Re: [PATCH v4 08/12] PCI: Introduce /sys/bus/pci/devices/.../remove

[Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>]

Alex Chiang wrote:
> * Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>:
>> Alex Chiang wrote:
>>> This patch adds an attribute named "remove" to a PCI device's sysfs
>>> directory.  Writing a non-zero value to this attribute will remove the PCI
>>> device and any children of it.
>>>
>>> Trent Piepho wrote the original implementation and documentation.
>>>
>>> Thanks to Vegard Nossum for testing under kmemcheck and finding locking
>>> issues with the sysfs interface.
>>>
>>> Cc: Trent Piepho <xyzzy@speakeasy.org>
>>> Signed-off-by: Alex Chiang <achiang@hp.com>
>>> ---
>>>
>>>  Documentation/ABI/testing/sysfs-bus-pci |    8 ++++++
>>>  Documentation/filesystems/sysfs-pci.txt |   10 +++++++
>>>  drivers/pci/pci-sysfs.c                 |   44 +++++++++++++++++++++++++++++++
>>>  3 files changed, 62 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
>>> index ea4aee2..5b1ddde 100644
>>> --- a/Documentation/ABI/testing/sysfs-bus-pci
>>> +++ b/Documentation/ABI/testing/sysfs-bus-pci
>>> @@ -50,6 +50,14 @@ Description:
>>>  		re-discover previously removed devices.
>>>  		Depends on CONFIG_HOTPLUG.
>>>  +What:		/sys/bus/pci/devices/.../remove
>>> +Date:		January 2009
>>> +Contact:	Linux PCI developers <linux-pci@vger.kernel.org>
>>> +Description:
>>> +		Writing a non-zero value to this attribute will
>>> +		hot-remove the PCI device and any of its children.
>>> +		Depends on CONFIG_HOTPLUG.
>>> +
>>>  What:		/sys/bus/pci/devices/.../vpd
>>>  Date:		February 2008
>>>  Contact:	Ben Hutchings <bhutchings@solarflare.com>
>>> diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
>>> index 9f8740c..26e4b8b 100644
>>> --- a/Documentation/filesystems/sysfs-pci.txt
>>> +++ b/Documentation/filesystems/sysfs-pci.txt
>>> @@ -12,6 +12,7 @@ that support it.  For example, a given bus might look like this:
>>>       |   |-- enable
>>>       |   |-- irq
>>>       |   |-- local_cpus
>>> +     |   |-- remove
>>>       |   |-- resource
>>>       |   |-- resource0
>>>       |   |-- resource1
>>> @@ -36,6 +37,7 @@ files, each with their own function.
>>>         enable	           Whether the device is enabled (ascii, rw)
>>>         irq		   IRQ number (ascii, ro)
>>>         local_cpus	   nearby CPU mask (cpumask, ro)
>>> +       remove		   remove device from kernel's list (ascii, wo)
>>>         resource		   PCI resource host addresses (ascii, ro)
>>>         resource0..N	   PCI resource N, if present (binary, mmap)
>>>         resource0_wc..N_wc  PCI WC map resource N, if prefetchable (binary, mmap)
>>> @@ -46,6 +48,7 @@ files, each with their own function.
>>>     ro - read only file
>>>    rw - file is readable and writable
>>> +  wo - write only file
>>>    mmap - file is mmapable
>>>    ascii - file contains ascii text
>>>    binary - file contains binary data
>>> @@ -73,6 +76,13 @@ that the device must be enabled for a rom read to return data succesfully.
>>>  In the event a driver is not bound to the device, it can be enabled using the
>>>  'enable' file, documented above.
>>>  +The 'remove' file is used to remove the PCI device, by writing a 
>>> non-zero
>>> +integer to the file.  This does not involve any kind of hot-plug functionality,
>>> +e.g. powering off the device.  The device is removed from the kernel's list of
>>> +PCI devices, the sysfs directory for it is removed, and the device will be
>>> +removed from any drivers attached to it. Removal of PCI root buses is
>>> +disallowed.
>>> +
>>>  Accessing legacy resources through sysfs
>>>  ----------------------------------------
>>>  diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
>>> index 22dbc65..6e2b1fd 100644
>>> --- a/drivers/pci/pci-sysfs.c
>>> +++ b/drivers/pci/pci-sysfs.c
>>> @@ -246,6 +246,47 @@ struct bus_attribute pci_bus_attrs[] = {
>>>  	__ATTR(rescan, S_IWUSR, NULL, bus_rescan_store),
>>>  	__ATTR_NULL
>>>  };
>>> +
>>> +static void remove_callback(struct device *dev)
>>> +{
>>> +	int bridge = 0;
>>> +	struct pci_dev *pdev = to_pci_dev(dev);
>>> +
>>> +	mutex_lock(&pci_remove_rescan_mutex);
>>> +
>>> +	if (pdev->subordinate)
>>> +		bridge = 1;
>>> +
>>> +	pci_remove_bus_device(pdev);
>>> +	if (bridge && list_empty(&pdev->bus->devices))
>>> +		pci_remove_bus(pdev->bus);
>> I cannot understand the above two lines. Could you explain
>> what it intend?
> 
> If the user says:
> 
> 	echo 1 > /sys/bus/pci/devices/.../remove
> 
> And that device is a bridge, then we need to specifically call
> pci_remove_bus as well, to actually remove the bus itself.
> Without it, pci_bus_remove_device() will remove all of its
> children (and subordinate buses) in a depth-first manner, but we
> will never actually remove the bus that the user specified.
> 

