bpftool: Switch to libbpf's hashmap for PIDs/names references

In order to show PIDs and names for processes holding references to BPF
programs, maps, links, or BTF objects, bpftool creates hash maps to
store all relevant information. This commit is part of a set that
transitions from the kernel's hash map implementation to the one coming
with libbpf.

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 is the third and final step of the transition, in which we convert
the hash maps used for storing the information about the processes
holding references to BPF objects (programs, maps, links, BTF), and at
last we drop the inclusion of tools/include/linux/hashtable.h.

Note: Checkpatch complains about the use of __weak declarations, and the
missing empty lines after the bunch of empty function declarations when
compiling without the BPF skeletons (none of these were introduced in
this patch). We want to keep things as they are, and the reports should
be safe to ignore.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211023205154.6710-6-quentin@isovalent.com

tools/bpf/bpftool/btf.c

@@ -9,7 +9,6 @@
 #include <string.h>
 #include <unistd.h>
 #include <linux/btf.h>
-#include <linux/hashtable.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 
@@ -797,7 +796,7 @@ show_btf_plain(struct bpf_btf_info *info, int fd,
 		       hash_field_as_u32(entry->value));
 	}
 
-	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
+	emit_obj_refs_plain(refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
 }
@@ -830,7 +829,7 @@ show_btf_json(struct bpf_btf_info *info, int fd,
 	}
 	jsonw_end_array(json_wtr);	/* map_ids */
 
-	emit_obj_refs_json(&refs_table, info->id, json_wtr); /* pids */
+	emit_obj_refs_json(refs_table, info->id, json_wtr); /* pids */
 
 	jsonw_bool_field(json_wtr, "kernel", info->kernel_btf);
 
@@ -961,7 +960,7 @@ static int do_show(int argc, char **argv)
 exit_free:
 	hashmap__free(btf_prog_table);
 	hashmap__free(btf_map_table);
-	delete_obj_refs_table(&refs_table);
+	delete_obj_refs_table(refs_table);
 
 	return err;
 }

tools/bpf/bpftool/link.c

@@ -170,7 +170,7 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
 		jsonw_end_array(json_wtr);
 	}
 
-	emit_obj_refs_json(&refs_table, info->id, json_wtr);
+	emit_obj_refs_json(refs_table, info->id, json_wtr);
 
 	jsonw_end_object(json_wtr);
 
@@ -253,7 +253,7 @@ static int show_link_close_plain(int fd, struct bpf_link_info *info)
 					    u32_as_hash_field(info->id))
 			printf("\n\tpinned %s", (char *)entry->value);
 	}
-	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
+	emit_obj_refs_plain(refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
 
@@ -352,7 +352,7 @@ static int do_show(int argc, char **argv)
 	if (json_output)
 		jsonw_end_array(json_wtr);
 
-	delete_obj_refs_table(&refs_table);
+	delete_obj_refs_table(refs_table);
 
 	if (show_pinned)
 		delete_pinned_obj_table(link_table);

tools/bpf/bpftool/main.c

@@ -10,8 +10,9 @@
 #include <string.h>
 
 #include <bpf/bpf.h>
-#include <bpf/libbpf.h>
 #include <bpf/btf.h>
+#include <bpf/hashmap.h>
+#include <bpf/libbpf.h>
 
 #include "main.h"
 
@@ -31,7 +32,7 @@ bool verifier_logs;
 bool relaxed_maps;
 bool use_loader;
 struct btf *base_btf;
-struct obj_refs_table refs_table;
+struct hashmap *refs_table;
 
 static void __noreturn clean_and_exit(int i)
 {

tools/bpf/bpftool/main.h

@@ -11,7 +11,6 @@
 #include <linux/bpf.h>
 #include <linux/compiler.h>
 #include <linux/kernel.h>
-#include <linux/hashtable.h>
 #include <tools/libc_compat.h>
 
 #include <bpf/hashmap.h>
@@ -92,7 +91,7 @@ extern bool verifier_logs;
 extern bool relaxed_maps;
 extern bool use_loader;
 extern struct btf *base_btf;
-extern struct obj_refs_table refs_table;
+extern struct hashmap *refs_table;
 
 void __printf(1, 2) p_err(const char *fmt, ...);
 void __printf(1, 2) p_info(const char *fmt, ...);
@@ -106,18 +105,12 @@ void set_max_rlimit(void);
 
 int mount_tracefs(const char *target);
 
