bpf: bpftool, add flag to allow non-compat map definitions

Multiple map definition structures exist and user may have non-zero
fields in their definition that are not recognized by bpftool and
libbpf. The normal behavior is to then fail loading the map. Although
this is a good default behavior users may still want to load the map
for debugging or other reasons. This patch adds a --mapcompat flag
that can be used to override the default behavior and allow loading
the map even when it has additional non-zero fields.

For now the only user is 'bpftool prog' we can switch over other
subcommands as needed. The library exposes an API that consumes
a flags field now but I kept the original API around also in case
users of the API don't want to expose this. The flags field is an
int in case we need more control over how the API call handles
errors/features/etc in the future.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/Documentation/bpftool.rst

@@ -57,6 +57,10 @@ OPTIONS
 	-p, --pretty
 		  Generate human-readable JSON output. Implies **-j**.
 
+	-m, --mapcompat
+		  Allow loading maps with unknown map definitions.
+
+
 SEE ALSO
 ========
 	**bpftool-map**\ (8), **bpftool-prog**\ (8), **bpftool-cgroup**\ (8)

tools/bpf/bpftool/bash-completion/bpftool

@@ -184,7 +184,7 @@ _bpftool()
 
     # Deal with options
     if [[ ${words[cword]} == -* ]]; then
-        local c='--version --json --pretty --bpffs'
+        local c='--version --json --pretty --bpffs --mapcompat'
         COMPREPLY=( $( compgen -W "$c" -- "$cur" ) )
         return 0
     fi

tools/bpf/bpftool/main.c

@@ -55,6 +55,7 @@ json_writer_t *json_wtr;
 bool pretty_output;
 bool json_output;
 bool show_pinned;
+int bpf_flags;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
 
@@ -341,6 +342,7 @@ int main(int argc, char **argv)
 		{ "pretty",	no_argument,	NULL,	'p' },
 		{ "version",	no_argument,	NULL,	'V' },
 		{ "bpffs",	no_argument,	NULL,	'f' },
+		{ "mapcompat",	no_argument,	NULL,	'm' },
 		{ 0 }
 	};
 	int opt, ret;
@@ -355,7 +357,7 @@ int main(int argc, char **argv)
 	hash_init(map_table.table);
 
 	opterr = 0;
-	while ((opt = getopt_long(argc, argv, "Vhpjf",
+	while ((opt = getopt_long(argc, argv, "Vhpjfm",
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
@@ -379,6 +381,9 @@ int main(int argc, char **argv)
 		case 'f':
 			show_pinned = true;
 			break;
+		case 'm':
+			bpf_flags = MAPS_RELAX_COMPAT;
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)

tools/bpf/bpftool/main.h

@@ -74,7 +74,7 @@
 #define HELP_SPEC_PROGRAM						\
 	"PROG := { id PROG_ID | pinned FILE | tag PROG_TAG }"
 #define HELP_SPEC_OPTIONS						\
-	"OPTIONS := { {-j|--json} [{-p|--pretty}] | {-f|--bpffs} }"
+	"OPTIONS := { {-j|--json} [{-p|--pretty}] | {-f|--bpffs} | {-m|--mapcompat}"
 #define HELP_SPEC_MAP							\
 	"MAP := { id MAP_ID | pinned FILE }"
 
@@ -89,6 +89,7 @@ extern const char *bin_name;
 extern json_writer_t *json_wtr;
 extern bool json_output;
 extern bool show_pinned;
+extern int bpf_flags;
 extern struct pinned_obj_table prog_table;
 extern struct pinned_obj_table map_table;
 

tools/bpf/bpftool/prog.c

@@ -908,7 +908,7 @@ static int do_load(int argc, char **argv)
 		}
 	}
 
-	obj = bpf_object__open_xattr(&attr);
+	obj = __bpf_object__open_xattr(&attr, bpf_flags);
 	if (IS_ERR_OR_NULL(obj)) {
 		p_err("failed to open object file");
 		goto err_free_reuse_maps;

tools/lib/bpf/bpf.h

@@ -69,6 +69,9 @@ struct bpf_load_program_attr {
 	__u32 prog_ifindex;
 };
 
