bpf: net: Refactor bpf_iter target registration

Currently bpf_iter_reg_target takes parameters from target
and allocates memory to save them. This is really not
necessary, esp. in the future we may grow information
passed from targets to bpf_iter manager.

The patch refactors the code so target reg_info
becomes static and bpf_iter manager can just take
a reference to it.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200513180219.2949605-1-yhs@fb.com

include/linux/bpf.h

@@ -1153,7 +1153,7 @@ struct bpf_iter_meta {
 	u64 seq_num;
 };
 
-int bpf_iter_reg_target(struct bpf_iter_reg *reg_info);
+int bpf_iter_reg_target(const struct bpf_iter_reg *reg_info);
 void bpf_iter_unreg_target(const char *target);
 bool bpf_iter_prog_supported(struct bpf_prog *prog);
 int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);

kernel/bpf/bpf_iter.c

@@ -8,11 +8,7 @@
 
 struct bpf_iter_target_info {
 	struct list_head list;
-	const char *target;
-	const struct seq_operations *seq_ops;
-	bpf_iter_init_seq_priv_t init_seq_private;
-	bpf_iter_fini_seq_priv_t fini_seq_private;
-	u32 seq_priv_size;
+	const struct bpf_iter_reg *reg_info;
 	u32 btf_id;	/* cached value */
 };
 
@@ -222,8 +218,8 @@ static int iter_release(struct inode *inode, struct file *file)
 	iter_priv = container_of(seq->private, struct bpf_iter_priv_data,
 				 target_private);
 
-	if (iter_priv->tinfo->fini_seq_private)
-		iter_priv->tinfo->fini_seq_private(seq->private);
+	if (iter_priv->tinfo->reg_info->fini_seq_private)
+		iter_priv->tinfo->reg_info->fini_seq_private(seq->private);
 
 	bpf_prog_put(iter_priv->prog);
 	seq->private = iter_priv;
@@ -238,7 +234,12 @@ const struct file_operations bpf_iter_fops = {
 	.release	= iter_release,
 };
 
-int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
+/* The argument reg_info will be cached in bpf_iter_target_info.
+ * The common practice is to declare target reg_info as
+ * a const static variable and passed as an argument to
+ * bpf_iter_reg_target().
+ */
+int bpf_iter_reg_target(const struct bpf_iter_reg *reg_info)
 {
 	struct bpf_iter_target_info *tinfo;
 
@@ -246,11 +247,7 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
 	if (!tinfo)
 		return -ENOMEM;
 
-	tinfo->target = reg_info->target;
-	tinfo->seq_ops = reg_info->seq_ops;
-	tinfo->init_seq_private = reg_info->init_seq_private;
-	tinfo->fini_seq_private = reg_info->fini_seq_private;
-	tinfo->seq_priv_size = reg_info->seq_priv_size;
+	tinfo->reg_info = reg_info;
 	INIT_LIST_HEAD(&tinfo->list);
 
 	mutex_lock(&targets_mutex);
@@ -267,7 +264,7 @@ void bpf_iter_unreg_target(const char *target)
 
 	mutex_lock(&targets_mutex);
 	list_for_each_entry(tinfo, &targets, list) {
-		if (!strcmp(target, tinfo->target)) {
+		if (!strcmp(target, tinfo->reg_info->target)) {
 			list_del(&tinfo->list);
 			kfree(tinfo);
 			found = true;
@@ -303,7 +300,7 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 			supported = true;
 			break;
 		}
-		if (!strcmp(attach_fname + prefix_len, tinfo->target)) {
+		if (!strcmp(attach_fname + prefix_len, tinfo->reg_info->target)) {
 			cache_btf_id(tinfo, prog);
 			supported = true;
 			break;
@@ -431,15 +428,16 @@ static int prepare_seq_file(struct file *file, struct bpf_iter_link *link)
 
 	tinfo = link->tinfo;
 	total_priv_dsize = offsetof(struct bpf_iter_priv_data, target_private) +
-			   tinfo->seq_priv_size;
-	priv_data = __seq_open_private(file, tinfo->seq_ops, total_priv_dsize);
+			   tinfo->reg_info->seq_priv_size;
+	priv_data = __seq_open_private(file, tinfo->reg_info->seq_ops,
+				       total_priv_dsize);
 	if (!priv_data) {
 		err = -ENOMEM;
 		goto release_prog;
 	}
 
