[PATCH bpf-next v4 3/8] bpftool: Add gen btf command

["Mauricio Vásquez" <mauricio@kinvolk.io>]

This command is implemented under the "gen" command in bpftool and the
syntax is the following:

$ bpftool gen btf INPUT OUTPUT OBJECT(S)

INPUT can be either a single BTF file or a folder containing BTF files,
when it's a folder, a BTF file is generated for each BTF file contained
in this folder. OUTPUT is the file (or folder) where generated files are
stored and OBJECT(S) is the list of bpf objects we want to generate the
BTF file(s) for (each generated BTF file contains all the types needed
by all the objects).

Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Rafael David Tinoco <rafael.tinoco@aquasec.com>
Signed-off-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
Signed-off-by: Leonardo Di Donato <leonardo.didonato@elastic.co>
---
 tools/bpf/bpftool/gen.c | 117 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 117 insertions(+)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 43e3f8700ecc..cdeb1047d79d 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -5,6 +5,7 @@
 #define _GNU_SOURCE
 #endif
 #include <ctype.h>
+#include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/err.h>
@@ -1084,6 +1085,7 @@ static int do_help(int argc, char **argv)
 	fprintf(stderr,
 		"Usage: %1$s %2$s object OUTPUT_FILE INPUT_FILE [INPUT_FILE...]\n"
 		"       %1$s %2$s skeleton FILE [name OBJECT_NAME]\n"
+		"       %1$s %2$s btf INPUT OUTPUT OBJECT(S)\n"
 		"       %1$s %2$s help\n"
 		"\n"
 		"       " HELP_SPEC_OPTIONS " |\n"
@@ -1094,9 +1096,124 @@ static int do_help(int argc, char **argv)
 	return 0;
 }
 
+/* Create BTF file for a set of BPF objects */
+static int btfgen(const char *src_btf, const char *dst_btf, const char *objspaths[])
+{
+	return -EOPNOTSUPP;
+}
+
+static int is_file(const char *path)
+{
+	struct stat st;
+
+	if (stat(path, &st) < 0)
+		return -1;
+
+	switch (st.st_mode & S_IFMT) {
+	case S_IFDIR:
+		return 0;
+	case S_IFREG:
+		return 1;
+	default:
+		return -1;
+	}
+}
+
+static int do_gen_btf(int argc, char **argv)
+{
+	char src_btf_path[PATH_MAX], dst_btf_path[PATH_MAX];
+	bool input_is_file, output_is_file = false;
+	const char *input, *output;
+	const char **objs = NULL;
+	struct dirent *dir;
+	DIR *d = NULL;
+	int i, err;
+
+	if (!REQ_ARGS(3)) {
+		usage();
+		return -1;
+	}
+
+	input = GET_ARG();
+	err = is_file(input);
+	if (err < 0) {
+		p_err("failed to stat %s: %s", input, strerror(errno));
+		return err;
+	}
+	input_is_file = err;
+
+	output = GET_ARG();
+	err = is_file(output);
+	if (err != 0)
+		output_is_file = true;
+
+	objs = (const char **) malloc((argc + 1) * sizeof(*objs));
+	if (!objs)
+		return -ENOMEM;
+
+	i = 0;
+	while (argc > 0)
+		objs[i++] = GET_ARG();
+
+	objs[i] = NULL;
+
+	/* single BTF file */
+	if (input_is_file) {
+		printf("SBTF: %s\n", input);
+
+		if (output_is_file) {
+			err = btfgen(input, output, objs);
+			goto out;
+		}
+		snprintf(dst_btf_path, sizeof(dst_btf_path), "%s/%s", output,
+			 basename(input));
+		err = btfgen(input, dst_btf_path, objs);
+		goto out;
+	}
+
+	if (output_is_file) {
+		p_err("can't have just one file as output");
+		err = -EINVAL;
+		goto out;
+	}
+
+	/* directory with BTF files */
+	d = opendir(input);
+	if (!d) {
+		p_err("error opening input dir: %s", strerror(errno));
+		err = -errno;
+		goto out;
+	}
+
+	while ((dir = readdir(d)) != NULL) {
+		if (dir->d_type != DT_REG)
+			continue;
+
+		if (strncmp(dir->d_name + strlen(dir->d_name) - 4, ".btf", 4))
+			continue;
+
+		snprintf(src_btf_path, sizeof(src_btf_path), "%s/%s", input, dir->d_name);
+		snprintf(dst_btf_path, sizeof(dst_btf_path), "%s/%s", output, dir->d_name);
+
+		printf("SBTF: %s\n", src_btf_path);
+
+		err = btfgen(src_btf_path, dst_btf_path, objs);
+		if (err)
+			goto out;
+	}
+
+out:
+	if (!err)
+		printf("STAT: done!\n");
+	free(objs);
+	closedir(d);
+	return err;
+}
+
 static const struct cmd cmds[] = {
 	{ "object",	do_object },
 	{ "skeleton",	do_skeleton },
+	{ "btf",	do_gen_btf},
 	{ "help",	do_help },
 	{ 0 }
 };
-- 
2.25.1