bpftool: Switch to libbpf's hashmap for pinned paths of BPF objects

In order to show pinned paths for BPF programs, maps, or links when
listing them with the "-f" option, bpftool creates hash maps to store
all relevant paths under the bpffs. So far, it would rely on the
kernel implementation (from tools/include/linux/hashtable.h).

We can make bpftool rely on libbpf's implementation instead. The
motivation is to make bpftool less dependent of kernel headers, to ease
the path to a potential out-of-tree mirror, like libbpf has.

This commit is the first step of the conversion: the hash maps for
pinned paths for programs, maps, and links are converted to libbpf's
hashmap.{c,h}. Other hash maps used for the PIDs of process holding
references to BPF objects are left unchanged for now. On the build side,
this requires adding a dependency to a second header internal to libbpf,
and making it a dependency for the bootstrap bpftool version as well.
The rest of the changes are a rather straightforward conversion.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211023205154.6710-4-quentin@isovalent.com

Author: qmonnet

tools/bpf/bpftool/Makefile

@@ -31,9 +31,9 @@ LIBBPF = $(LIBBPF_OUTPUT)libbpf.a
 LIBBPF_BOOTSTRAP_OUTPUT = $(BOOTSTRAP_OUTPUT)libbpf/
 LIBBPF_BOOTSTRAP = $(LIBBPF_BOOTSTRAP_OUTPUT)libbpf.a
 
-# We need to copy nlattr.h which is not otherwise exported by libbpf, but still
-# required by bpftool.
-LIBBPF_INTERNAL_HDRS := $(addprefix $(LIBBPF_HDRS_DIR)/,nlattr.h)
+# We need to copy hashmap.h and nlattr.h which is not otherwise exported by
+# libbpf, but still required by bpftool.
+LIBBPF_INTERNAL_HDRS := $(addprefix $(LIBBPF_HDRS_DIR)/,hashmap.h nlattr.h)
 
 ifeq ($(BPFTOOL_VERSION),)
 BPFTOOL_VERSION := $(shell make -rR --no-print-directory -sC ../../.. kernelversion)
@@ -209,7 +209,7 @@ $(BPFTOOL_BOOTSTRAP): $(BOOTSTRAP_OBJS) $(LIBBPF_BOOTSTRAP)
 $(OUTPUT)bpftool: $(OBJS) $(LIBBPF)
 	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(OBJS) $(LIBS)
 
-$(BOOTSTRAP_OUTPUT)%.o: %.c | $(BOOTSTRAP_OUTPUT)
+$(BOOTSTRAP_OUTPUT)%.o: %.c $(LIBBPF_INTERNAL_HDRS) | $(BOOTSTRAP_OUTPUT)
 	$(QUIET_CC)$(HOSTCC) $(CFLAGS) -c -MMD -o $@ $<
 
 $(OUTPUT)%.o: %.c

tools/bpf/bpftool/common.c

@@ -22,6 +22,7 @@
 #include <sys/vfs.h>
 
 #include <bpf/bpf.h>
+#include <bpf/hashmap.h>
 #include <bpf/libbpf.h> /* libbpf_num_possible_cpus */
 
 #include "main.h"
@@ -393,17 +394,17 @@ void print_hex_data_json(uint8_t *data, size_t len)
 }
 
 /* extra params for nftw cb */
-static struct pinned_obj_table *build_fn_table;
+static struct hashmap *build_fn_table;
 static enum bpf_obj_type build_fn_type;
 
 static int do_build_table_cb(const char *fpath, const struct stat *sb,
 			     int typeflag, struct FTW *ftwbuf)
 {
 	struct bpf_prog_info pinned_info;
 	__u32 len = sizeof(pinned_info);
-	struct pinned_obj *obj_node;
 	enum bpf_obj_type objtype;
 	int fd, err = 0;
+	char *path;
 
 	if (typeflag != FTW_F)
 		goto out_ret;
@@ -420,28 +421,26 @@ static int do_build_table_cb(const char *fpath, const struct stat *sb,
 	if (bpf_obj_get_info_by_fd(fd, &pinned_info, &len))
 		goto out_close;
 
-	obj_node = calloc(1, sizeof(*obj_node));
-	if (!obj_node) {
+	path = strdup(fpath);
+	if (!path) {
 		err = -1;
 		goto out_close;
 	}
 
-	obj_node->id = pinned_info.id;
-	obj_node->path = strdup(fpath);
-	if (!obj_node->path) {
-		err = -1;
-		free(obj_node);
+	err = hashmap__append(build_fn_table, u32_as_hash_field(pinned_info.id), path);
+	if (err) {
+		p_err("failed to append entry to hashmap for ID %u, path '%s': %s",
+		      pinned_info.id, path, strerror(errno));
 		goto out_close;
 	}
 
