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

[Stephen Hemminger <stephen@networkplumber.org>]

On Sun, 17 Mar 2019 06:53:02 +0000
Matan Azrad <matan@mellanox.com> wrote:

> 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).

Right now FAILSAFE, TAP and MLX5 are all optional in how VPP builds.
If FAILSAFE or TAP is not configured then vdev_netvsc will try and configure them anyway
and fail obscurely.

My current preference would be:
	RTE_BUILD_BUG_ON(!defined(CONFIG_RTE_LIBRTE_PMD_FAILSAFE));