PCI Hotplug: restore fakephp interface with complete reimplementation

A complete re-implementation of fakephp is necessary if it is to
present its former interface (pre-2.6.27, when it broke). The
reason is that PCI hotplug drivers call pci_hp_register(), which
enforces the rule that only one /sys/bus/pci/slots/ file may be
created per physical slot.

The change breaks the old fakephp's assumption that it could
create a file per function. So we re-implement fakephp to avoid
using the standard PCI hotplug API so that we can restore the old
fakephp user interface.

It puts entries in /sys/bus/pci/slots with the names of all PCI
devices/functions, exactly symmetrical to what is shown in
/sys/bus/pci/devices. Each slots/ entry has a "power" attribute,
which works the same way as the fakephp driver's power attribute
has worked.

There are a few improvements over old fakephp, which couldn't handle
PCI devices being added or removed via a means outside of
fakephp's knowledge.  If a device was added another way, old fakephp
didn't notice and didn't create the fake slot for it.  If a
device was removed another way, old fakephp didn't delete the fake
slot for it (and accessing the stale slot caused an oops).

The new implementation overcomes these limitations. As a
consequence, removing a bridge with other devices behind it now
works as well, which is something else old fakephp couldn't do
previously.

This duplicates a tiny bit of the code in the PCI core that does
this same function.  Re-using that code ends up being more
complex than duplicating it, and it makes code in the PCI core
more ugly just to support this legacy fakephp interface
compatibility layer.

Reviewed-by: James Cameron <qz@hp.com>
Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 162 insertions, 0 deletions

diff --git a/drivers/pci/hotplug/legacy_fakephp.c b/drivers/pci/hotplug/legacy_fakephp.c
new file mode 100644
index 000000000000..2dc7828df480
--- /dev/null
+++ b/drivers/pci/hotplug/legacy_fakephp.c
@@ -0,0 +1,162 @@
+/* Works like the fakephp driver used to, except a little better.
+ *
+ * - It's possible to remove devices with subordinate busses.
+ * - New PCI devices that appear via any method, not just a fakephp triggered
+ *   rescan, will be noticed.
+ * - Devices that are removed via any method, not just a fakephp triggered
+ *   removal, will also be noticed.
+ *
+ * Uses nothing from the pci-hotplug subsystem.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/list.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>
+#include <linux/init.h>
+#include <linux/pci.h>
+#include "../pci.h"
+
+struct legacy_slot {
+        struct kobject          kobj;
+        struct pci_dev          *dev;
+        struct list_head        list;
+};
+
+static LIST_HEAD(legacy_list);
+
+static ssize_t legacy_show(struct kobject *kobj, struct attribute *attr,
+                           char *buf)
+{
+        struct legacy_slot *slot = container_of(kobj, typeof(*slot), kobj);
+        strcpy(buf, "1\n");
+        return 2;
+}
+
+static void remove_callback(void *data)
+{
+        pci_remove_bus_device((struct pci_dev *)data);
+}
+
+static ssize_t legacy_store(struct kobject *kobj, struct attribute *attr,
+                            const char *buf, size_t len)
+{
+        struct legacy_slot *slot = container_of(kobj, typeof(*slot), kobj);
+        unsigned long val;
+
+        if (strict_strtoul(buf, 0, &val) < 0)
+                return -EINVAL;
+
+        if (val)
+                pci_rescan_bus(slot->dev->bus);
+        else
+                sysfs_schedule_callback(&slot->dev->dev.kobj, remove_callback,
+                                        slot->dev, THIS_MODULE);
+        return len;
+}
+
+static struct attribute *legacy_attrs[] = {
+        &(struct attribute){ .name = "power", .mode = 0644 },
+        NULL,
+};
+
+static void legacy_release(struct kobject *kobj)
+{
+        struct legacy_slot *slot = container_of(kobj, typeof(*slot), kobj);
+
+        pci_dev_put(slot->dev);
+        kfree(slot);
+}
+
+static struct kobj_type legacy_ktype = {
+        .sysfs_ops = &(struct sysfs_ops){
+                .store = legacy_store, .show = legacy_show
+        },
+        .release = &legacy_release,
+        .default_attrs = legacy_attrs,
+};
+
+static int legacy_add_slot(struct pci_dev *pdev)
+{
+        struct legacy_slot *slot = kzalloc(sizeof(*slot), GFP_KERNEL);
+
+        if (!slot)
+                return -ENOMEM;
+
+        if (kobject_init_and_add(&slot->kobj, &legacy_ktype,
+                                 &pci_slots_kset->kobj, "%s",
+                                 pdev->dev.bus_id)) {
+                dev_warn(&pdev->dev, "Failed to created legacy fake slot\n");
+                return -EINVAL;
+        }
+        slot->dev = pci_dev_get(pdev);
+
+        list_add(&slot->list, &legacy_list);
+
+        return 0;
+}
+
+static int legacy_notify(struct notifier_block *nb,
+                         unsigned long action, void *data)
+{
+        struct pci_dev *pdev = to_pci_dev(data);
+
+        if (action == BUS_NOTIFY_ADD_DEVICE) {
+                legacy_add_slot(pdev);
+        } else if (action == BUS_NOTIFY_DEL_DEVICE) {
+                struct legacy_slot *slot;
+
+                list_for_each_entry(slot, &legacy_list, list)
+                        if (slot->dev == pdev)
+                                goto found;
+
+                dev_warn(&pdev->dev, "Missing legacy fake slot?");
+                return -ENODEV;
+found:
+                kobject_del(&slot->kobj);
+                list_del(&slot->list);
+                kobject_put(&slot->kobj);
+        }
+
+        return 0;
+}
+
+static struct notifier_block legacy_notifier = {
+        .notifier_call = legacy_notify
+};
+
+static int __init init_legacy(void)
+{
+        struct pci_dev *pdev = NULL;
+
+        /* Add existing devices */
+        while ((pdev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, pdev)))
+                legacy_add_slot(pdev);
+
+        /* Be alerted of any new ones */
+        bus_register_notifier(&pci_bus_type, &legacy_notifier);
+        return 0;
+}
+module_init(init_legacy);
+
+static void __exit remove_legacy(void)
+{
+        struct legacy_slot *slot, *tmp;
+
+        bus_unregister_notifier(&pci_bus_type, &legacy_notifier);
+
+        list_for_each_entry_safe(slot, tmp, &legacy_list, list) {
+                list_del(&slot->list);
+                kobject_del(&slot->kobj);
+                kobject_put(&slot->kobj);
+        }
+}
+module_exit(remove_legacy);
+
+
+MODULE_AUTHOR("Trent Piepho <xyzzy@speakeasy.org>");
+MODULE_DESCRIPTION("Legacy version of the fakephp interface");
+MODULE_LICENSE("GPL");