Re: [dpdk-stable] [PATCH v1 2/3] net/ring: fix eth_dev device pointer on allocation

["Gaëtan Rivet" <grive@u256.net>]

On 06/05/20 12:48 +0100, Ferruh Yigit wrote:
> On 5/5/2020 8:10 PM, Gaetan Rivet wrote:
> > When a net_ring device is allocated, its device pointer is not set
> > before calling rte_eth_dev_probing_finish, which is incorrect.
> > 
> > The following:
> >   commit: 96cb19521147 ("net/ring: use EAL APIs in PMD specific API")
> >   commit: a6992e961050 ("net/ring: set ethernet device field")
> > 
> > already attempted to fix this issue in 17.08, which was fine at the
> > time. Adding the hook rte_eth_dev_probing_finish() however created this
> > bug, as the eth_dev exposed when this hook is executed is expected to be
> > complete.
> > 
> > Remove the prior attempts to fix the issue in rte_pmd_ring_probe() and
> > write the pointer properly in do_eth_dev_ring_create().
> > 
> > Cc: stable@dpdk.org
> > Fixes: fbe90cdd776c ("ethdev: add probing finish function")
> > Cc: ferruh.yigit@intel.com
> > Cc: thomas@monjalon.net
> > Signed-off-by: Gaetan Rivet <grive@u256.net>
> 
> <...>
> 
> > @@ -325,10 +346,17 @@ do_eth_dev_ring_create(const char *name,
> >  	data->kdrv = RTE_KDRV_NONE;
> >  	data->numa_node = numa_node;
> >  
> > -	/* finally assign rx and tx ops */
> > +	/* assign rx and tx ops */
> >  	eth_dev->rx_pkt_burst = eth_ring_rx;
> >  	eth_dev->tx_pkt_burst = eth_ring_tx;
> >  
> > +	/* finally set the rte_device pointer in eth_dev. */
> > +	eth_dev->device = ring_device_from_name(name);
> > +	if (eth_dev->device == NULL) {
> > +		rte_errno = ENODEV;
> > +		goto error;
> > +	}
> > +
> >  	rte_eth_dev_probing_finish(eth_dev);
> >  	*eth_dev_p = eth_dev;
> 
> Why not move the 'rte_eth_dev_probing_finish()' to the 'rte_pmd_ring_probe()',
> below where 'eth_dev->device' set?

Hi Ferruh,

Sure it would work. The reason I did it this way is two-fold:

  * I disliked having two places where eth_dev->device was conditionally
    set. It makes it harder to read rte_pmd_ring_probe.

  * I was actually thinking, doing this patch, that we should modify
    rte_eth_dev_allocate() to take an rte_device as parameter, as all
    eth_dev are meant to be backed by an rte_device. Keeping this in
    mind, I meant to move writing the pointer closer to the
    rte_eth_dev_allocate() call.

But you are right that it is needlessly verbose, using
vdev_bus->find_device() to do this stuff. I'm ok with changing it as you
described if you prefer.

-- 
Gaëtan