+	struct btf_var_secinfo *vsi;
+	struct btf *btf = NULL;
+	unsigned int i, vlen;
+	__u32 map_info_len;
+	void *value = NULL;
+	int key = 0;
+	int map_id;
+	int map_fd;
+	int err;
+
+	if (!num_maps)
+		return;
+
+	map_id = bpf_prog_find_metadata(fd);
+	if (map_id < 0)
+		return;
+
+	map_fd = bpf_map_get_fd_by_id(map_id);
+	if (map_fd < 0) {
+		p_err("can't get map by id (%u): %s", map_id, strerror(errno));
+		return;
+	}
+
+	map_info_len = sizeof(map_info);
+	err = bpf_obj_get_info_by_fd(map_fd, &map_info, &map_info_len);
+	if (err) {
+		p_err("can't get map info of id (%u): %s", map_id,
+		      strerror(errno));
+		goto out_close;
+	}
+
+	value = malloc(map_info.value_size);
+	if (!value) {
+		p_err("mem alloc failed");
+		goto out_close;
+	}
+
+	if (bpf_map_lookup_elem(map_fd, &key, value)) {
+		p_err("metadata map lookup failed: %s", strerror(errno));
+		goto out_free;
+	}
+
+	err = btf__get_from_id(map_info.btf_id, &btf);
+	if (err || !btf) {
+		p_err("metadata BTF get failed: %s", strerror(-err));
+		goto out_free;
+	}
+
+	t_datasec = btf__type_by_id(btf, map_info.btf_value_type_id);
+	if (BTF_INFO_KIND(t_datasec->info) != BTF_KIND_DATASEC) {
+		p_err("bad metadata BTF");
+		goto out_free;
+	}
+
+	vlen = BTF_INFO_VLEN(t_datasec->info);
+	vsi = (struct btf_var_secinfo *)(t_datasec + 1);
+
+	/* We don't proceed to check the kinds of the elements of the DATASEC.
+	 * The verifier enforce then to be BTF_KIND_VAR.
+	 */
+
+	if (json_output) {
+		struct btf_dumper d = {
+			.btf = btf,
+			.jw = json_wtr,
+			.is_plain_text = false,
+		};
+
+		jsonw_name(json_wtr, "metadata");
+
+		jsonw_start_object(json_wtr);
+		for (i = 0; i < vlen; i++) {
+			t_var = btf__type_by_id(btf, vsi[i].type);
+
+			jsonw_name(json_wtr, btf__name_by_offset(btf, t_var->name_off));
+			err = btf_dumper_type(&d, t_var->type, value + vsi[i].offset);
+			if (err) {
+				p_err("btf dump failed");
+				break;
+			}
+		}
+		jsonw_end_object(json_wtr);
+	} else {
+		json_writer_t *btf_wtr = jsonw_new(stdout);
+		struct btf_dumper d = {
+			.btf = btf,
+			.jw = btf_wtr,
+			.is_plain_text = true,
+		};
+		if (!btf_wtr) {
+			p_err("jsonw alloc failed");
+			goto out_free;
+		}
+
+		printf("\tmetadata:");
+
+		for (i = 0; i < vlen; i++) {
+			t_var = btf__type_by_id(btf, vsi[i].type);
+
+			printf("\n\t\t%s = ", btf__name_by_offset(btf, t_var->name_off));
+
+			jsonw_reset(btf_wtr);
+			err = btf_dumper_type(&d, t_var->type, value + vsi[i].offset);
+			if (err) {
+				p_err("btf dump failed");
+				break;
+			}
+		}
+
+		jsonw_destroy(&btf_wtr);
+	}
+
+out_free:
+	btf__free(btf);
+	free(value);
+
+out_close:
+	close(map_fd);
+}
+
 static void print_prog_header_json(struct bpf_prog_info *info)
 {
 	jsonw_uint_field(json_wtr, "id", info->id);
@@ -228,6 +352,9 @@  static void print_prog_json(struct bpf_prog_info *info, int fd)
 
 	emit_obj_refs_json(&refs_table, info->id, json_wtr);
 
+	if (dump_metadata)
+		show_prog_metadata(fd, info->nr_map_ids);
+
 	jsonw_end_object(json_wtr);
 }
 
@@ -297,6 +424,9 @@  static void print_prog_plain(struct bpf_prog_info *info, int fd)
 	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
+
+	if (dump_metadata)
+		show_prog_metadata(fd, info->nr_map_ids);
 }
 
 static int show_prog(int fd)