-	hash_add(build_fn_table->table, &obj_node->hash, obj_node->id);
 out_close:
 	close(fd);
 out_ret:
 	return err;
 }
 
-int build_pinned_obj_table(struct pinned_obj_table *tab,
+int build_pinned_obj_table(struct hashmap *tab,
 			   enum bpf_obj_type type)
 {
 	struct mntent *mntent = NULL;
@@ -470,17 +469,18 @@ int build_pinned_obj_table(struct pinned_obj_table *tab,
 	return err;
 }
 
-void delete_pinned_obj_table(struct pinned_obj_table *tab)
+void delete_pinned_obj_table(struct hashmap *map)
 {
-	struct pinned_obj *obj;
-	struct hlist_node *tmp;
-	unsigned int bkt;
+	struct hashmap_entry *entry;
+	size_t bkt;
 
-	hash_for_each_safe(tab->table, bkt, tmp, obj, hash) {
-		hash_del(&obj->hash);
-		free(obj->path);
-		free(obj);
-	}
+	if (!map)
+		return;
+
+	hashmap__for_each_entry(map, entry, bkt)
+		free(entry->value);
+
+	hashmap__free(map);
 }
 
 unsigned int get_page_size(void)
@@ -962,3 +962,13 @@ int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len)
 
 	return fd;
 }
+
+size_t hash_fn_for_key_as_id(const void *key, void *ctx)
+{
+	return (size_t)key;
+}
+
+bool equal_fn_for_key_as_id(const void *k1, const void *k2, void *ctx)
+{
+	return k1 == k2;
+}

tools/bpf/bpftool/link.c

@@ -7,6 +7,7 @@
 #include <unistd.h>
 
 #include <bpf/bpf.h>
+#include <bpf/hashmap.h>
 
 #include "json_writer.h"
 #include "main.h"
@@ -20,7 +21,7 @@ static const char * const link_type_name[] = {
 	[BPF_LINK_TYPE_NETNS]			= "netns",
 };
 
-static struct pinned_obj_table link_table;
+static struct hashmap *link_table;
 
 static int link_parse_fd(int *argc, char ***argv)
 {
@@ -158,15 +159,14 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
 		break;
 	}
 
-	if (!hash_empty(link_table.table)) {
-		struct pinned_obj *obj;
+	if (!hashmap__empty(link_table)) {
+		struct hashmap_entry *entry;
 
 		jsonw_name(json_wtr, "pinned");
 		jsonw_start_array(json_wtr);
-		hash_for_each_possible(link_table.table, obj, hash, info->id) {
-			if (obj->id == info->id)
-				jsonw_string(json_wtr, obj->path);
-		}
+		hashmap__for_each_key_entry(link_table, entry,
+					    u32_as_hash_field(info->id))
+			jsonw_string(json_wtr, entry->value);
 		jsonw_end_array(json_wtr);
 	}
 
@@ -246,13 +246,12 @@ static int show_link_close_plain(int fd, struct bpf_link_info *info)
 		break;
 	}
 
-	if (!hash_empty(link_table.table)) {
-		struct pinned_obj *obj;
+	if (!hashmap__empty(link_table)) {
+		struct hashmap_entry *entry;
 
-		hash_for_each_possible(link_table.table, obj, hash, info->id) {
-			if (obj->id == info->id)
-				printf("\n\tpinned %s", obj->path);
-		}
+		hashmap__for_each_key_entry(link_table, entry,
+					    u32_as_hash_field(info->id))
+			printf("\n\tpinned %s", (char *)entry->value);
 	}
 	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
 
@@ -305,8 +304,13 @@ static int do_show(int argc, char **argv)
 	int err, fd;
 
 	if (show_pinned) {
-		hash_init(link_table.table);
-		build_pinned_obj_table(&link_table, BPF_OBJ_LINK);
+		link_table = hashmap__new(hash_fn_for_key_as_id,
+					  equal_fn_for_key_as_id, NULL);
+		if (!link_table) {
+			p_err("failed to create hashmap for pinned paths");
+			return -1;
+		}
+		build_pinned_obj_table(link_table, BPF_OBJ_LINK);
 	}
 	build_obj_refs_table(&refs_table, BPF_OBJ_LINK);
 
@@ -351,7 +355,7 @@ static int do_show(int argc, char **argv)
 	delete_obj_refs_table(&refs_table);
 
 	if (show_pinned)
-		delete_pinned_obj_table(&link_table);
+		delete_pinned_obj_table(link_table);
 
 	return errno == ENOENT ? 0 : -1;
 }

tools/bpf/bpftool/main.h

@@ -14,6 +14,7 @@
 #include <linux/hashtable.h>
 #include <tools/libc_compat.h>
 
+#include <bpf/hashmap.h>
 #include <bpf/libbpf.h>
 
 #include "json_writer.h"
@@ -105,16 +106,6 @@ void set_max_rlimit(void);
 
 int mount_tracefs(const char *target);
 
