Date: Thu, 21 Dec 2023 16:47:59 -0800
From: David Wei <dw@...idwei.uk>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Jakub Kicinski <kuba@...nel.org>, Sabrina Dubroca <sd@...asysnail.net>,
 netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v4 2/5] netdevsim: allow two netdevsim ports to
 be connected

On 2023-12-20 01:09, Jiri Pirko wrote:
> Wed, Dec 20, 2023 at 02:47:44AM CET, dw@...idwei.uk wrote:
>> Add a debugfs file in
>> /sys/kernel/debug/netdevsim/netdevsimN/ports/A/peer
>>
>> Writing "M B" to this file will link port A of netdevsim N with port B
>> of netdevsim M. Reading this file will return the linked netdevsim id
>> and port, if any.
>>
>> nsim_dev_list_lock and rtnl_lock are held during read/write of peer to
>> prevent concurrent modification of netdevsims or their ports.
>>
>> Signed-off-by: David Wei <dw@...idwei.uk>
>> ---
>> drivers/net/netdevsim/dev.c       | 127 +++++++++++++++++++++++++++---
>> drivers/net/netdevsim/netdev.c    |   6 ++
>> drivers/net/netdevsim/netdevsim.h |   1 +
>> 3 files changed, 121 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
>> index e30a12130e07..e4621861c70b 100644
>> --- a/drivers/net/netdevsim/dev.c
>> +++ b/drivers/net/netdevsim/dev.c
>> @@ -391,6 +391,117 @@ static const struct file_operations nsim_dev_rate_parent_fops = {
>> 	.owner = THIS_MODULE,
>> };
>>
>> +static struct nsim_dev *nsim_dev_find_by_id(unsigned int id)
>> +{
>> +	struct nsim_dev *dev;
>> +
>> +	list_for_each_entry(dev, &nsim_dev_list, list)
>> +		if (dev->nsim_bus_dev->dev.id == id)
>> +			return dev;
>> +
>> +	return NULL;
>> +}
>> +
>> +static struct nsim_dev_port *
>> +__nsim_dev_port_lookup(struct nsim_dev *nsim_dev, enum nsim_dev_port_type type,
>> +		       unsigned int port_index)
>> +{
>> +	struct nsim_dev_port *nsim_dev_port;
>> +
>> +	port_index = nsim_dev_port_index(type, port_index);
>> +	list_for_each_entry(nsim_dev_port, &nsim_dev->port_list, list)
>> +		if (nsim_dev_port->port_index == port_index)
>> +			return nsim_dev_port;
>> +	return NULL;
>> +}
>> +
>> +static ssize_t nsim_dev_peer_read(struct file *file, char __user *data,
>> +				  size_t count, loff_t *ppos)
>> +{
>> +	struct nsim_dev_port *nsim_dev_port;
>> +	struct netdevsim *peer;
>> +	unsigned int id, port;
>> +	char buf[23];
>> +	ssize_t ret;
>> +
>> +	mutex_lock(&nsim_dev_list_lock);
>> +	rtnl_lock();
>> +	nsim_dev_port = file->private_data;
>> +	peer = rtnl_dereference(nsim_dev_port->ns->peer);
>> +	if (!peer)
>> +		goto out;
>> +
>> +	id = peer->nsim_bus_dev->dev.id;
>> +	port = peer->nsim_dev_port->port_index;
>> +	ret = scnprintf(buf, sizeof(buf), "%u %u\n", id, port);
>> +	ret = simple_read_from_buffer(data, count, ppos, buf, ret);
>> +
>> +out:
>> +	rtnl_unlock();
>> +	mutex_unlock(&nsim_dev_list_lock);
>> +
>> +	return ret;
>> +}
>> +
>> +static ssize_t nsim_dev_peer_write(struct file *file,
>> +				   const char __user *data,
>> +				   size_t count, loff_t *ppos)
>> +{
>> +	struct nsim_dev_port *nsim_dev_port, *peer_dev_port;
>> +	struct nsim_dev *peer_dev;
>> +	unsigned int id, port;
>> +	char buf[22];
>> +	ssize_t ret;
>> +
>> +	if (count >= sizeof(buf))
>> +		return -ENOSPC;
>> +
>> +	ret = copy_from_user(buf, data, count);
>> +	if (ret)
>> +		return -EFAULT;
>> +	buf[count] = '\0';
>> +
>> +	ret = sscanf(buf, "%u %u", &id, &port);
>> +	if (ret != 2) {
>> +		pr_err("Format for adding a peer is \"id port\" (uint uint)");
>> +		return -EINVAL;
>> +	}
>> +
>> +	ret = -EINVAL;
>> +	mutex_lock(&nsim_dev_list_lock);
>> +	rtnl_lock();
>> +	peer_dev = nsim_dev_find_by_id(id);
>> +	if (!peer_dev)
>> +		goto out;
> 
> Tell the user what's wrong please.

Okay.

