PCI: add rescan to /sys/.../pci_bus/.../

After remove the device from /sys, we have to rescan all or
find out the bridge and access /sys../device/rescan there.

this patch add /sys/.../pci_bus/.../rescan. So user can rescan more easy.
that is more clean and easy to understand.

like after remove 0000:c4:00.0, you can rescan 0000:c4 directly.

-v2: According to Jesse, use function instead of exposing attr, so could hide
	#ifdef in header file.
     also add code to remove rescan file in remove path.
-v3: GregKH pointed out that we should use dev_attrs to avoid racing.
     So add pcibus_attrs and make it to be member of pcibus_attrs.
-v4: Change name to pcibus_dev_attrs according to GregKH

Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/pci-sysfs.c

@@ -318,6 +318,25 @@ remove_store(struct device *dev, struct device_attribute *dummy,
 		count = ret;
 	return count;
 }
+
+static ssize_t
+dev_bus_rescan_store(struct device *dev, struct device_attribute *attr,
+		 const char *buf, size_t count)
+{
+	unsigned long val;
+	struct pci_bus *bus = to_pci_bus(dev);
+
+	if (strict_strtoul(buf, 0, &val) < 0)
+		return -EINVAL;
+
+	if (val) {
+		mutex_lock(&pci_remove_rescan_mutex);
+		pci_rescan_bus(bus);
+		mutex_unlock(&pci_remove_rescan_mutex);
+	}
+	return count;
+}
+
 #endif
 
 struct device_attribute pci_dev_attrs[] = {
@@ -347,6 +366,13 @@ struct device_attribute pci_dev_attrs[] = {
 	__ATTR_NULL,
 };
 
+struct device_attribute pcibus_dev_attrs[] = {
+#ifdef CONFIG_HOTPLUG
+	__ATTR(rescan, (S_IWUSR|S_IWGRP), NULL, dev_bus_rescan_store),
+#endif
+	__ATTR_NULL,
+};
+
 static ssize_t
 boot_vga_show(struct device *dev, struct device_attribute *attr, char *buf)
 {