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

[Matan Azrad <matan@mellanox.com>]

Hi

From: Stephen Hemminger
> 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.

Why?
Can't you condition the vdev_netvsc compilation in failsafe and tap compilation?

1 more option:
To condition the vdev_netvsc automated probing (in vdev_netvsc_custom_scan_add) by "ifdef" statement in failsafe and tap compilation existence.

Moreover, you can add clearer massage for this case if vdev_netvsc is running (vdev_netvsc_vdev_probe).

Matan.