-struct pinned_obj_table {
-	DECLARE_HASHTABLE(table, 16);
-};
-
-struct pinned_obj {
-	__u32 id;
-	char *path;
-	struct hlist_node hash;
-};
-
 struct obj_refs_table {
 	DECLARE_HASHTABLE(table, 16);
 };
@@ -134,9 +125,9 @@ struct obj_refs {
 struct btf;
 struct bpf_line_info;
 
-int build_pinned_obj_table(struct pinned_obj_table *table,
+int build_pinned_obj_table(struct hashmap *table,
 			   enum bpf_obj_type type);
-void delete_pinned_obj_table(struct pinned_obj_table *tab);
+void delete_pinned_obj_table(struct hashmap *table);
 __weak int build_obj_refs_table(struct obj_refs_table *table,
 				enum bpf_obj_type type);
 __weak void delete_obj_refs_table(struct obj_refs_table *table);
@@ -256,4 +247,18 @@ int do_filter_dump(struct tcmsg *ifinfo, struct nlattr **tb, const char *kind,
 
 int print_all_levels(__maybe_unused enum libbpf_print_level level,
 		     const char *format, va_list args);
+
+size_t hash_fn_for_key_as_id(const void *key, void *ctx);
+bool equal_fn_for_key_as_id(const void *k1, const void *k2, void *ctx);
+
+static inline void *u32_as_hash_field(__u32 x)
+{
+	return (void *)(uintptr_t)x;
+}
+
+static inline bool hashmap__empty(struct hashmap *map)
+{
+	return map ? hashmap__size(map) == 0 : true;
+}
+
 #endif

tools/bpf/bpftool/map.c

@@ -17,6 +17,7 @@
 
 #include <bpf/bpf.h>
 #include <bpf/btf.h>
+#include <bpf/hashmap.h>
 
 #include "json_writer.h"
 #include "main.h"
@@ -56,7 +57,7 @@ const char * const map_type_name[] = {
 
 const size_t map_type_name_size = ARRAY_SIZE(map_type_name);
 
-static struct pinned_obj_table map_table;
+static struct hashmap *map_table;
 
 static bool map_is_per_cpu(__u32 type)
 {
@@ -537,15 +538,14 @@ static int show_map_close_json(int fd, struct bpf_map_info *info)
 	if (info->btf_id)
 		jsonw_int_field(json_wtr, "btf_id", info->btf_id);
 
-	if (!hash_empty(map_table.table)) {
-		struct pinned_obj *obj;
+	if (!hashmap__empty(map_table)) {
+		struct hashmap_entry *entry;
 
 		jsonw_name(json_wtr, "pinned");
 		jsonw_start_array(json_wtr);
-		hash_for_each_possible(map_table.table, obj, hash, info->id) {
-			if (obj->id == info->id)
-				jsonw_string(json_wtr, obj->path);
-		}
+		hashmap__for_each_key_entry(map_table, entry,
+					    u32_as_hash_field(info->id))
+			jsonw_string(json_wtr, entry->value);
 		jsonw_end_array(json_wtr);
 	}
 
@@ -612,13 +612,12 @@ static int show_map_close_plain(int fd, struct bpf_map_info *info)
 	}
 	close(fd);
 
-	if (!hash_empty(map_table.table)) {
-		struct pinned_obj *obj;
+	if (!hashmap__empty(map_table)) {
+		struct hashmap_entry *entry;
 
-		hash_for_each_possible(map_table.table, obj, hash, info->id) {
-			if (obj->id == info->id)
-				printf("\n\tpinned %s", obj->path);
-		}
+		hashmap__for_each_key_entry(map_table, entry,
+					    u32_as_hash_field(info->id))
+			printf("\n\tpinned %s", (char *)entry->value);
 	}
 	printf("\n");
 
@@ -697,8 +696,13 @@ static int do_show(int argc, char **argv)
 	int fd;
 
 	if (show_pinned) {
-		hash_init(map_table.table);
-		build_pinned_obj_table(&map_table, BPF_OBJ_MAP);
+		map_table = hashmap__new(hash_fn_for_key_as_id,
+					 equal_fn_for_key_as_id, NULL);
+		if (!map_table) {
+			p_err("failed to create hashmap for pinned paths");
+			return -1;
+		}
+		build_pinned_obj_table(map_table, BPF_OBJ_MAP);
 	}
 	build_obj_refs_table(&refs_table, BPF_OBJ_MAP);
 
@@ -747,7 +751,7 @@ static int do_show(int argc, char **argv)
 	delete_obj_refs_table(&refs_table);
 
 	if (show_pinned)
-		delete_pinned_obj_table(&map_table);
+		delete_pinned_obj_table(map_table);
 
 	return errno == ENOENT ? 0 : -1;
 }