From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Subject: Re: [PATCH 8/9] PCI: hotplug: Embed hotplug_slot To: Lukas Wunner , Bjorn Helgaas , linux-pci@vger.kernel.org, Sinan Kaya , Mika Westerberg Cc: Scott Murray , linux-s390@vger.kernel.org, Greg Kroah-Hartman , acpi4asus-user@lists.sourceforge.net, "Rafael J. Wysocki" , Gavin Shan , platform-driver-x86@vger.kernel.org, linux-acpi@vger.kernel.org, Paul Mackerras , Sebastian Ott , Corentin Chary , Darren Hart , linuxppc-dev@lists.ozlabs.org, Andy Shevchenko , Gerald Schaefer , Len Brown References: <9918fbca94bcfc03d1560b191d138d3e6664cc86.1534686485.git.lukas@wunner.de> From: Tyrel Datwyler Date: Mon, 20 Aug 2018 17:43:17 -0700 MIME-Version: 1.0 In-Reply-To: <9918fbca94bcfc03d1560b191d138d3e6664cc86.1534686485.git.lukas@wunner.de> Content-Type: text/plain; charset=utf-8 Message-Id: List-ID: On 08/19/2018 07:29 AM, Lukas Wunner wrote: > 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 > Cc: Rafael J. Wysocki > Cc: Len Brown > Cc: Scott Murray > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Michael Ellerman > Cc: Gavin Shan > Cc: Sebastian Ott > Cc: Gerald Schaefer > Cc: Corentin Chary > Cc: Darren Hart