debugfs for nexthop [xxx]

- Eventually this will be part of netdevsim as an interface to the
  simulated offload, but until then, this will be good for testing.

net/ipv4/nexthop.c

@@ -5,6 +5,7 @@
  * Copyright (c) 2017-19 David Ahern <dsa@cumulusnetworks.com>
  */
 
+#include <linux/debugfs.h>
 #include <linux/nexthop.h>
 #include <linux/rtnetlink.h>
 #include <linux/slab.h>
@@ -2592,8 +2593,106 @@ static struct pernet_operations nexthop_net_ops = {
 	.exit = nexthop_net_exit,
 };
 
+static struct nexthop_debugfs {
+	struct dentry *ddir;
+	struct dentry *bucket_activity;
+} *nexthop_debugfs;
+
+static ssize_t nexthop_dfs_bucket_activity_write(struct file *file,
+						 const char __user *user_buf,
+						 size_t size, loff_t *ppos)
+{
+	const char *tok_bucketid;
+	const char *tok_nhid;
+	struct nexthop *nh;
+	loff_t pos = *ppos;
+	char buf[128];
+	u16 bucketid; // xxx or u32 if we choose so
+	char *ptr;
+	u32 nhid;
+	int err;
+
+	if (pos < 0)
+		return -EINVAL;
+	if (pos == size)
+		goto skip;
+	if (pos)
+		return -EINVAL;
+	if (size > sizeof(buf))
+		return -ENOMEM;
+        if (copy_from_user(buf, user_buf, size))
+                return -EFAULT;
+
+	buf[sizeof(buf) - 1] = '\0';
+	ptr = buf;
+	tok_nhid = strsep(&ptr, " \t");
+	tok_bucketid = strsep(&ptr, " \t");
+
+	if (!tok_nhid || !tok_bucketid || ptr)
+		return -EINVAL;
+
+	err = kstrtou32(tok_nhid, 0, &nhid);
+	if (err)
+		return err;
+
+	err = kstrtou16(tok_bucketid, 0, &bucketid);
+	if (err)
+		return err;
+
+	rcu_read_lock();
+	nh = nexthop_find_by_id(&init_net, nhid);
+	if (!nh || !nexthop_select_path(nh, bucketid))
+		err = -ENOENT;
+	rcu_read_unlock();
+
+skip:
+	*ppos = size;
+	return err ?: size;
+}
+
+static const struct file_operations nexthop_debugfs_bucket_activity_ops = {
+        .write = nexthop_dfs_bucket_activity_write,
+        .llseek = no_llseek,
+};
+
+static struct nexthop_debugfs *nexthop_debugfs_alloc(void)
+{
+	struct nexthop_debugfs *dfs;
+	int err;
+
+	dfs = kzalloc(sizeof(*dfs), GFP_KERNEL);
+	if (!dfs)
+		return NULL;
+
+	dfs->ddir = debugfs_create_dir("nexthop", NULL);
+	if (IS_ERR(dfs->ddir)) {
+		err = PTR_ERR(dfs->ddir);
+		goto err_create_dir;
+	}
+
+	dfs->bucket_activity = debugfs_create_file("bucket_activity", S_IWUSR,
+						   dfs->ddir, NULL,
+						   &nexthop_debugfs_bucket_activity_ops);
+	if (IS_ERR(dfs->bucket_activity)) {
+		err = PTR_ERR(dfs->bucket_activity);
+		goto err_create_bucket_activity;
+	}
+
+	return dfs;
+
+err_create_bucket_activity:
+	debugfs_remove_recursive(dfs->ddir);
+err_create_dir:
+	kfree(dfs);
+	return ERR_PTR(err);
+}
+
 static int __init nexthop_init(void)
 {
+	nexthop_debugfs = nexthop_debugfs_alloc();
+	if (IS_ERR(nexthop_debugfs))
+		return PTR_ERR(nexthop_debugfs);
+
 	register_pernet_subsys(&nexthop_net_ops);
 
 	register_netdevice_notifier(&nh_netdev_notifier);