+/* Flags to direct loading requirements */
+#define MAPS_RELAX_COMPAT	0x01
+
 /* Recommend log buffer size */
 #define BPF_LOG_BUF_SIZE (256 * 1024)
 int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,

tools/lib/bpf/libbpf.c

@@ -562,8 +562,9 @@ static int compare_bpf_map(const void *_a, const void *_b)
 }
 
 static int
-bpf_object__init_maps(struct bpf_object *obj)
+bpf_object__init_maps(struct bpf_object *obj, int flags)
 {
+	bool strict = !(flags & MAPS_RELAX_COMPAT);
 	int i, map_idx, map_def_sz, nr_maps = 0;
 	Elf_Scn *scn;
 	Elf_Data *data;
@@ -685,7 +686,8 @@ bpf_object__init_maps(struct bpf_object *obj)
 						   "has unrecognized, non-zero "
 						   "options\n",
 						   obj->path, map_name);
-					return -EINVAL;
+					if (strict)
+						return -EINVAL;
 				}
 			}
 			memcpy(&obj->maps[map_idx].def, def,
@@ -716,7 +718,7 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
 	return false;
 }
 
-static int bpf_object__elf_collect(struct bpf_object *obj)
+static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 {
 	Elf *elf = obj->efile.elf;
 	GElf_Ehdr *ep = &obj->efile.ehdr;
@@ -843,7 +845,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 		return LIBBPF_ERRNO__FORMAT;
 	}
 	if (obj->efile.maps_shndx >= 0) {
-		err = bpf_object__init_maps(obj);
+		err = bpf_object__init_maps(obj, flags);
 		if (err)
 			goto out;
 	}
@@ -1515,7 +1517,7 @@ static int bpf_object__validate(struct bpf_object *obj, bool needs_kver)
 
 static struct bpf_object *
 __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz,
-		   bool needs_kver)
+		   bool needs_kver, int flags)
 {
 	struct bpf_object *obj;
 	int err;
@@ -1531,7 +1533,7 @@ __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz,
 
 	CHECK_ERR(bpf_object__elf_init(obj), err, out);
 	CHECK_ERR(bpf_object__check_endianness(obj), err, out);
-	CHECK_ERR(bpf_object__elf_collect(obj), err, out);
+	CHECK_ERR(bpf_object__elf_collect(obj, flags), err, out);
 	CHECK_ERR(bpf_object__collect_reloc(obj), err, out);
 	CHECK_ERR(bpf_object__validate(obj, needs_kver), err, out);
 
@@ -1542,7 +1544,8 @@ out:
 	return ERR_PTR(err);
 }
 
-struct bpf_object *bpf_object__open_xattr(struct bpf_object_open_attr *attr)
+struct bpf_object *__bpf_object__open_xattr(struct bpf_object_open_attr *attr,
+					    int flags)
 {
 	/* param validation */
 	if (!attr->file)
@@ -1551,7 +1554,13 @@ struct bpf_object *bpf_object__open_xattr(struct bpf_object_open_attr *attr)
 	pr_debug("loading %s\n", attr->file);
 
 	return __bpf_object__open(attr->file, NULL, 0,
-				  bpf_prog_type__needs_kver(attr->prog_type));
+				  bpf_prog_type__needs_kver(attr->prog_type),
+				  flags);
+}
+
+struct bpf_object *bpf_object__open_xattr(struct bpf_object_open_attr *attr)
+{
+	return __bpf_object__open_xattr(attr, 0);
 }
 
 struct bpf_object *bpf_object__open(const char *path)
@@ -1584,7 +1593,7 @@ struct bpf_object *bpf_object__open_buffer(void *obj_buf,
 	pr_debug("loading object '%s' from buffer\n",
 		 name);
 
-	return __bpf_object__open(name, obj_buf, obj_buf_sz, true);
+	return __bpf_object__open(name, obj_buf, obj_buf_sz, true, true);
 }
 
 int bpf_object__unload(struct bpf_object *obj)

tools/lib/bpf/libbpf.h

@@ -61,6 +61,8 @@ struct bpf_object_open_attr {
 
 struct bpf_object *bpf_object__open(const char *path);
 struct bpf_object *bpf_object__open_xattr(struct bpf_object_open_attr *attr);
+struct bpf_object *__bpf_object__open_xattr(struct bpf_object_open_attr *attr,
+					    int flags);
 struct bpf_object *bpf_object__open_buffer(void *obj_buf,
 					   size_t obj_buf_sz,
 					   const char *name);