-	if (tinfo->init_seq_private) {
-		err = tinfo->init_seq_private(priv_data->target_private);
+	if (tinfo->reg_info->init_seq_private) {
+		err = tinfo->reg_info->init_seq_private(priv_data->target_private);
 		if (err)
 			goto release_seq_file;
 	}

kernel/bpf/map_iter.c

@@ -81,17 +81,17 @@ static const struct seq_operations bpf_map_seq_ops = {
 	.show	= bpf_map_seq_show,
 };
 
-static int __init bpf_map_iter_init(void)
-{
-	struct bpf_iter_reg reg_info = {
+static const struct bpf_iter_reg bpf_map_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);
+static int __init bpf_map_iter_init(void)
+{
+	return bpf_iter_reg_target(&bpf_map_reg_info);
 }
 
 late_initcall(bpf_map_iter_init);

kernel/bpf/task_iter.c

@@ -306,22 +306,24 @@ static const struct seq_operations task_file_seq_ops = {
 	.show	= task_file_seq_show,
 };
 
-static int __init task_iter_init(void)
-{
-	struct bpf_iter_reg task_file_reg_info = {
-		.target			= "task_file",
-		.seq_ops		= &task_file_seq_ops,
-		.init_seq_private	= init_seq_pidns,
-		.fini_seq_private	= fini_seq_pidns,
-		.seq_priv_size		= sizeof(struct bpf_iter_seq_task_file_info),
-	};
-	struct bpf_iter_reg task_reg_info = {
+static const struct bpf_iter_reg task_reg_info = {
 	.target			= "task",
 	.seq_ops		= &task_seq_ops,
 	.init_seq_private	= init_seq_pidns,
 	.fini_seq_private	= fini_seq_pidns,
 	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_info),
-	};
+};
+
+static const struct bpf_iter_reg task_file_reg_info = {
+	.target			= "task_file",
+	.seq_ops		= &task_file_seq_ops,
+	.init_seq_private	= init_seq_pidns,
+	.fini_seq_private	= fini_seq_pidns,
+	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_file_info),
+};
+
+static int __init task_iter_init(void)
+{
 	int ret;
 
 	ret = bpf_iter_reg_target(&task_reg_info);

net/ipv6/route.c

@@ -6397,17 +6397,17 @@ void __init ip6_route_init_special_entries(void)
 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
 DEFINE_BPF_ITER_FUNC(ipv6_route, struct bpf_iter_meta *meta, struct fib6_info *rt)
 
-static int __init bpf_iter_register(void)
-{
-	struct bpf_iter_reg reg_info = {
+static const struct bpf_iter_reg ipv6_route_reg_info = {
 	.target			= "ipv6_route",
 	.seq_ops		= &ipv6_route_seq_ops,
 	.init_seq_private	= bpf_iter_init_seq_net,
 	.fini_seq_private	= bpf_iter_fini_seq_net,
 	.seq_priv_size		= sizeof(struct ipv6_route_iter),
-	};
+};
 
-	return bpf_iter_reg_target(&reg_info);
+static int __init bpf_iter_register(void)
+{
+	return bpf_iter_reg_target(&ipv6_route_reg_info);
 }
 
 static void bpf_iter_unregister(void)

net/netlink/af_netlink.c

@@ -2803,17 +2803,17 @@ static const struct rhashtable_params netlink_rhashtable_params = {
 };
 
 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
-static int __init bpf_iter_register(void)
-{
-	struct bpf_iter_reg reg_info = {
+static const struct bpf_iter_reg netlink_reg_info = {
 	.target			= "netlink",
 	.seq_ops		= &netlink_seq_ops,
 	.init_seq_private	= bpf_iter_init_seq_net,
 	.fini_seq_private	= bpf_iter_fini_seq_net,
 	.seq_priv_size		= sizeof(struct nl_seq_iter),
-	};
+};
 
-	return bpf_iter_reg_target(&reg_info);
+static int __init bpf_iter_register(void)
+{
+	return bpf_iter_reg_target(&netlink_reg_info);
 }
 #endif