netdev - Re: [PATCH net-next] net: restore DSA behavior of not overriding ndo_get_phys_port

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Date:   Wed, 22 Jul 2020 14:53:28 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>, kuba@...nel.org,
        davem@...emloft.net, netdev@...r.kernel.org
Cc:     andrew@...n.ch, vivien.didelot@...il.com, jiri@...lanox.com,
        edumazet@...gle.com, ap420073@...il.com, xiyou.wangcong@...il.com,
        maximmi@...lanox.com, mkubecek@...e.cz, richardcochran@...il.com
Subject: Re: [PATCH net-next] net: restore DSA behavior of not overriding
 ndo_get_phys_port_name if present

On 7/22/20 1:53 PM, Vladimir Oltean wrote:
> Prior to the commit below, dsa_master_ndo_setup() used to avoid
> overriding .ndo_get_phys_port_name() unless the callback was empty.
> 
> https://elixir.bootlin.com/linux/v5.7.7/source/net/dsa/master.c#L269
> 
> Now, it overrides it unconditionally.
> 
> This matters for boards where DSA switches are hanging off of other DSA
> switches, or switchdev interfaces.
> Say a user has these udev rules for the top-level switch:
> 
> ACTION=="add", SUBSYSTEM=="net", KERNELS=="0000:00:00.5", DRIVERS=="mscc_felix", ATTR{phys_port_name}=="p0", NAME="swp0"
> ACTION=="add", SUBSYSTEM=="net", KERNELS=="0000:00:00.5", DRIVERS=="mscc_felix", ATTR{phys_port_name}=="p1", NAME="swp1"
> ACTION=="add", SUBSYSTEM=="net", KERNELS=="0000:00:00.5", DRIVERS=="mscc_felix", ATTR{phys_port_name}=="p2", NAME="swp2"
> ACTION=="add", SUBSYSTEM=="net", KERNELS=="0000:00:00.5", DRIVERS=="mscc_felix", ATTR{phys_port_name}=="p3", NAME="swp3"
> ACTION=="add", SUBSYSTEM=="net", KERNELS=="0000:00:00.5", DRIVERS=="mscc_felix", ATTR{phys_port_name}=="p4", NAME="swp4"
> ACTION=="add", SUBSYSTEM=="net", KERNELS=="0000:00:00.5", DRIVERS=="mscc_felix", ATTR{phys_port_name}=="p5", NAME="swp5"
> 
> If the DSA switches below start randomly overriding
> ndo_get_phys_port_name with their own CPU port, bad things can happen.
> Not only may the CPU port number be not unique among different
> downstream DSA switches, but one of the upstream switchdev interfaces
> may also happen to have a port with the same number. So, we may even end
> up in a situation where all interfaces of the top-level switch end up
> having a phys_port_name attribute of "p0". Clearly not ok if the purpose
> of the udev rules is to assign unique names.
> 
> Fix this by restoring the old behavior, which did not overlay this
> operation on top of the DSA master logic, if there was one in place
> already.
> 
> Fixes: 3369afba1e46 ("net: Call into DSA netdevice_ops wrappers")
> Signed-off-by: Vladimir Oltean <olteanv@...il.com>
> ---
> This is brain-dead, please consider killing this and retrieving the CPU
> port number from "devlink port"...

That is fair enough. Do you want to submit such a change while you are
at it?

> 
> pci/0000:00:00.5/0: type eth netdev swp0 flavour physical port 0
> pci/0000:00:00.5/2: type eth netdev swp2 flavour physical port 2
> pci/0000:00:00.5/4: type notset flavour cpu port 4
> spi/spi2.0/0: type eth netdev sw0p0 flavour physical port 0
> spi/spi2.0/1: type eth netdev sw0p1 flavour physical port 1
> spi/spi2.0/2: type eth netdev sw0p2 flavour physical port 2
> spi/spi2.0/4: type notset flavour cpu port 4
> spi/spi2.1/0: type eth netdev sw1p0 flavour physical port 0
> spi/spi2.1/1: type eth netdev sw1p1 flavour physical port 1
> spi/spi2.1/2: type eth netdev sw1p2 flavour physical port 2
> spi/spi2.1/3: type eth netdev sw1p3 flavour physical port 3
> spi/spi2.1/4: type notset flavour cpu port 4
> 
>  net/core/dev.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 19f1abc26fcd..60778bd8c3b1 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -8603,15 +8603,20 @@ int dev_get_phys_port_name(struct net_device *dev,
>  	const struct net_device_ops *ops = dev->netdev_ops;
>  	int err;
>  
> -	err  = dsa_ndo_get_phys_port_name(dev, name, len);
> -	if (err == 0 || err != -EOPNOTSUPP)
> -		return err;
> -
>  	if (ops->ndo_get_phys_port_name) {
>  		err = ops->ndo_get_phys_port_name(dev, name, len);
>  		if (err != -EOPNOTSUPP)
>  			return err;
> +	} else {
> +		/* DSA may override this operation, but only if the master
> +		 * isn't a switchdev or another DSA, in that case it breaks
> +		 * their port numbering.
> +		 */
> +		err  = dsa_ndo_get_phys_port_name(dev, name, len);

Extraneous space here.

Acked-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian