netdev - Re: [patch net-next v3 02/10] switchdev: introduce transaction item queue for attr_set and obj

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Message-Id: <20150924.225508.2124748200966556070.davem@davemloft.net>
Date:	Thu, 24 Sep 2015 22:55:08 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	sfeldma@...il.com
Cc:	vivien.didelot@...oirfairelinux.com, jiri@...nulli.us,
	netdev@...r.kernel.org, idosch@...lanox.com, eladr@...lanox.com,
	f.fainelli@...il.com, linux@...ck-us.net, rami.rosen@...el.com,
	roopa@...ulusnetworks.com, pjonnala@...adcom.com, andrew@...n.ch,
	gospo@...ulusnetworks.com, jiri@...lanox.com
Subject: Re: [patch net-next v3 02/10] switchdev: introduce transaction
 item queue for attr_set and obj_add

From: Scott Feldman <sfeldma@...il.com>
Date: Thu, 24 Sep 2015 22:29:43 -0700

> I'd rather keep 2-phase not optional, or at least make it some what of
> a pain for drivers to opt-out of 2-phase.  Forcing the driver to see
> both phases means the driver needs to put some code to skip phase 1
> (and hopefully has some persistent comment explaining why its being
> skipped).  Something like:
> 
> /* I'm skipping phase 1 prepare for this operation.  I have infinite hardware
>  * resources and I'm not setting any persistent state in the driver or device
>  * and I don't need any dynamic resources from the kernel, so its impossible
>  * for me to fail phase 2 commit.  Nothing to prepare, sorry.
>  */

I agree with Scott here.

If you can opt out of something, you can not think about it and thus
more likely get it wrong.

I can just see a driver not implementing prepare at all and then doing
stupid things in commit when they hit some resource limit or whatever,
rather than taking care of such issues in prepare.
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