bpftool: Add support for custom BTF path in prog load/loadall

This patch exposes the btf_custom_path feature to bpftool, allowing users
to specify a custom BTF file when loading BPF programs using prog load or
prog loadall commands. This feature is already supported by libbpf, and
this patch makes it accessible through the bpftool command-line interface.

Signed-off-by: Jiayuan Chen <[email protected]>

Author: mrpre

tools/bpf/bpftool/prog.c

@@ -1681,8 +1681,17 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 		} else if (is_prefix(*argv, "autoattach")) {
 			auto_attach = true;
 			NEXT_ARG();
+		} else if (is_prefix(*argv, "custom_btf")) {
+			NEXT_ARG();
+
+			if (!REQ_ARGS(1))
+				goto err_free_reuse_maps;
+
+			open_opts.btf_custom_path = GET_ARG();
 		} else {
-			p_err("expected no more arguments, 'type', 'map' or 'dev', got: '%s'?",
+			p_err("expected no more arguments, "
+			      "'type', 'map', 'dev', 'offload_dev', 'xdpmeta_dev', 'pinmaps', "
+			      "'autoattach', or 'custom_btf', got: '%s'?",
 			      *argv);
 			goto err_free_reuse_maps;
 		}