[PATCH bpf-next 1/6] tools: bpftool: add --log-libbpf option to get debug info from libbpf

[Quentin Monnet <quentin.monnet@netronome.com>]

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

Add a new "--log-libbpf LOG_LEVEL" option to bpftool to provide more
flexibility on the log level for libbpf. LOG_LEVEL is a comma-separated
list of levels of log to print ("warn", "info", "debug"). The value
corresponding to the default behaviour would be "warn,info".

Internally, we simply use the function provided by libbpf to replace the
default printing function by one that prints logs for all required
levels.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
---
 .../bpftool/Documentation/bpftool-prog.rst    |  6 ++
 tools/bpf/bpftool/bash-completion/bpftool     | 41 ++++++++++++-
 tools/bpf/bpftool/main.c                      | 61 ++++++++++++++++---
 3 files changed, 100 insertions(+), 8 deletions(-)

diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
index e8118544d118..77d9570488d1 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
@@ -174,6 +174,12 @@ OPTIONS
 		  Do not automatically attempt to mount any virtual file system
 		  (such as tracefs or BPF virtual file system) when necessary.
 
+	--log-libbpf *LOG_LEVEL*
+		  Set the log level for libbpf output when attempting to load
+		  programs. *LOG_LEVEL* must be a comma-separated list of the
+		  levels of information to print, which can be **warn**,
+		  **info** or **debug**. The default is **warn,info**.
+
 EXAMPLES
 ========
 **# bpftool prog show**
diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
index 50e402a5a9c8..a232da1b158d 100644
--- a/tools/bpf/bpftool/bash-completion/bpftool
+++ b/tools/bpf/bpftool/bash-completion/bpftool
@@ -44,6 +44,34 @@ _bpftool_one_of_list()
     COMPREPLY+=( $( compgen -W "$*" -- "$cur" ) )
 }
 
+# Complete a comma-separated list of items. For example:
+#     _bpftool_cslist "abc def ghi"
+# will suggest:
+#     - "abc" and "abc,"        to complete "a"
+#     - "abc,def" and "abc,ghi" to complete "abc,"
+#     - "abc,ghi,def"           to complete "abc,ghi,"
+_bpftool_cslist()
+{
+    local array_arg array_cur array_comp prevsubwords w ifs_back
+    read -r -a array_arg <<< "$*"
+    ifs_back=$IFS
+    IFS="," read -r -a array_cur <<< "$cur"
+    IFS=$ifs_back
+    prevsubwords=${cur%,*}
+    for w in "${array_arg[@]}"; do
+            if [[ ! "$cur" =~ "," ]]; then
+                array_comp+=( "$w" "$w," )
+            elif [[ ! "$cur" =~ "$w," ]]; then
+                if [[ "${#array_arg[@]}" > ${#array_cur[@]} ]]; then
+                    array_comp+=( "$prevsubwords,$w" "$prevsubwords,$w," )
+                else
+                    array_comp+=( "$prevsubwords,$w" )
+                fi
+            fi
+    done
+    COMPREPLY+=( $( compgen -W "${array_comp[*]}" -- "$cur" ) )
+}
+
 _bpftool_get_map_ids()
 {
     COMPREPLY+=( $( compgen -W "$( bpftool -jp map  2>&1 | \
@@ -181,7 +209,7 @@ _bpftool()
 
     # Deal with options
     if [[ ${words[cword]} == -* ]]; then
-        local c='--version --json --pretty --bpffs --mapcompat'
+        local c='--version --json --pretty --bpffs --mapcompat --log-libbpf'
         COMPREPLY=( $( compgen -W "$c" -- "$cur" ) )
         return 0
     fi
@@ -203,12 +231,23 @@ _bpftool()
             COMPREPLY=( $( compgen -W 'file' -- "$cur" ) )
             return 0
             ;;
+        --log-libbpf)
+            _bpftool_cslist 'warn info debug'
+            return 0
+            ;;
     esac
 
