• Lukas Wunner's avatar
    PCI: hotplug: Embed hotplug_slot · 125450f8
    Lukas Wunner authored
    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: default avatarLukas Wunner <lukas@wunner.de>
    Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
    Reviewed-by: default avatarRafael 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>
    125450f8
pci_hotplug.h 5.46 KB