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

[Kenji Kaneshige]

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@xxxxxxxxxxxxx>
> Signed-off-by: Alex Chiang <achiang@xxxxxx>
> ---
>
>  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@xxxxxxxxxxxxxxx>
> +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@xxxxxxxxxxxxxx>
> 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?

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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