Re: [dpdk-dev] [RFC] net/vdev_netvsc: check for required related drivers

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 14 Mar 2019 11:26:05 +0000
Matan Azrad <matan@mellanox.com> wrote:

> Hi
> 
> From: Stephen Hemminger
> > The vdev_netvsc virtual driver that is used to do initialization on Hyper-
> > V/Azure won't work without failsafe and tap device.
> > If the related devices aren't present, it causes confusing errors later in
> > initialization when it crafts devargs and attempts to send them to a device
> > driver that isn't there.
> > 
> > Unfortunately, this is common with VPP where the TAP and FAILSAFE PMD's
> > are both optional.  The suggestion here is to detect this in the startup phase
> > earlier.
> > 
> > Alternative would be to use RTE_BUILD_BUG_ON(!defined(...)) but that
> > would break people doing normal VPP build.
> >   
> 
> The failsafe and tap devices are created by the vdev_netvsc PMD, so it is not expected to find them in the scan time.
> If the VM doesn't want vdev_netvsc driver to run, it have 2 options:
> 1. assign IP to the netvsc netdevs. 
> 2. run --vdev="vdev_netvsc0,ignore=1" - see documentation for more info.
> 


How do we improve the error reporting for configurations that have run Hyper-V/Azure
but forget to build failsafe, tap or mlx5 device drivers. Right now the error messages
are confusing, misleading and waste significant amount of developer time.

What solution do you propose? The DPDK build system is not as smart as kernel
Kconfig, there is no way to force dependencies.