netdev - Re: [PATCH net-next v5 2/5] netdevsim: allow two netdevsim ports to be connected

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Date: Tue, 9 Jan 2024 08:57:59 -0800
From: David Wei <dw@...idwei.uk>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jiri Pirko <jiri@...nulli.us>, 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 v5 2/5] netdevsim: allow two netdevsim ports to
 be connected

On 2024-01-03 17:39, Jakub Kicinski wrote:
> On Wed, 27 Dec 2023 17:46:30 -0800 David Wei wrote:
>> +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 is peer netdevsim \"id port\" (uint uint)\n");
> 
> netif_err() or dev_err() ? Granted the rest of the file seems to use
> pr_err(), but I'm not sure why...

I can change it to use one of these two in this patchset, then I can
chnage the others separately in another patch. How does that sound?

> 
>> +		return -EINVAL;
>> +	}
> 
> Could you put a sleep() here and test removing the device while some
> thread is stuck here? I don't recall exactly but I thought debugfs
> remove waits for concurrent reads and writes which could be problematic
> given we take all the locks under the sun here..

Yep, I'll test this.

> 
>> +	ret = -EINVAL;
>> +	mutex_lock(&nsim_dev_list_lock);
>> +	peer_dev = nsim_dev_find_by_id(id);
>> +	if (!peer_dev) {
>> +		pr_err("Peer netdevsim %u does not exist\n", id);
>> +		goto out_mutex;
>> +	}
>> +
>> +	devl_lock(priv_to_devlink(peer_dev));
>> +	rtnl_lock();
>> +	nsim_dev_port = file->private_data;
>> +	peer_dev_port = __nsim_dev_port_lookup(peer_dev, NSIM_DEV_PORT_TYPE_PF,
>> +					       port);
>> +	if (!peer_dev_port) {
>> +		pr_err("Peer netdevsim %u port %u does not exist\n", id, port);
>> +		goto out_devl;
>> +	}
>> +
>> +	if (nsim_dev_port == peer_dev_port) {
>> +		pr_err("Cannot link netdevsim to itself\n");
>> +		goto out_devl;
>> +	}
>> +
>> +	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_devl:
> 
> out_unlock_rtnl
> 
>> +	rtnl_unlock();
>> +	devl_unlock(priv_to_devlink(peer_dev));
>> +out_mutex:
> 
> out_unlock_dev_list
> 
>> +	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,
> 
> You don't support seek, you want some form of no_seek here.
> 
>> +	.owner = THIS_MODULE,
>> +};