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

[Kenji Kaneshige]

Alex Chiang wrote:
> * Kenji Kaneshige <kaneshige.kenji@xxxxxxxxxxxxxx>:
> > 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?
>
> 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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