     # Remove all options so completions don't have to deal with them.
     local i
     for (( i=1; i < ${#words[@]}; )); do
         if [[ ${words[i]::1} == - ]]; then
+            # Remove arguments for options, if necessary
+            case ${words[i]} in
+                --log-libbpf)
+                    words=( "${words[@]:0:i+1}" "${words[@]:i+2}" )
+                    [[ $i -le $cword ]] && cword=$(( cword - 1 ))
+                    ;;
+            esac
             words=( "${words[@]:0:i}" "${words[@]:i+1}" )
             [[ $i -le $cword ]] && cword=$(( cword - 1 ))
         else
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 1ac1fc520e6a..6318be6feb5c 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -10,6 +10,7 @@
 #include <string.h>
 
 #include <bpf.h>
+#include <libbpf.h>
 
 #include "main.h"
 
@@ -26,6 +27,7 @@ bool json_output;
 bool show_pinned;
 bool block_mount;
 int bpf_flags;
+int log_level_libbpf;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
 
@@ -77,6 +79,46 @@ static int do_version(int argc, char **argv)
 	return 0;
 }
 
+static int __printf(2, 0)
+print_selected_levels(enum libbpf_print_level level, const char *format,
+		      va_list args)
+{
+	if (!(log_level_libbpf & (1 << level)))
+		return 0;
+
+	return vfprintf(stderr, format, args);
+}
+
+static int set_libbpf_loglevel(const char *log_str)
+{
+	char *log_str_cpy, *token;
+
+	log_str_cpy = strdup(log_str);
+	if (!log_str_cpy) {
+		p_err("mem alloc failed");
+		return -1;
+	}
+
+	token = strtok(log_str_cpy, ",");
+	while (token) {
+		if (is_prefix(token, "warn"))
+			log_level_libbpf |= (1 << LIBBPF_WARN);
+		else if (is_prefix(token, "info"))
+			log_level_libbpf |= (1 << LIBBPF_INFO);
+		else if (is_prefix(token, "debug"))
+			log_level_libbpf |= (1 << LIBBPF_DEBUG);
+		else
+			p_info("unrecognized log level for libbpf: %s", token);
+
+		token = strtok(NULL, ",");
+	}
+	free(log_str_cpy);
+
+	libbpf_set_print(print_selected_levels);
+
+	return 0;
+}
+
 int cmd_select(const struct cmd *cmds, int argc, char **argv,
 	       int (*help)(int argc, char **argv))
 {
@@ -310,13 +352,14 @@ static int do_batch(int argc, char **argv)
 int main(int argc, char **argv)
 {
 	static const struct option options[] = {
-		{ "json",	no_argument,	NULL,	'j' },
-		{ "help",	no_argument,	NULL,	'h' },
-		{ "pretty",	no_argument,	NULL,	'p' },
-		{ "version",	no_argument,	NULL,	'V' },
-		{ "bpffs",	no_argument,	NULL,	'f' },
-		{ "mapcompat",	no_argument,	NULL,	'm' },
-		{ "nomount",	no_argument,	NULL,	'n' },
+		{ "json",	no_argument,		NULL,	'j' },
+		{ "help",	no_argument,		NULL,	'h' },
+		{ "pretty",	no_argument,		NULL,	'p' },
+		{ "version",	no_argument,		NULL,	'V' },
+		{ "bpffs",	no_argument,		NULL,	'f' },
+		{ "mapcompat",	no_argument,		NULL,	'm' },
+		{ "nomount",	no_argument,		NULL,	'n' },
+		{ "log-libbpf",	required_argument,	NULL,	'd' },
 		{ 0 }
 	};
 	int opt, ret;
@@ -362,6 +405,10 @@ int main(int argc, char **argv)
 		case 'n':
 			block_mount = true;
 			break;
+		case 'd':
+			if (set_libbpf_loglevel(optarg))
+				return -1;
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)
-- 
2.17.1