bpftool: Add ability to specify custom skeleton object name

Add optional name OBJECT_NAME parameter to `gen skeleton` command to override
default object name, normally derived from input file name. This allows much
more flexibility during build time.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-9-andrii@kernel.org

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

@@ -19,7 +19,7 @@ SYNOPSIS
 GEN COMMANDS
 =============
 
-|	**bpftool** **gen skeleton** *FILE*
+|	**bpftool** **gen skeleton** *FILE* [**name** *OBJECT_NAME*]
 |	**bpftool** **gen help**
 
 DESCRIPTION
@@ -75,10 +75,13 @@ DESCRIPTION
 		  specific maps, programs, etc.
 
 		  As part of skeleton, few custom functions are generated.
-		  Each of them is prefixed with object name, derived from
-		  object file name. I.e., if BPF object file name is
-		  **example.o**, BPF object name will be **example**. The
-		  following custom functions are provided in such case:
+		  Each of them is prefixed with object name. Object name can
+		  either be derived from object file name, i.e., if BPF object
+		  file name is **example.o**, BPF object name will be
+		  **example**. Object name can be also specified explicitly
+		  through **name** *OBJECT_NAME* parameter. The following
+		  custom functions are provided (assuming **example** as
+		  the object name):
 
 		  - **example__open** and **example__open_opts**.
 		    These functions are used to instantiate skeleton. It

tools/bpf/bpftool/bash-completion/bpftool

@@ -982,7 +982,16 @@ _bpftool()
         gen)
             case $command in
                 skeleton)
-                    _filedir
+                    case $prev in
+                        $command)
+                            _filedir
+                            return 0
+                            ;;
+                        *)
+                            _bpftool_once_attr 'name'
+                            return 0
+                            ;;
+                    esac
                     ;;
                 *)
                     [[ $prev == $object ]] && \

tools/bpf/bpftool/gen.c

@@ -273,7 +273,7 @@ static int do_skeleton(int argc, char **argv)
 	char header_guard[MAX_OBJ_NAME_LEN + sizeof("__SKEL_H__")];
 	size_t i, map_cnt = 0, prog_cnt = 0, file_sz, mmap_sz;
 	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
-	char obj_name[MAX_OBJ_NAME_LEN], *obj_data;
+	char obj_name[MAX_OBJ_NAME_LEN] = "", *obj_data;
 	struct bpf_object *obj = NULL;
 	const char *file, *ident;
 	struct bpf_program *prog;
@@ -288,6 +288,28 @@ static int do_skeleton(int argc, char **argv)
 	}
 	file = GET_ARG();
 
+	while (argc) {
+		if (!REQ_ARGS(2))
+			return -1;
+
+		if (is_prefix(*argv, "name")) {
+			NEXT_ARG();
+
+			if (obj_name[0] != '\0') {
+				p_err("object name already specified");
+				return -1;
+			}
+
+			strncpy(obj_name, *argv, MAX_OBJ_NAME_LEN - 1);
+			obj_name[MAX_OBJ_NAME_LEN - 1] = '\0';
+		} else {
+			p_err("unknown arg %s", *argv);
+			return -1;
+		}
+
+		NEXT_ARG();
+	}
+
 	if (argc) {
 		p_err("extra unknown arguments");
 		return -1;
@@ -310,7 +332,8 @@ static int do_skeleton(int argc, char **argv)
 		p_err("failed to mmap() %s: %s", file, strerror(errno));
 		goto out;
 	}
-	get_obj_name(obj_name, file);
+	if (obj_name[0] == '\0')
+		get_obj_name(obj_name, file);
 	opts.object_name = obj_name;
 	obj = bpf_object__open_mem(obj_data, file_sz, &opts);
 	if (IS_ERR(obj)) {
@@ -599,7 +622,7 @@ static int do_help(int argc, char **argv)
 	}
 
 	fprintf(stderr,
-		"Usage: %1$s %2$s skeleton FILE\n"
+		"Usage: %1$s %2$s skeleton FILE [name OBJECT_NAME]\n"
 		"       %1$s %2$s help\n"
 		"\n"
 		"       " HELP_SPEC_OPTIONS "\n"