linux-kernel - Re: [PATCH net-next] IB/hfi1: allocate dummy net

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Message-ID: <20240311102251.GJ12921@unreal>
Date: Mon, 11 Mar 2024 12:22:51 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
	Jason Gunthorpe <jgg@...pe.ca>, kuba@...nel.org,
	keescook@...omium.org,
	"open list:HFI1 DRIVER" <linux-rdma@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] IB/hfi1: allocate dummy net_device dynamically

On Mon, Mar 11, 2024 at 03:08:54AM -0700, Breno Leitao wrote:
> Hello Leon,
> 
> On Sun, Mar 10, 2024 at 12:14:51PM +0200, Leon Romanovsky wrote:
> > On Fri, Mar 08, 2024 at 10:29:50AM -0800, Breno Leitao wrote:
> > > struct net_device shouldn't be embedded into any structure, instead,
> > > the owner should use the priv space to embed their state into net_device.
> > 
> > Why?
> 
> From my experience, you can leverage all the helpers to deal with the
> relationship between struct net_device and you private structure. Here
> are some examples that comes to my mind:
> 
> * alloc_netdev() allocates the private structure for you
> * netdev_priv() gets the private structure for you
> * dev->priv_destructor sets the destructure to be called when the
>   interface goes away or failures.

Everything above is true, but it doesn't relevant to HFI1 devices which
are not netdev devices.

> 
> > > @@ -360,7 +360,11 @@ int hfi1_alloc_rx(struct hfi1_devdata *dd)
> > >  	if (!rx)
> > >  		return -ENOMEM;
> > >  	rx->dd = dd;
> > > -	init_dummy_netdev(&rx->rx_napi);
> > > +	rx->rx_napi = alloc_netdev(sizeof(struct iwl_trans_pcie *),
> > > +				   "dummy", NET_NAME_UNKNOWN,
> > 
> > Will it create multiple "dummy" netdev in the system? Will all devices
> > have the same "dummy" name?
> 
> Are these devices visible to userspace?

HFI devices yes, dummy device no.

> 
> This allocation are using NET_NAME_UNKNOWN, which implies that the
> device is not expose to userspace.

Great

> 
> Would you prefer a different name?

I prefer to see some new wrapper over plain alloc_netdev, which will
create this dummy netdevice. For example, alloc_dummy_netdev(...).

> 
> > > +				   init_dummy_netdev); +	if
> > > (!rx->rx_napi) +		return -ENOMEM;
> > 
> > You forgot to release previously allocated "rx" here.
> 
> Good catch, I will update.

Thanks

> 
> Thanks