[PATCH bpf-next] bpftool: Add "bootstrap" feature to version output

Quentin Monnet
2022-10-20T10:03:44Z

Along with the version number, "bpftool version" displays a list of
features that were selected at compilation time for bpftool. It would be
useful to indicate in that list whether a binary is a bootstrap version
of bpftool. Given that an increasing number of components rely on
bootstrap versions for generating skeletons, this could help understand
what a binary is capable of if it has been copied outside of the usual
"bootstrap" directory.

To detect a bootstrap version, we simply rely on the absence of
implementation for the do_prog() function. To do this, we must move the
(unchanged) list of commands before do_version(), which in turn requires
renaming this "cmds" array to avoid shadowing it with the "cmds"
argument in cmd_select().

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
---
tools/bpf/bpftool/main.c | 81 ++++++++++++++++++++++++----------------
1 file changed, 49 insertions(+), 32 deletions(-)

diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 8bf3615f684f..b22223df4431 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -71,6 +71,27 @@ static int do_help(int argc, char **argv)
return 0;
}

+static int do_batch(int argc, char **argv);
+static int do_version(int argc, char **argv);
+
+static const struct cmd commands[] = {
+ { "help", do_help },
+ { "batch", do_batch },
+ { "prog", do_prog },
+ { "map", do_map },
+ { "link", do_link },
+ { "cgroup", do_cgroup },
+ { "perf", do_perf },
+ { "net", do_net },
+ { "feature", do_feature },
+ { "btf", do_btf },
+ { "gen", do_gen },
+ { "struct_ops", do_struct_ops },
+ { "iter", do_iter },
+ { "version", do_version },
+ { 0 }
+};
+
#ifndef BPFTOOL_VERSION
/* bpftool's major and minor version numbers are aligned on libbpf's. There is
* an offset of 6 for the version number, because bpftool's version was higher
@@ -82,6 +103,15 @@ static int do_help(int argc, char **argv)
#define BPFTOOL_PATCH_VERSION 0
#endif

+static void
+print_feature(const char *feature, bool state, unsigned int *nb_features)
+{
+ if (state) {
+ printf("%s %s", *nb_features ? "," : "", feature);
+ *nb_features = *nb_features + 1;
+ }
+}
+
static int do_version(int argc, char **argv)
{
#ifdef HAVE_LIBBFD_SUPPORT
@@ -94,6 +124,18 @@ static int do_version(int argc, char **argv)
#else
const bool has_skeletons = true;
#endif
+ bool bootstrap = false;
+ int i;
+
+ for (i = 0; commands[i].cmd; i++) {
+ if (!strcmp(commands[i].cmd, "prog")) {
+ /* Assume we run a bootstrap version if "bpftool prog"
+ * is not available.
+ */
+ bootstrap = !commands[i].func;
+ break;
+ }
+ }

if (json_output) {
jsonw_start_object(json_wtr); /* root object */
@@ -114,6 +156,7 @@ static int do_version(int argc, char **argv)
jsonw_bool_field(json_wtr, "libbfd", has_libbfd);
jsonw_bool_field(json_wtr, "libbpf_strict", !legacy_libbpf);
jsonw_bool_field(json_wtr, "skeletons", has_skeletons);
+ jsonw_bool_field(json_wtr, "bootstrap", bootstrap);
jsonw_end_object(json_wtr); /* features */

jsonw_end_object(json_wtr); /* root object */
@@ -128,16 +171,10 @@ static int do_version(int argc, char **argv)
#endif
printf("using libbpf %s\n", libbpf_version_string());
printf("features:");
- if (has_libbfd) {
- printf(" libbfd");
- nb_features++;
- }
- if (!legacy_libbpf) {
- printf("%s libbpf_strict", nb_features++ ? "," : "");
- nb_features++;
- }
- if (has_skeletons)
- printf("%s skeletons", nb_features++ ? "," : "");
+ print_feature("libbfd", has_libbfd, &nb_features);
+ print_feature("libbpf_strict", !legacy_libbpf, &nb_features);
+ print_feature("skeletons", has_skeletons, &nb_features);
+ print_feature("bootstrap", bootstrap, &nb_features);
printf("\n");
}
return 0;
@@ -279,26 +316,6 @@ static int make_args(char *line, char *n_argv[], int maxargs, int cmd_nb)
return n_argc;
}

-static int do_batch(int argc, char **argv);
-
-static const struct cmd cmds[] = {
- { "help", do_help },
- { "batch", do_batch },
- { "prog", do_prog },
- { "map", do_map },
- { "link", do_link },
- { "cgroup", do_cgroup },
- { "perf", do_perf },
- { "net", do_net },
- { "feature", do_feature },
- { "btf", do_btf },
- { "gen", do_gen },
- { "struct_ops", do_struct_ops },
- { "iter", do_iter },
- { "version", do_version },
- { 0 }
-};
-
static int do_batch(int argc, char **argv)
{
char buf[BATCH_LINE_LEN_MAX], contline[BATCH_LINE_LEN_MAX];
@@ -386,7 +403,7 @@ static int do_batch(int argc, char **argv)
jsonw_name(json_wtr, "output");
}

- err = cmd_select(cmds, n_argc, n_argv, do_help);
+ err = cmd_select(commands, n_argc, n_argv, do_help);

if (json_output)
jsonw_end_object(json_wtr);
@@ -528,7 +545,7 @@ int main(int argc, char **argv)
if (version_requested)
return do_version(argc, argv);

- ret = cmd_select(cmds, argc, argv, do_help);
+ ret = cmd_select(commands, argc, argv, do_help);

if (json_output)
jsonw_destroy(&json_wtr);
--
2.34.1