linux-kernel - Re: [RFC PATCH 1/6] driver core: add a bus notification to temporarily reject driver binding

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Date:	Sun, 11 Nov 2012 06:21:52 +0100
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Jiang Liu <liuj97@...il.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Joerg Roedel <joerg.roedel@....com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Hanjun Guo <guohanjun@...wei.com>
Subject: Re: [RFC PATCH 1/6] driver core: add a bus notification to
 temporarily reject driver binding

On Sat, Nov 10, 2012 at 09:57:14PM +0800, Jiang Liu wrote:
>  From: Jiang Liu <jiang.liu@...wei.com>
> 
> There are several requirements to temporarily reject device driver
> binding. Possible usage cases as below:
> 1) We should avoid binding an unsafe driver to a device belonging to
>    an active VFIO group, otherwise it will break the DMA isolation
>    property of VFIO.
> 2) When hot-removing a PCI hierachy, we should avoid binding device
>    drivers to PCI devices going to be removed during the window
>    between unbinding of device driver and destroying of device nodes.
> 3) When hot-adding a PCI host bridge, we should temporarily disable
>    driver binding before setting up corresponding IOMMU and IOAPIC.
> 
> We may add a flag into struct device to temporarily disable driver
> binding as in this thread https://patchwork.kernel.org/patch/1535721/.

I totally do not understand.  The bus controls this, if it does not want
to bind a device to a driver, then don't do it.  It's really quite
simple to just block the probe callback the bus gets, right?  Why create
all of this extra, and confusing, interface instead?

> This patch proposes another solution to temporarily disable driver
> binding by using bus notification mechanisms. It adds an notification
> event to solicit if anybody has objections when binding a driver to a
> device.

Sorry, but no, don't do this, it's way more confusing.

greg k-h
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