-struct obj_refs_table {
-	DECLARE_HASHTABLE(table, 16);
-};
-
 struct obj_ref {
 	int pid;
 	char comm[16];
 };
 
 struct obj_refs {
-	struct hlist_node node;
-	__u32 id;
 	int ref_cnt;
 	struct obj_ref *refs;
 };
@@ -128,12 +121,12 @@ struct bpf_line_info;
 int build_pinned_obj_table(struct hashmap *table,
 			   enum bpf_obj_type type);
 void delete_pinned_obj_table(struct hashmap *table);
-__weak int build_obj_refs_table(struct obj_refs_table *table,
+__weak int build_obj_refs_table(struct hashmap **table,
 				enum bpf_obj_type type);
-__weak void delete_obj_refs_table(struct obj_refs_table *table);
-__weak void emit_obj_refs_json(struct obj_refs_table *table, __u32 id,
+__weak void delete_obj_refs_table(struct hashmap *table);
+__weak void emit_obj_refs_json(struct hashmap *table, __u32 id,
 			       json_writer_t *json_wtr);
-__weak void emit_obj_refs_plain(struct obj_refs_table *table, __u32 id,
+__weak void emit_obj_refs_plain(struct hashmap *table, __u32 id,
 				const char *prefix);
 void print_dev_plain(__u32 ifindex, __u64 ns_dev, __u64 ns_inode);
 void print_dev_json(__u32 ifindex, __u64 ns_dev, __u64 ns_inode);

tools/bpf/bpftool/map.c

@@ -549,7 +549,7 @@ static int show_map_close_json(int fd, struct bpf_map_info *info)
 		jsonw_end_array(json_wtr);
 	}
 
-	emit_obj_refs_json(&refs_table, info->id, json_wtr);
+	emit_obj_refs_json(refs_table, info->id, json_wtr);
 
 	jsonw_end_object(json_wtr);
 
@@ -637,7 +637,7 @@ static int show_map_close_plain(int fd, struct bpf_map_info *info)
 	if (frozen)
 		printf("%sfrozen", info->btf_id ? "  " : "");
 
-	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
+	emit_obj_refs_plain(refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
 	return 0;
@@ -748,7 +748,7 @@ static int do_show(int argc, char **argv)
 	if (json_output)
 		jsonw_end_array(json_wtr);
 
-	delete_obj_refs_table(&refs_table);
+	delete_obj_refs_table(refs_table);
 
 	if (show_pinned)
 		delete_pinned_obj_table(map_table);

tools/bpf/bpftool/pids.c

@@ -6,35 +6,37 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+
 #include <bpf/bpf.h>
+#include <bpf/hashmap.h>
 
 #include "main.h"
 #include "skeleton/pid_iter.h"
 
 #ifdef BPFTOOL_WITHOUT_SKELETONS
 
-int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
+int build_obj_refs_table(struct hashmap **map, enum bpf_obj_type type)
 {
 	return -ENOTSUP;
 }
-void delete_obj_refs_table(struct obj_refs_table *table) {}
-void emit_obj_refs_plain(struct obj_refs_table *table, __u32 id, const char *prefix) {}
-void emit_obj_refs_json(struct obj_refs_table *table, __u32 id, json_writer_t *json_writer) {}
+void delete_obj_refs_table(struct hashmap *map) {}
+void emit_obj_refs_plain(struct hashmap *map, __u32 id, const char *prefix) {}
+void emit_obj_refs_json(struct hashmap *map, __u32 id, json_writer_t *json_writer) {}
 
 #else /* BPFTOOL_WITHOUT_SKELETONS */
 
 #include "pid_iter.skel.h"
 
-static void add_ref(struct obj_refs_table *table, struct pid_iter_entry *e)
+static void add_ref(struct hashmap *map, struct pid_iter_entry *e)
 {
+	struct hashmap_entry *entry;
 	struct obj_refs *refs;
 	struct obj_ref *ref;
+	int err, i;
 	void *tmp;
-	int i;
 
-	hash_for_each_possible(table->table, refs, node, e->id) {
-		if (refs->id != e->id)
-			continue;
+	hashmap__for_each_key_entry(map, entry, u32_as_hash_field(e->id)) {
+		refs = entry->value;
 
 		for (i = 0; i < refs->ref_cnt; i++) {
 			if (refs->refs[i].pid == e->pid)
@@ -64,7 +66,6 @@ static void add_ref(struct obj_refs_table *table, struct pid_iter_entry *e)
 		return;
 	}
 
-	refs->id = e->id;
 	refs->refs = malloc(sizeof(*refs->refs));
 	if (!refs->refs) {
 		free(refs);
@@ -76,7 +77,11 @@ static void add_ref(struct obj_refs_table *table, struct pid_iter_entry *e)
 	ref->pid = e->pid;
 	memcpy(ref->comm, e->comm, sizeof(ref->comm));
 	refs->ref_cnt = 1;
-	hash_add(table->table, &refs->node, e->id);
+
+	err = hashmap__append(map, u32_as_hash_field(e->id), refs);
+	if (err)
+		p_err("failed to append entry to hashmap for ID %u: %s",
+		      e->id, strerror(errno));
 }
 
 static int __printf(2, 0)
@@ -87,15 +92,19 @@ libbpf_print_none(__maybe_unused enum libbpf_print_level level,
 	return 0;
 }
 
