tools: bpftool: add -d option to get debug output from libbpf

libbpf has three levels of priority for output messages: warn, info,
debug. By default, debug output is not printed to the console.

Add a new "--debug" (short name: "-d") option to bpftool to print libbpf
logs for all three levels.

Internally, we simply use the function provided by libbpf to replace the
default printing function by one that prints logs regardless of their
level.

v2:
- Remove the possibility to select the log-levels to use (v1 offered a
  combination of "warn", "info" and "debug").
- Rename option and offer a short name: -d|--debug.
- Add option description to all bpftool manual pages (instead of
  bpftool-prog.rst only), as all commands use libbpf.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/Documentation/bpftool-btf.rst

@@ -72,6 +72,10 @@ OPTIONS
 	-p, --pretty
 		  Generate human-readable JSON output. Implies **-j**.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
 EXAMPLES
 ========
 **# bpftool btf dump id 1226**

tools/bpf/bpftool/Documentation/bpftool-cgroup.rst

@@ -113,6 +113,10 @@ OPTIONS
 	-f, --bpffs
 		  Show file names of pinned programs.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
 EXAMPLES
 ========
 |

tools/bpf/bpftool/Documentation/bpftool-feature.rst

@@ -73,6 +73,10 @@ OPTIONS
 	-p, --pretty
 		  Generate human-readable JSON output. Implies **-j**.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
 SEE ALSO
 ========
 	**bpf**\ (2),

tools/bpf/bpftool/Documentation/bpftool-map.rst

@@ -152,6 +152,10 @@ OPTIONS
 		  Do not automatically attempt to mount any virtual file system
 		  (such as tracefs or BPF virtual file system) when necessary.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
 EXAMPLES
 ========
 **# bpftool map show**

tools/bpf/bpftool/Documentation/bpftool-net.rst

@@ -65,6 +65,10 @@ OPTIONS
 	-p, --pretty
 		  Generate human-readable JSON output. Implies **-j**.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
 EXAMPLES
 ========
 

tools/bpf/bpftool/Documentation/bpftool-perf.rst

@@ -53,6 +53,10 @@ OPTIONS
 	-p, --pretty
 		  Generate human-readable JSON output. Implies **-j**.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
 EXAMPLES
 ========
 

tools/bpf/bpftool/Documentation/bpftool-prog.rst

@@ -174,6 +174,10 @@ OPTIONS
 		  Do not automatically attempt to mount any virtual file system
 		  (such as tracefs or BPF virtual file system) when necessary.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
 EXAMPLES
 ========
 **# bpftool prog show**

tools/bpf/bpftool/Documentation/bpftool.rst

@@ -66,6 +66,9 @@ OPTIONS
 		  Do not automatically attempt to mount any virtual file system
 		  (such as tracefs or BPF virtual file system) when necessary.
 
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
 
 SEE ALSO
 ========

tools/bpf/bpftool/bash-completion/bpftool

@@ -187,7 +187,7 @@ _bpftool()
 
     # Deal with options
     if [[ ${words[cword]} == -* ]]; then
-        local c='--version --json --pretty --bpffs --mapcompat'
+        local c='--version --json --pretty --bpffs --mapcompat --debug'
         COMPREPLY=( $( compgen -W "$c" -- "$cur" ) )
         return 0
     fi

tools/bpf/bpftool/main.c

@@ -10,6 +10,7 @@
 #include <string.h>
 
 #include <bpf.h>
+#include <libbpf.h>
 
 #include "main.h"
 
@@ -77,6 +78,13 @@ static int do_version(int argc, char **argv)
 	return 0;
 }
 
+static int __printf(2, 0)
+print_all_levels(__maybe_unused enum libbpf_print_level level,
+		 const char *format, va_list args)
+{
+	return vfprintf(stderr, format, args);
+}
+
 int cmd_select(const struct cmd *cmds, int argc, char **argv,
 	       int (*help)(int argc, char **argv))
 {
@@ -317,6 +325,7 @@ int main(int argc, char **argv)
 		{ "bpffs",	no_argument,	NULL,	'f' },
 		{ "mapcompat",	no_argument,	NULL,	'm' },
 		{ "nomount",	no_argument,	NULL,	'n' },
+		{ "debug",	no_argument,	NULL,	'd' },
 		{ 0 }
 	};
 	int opt, ret;
@@ -332,7 +341,7 @@ int main(int argc, char **argv)
 	hash_init(map_table.table);
 
 	opterr = 0;
-	while ((opt = getopt_long(argc, argv, "Vhpjfmn",
+	while ((opt = getopt_long(argc, argv, "Vhpjfmnd",
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
@@ -362,6 +371,9 @@ int main(int argc, char **argv)
 		case 'n':
 			block_mount = true;
 			break;
+		case 'd':
+			libbpf_set_print(print_all_levels);
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)