Change Details

When running on Xen, with interfaces provided by the xen-netback driver, `sg` offload must be enabled before the MTU can be increased beyond 1500 — otherwise setting MTU on the underlying interface fails and VyOS produces its crash report. Discussed in: [forum](https://forum.vyos.io/t/cannot-change-mtu-oserror-errno-22-invalid-argument/5513/7?u=maznu) Relevant [line 367 of xen-netback/interface.c](https://elixir.bootlin.com/linux/latest/source/drivers/net/xen-netback/interface.c#L367) Probably just needs a warning that `sg` needs enabling if MTU > 1500 is requested.

When running on Xen, with interfaces provided by the xen-netback driver, `sg` offload must be enabled before the MTU can be increased beyond 1500 — otherwise setting MTU on the underlying interface fails and VyOS produces its crash report. Discussed in [forum](https://forum.vyos.io/t/cannot-change-mtu-oserror-errno-22-invalid-argument/5513/7?u=maznu) with reference to relevant [line 367 of xen-netback/interface.c](https://elixir.bootlin.com/linux/latest/source/drivers/net/xen-netback/interface.c#L367) If VyOS can determine that the ethernet device being configured is a `xen-netback` driver, then VyOS should refuse configuration of MTU>1500 unless `sg` is enabled. Alternatively, a dirty fix would be to emit a warning that `sg` might needed if the user is configuring jumbo MTUs.

When running on Xen, with interfaces provided by the xen-netback driver, `sg` offload must be enabled before the MTU can be increased beyond 1500 — otherwise setting MTU on the underlying interface fails and VyOS produces its crash report. Discussed in: [forum](https://forum.vyos.io/t/cannot-change-mtu-oserror-errno-22-invalid-argument/5513/7?u=maznu) with reference to relevant [line 367 of xen-netback/interface.c](https://elixir.bootlin.com/linux/latest/source/drivers/net/xen-netback/interface.c#L367) Relevant [line 367 of xen-netback/interface.c](https://elixir.bootlin.com/linux/latest/source/drivers/net/xen-netback/interface.c#L367)If VyOS can determine that the ethernet device being configured is a `xen-netback` driver, then VyOS should refuse configuration of MTU>1500 unless `sg` is enabled. Probably just needsAlternatively, a dirty fix would be to emit a warning that `sg` needs enablingmight needed if MTU > 1500 is requestedthe user is configuring jumbo MTUs.