Re: [PATCH 1/1] RDMA/mlx5: Make mlx5 device work with ib_device_get_by_netdev

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Oct 19, 2022 at 09:08:14AM +0000, yanjun.zhu@linux.dev wrote:
> October 18, 2022 4:24 PM, "Leon Romanovsky" <leon@kernel.org> wrote:
> 
> > On Sun, Oct 16, 2022 at 02:19:25AM -0400, Zhu Yanjun wrote:
> > 
> >> From: Zhu Yanjun <yanjun.zhu@linux.dev>
> >> 
> >> Before mlx5 ib device is registered, the function ib_device_set_netdev
> >> is not called to map the mlx5 ib device with the related net device.
> >> 
> >> As such, when the function ib_device_get_by_netdev is called to get ib
> >> device, NULL is returned.
> >> 
> >> Other ib devices, such as irdma, rxe and so on, the function
> >> ib_device_get_by_netdev can get ib device from the related net device.
> > 
> > Ohh, you opened Pandora box, everything around it looks half-backed.
> > 
> > mlx4 and mlx5 don't call to ib_device_set_netdev(), because they have
> > .get_netdev() callback. This callback is not an easy task to eliminate
> > and many internal attempts failed to eliminate them.
> > 
> > This caused to very questionable ksmbd_rdma_capable_netdev()
> > implementation where ksmbd first checked internal ib_dev callback
> > and tried to use ib_device_get_by_netdev(). And to smc_ib, which
> > didn't even bother to use ib_device_get_by_netdev().
> 
> Thanks.
> 
> I read the function ksmbd_rdma_capable_netdev carefully.
> Mlx5 and mlx4 do not call ib_device_set_netdev to map net device and ib devices.
> This brings a lot of problems. 

ULPs are not allowed to use these interfaces, they are for driver
implementations.

It is an error that ksmbd_rdma_capable_netdev() calls it in the first
place.

Jason