linux-kernel - Re: [REPOST][PATCH 1/2] driver core: Add new device_driver flag to allow binding via sysfs only

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Date:	Tue, 03 Dec 2013 16:34:33 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Kim Phillips <kim.phillips@...aro.org>,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	kvm@...r.kernel.org, scottwood@...escale.com, R65777@...escale.com,
	B07421@...escale.com, B08248@...escale.com,
	christoffer.dall@...aro.org, alex.williamson@...hat.com,
	a.motakis@...tualopensystems.com, agraf@...e.de,
	B16395@...escale.com
Subject: Re: [REPOST][PATCH 1/2] driver core: Add new device_driver flag to
 allow binding via sysfs only

On 2013-12-03 13:34, Kim Phillips wrote:
> VFIO supports pass-through of devices to user space - for sake
> of illustration, say a PCI e1000 device:
> 
> - the e1000 is first unbound from the PCI e1000 driver via sysfs
> - the vfio-pci driver is told via new_id that it now handles e1000 devices
> - the e1000 is explicitly bound to vfio-pci through sysfs
> 
> However, now we have two drivers in the system that both handle e1000
> devices.  A hotplug event could then occur and it is ambiguous as to which
> driver will claim the device.  The desired semantics is that vfio-pci is
> only bound to devices by explicit request in sysfs.  This patch makes this
> possible by introducing a sysfs_bind_only flag in struct device_driver.
> 
> Signed-off-by: Stuart Yoder <stuart.yoder@...escale.com>
> Signed-off-by: Kim Phillips <kim.phillips@...aro.org>
> ---
> rebased onto 3.13-rc2, and reposted from first submission which
> recieved no comments:
> 
> https://lkml.org/lkml/2013/10/11/53
> 
>  drivers/base/dd.c      | 5 ++++-
>  include/linux/device.h | 2 ++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 0605176..b83b16d 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -389,7 +389,7 @@ static int __device_attach(struct device_driver *drv, void *data)
>  {
>  	struct device *dev = data;
>  
> -	if (!driver_match_device(drv, dev))
> +	if (drv->sysfs_bind_only || !driver_match_device(drv, dev))
>  		return 0;
>  
>  	return driver_probe_device(drv, dev);
> @@ -476,6 +476,9 @@ static int __driver_attach(struct device *dev, void *data)
>   */
>  int driver_attach(struct device_driver *drv)
>  {
> +	if (drv->sysfs_bind_only)
> +		return 0;
> +
>  	return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
>  }
>  EXPORT_SYMBOL_GPL(driver_attach);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 952b010..ed441d1 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -200,6 +200,7 @@ extern struct klist *bus_get_device_klist(struct bus_type *bus);
>   * @owner:	The module owner.
>   * @mod_name:	Used for built-in modules.
>   * @suppress_bind_attrs: Disables bind/unbind via sysfs.
> + * @sysfs_bind_only: Only allow bind/unbind via sysfs.
>   * @of_match_table: The open firmware table.
>   * @acpi_match_table: The ACPI match table.
>   * @probe:	Called to query the existence of a specific device,
> @@ -233,6 +234,7 @@ struct device_driver {
>  	const char		*mod_name;	/* used for built-in modules */
>  
>  	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
> +	bool sysfs_bind_only;		/* only allow bind/unbind via sysfs */
>  
>  	const struct of_device_id	*of_match_table;
>  	const struct acpi_device_id	*acpi_match_table;
> 

I think I only discussed this with Stuart in person at the KVM Forum:
Why not deriving the property "sysfs bind only" from the fact that a
device does wild-card binding? Are there use cases that benefit from
decoupling both features?

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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