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

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Message-Id: <20131209125802.0e2b86a3daa9d9ad5a7d43bf@linaro.org>
Date:	Mon, 9 Dec 2013 12:58:02 -0600
From:	Kim Phillips <kim.phillips@...aro.org>
To:	scottwood@...escale.com
Cc:	jan.kiszka@...mens.com, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, kvm@...r.kernel.org,
	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 Thu, 5 Dec 2013 16:38:15 -0600
Scott Wood <scottwood@...escale.com> wrote:

> On Thu, 2013-12-05 at 17:45 +0000, Kim Phillips wrote:
> > On Tue, 03 Dec 2013 16:34:33 +0100
> > Jan Kiszka <jan.kiszka@...mens.com> wrote:
> > 
> > > 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?
> > 
> > you mean merge the two new flags sysfs_bind_only and platform driver's
> > match_any_dev into one new single driver flag, right?  good question.
> 
> What would combining them solve, other than making it more likely that
> Greg complains about the wildcard because it would no longer be handled
> at the bus level where all the other matching goes on?
> 
> They are logically separate things.  That doesn't change just because we
> currently plan to use them together.

Jan?  Given the above, what would be the advantage of merging
sysfs_bind_only and (PCI drivers' PCI_ANY_ID and platform drivers'
match_any_dev)?

Kim
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