From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH] ethdev: fix rte_eth_dev_owner_unset
Date: Tue, 14 Aug 2018 09:55:21 -0700
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To: Matan Azrad <matan@mellanox.com>
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On Tue, 14 Aug 2018 05:52:20 +0000
Matan Azrad <matan@mellanox.com> wrote:

> Hi Stephen
> 
> From: Stephen Hemminger
> > The rte_eth_dev_owner_unset function is unusable because it always
> > returns -EINVAL. This is because the magic (unowned) value is flagged as not
> > valid.
> >   
> 
> It's OK to raise an error when you do unset for unowned device.
> It means that unset owner should be called for owned device.
> 

Original code was broken. The following would always fail.

	rte_eth_dev_owner_new(&owner.id);
	sprintf(owner.name, "example");
	rte_eth_dev_owner_set(port_id, &owner);
	rte_eth_dev_owner_unset(port_id, owner.id);

That is because of:
	rte_eth_dev_owner_unset(port_id, owner_id)
		_rte_eth_dev_owner_set(port_id, owner_id, &new_owner)  << new_owner.id == RTE_ETH_DEV_NO_OWNER (0)


	if (!rte_eth_is_valid_owner_id(new_owner->id) &&  << new_owner->id == RTE_ETH_DEV_NO_OWNER (which is flagged as invalid)
	    !rte_eth_is_valid_owner_id(old_owner_id))
		return -EINVAL;

The failsafe driver never checks the return value, and therefore doesn't see that it never clears ownership.