bpf: Add bpf_map iterator

Implement seq_file operations to traverse all bpf_maps.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200509175909.2476096-1-yhs@fb.com

include/linux/bpf.h

@@ -1082,6 +1082,7 @@ int  generic_map_update_batch(struct bpf_map *map,
 int  generic_map_delete_batch(struct bpf_map *map,
 			      const union bpf_attr *attr,
 			      union bpf_attr __user *uattr);
+struct bpf_map *bpf_map_get_curr_or_next(u32 *id);
 
 extern int sysctl_unprivileged_bpf_disabled;
 

kernel/bpf/Makefile

@@ -2,7 +2,7 @@
 obj-y := core.o
 CFLAGS_core.o += $(call cc-disable-warning, override-init)
 
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o
 obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o

kernel/bpf/map_iter.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#include <linux/bpf.h>
+#include <linux/fs.h>
+#include <linux/filter.h>
+#include <linux/kernel.h>
+
+struct bpf_iter_seq_map_info {
+	u32 mid;
+};
+
+static void *bpf_map_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct bpf_iter_seq_map_info *info = seq->private;
+	struct bpf_map *map;
+
+	map = bpf_map_get_curr_or_next(&info->mid);
+	if (!map)
+		return NULL;
+
+	++*pos;
+	return map;
+}
+
+static void *bpf_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct bpf_iter_seq_map_info *info = seq->private;
+	struct bpf_map *map;
+
+	++*pos;
+	++info->mid;
+	bpf_map_put((struct bpf_map *)v);
+	map = bpf_map_get_curr_or_next(&info->mid);
+	if (!map)
+		return NULL;
+
+	return map;
+}
+
+struct bpf_iter__bpf_map {
+	__bpf_md_ptr(struct bpf_iter_meta *, meta);
+	__bpf_md_ptr(struct bpf_map *, map);
+};
+
+DEFINE_BPF_ITER_FUNC(bpf_map, struct bpf_iter_meta *meta, struct bpf_map *map)
+
+static int __bpf_map_seq_show(struct seq_file *seq, void *v, bool in_stop)
+{
+	struct bpf_iter__bpf_map ctx;
+	struct bpf_iter_meta meta;
+	struct bpf_prog *prog;
+	int ret = 0;
+
+	ctx.meta = &meta;
+	ctx.map = v;
+	meta.seq = seq;
+	prog = bpf_iter_get_info(&meta, in_stop);
+	if (prog)
+		ret = bpf_iter_run_prog(prog, &ctx);
+
+	return ret;
+}
+
+static int bpf_map_seq_show(struct seq_file *seq, void *v)
+{
+	return __bpf_map_seq_show(seq, v, false);
+}
+
+static void bpf_map_seq_stop(struct seq_file *seq, void *v)
+{
+	if (!v)
+		(void)__bpf_map_seq_show(seq, v, true);
+	else
+		bpf_map_put((struct bpf_map *)v);
+}
+
+static const struct seq_operations bpf_map_seq_ops = {
+	.start	= bpf_map_seq_start,
+	.next	= bpf_map_seq_next,
+	.stop	= bpf_map_seq_stop,
+	.show	= bpf_map_seq_show,
+};
+
+static int __init bpf_map_iter_init(void)
+{
+	struct bpf_iter_reg reg_info = {
+		.target			= "bpf_map",
+		.seq_ops		= &bpf_map_seq_ops,
+		.init_seq_private	= NULL,
+		.fini_seq_private	= NULL,
+		.seq_priv_size		= sizeof(struct bpf_iter_seq_map_info),
+	};
+
+	return bpf_iter_reg_target(&reg_info);
+}
+
+late_initcall(bpf_map_iter_init);

kernel/bpf/syscall.c

@@ -2934,6 +2934,25 @@ static int bpf_obj_get_next_id(const union bpf_attr *attr,
 	return err;
 }
 
+struct bpf_map *bpf_map_get_curr_or_next(u32 *id)
+{
+	struct bpf_map *map;
+
+	spin_lock_bh(&map_idr_lock);
+again:
+	map = idr_get_next(&map_idr, id);
+	if (map) {
+		map = __bpf_map_inc_not_zero(map, false);
+		if (IS_ERR(map)) {
+			(*id)++;
+			goto again;
+		}
+	}
+	spin_unlock_bh(&map_idr_lock);
+
+	return map;
+}
+
 #define BPF_PROG_GET_FD_BY_ID_LAST_FIELD prog_id
 
 struct bpf_prog *bpf_prog_by_id(u32 id)