netdev - Re: [PATCH 2/3] IB/ipoib: Stop using dev

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Date:   Mon, 13 Aug 2018 16:57:24 +0300
From:   Arseny Maslennikov <ar@...msu.ru>
To:     Yuval Shaia <yuval.shaia@...cle.com>
Cc:     linux-rdma@...r.kernel.org, Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/3] IB/ipoib: Stop using dev_id to expose port numbers

On Mon, Aug 13, 2018 at 03:40:20PM +0300, Yuval Shaia wrote:
> On Mon, Aug 13, 2018 at 02:42:23PM +0300, Arseny Maslennikov wrote:
> > Some InfiniBand network devices have multiple ports on the same PCI
> > function. Prior to this the kernel erroneously used the `dev_id' sysfs
> > field of those network interfaces to convey the port number to userspace.
> > 
> > `dev_id' is currently reserved for distinguishing stacked ifaces
> > (e.g: VLANs) with the same hardware address as their parent device.
> > 
> > Similar fixes to net/mlx4_en and many other drivers, which started
> > exporting this information through `dev_id' before 3.15, were accepted
> > into the kernel 4 years ago.
> > See 76a066f2a2a0268b565459c417b59724b5a3197b, commit message:
> > `net/mlx4_en: Expose port number through sysfs'.
> > 
> > I would be OK with this commit not being backported to stable, since
> > it might break admin-supplied udev rules and the likes.
> > 
> > Signed-off-by: Arseny Maslennikov <ar@...msu.ru>
> > ---
> >  drivers/infiniband/ulp/ipoib/ipoib_main.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > index 6eb0594fffec..f64535038147 100644
> > --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > @@ -2252,7 +2252,6 @@ static struct net_device *ipoib_add_port(const char *format,
> >  	}
> >  
> >  	SET_NETDEV_DEV(priv->dev, hca->dev.parent);
> > -	priv->dev->dev_id = port - 1;
> 
> Correct me if i'm wrong here but besides some changes in commit message
> looks like patch 1/3 is the same as 2/3, isn't it?
> 
> Yuval
> 

1/3 has an extra line, 2/3 removes a different line.

(a) If you apply both 1/3 and 2/3, the port number can be seen at
/sys/class/net/*/dev_port and not at .../dev_id.

(b) If you apply only 1/3, the port number can be seen at _both_
.../dev_port and .../dev_id (to preserve backward compatibility with
e.g. existing udev rules that rely on "ATTR{dev_id}")

By splitting those up we have both options (a) and (b) available,
so the maintainers are free to decide which one is wiser.

> >  	priv->dev->dev_port = port - 1;
> >  
> >  	result = ib_query_port(hca, port, &attr);
> > -- 
> > 2.18.0
> > 

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