Date:	Fri, 03 May 2013 01:36:04 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Toshi Kani <toshi.kani@...com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	isimatu.yasuaki@...fujitsu.com,
	vasilis.liaskovitis@...fitbricks.com, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 1/4] Driver core: Add offline/online device operations

On Thursday, May 02, 2013 05:11:27 PM Toshi Kani wrote:
> On Thu, 2013-05-02 at 14:27 +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > In some cases, graceful hot-removal of devices is not possible,
> > although in principle the devices in question support hotplug.
> > For example, that may happen for the last CPU in the system or
> > for memory modules holding kernel memory.
> > 
> > In those cases it is nice to be able to check if the given device
> > can be gracefully hot-removed before triggering a removal procedure
> > that cannot be aborted or reversed.  Unfortunately, however, the
> > kernel currently doesn't provide any support for that.
> > 
> > To address that deficiency, introduce support for offline and
> > online operations that can be performed on devices, respectively,
> > before a hot-removal and in case when it is necessary (or convenient)
> > to put a device back online after a successful offline (that has not
> > been followed by removal).  The idea is that the offline will fail
> > whenever the given device cannot be gracefully removed from the
> > system and it will not be allowed to use the device after a
> > successful offline (until a subsequent online) in analogy with the
> > existing CPU offline/online mechanism.
> > 
> > For now, the offline and online operations are introduced at the
> > bus type level, as that should be sufficient for the most urgent use
> > cases (CPUs and memory modules).  In the future, however, the
> > approach may be extended to cover some more complicated device
> > offline/online scenarios involving device drivers etc.
> > 
> > The lock_device_hotplug() and unlock_device_hotplug() functions are
> > introduced because subsequent patches need to put larger pieces of
> > code under device_hotplug_lock to prevent race conditions between
> > device offline and removal from happening.
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Looks good.  For patch 1/4 to 3/4:
> 
> Reviewed-by: Toshi Kani <toshi.kani@...com>

Thanks!

> I have one minor comment below.
> 
> > ---
> >  Documentation/ABI/testing/sysfs-devices-online |   20 +++
> >  drivers/base/core.c                            |  130 +++++++++++++++++++++++++
> >  include/linux/device.h                         |   21 ++++
> >  3 files changed, 171 insertions(+)
> > 
> > Index: linux-pm/include/linux/device.h
> > ===================================================================
> > --- linux-pm.orig/include/linux/device.h
> > +++ linux-pm/include/linux/device.h
> > @@ -70,6 +70,10 @@ extern void bus_remove_file(struct bus_t
> >   *		the specific driver's probe to initial the matched device.
> >   * @remove:	Called when a device removed from this bus.
> >   * @shutdown:	Called at shut-down time to quiesce the device.
> > + *
> > + * @online:	Called to put the device back online (after offlining it).
> > + * @offline:	Called to put the device offline for hot-removal. May fail.
> > + *
> >   * @suspend:	Called when a device on this bus wants to go to sleep mode.
> >   * @resume:	Called to bring a device on this bus out of sleep mode.
> >   * @pm:		Power management operations of this bus, callback the specific
> > @@ -103,6 +107,9 @@ struct bus_type {
> >  	int (*remove)(struct device *dev);
> >  	void (*shutdown)(struct device *dev);
> >  
> > +	int (*online)(struct device *dev);
> > +	int (*offline)(struct device *dev);
> > +
> >  	int (*suspend)(struct device *dev, pm_message_t state);
> >  	int (*resume)(struct device *dev);
> >  
> > @@ -646,6 +653,8 @@ struct acpi_dev_node {
> >   * @release:	Callback to free the device after all references have
> >   * 		gone away. This should be set by the allocator of the
> >   * 		device (i.e. the bus driver that discovered the device).
> > + * @offline_disabled: If set, the device is permanently online.
> > + * @offline:	Set after successful invocation of bus type's .offline().
> >   *
> >   * At the lowest level, every device in a Linux system is represented by an
> >   * instance of struct device. The device structure contains the information
> > @@ -718,6 +727,9 @@ struct device {
> >  
> >  	void	(*release)(struct device *dev);
> >  	struct iommu_group	*iommu_group;
> > +
> > +	bool			offline_disabled:1;
> > +	bool			offline:1;
> >  };
> >  
> >  static inline struct device *kobj_to_dev(struct kobject *kobj)
> > @@ -853,6 +865,15 @@ extern const char *device_get_devnode(st
> >  extern void *dev_get_drvdata(const struct device *dev);
> >  extern int dev_set_drvdata(struct device *dev, void *data);
> >  
> > +static inline bool device_supports_offline(struct device *dev)
> 
> Since we renamed "offline" to "hotplug" for the lock interfaces, should
> this function be renamed to device_supports_hotplug() as well?

Well, "offline" is more specific, as there may be devices that don't
support offline/online, but support hotplug otherwise.  That's why I didn't
change it.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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