On Thu, 2013-05-02 at 14:27 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wyso...@intel.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.wyso...@intel.com>
Looks good. For patch 1/4 to 3/4:
Reviewed-by: Toshi Kani <toshi.k...@hp.com>
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?
Thanks,
-Toshi
> +{
> + return dev->bus && dev->bus->offline && dev->bus->online;
> +}
> +
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