netdev - Re: [PATCH net-next 2/2] net: dsa: microchip: add KSZ8 change_tag

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Message-ID: <CAHvy4ArnEy+28xO3_m6EPFQxOKR1cJNkWLEVbx6JFBzLj6VMUg@mail.gmail.com>
Date: Mon, 19 Aug 2024 16:41:29 +0200
From: Pieter <vtpieter@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Vladimir Oltean <olteanv@...il.com>, Woojung Huh <woojung.huh@...rochip.com>, 
	UNGLinuxDriver@...rochip.com, Florian Fainelli <f.fainelli@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Russell King <linux@...linux.org.uk>, Pieter Van Trappen <pieter.van.trappen@...n.ch>, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: dsa: microchip: add KSZ8
 change_tag_protocol support

> > > On Mon, Aug 19, 2024 at 03:43:42PM +0200, Pieter wrote:
> > > > Right so I'm managing it but I don't care from which port the packets
> > > > originate, so I could disable the tagging in my case.
> > > >
> > > > My problem is that with tagging enabled, I cannot use the DSA conduit
> > > > interface as a regular one to open sockets etc.
> > >
> > > Open the socket on the bridge interface then?
> >
> > Assuming this works, how to tell all user space programs to use br0 instead
> > of eth0?
>
> How did you tell userspace to use eth0?
>
> In general, you don't tell userspace anything about interfaces. You
> open a client socket to a destination IP address, and the kernel
> routing tables are used to determine the egress interface. In general,
> it will use a public scope IP address from that interface as the
> source address.

Hi Andrew, Vladimir,
thanks for your explanation and patience!

It works as you said, I will have to do some changes to userspace to
ensure the DHCP client uses br0 instead of eth0 but that's it.
I just tried and br0 obtains the IP address and all is good, with
DSA tagging enabled.

This patch can be dropped, sorry for the hassle.

> The conduit interface should not have an IP address, its just
> plumbing, but not otherwise used. Your IP address is on br0, so by
> default the kernel will use the IP address from it.
>
>         Andrew
>