Merge branch 'libbpf-support-more-map-options'

Craig Gallek says:

====================
libbpf: support more map options

The functional change to this series is the ability to use flags when
creating maps from object files loaded by libbpf.  In order to do this,
the first patch updates the library to handle map definitions that
differ in size from libbpf's struct bpf_map_def.

For object files with a larger map definition, libbpf will continue to load
if the unknown fields are all zero, otherwise the map is rejected.  If the
map definition in the object file is smaller than expected, libbpf will use
zero as a default value in the missing fields.
====================

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 43 insertions, 30 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 4f402dcdf372..5aa45f89da93 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -579,31 +579,6 @@ bpf_object__init_kversion(struct bpf_object *obj,
 	return 0;
 }
 
-static int
-bpf_object__validate_maps(struct bpf_object *obj)
-{
-	int i;
-
-	/*
-	 * If there's only 1 map, the only error case should have been
-	 * catched in bpf_object__init_maps().
-	 */
-	if (!obj->maps || !obj->nr_maps || (obj->nr_maps == 1))
-		return 0;
-
-	for (i = 1; i < obj->nr_maps; i++) {
-		const struct bpf_map *a = &obj->maps[i - 1];
-		const struct bpf_map *b = &obj->maps[i];
-
-		if (b->offset - a->offset < sizeof(struct bpf_map_def)) {
-			pr_warning("corrupted map section in %s: map \"%s\" too small\n",
-				   obj->path, a->name);
-			return -EINVAL;
-		}
-	}
-	return 0;
-}
-
 static int compare_bpf_map(const void *_a, const void *_b)
 {
 	const struct bpf_map *a = _a;
@@ -615,7 +590,7 @@ static int compare_bpf_map(const void *_a, const void *_b)
 static int
 bpf_object__init_maps(struct bpf_object *obj)
 {
-	int i, map_idx, nr_maps = 0;
+	int i, map_idx, map_def_sz, nr_maps = 0;
 	Elf_Scn *scn;
 	Elf_Data *data;
 	Elf_Data *symbols = obj->efile.symbols;
@@ -658,6 +633,15 @@ bpf_object__init_maps(struct bpf_object *obj)
 	if (!nr_maps)
 		return 0;
 
+	/* Assume equally sized map definitions */
+	map_def_sz = data->d_size / nr_maps;
+	if (!data->d_size || (data->d_size % nr_maps) != 0) {
+		pr_warning("unable to determine map definition size "
+			   "section %s, %d maps in %zd bytes\n",
+			   obj->path, nr_maps, data->d_size);
+		return -EINVAL;
+	}
+
 	obj->maps = calloc(nr_maps, sizeof(obj->maps[0]));
 	if (!obj->maps) {
 		pr_warning("alloc maps for object failed\n");
@@ -690,7 +674,7 @@ bpf_object__init_maps(struct bpf_object *obj)
 				      obj->efile.strtabidx,
 				      sym.st_name);
 		obj->maps[map_idx].offset = sym.st_value;
-		if (sym.st_value + sizeof(struct bpf_map_def) > data->d_size) {
+		if (sym.st_value + map_def_sz > data->d_size) {
 			pr_warning("corrupted maps section in %s: last map \"%s\" too small\n",
 				   obj->path, map_name);
 			return -EINVAL;
@@ -704,12 +688,40 @@ bpf_object__init_maps(struct bpf_object *obj)
 		pr_debug("map %d is \"%s\"\n", map_idx,
 			 obj->maps[map_idx].name);
 		def = (struct bpf_map_def *)(data->d_buf + sym.st_value);
-		obj->maps[map_idx].def = *def;
+		/*
+		 * If the definition of the map in the object file fits in
+		 * bpf_map_def, copy it.  Any extra fields in our version
+		 * of bpf_map_def will default to zero as a result of the
+		 * calloc above.
+		 */
+		if (map_def_sz <= sizeof(struct bpf_map_def)) {
+			memcpy(&obj->maps[map_idx].def, def, map_def_sz);
+		} else {
+			/*
+			 * Here the map structure being read is bigger than what
+			 * we expect, truncate if the excess bits are all zero.
+			 * If they are not zero, reject this map as
+			 * incompatible.
+			 */
+			char *b;
+			for (b = ((char *)def) + sizeof(struct bpf_map_def);
+			     b < ((char *)def) + map_def_sz; b++) {
+				if (*b != 0) {
+					pr_warning("maps section in %s: \"%s\" "
+						   "has unrecognized, non-zero "
+						   "options\n",
+						   obj->path, map_name);
+					return -EINVAL;
+				}
+			}
+			memcpy(&obj->maps[map_idx].def, def,
+			       sizeof(struct bpf_map_def));
+		}
 		map_idx++;
 	}
 
 	qsort(obj->maps, obj->nr_maps, sizeof(obj->maps[0]), compare_bpf_map);
-	return bpf_object__validate_maps(obj);
+	return 0;
 }
 
 static int bpf_object__elf_collect(struct bpf_object *obj)
@@ -930,7 +942,7 @@ bpf_object__create_maps(struct bpf_object *obj)
 					   def->key_size,
 					   def->value_size,
 					   def->max_entries,
-					   0);
+					   def->map_flags);
 		if (*pfd < 0) {
 			size_t j;
 			int err = *pfd;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 7959086eb9c9..6e20003109e0 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -207,6 +207,7 @@ struct bpf_map_def {
 	unsigned int key_size;
 	unsigned int value_size;
 	unsigned int max_entries;
+	unsigned int map_flags;
 };
 
 /*