-int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
+int build_obj_refs_table(struct hashmap **map, enum bpf_obj_type type)
 {
 	struct pid_iter_entry *e;
 	char buf[4096 / sizeof(*e) * sizeof(*e)];
 	struct pid_iter_bpf *skel;
 	int err, ret, fd = -1, i;
 	libbpf_print_fn_t default_print;
 
-	hash_init(table->table);
+	*map = hashmap__new(hash_fn_for_key_as_id, equal_fn_for_key_as_id, NULL);
+	if (!*map) {
+		p_err("failed to create hashmap for PID references");
+		return -1;
+	}
 	set_max_rlimit();
 
 	skel = pid_iter_bpf__open();
@@ -151,7 +160,7 @@ int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
 
 		e = (void *)buf;
 		for (i = 0; i < ret; i++, e++) {
-			add_ref(table, e);
+			add_ref(*map, e);
 		}
 	}
 	err = 0;
@@ -162,39 +171,44 @@ int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
 	return err;
 }
 
-void delete_obj_refs_table(struct obj_refs_table *table)
+void delete_obj_refs_table(struct hashmap *map)
 {
-	struct obj_refs *refs;
-	struct hlist_node *tmp;
-	unsigned int bkt;
+	struct hashmap_entry *entry;
+	size_t bkt;
+
+	if (!map)
+		return;
+
+	hashmap__for_each_entry(map, entry, bkt) {
+		struct obj_refs *refs = entry->value;
 
-	hash_for_each_safe(table->table, bkt, tmp, refs, node) {
-		hash_del(&refs->node);
 		free(refs->refs);
 		free(refs);
 	}
+
+	hashmap__free(map);
 }
 
-void emit_obj_refs_json(struct obj_refs_table *table, __u32 id,
+void emit_obj_refs_json(struct hashmap *map, __u32 id,
 			json_writer_t *json_writer)
 {
-	struct obj_refs *refs;
-	struct obj_ref *ref;
-	int i;
+	struct hashmap_entry *entry;
 
-	if (hash_empty(table->table))
+	if (hashmap__empty(map))
 		return;
 
-	hash_for_each_possible(table->table, refs, node, id) {
-		if (refs->id != id)
-			continue;
+	hashmap__for_each_key_entry(map, entry, u32_as_hash_field(id)) {
+		struct obj_refs *refs = entry->value;
+		int i;
+
 		if (refs->ref_cnt == 0)
 			break;
 
 		jsonw_name(json_writer, "pids");
 		jsonw_start_array(json_writer);
 		for (i = 0; i < refs->ref_cnt; i++) {
-			ref = &refs->refs[i];
+			struct obj_ref *ref = &refs->refs[i];
+
 			jsonw_start_object(json_writer);
 			jsonw_int_field(json_writer, "pid", ref->pid);
 			jsonw_string_field(json_writer, "comm", ref->comm);
@@ -205,24 +219,24 @@ void emit_obj_refs_json(struct obj_refs_table *table, __u32 id,
 	}
 }
 
-void emit_obj_refs_plain(struct obj_refs_table *table, __u32 id, const char *prefix)
+void emit_obj_refs_plain(struct hashmap *map, __u32 id, const char *prefix)
 {
-	struct obj_refs *refs;
-	struct obj_ref *ref;
-	int i;
+	struct hashmap_entry *entry;
 
-	if (hash_empty(table->table))
+	if (hashmap__empty(map))
 		return;
 
-	hash_for_each_possible(table->table, refs, node, id) {
-		if (refs->id != id)
-			continue;
+	hashmap__for_each_key_entry(map, entry, u32_as_hash_field(id)) {
+		struct obj_refs *refs = entry->value;
+		int i;
+
 		if (refs->ref_cnt == 0)
 			break;
 
 		printf("%s", prefix);
 		for (i = 0; i < refs->ref_cnt; i++) {
-			ref = &refs->refs[i];
+			struct obj_ref *ref = &refs->refs[i];
+
 			printf("%s%s(%d)", i == 0 ? "" : ", ", ref->comm, ref->pid);
 		}
 		break;

tools/bpf/bpftool/prog.c

@@ -430,7 +430,7 @@ static void print_prog_json(struct bpf_prog_info *info, int fd)
 		jsonw_end_array(json_wtr);
 	}
 
-	emit_obj_refs_json(&refs_table, info->id, json_wtr);
+	emit_obj_refs_json(refs_table, info->id, json_wtr);
 
 	show_prog_metadata(fd, info->nr_map_ids);
 
@@ -501,7 +501,7 @@ static void print_prog_plain(struct bpf_prog_info *info, int fd)
 	if (info->btf_id)
 		printf("\n\tbtf_id %d", info->btf_id);
 
-	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
+	emit_obj_refs_plain(refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
 
@@ -619,7 +619,7 @@ static int do_show(int argc, char **argv)
 	if (json_output)
 		jsonw_end_array(json_wtr);
 
-	delete_obj_refs_table(&refs_table);
+	delete_obj_refs_table(refs_table);
 
 	if (show_pinned)
 		delete_pinned_obj_table(prog_table);