Do you mean user removes bridge device to remove its *primary*
bus? It is very strange. I think the bus should be removed
when its parent bridge is removed.

> In other words, without it, we will still see the bus in:
> 
> 	/sys/class/pci_bus/...
>

What is the problem?
 
> We only want to remove the bus if it has no children left. I
> think the check for list_empty(&pdev->bus->devices) might be
> overkill... I can try taking that bit out and testing again.
>

I think we don't need the two lines. But if you do that, you
need list_empty(&pdev->bus->devices), doesn't it? On the other
hand, we must not check 'bridge' in the if statement. Or bus
will never be removed when non-bridge device is removed last
on the bus.

Again, I think we don't need the two lines. But am I
misunderstanding something?

Thanks,
Kenji Kaneshige

 
> Thanks for the review.
> 
> /ac
> 
>> Thanks,
>> Kenji Kaneshige
>>
>>
>>> +
>>> +	mutex_unlock(&pci_remove_rescan_mutex);
>>> +}
>>> +
>>> +static ssize_t
>>> +remove_store(struct device *dev, struct device_attribute *dummy,
>>> +	     const char *buf, size_t count)
>>> +{
>>> +	int ret = 0;
>>> +	unsigned long val;
>>> +	struct pci_dev *pdev = to_pci_dev(dev);
>>> +
>>> +	if (strict_strtoul(buf, 0, &val) < 0)
>>> +		return -EINVAL;
>>> +
>>> +	if (!capable(CAP_SYS_ADMIN))
>>> +		return -EPERM;
>>> +
>>> +	if (pdev->subordinate && pci_is_root_bus(pdev->bus))
>>> +		return -EBUSY;
>>> +
>>> +	if (val)
>>> +		ret = device_schedule_callback(dev, remove_callback);
>>> +	if (ret)
>>> +		count = ret;
>>> +	return count;
>>> +}
>>>  #endif
>>>   struct device_attribute pci_dev_attrs[] = {
>>> @@ -266,6 +307,9 @@ struct device_attribute pci_dev_attrs[] = {
>>>  	__ATTR(broken_parity_status,(S_IRUGO|S_IWUSR),
>>>  		broken_parity_status_show,broken_parity_status_store),
>>>  	__ATTR(msi_bus, 0644, msi_bus_show, msi_bus_store),
>>> +#ifdef CONFIG_HOTPLUG
>>> +	__ATTR(remove, S_IWUSR, NULL, remove_store),
>>> +#endif
>>>  	__ATTR_NULL,
>>>  };
>>>  
>>>
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>>>
>>
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