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Date: Thu, 19 Mar 2009 10:41:19 -0600
From: Alex Chiang <achiang@...com>
To: Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
Cc: jbarnes@...tuousgeek.org, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, Trent Piepho <xyzzy@...akeasy.org>
Subject: Re: [PATCH v4 08/12] PCI: Introduce /sys/bus/pci/devices/.../remove
* Kenji Kaneshige <kaneshige.kenji@...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@...akeasy.org>
>> Signed-off-by: Alex Chiang <achiang@...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@...r.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@...arflare.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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>>
>>
>
>
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