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

[Alex Chiang <achiang@hp.com>]

* 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.

In other words, without it, we will still see the bus in:

	/sys/class/pci_bus/...

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.

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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>>
>
>