PCI: hotplug: Embed hotplug_slot

When the PCI hotplug core and its first user, cpqphp, were introduced in
February 2002 with historic commit a8a2069f432c, cpqphp allocated a slot
struct for its internal use plus a hotplug_slot struct to be registered
with the hotplug core and linked the two with pointers:
https://git.kernel.org/tglx/history/c/a8a2069f432c

Nowadays, the predominant pattern in the tree is to embed ("subclass")
such structures in one another and cast to the containing struct with
container_of().  But it wasn't until July 2002 that container_of() was
introduced with historic commit ec4f214232cf:
https://git.kernel.org/tglx/history/c/ec4f214232cf

pnv_php, introduced in 2016, did the right thing and embedded struct
hotplug_slot in its internal struct pnv_php_slot, but all other drivers
cargo-culted cpqphp's design and linked separate structs with pointers.

Embedding structs is preferrable to linking them with pointers because
it requires fewer allocations, thereby reducing overhead and simplifying
error paths.  Casting an embedded struct to the containing struct
becomes a cheap subtraction rather than a dereference.  And having fewer
pointers reduces the risk of them pointing nowhere either accidentally
or due to an attack.

Convert all drivers to embed struct hotplug_slot in their internal slot
struct.  The "private" pointer in struct hotplug_slot thereby becomes
unused, so drop it.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>  # drivers/pci/hotplug/rpa*
Acked-by: Sebastian Ott <sebott@linux.ibm.com>        # drivers/pci/hotplug/s390*
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com> # drivers/platform/x86
Cc: Len Brown <lenb@kernel.org>
Cc: Scott Murray <scott@spiteful.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Oliver OHalloran <oliveroh@au1.ibm.com>
Cc: Gavin Shan <gwshan@linux.vnet.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Corentin Chary <corentin.chary@gmail.com>
Cc: Darren Hart <dvhart@infradead.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/pci/hotplug/shpchp.h b/drivers/pci/hotplug/shpchp.h
index a7bb816e6f25..f7f13ee5d06e 100644
--- a/drivers/pci/hotplug/shpchp.h
+++ b/drivers/pci/hotplug/shpchp.h
@@ -73,7 +73,7 @@ struct slot {
 	u8 pwr_save;
 	struct controller *ctrl;
 	const struct hpc_ops *hpc_ops;
-	struct hotplug_slot *hotplug_slot;
+	struct hotplug_slot hotplug_slot;
 	struct list_head	slot_list;
 	struct delayed_work work;	/* work for button event */
 	struct mutex lock;
@@ -171,7 +171,7 @@ int shpc_init(struct controller *ctrl, struct pci_dev *pdev);
 
 static inline const char *slot_name(struct slot *slot)
 {
-	return hotplug_slot_name(slot->hotplug_slot);
+	return hotplug_slot_name(&slot->hotplug_slot);
 }
 
 struct ctrl_reg {
@@ -209,7 +209,7 @@ enum ctrl_offsets {
 
 static inline struct slot *get_slot(struct hotplug_slot *hotplug_slot)
 {
-	return hotplug_slot->private;
+	return container_of(hotplug_slot, struct slot, hotplug_slot);
 }
 
 static inline struct slot *shpchp_find_slot(struct controller *ctrl, u8 device)