• Vladimir Oltean's avatar
    net: dsa: stop overriding master's ndo_get_phys_port_name · 5df5661a
    Vladimir Oltean authored
    The purpose of this override is to give the user an indication of what
    the number of the CPU port is (in DSA, the CPU port is a hardware
    implementation detail and not a network interface capable of traffic).
    
    However, it has always failed (by design) at providing this information
    to the user in a reliable fashion.
    
    Prior to commit 3369afba ("net: Call into DSA netdevice_ops
    wrappers"), the behavior was to only override this callback if it was
    not provided by the DSA master.
    
    That was its first failure: if the DSA master itself was a DSA port or a
    switchdev, then the user would not see the number of the CPU port in
    /sys/class/net/eth0/phys_port_name, but the number of the DSA master
    port within its respective physical switch.
    
    But that was actually ok in a way. The commit mentioned above changed
    that behavior, and now overrides the master's ndo_get_phys_port_name
    unconditionally. That comes with problems of its own, which are worse in
    a way.
    
    The idea is that it's typical for switchdev users to have udev rules for
    consistent interface naming. These are based, among other things, on
    the phys_port_name attribute. If we let the DSA switch at the bottom
    to start randomly overriding ndo_get_phys_port_name with its own CPU
    port, we basically lose any predictability in interface naming, or even
    uniqueness, for that matter.
    
    So, there are reasons to let DSA override the master's callback (to
    provide a consistent interface, a number which has a clear meaning and
    must not be interpreted according to context), and there are reasons to
    not let DSA override it (it breaks udev matching for the DSA master).
    
    But, there is an alternative method for users to retrieve the number of
    the CPU port of each DSA switch in the system:
    
      $ devlink port
      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
    
    So remove this duplicated, unreliable and troublesome method. From this
    patch on, the phys_port_name attribute of the DSA master will only
    contain information about itself (if at all). If the users need reliable
    information about the CPU port they're probably using devlink anyway.
    Signed-off-by: default avatarVladimir Oltean <olteanv@gmail.com>
    Acked-by: default avatarflorian Fainelli <f.fainelli@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    5df5661a
master.c 8.77 KB