Re: [PATCH v2 2/2] net: add debugfs files for showing netns refcount tracking info

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Jeff Layton <jlayton@kernel.org>
Date: Tue, 08 Apr 2025 09:36:38 -0400
> CONFIG_NET_NS_REFCNT_TRACKER currently has no convenient way to display
> its tracking info. Add a new net_ns directory under the debugfs
> ref_tracker directory. Create a directory in there for every netns, with
> refcnt and notrefcnt files that show the currently tracked active and
> passive references.
> 
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  net/core/net_namespace.c | 151 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 151 insertions(+)
> 
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index 4303f2a4926243e2c0ff0c0387383cd8e0658019..7e9dc487f46d656ee4ae3d6d18d35bb2aba2b176 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -1512,3 +1512,154 @@ const struct proc_ns_operations netns_operations = {
>  	.owner		= netns_owner,
>  };
>  #endif
> +
> +#ifdef CONFIG_DEBUG_FS
> +#ifdef CONFIG_NET_NS_REFCNT_TRACKER
> +
> +#include <linux/debugfs.h>
> +
> +static struct dentry *ns_ref_tracker_dir;
> +static unsigned int ns_debug_net_id;
> +
> +struct ns_debug_net {
> +	struct dentry *netdir;
> +	struct dentry *refcnt;
> +	struct dentry *notrefcnt;
> +};
> +
> +#define MAX_NS_DEBUG_BUFSIZE	(32 * PAGE_SIZE)
> +
> +static int
> +ns_debug_tracker_show(struct seq_file *f, void *v)

I think there is no clear rule about where to break, but could you
remove \n after int so that it will match with other functions in
this file ?

Same for other new functions, looks like none of them go over 80 columns.

> +{
> +	struct ref_tracker_dir *tracker = f->private;
> +	int len, bufsize = PAGE_SIZE;
> +	char *buf;
> +
> +	for (;;) {
> +		buf = kvmalloc(bufsize, GFP_KERNEL);
> +		if (!buf)
> +			return -ENOMEM;
> +
> +		len = ref_tracker_dir_snprint(tracker, buf, bufsize);
> +		if (len < bufsize)
> +			break;
> +
> +		kvfree(buf);
> +		bufsize *= 2;
> +		if (bufsize > MAX_NS_DEBUG_BUFSIZE)
> +			return -ENOBUFS;
> +	}
> +	seq_write(f, buf, len);
> +	kvfree(buf);
> +	return 0;
> +}
> +
> +static int
> +ns_debug_ref_open(struct inode *inode, struct file *filp)
> +{
> +	int ret;
> +	struct net *net = inode->i_private;

nit: Please sort in the reverse xmas order.

https://docs.kernel.org/process/maintainer-netdev.html#local-variable-ordering-reverse-xmas-tree-rcs

> +
> +	ret = single_open(filp, ns_debug_tracker_show, &net->refcnt_tracker);
> +	if (!ret)
> +		net_passive_inc(net);
> +	return ret;
> +}
> +
> +static int
> +ns_debug_notref_open(struct inode *inode, struct file *filp)
> +{
> +	int ret;
> +	struct net *net = inode->i_private;

Same here.


> +
> +	ret = single_open(filp, ns_debug_tracker_show, &net->notrefcnt_tracker);
> +	if (!ret)
> +		net_passive_inc(net);
> +	return ret;
> +}
> +
> +static int
> +ns_debug_ref_release(struct inode *inode, struct file *filp)
> +{
> +	struct net *net = inode->i_private;
> +
> +	net_passive_dec(net);
> +	return single_release(inode, filp);
> +}
> +
> +static const struct file_operations ns_debug_ref_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= ns_debug_ref_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= ns_debug_ref_release,
> +};
> +
> +static const struct file_operations ns_debug_notref_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= ns_debug_notref_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= ns_debug_ref_release,
> +};
> +
> +static int
> +ns_debug_init_net(struct net *net)
> +{
> +	struct ns_debug_net *dnet = net_generic(net, ns_debug_net_id);
> +	char name[11]; /* 10 decimal digits + NULL term */
> +	int len;
> +
> +	len = snprintf(name, sizeof(name), "%u", net->ns.inum);
> +	if (len >= sizeof(name))
> +		return -EOVERFLOW;
> +
> +	dnet->netdir = debugfs_create_dir(name, ns_ref_tracker_dir);
> +	if (IS_ERR(dnet->netdir))
> +		return PTR_ERR(dnet->netdir);
> +
> +	dnet->refcnt = debugfs_create_file("refcnt", S_IFREG | 0400, dnet->netdir,
> +					   net, &ns_debug_ref_fops);
> +	if (IS_ERR(dnet->refcnt)) {
> +		debugfs_remove(dnet->netdir);
> +		return PTR_ERR(dnet->refcnt);
> +	}
> +
> +	dnet->notrefcnt = debugfs_create_file("notrefcnt", S_IFREG | 0400, dnet->netdir,
> +					      net, &ns_debug_notref_fops);
> +	if (IS_ERR(dnet->notrefcnt)) {
> +		debugfs_remove_recursive(dnet->netdir);
> +		return PTR_ERR(dnet->notrefcnt);
> +	}
> +
> +	return 0;
> +}
> +
> +static void
> +ns_debug_exit_net(struct net *net)
> +{
> +	struct ns_debug_net *dnet = net_generic(net, ns_debug_net_id);
> +
> +	debugfs_remove_recursive(dnet->netdir);
> +}
> +
> +static struct pernet_operations ns_debug_net_ops = {
> +	.init = ns_debug_init_net,
> +	.exit = ns_debug_exit_net,
> +	.id = &ns_debug_net_id,
> +	.size = sizeof(struct ns_debug_net),
> +};
> +
> +static int __init ns_debug_init(void)
> +{
> +	ns_ref_tracker_dir = debugfs_create_dir("net_ns", ref_tracker_debug_dir);
> +	if (IS_ERR(ns_ref_tracker_dir))
> +		return PTR_ERR(ns_ref_tracker_dir);
> +
> +	register_pernet_subsys(&ns_debug_net_ops);
> +	return 0;

register_pernet_subsys() could fail, so

	return register_pernet_subsys(&ns_debug_net_ops);


> +}
> +late_initcall(ns_debug_init);
> +#endif /* CONFIG_NET_NS_REFCNT_TRACKER */
> +#endif /* CONFIG_DEBUG_FS */
> 
> -- 
> 2.49.0
>