> 
>> +
>> +	peer_dev_port = __nsim_dev_port_lookup(peer_dev, NSIM_DEV_PORT_TYPE_PF,
>> +					       port);
>> +	if (!peer_dev_port)
>> +		goto out;
> 
> Tell the user what's wrong please.

Ditto.

> 
> 
>> +
>> +	nsim_dev_port = file->private_data;
>> +	if (nsim_dev_port == peer_dev_port)
> 
> Why fail here? IDK, success sounds better to me.

I don't want to link a port to itself. In my mental model a port is e.g.
a port on a switch. It doesn't make sense to connect it to itself.

> 
> 
>> +		goto out;
>> +
>> +	rcu_assign_pointer(nsim_dev_port->ns->peer, peer_dev_port->ns);
>> +	rcu_assign_pointer(peer_dev_port->ns->peer, nsim_dev_port->ns);
>> +	ret = count;
>> +
>> +out:
>> +	rtnl_unlock();
>> +	mutex_unlock(&nsim_dev_list_lock);
>> +
>> +	return ret;
>> +}
>> +
>> +static const struct file_operations nsim_dev_peer_fops = {
>> +	.open = simple_open,
>> +	.read = nsim_dev_peer_read,
>> +	.write = nsim_dev_peer_write,
>> +	.llseek = generic_file_llseek,
>> +	.owner = THIS_MODULE,
>> +};
>> +
>> static int nsim_dev_port_debugfs_init(struct nsim_dev *nsim_dev,
>> 				      struct nsim_dev_port *nsim_dev_port)
>> {
>> @@ -421,6 +532,9 @@ static int nsim_dev_port_debugfs_init(struct nsim_dev *nsim_dev,
>> 	}
>> 	debugfs_create_symlink("dev", nsim_dev_port->ddir, dev_link_name);
>>
>> +	debugfs_create_file("peer", 0600, nsim_dev_port->ddir,
>> +			    nsim_dev_port, &nsim_dev_peer_fops);
>> +
>> 	return 0;
>> }
>>
>> @@ -1702,19 +1816,6 @@ void nsim_drv_remove(struct nsim_bus_dev *nsim_bus_dev)
>> 	dev_set_drvdata(&nsim_bus_dev->dev, NULL);
>> }
>>
>> -static struct nsim_dev_port *
>> -__nsim_dev_port_lookup(struct nsim_dev *nsim_dev, enum nsim_dev_port_type type,
>> -		       unsigned int port_index)
>> -{
>> -	struct nsim_dev_port *nsim_dev_port;
>> -
>> -	port_index = nsim_dev_port_index(type, port_index);
>> -	list_for_each_entry(nsim_dev_port, &nsim_dev->port_list, list)
>> -		if (nsim_dev_port->port_index == port_index)
>> -			return nsim_dev_port;
>> -	return NULL;
>> -}
>> -
>> int nsim_drv_port_add(struct nsim_bus_dev *nsim_bus_dev, enum nsim_dev_port_type type,
>> 		      unsigned int port_index)
>> {
>> diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
>> index aecaf5f44374..434322f6a565 100644
>> --- a/drivers/net/netdevsim/netdev.c
>> +++ b/drivers/net/netdevsim/netdev.c
>> @@ -388,6 +388,7 @@ nsim_create(struct nsim_dev *nsim_dev, struct nsim_dev_port *nsim_dev_port)
>> 	ns->nsim_dev = nsim_dev;
>> 	ns->nsim_dev_port = nsim_dev_port;
>> 	ns->nsim_bus_dev = nsim_dev->nsim_bus_dev;
>> +	RCU_INIT_POINTER(ns->peer, NULL);
>> 	SET_NETDEV_DEV(dev, &ns->nsim_bus_dev->dev);
>> 	SET_NETDEV_DEVLINK_PORT(dev, &nsim_dev_port->devlink_port);
>> 	nsim_ethtool_init(ns);
>> @@ -407,8 +408,13 @@ nsim_create(struct nsim_dev *nsim_dev, struct nsim_dev_port *nsim_dev_port)
>> void nsim_destroy(struct netdevsim *ns)
>> {
>> 	struct net_device *dev = ns->netdev;
>> +	struct netdevsim *peer;
>>
>> 	rtnl_lock();
>> +	peer = rtnl_dereference(ns->peer);
>> +	if (peer)
>> +		RCU_INIT_POINTER(peer->peer, NULL);
>> +	RCU_INIT_POINTER(ns->peer, NULL);
>> 	unregister_netdevice(dev);
>> 	if (nsim_dev_port_is_pf(ns->nsim_dev_port)) {
>> 		nsim_macsec_teardown(ns);
>> diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
>> index babb61d7790b..24fc3fbda791 100644
>> --- a/drivers/net/netdevsim/netdevsim.h
>> +++ b/drivers/net/netdevsim/netdevsim.h
>> @@ -125,6 +125,7 @@ struct netdevsim {
>> 	} udp_ports;
>>
>> 	struct nsim_ethtool ethtool;
>> +	struct netdevsim __rcu *peer;
>> };
>>
>> struct netdevsim *
>> -- 
>> 2.39.3
>>

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