Subject: [PATCH bpf-next v1 02/19] bpf: implement an interface to register bpf_iter targets

From: Yonghong Song <[email-masked]>
Date: Mon, 27 Apr 2020 13:12:36 -0700

The target can call bpf_iter_reg_target() to register itself.
The needed information:
  target:           target name, reprsented as a directory hierarchy
  target_func_name: the kernel func name used by verifier to
                    verify bpf programs
  seq_ops:          the seq_file operations for the target
  seq_priv_size:    the private_data size needed by the seq_file
                    operations
  target_feature:   certain feature requested by the target for
                    bpf_iter to prepare for seq_file operations.

A little bit more explanations on the target name and target_feature.
For example, the target name can be "bpf_map", "task", "task/file",
which represents iterating all bpf_map's, all tasks, or all files
of all tasks.

The target feature is mostly for reusing existing seq_file operations.
For example, /proc/net/{tcp6, ipv6_route, netlink, ...} seq_file private
data contains a reference to net namespace. When bpf_iter tries to
reuse the same seq_ops, its seq_file private data need the net namespace
setup properly too. In this case, the bpf_iter infrastructure can help
set up properly before doing seq_file operations.

Signed-off-by: Yonghong Song <[email-masked]>
---
 include/linux/bpf.h   | 11 ++++++++++
 kernel/bpf/Makefile   |  2 +-
 kernel/bpf/bpf_iter.c | 50 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 kernel/bpf/bpf_iter.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 10960cfabea4..5e56abc1e2f1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -31,6 +31,7 @@ struct seq_file;
 struct btf;
 struct btf_type;
 struct exception_table_entry;
+struct seq_operations;
 
 extern struct idr btf_idr;
 extern spinlock_t btf_idr_lock;
@@ -1109,6 +1110,16 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd);
 int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
 int bpf_obj_get_user(const char __user *pathname, int flags);
 
+struct bpf_iter_reg {
+	const char *target;
+	const char *target_func_name;
+	const struct seq_operations *seq_ops;
+	u32 seq_priv_size;
+	u32 target_feature;
+};
+
+int bpf_iter_reg_target(struct bpf_iter_reg *reg_info);
+
 int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
 int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
 int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index f2d7be596966..6a8b0febd3f6 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -2,7 +2,7 @@
 obj-y := core.o
 CFLAGS_core.o += $(call cc-disable-warning, override-init)
 
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_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
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
new file mode 100644
index 000000000000..1115b978607a
--- /dev/null
+++ b/kernel/bpf/bpf_iter.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+
+#include <linux/fs.h>
+#include <linux/filter.h>
+#include <linux/bpf.h>
+
+struct bpf_iter_target_info {
+	struct list_head list;
+	const char *target;
+	const char *target_func_name;
+	const struct seq_operations *seq_ops;
+	u32 seq_priv_size;
+	u32 target_feature;
+};
+
+static struct list_head targets;
+static struct mutex targets_mutex;
+static bool bpf_iter_inited = false;
+
+int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
+{
+	struct bpf_iter_target_info *tinfo;
+
+	/* The earliest bpf_iter_reg_target() is called at init time
+	 * where the bpf_iter registration is serialized.
+	 */
+	if (!bpf_iter_inited) {
+		INIT_LIST_HEAD(&targets);
+		mutex_init(&targets_mutex);
+		bpf_iter_inited = true;
+	}
+
+	tinfo = kmalloc(sizeof(*tinfo), GFP_KERNEL);
+	if (!tinfo)
+		return -ENOMEM;
+
+	tinfo->target = reg_info->target;
+	tinfo->target_func_name = reg_info->target_func_name;
+	tinfo->seq_ops = reg_info->seq_ops;
+	tinfo->seq_priv_size = reg_info->seq_priv_size;
+	tinfo->target_feature = reg_info->target_feature;
+	INIT_LIST_HEAD(&tinfo->list);
+
+	mutex_lock(&targets_mutex);
+	list_add(&tinfo->list, &targets);
+	mutex_unlock(&targets_mutex);
+
+	return 0;
+}
-- 
2.24.1