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

1 files changed, 20 insertions, 16 deletions

diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
index a5effb1816b7..404cc5459c6b 100644
--- a/tools/bpf/bpftool/link.c
+++ b/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;
 }