netdev - Re: [PATCHv1] e1000e: Allow ethtool to enable/disable loopback.

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Message-ID: <BANLkTi=W3M-P_0BXVJvZx25xUcy7bLiWEg@mail.gmail.com>
Date:	Fri, 13 May 2011 09:49:35 +0200
From:	Michał Mirosław <mirqus@...il.com>
To:	Mahesh Bandewar <maheshb@...gle.com>
Cc:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	e1000-devel <e1000-devel@...ts.sourceforge.net>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCHv1] e1000e: Allow ethtool to enable/disable loopback.

W dniu 12 maja 2011 23:41 użytkownik Mahesh Bandewar
<maheshb@...gle.com> napisał:
> On Wed, May 11, 2011 at 10:50 PM, Michał Mirosław <mirqus@...il.com> wrote:
>> W dniu 12 maja 2011 01:11 użytkownik Mahesh Bandewar
>> <maheshb@...gle.com> napisał:
>>> On Wed, May 11, 2011 at 12:15 PM, Michał Mirosław <mirqus@...il.com> wrote:
>>>> If e1000_set_loopback() fails, this should set dev->features to passed
>>>> features (but keeping NETIF_F_LOOPBACK unchanged in dev->features) to
>>>> keep the state consistent.
>>> set_features() can return the return code of set_loopback() instead of
>>> 0; this way the consistency will be maintained.
>> Only as long as NETIF_F_LOOPBACK is the only bit set in hw_features.
>> netdev_update_features() can't really know which features were changed
>> and which failed when ndo_set_features callback returns non-zero.
> This is more of an API shortcoming. Callback will have to revert
> changes made (rollback) before returning non-zero value to keep it
> consistent.

It might just update dev->features to match instead of rollback. It
could also start some recovery process that eventually calls
netdev_update_features() again to try the change again.

IOW, the information what changes failed are returned implicitly in
modified dev->features. When callback returns 0,
netdev_update_features() assumes that all were set correctly and
updates dev->features itself.

Best Regards,
Michał Mirosław
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