From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-f194.google.com (mail-qt1-f194.google.com [209.85.160.194]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 42JxqM4fTBzF3DQ for ; Tue, 25 Sep 2018 07:17:19 +1000 (AEST) Received: by mail-qt1-f194.google.com with SMTP id h22-v6so3173059qtr.13 for ; Mon, 24 Sep 2018 14:17:19 -0700 (PDT) MIME-Version: 1.0 References: <20180912150142.157913-1-arnd@arndb.de> <20180912151134.436719-1-arnd@arndb.de> <20180914203506.GE35251@wrath> <20180914205748.GC19965@ZenIV.linux.org.uk> <20180918175108.GF35251@wrath> <20180918175952.GJ11367@ziepe.ca> <20180924203505.GC6008@ziepe.ca> In-Reply-To: <20180924203505.GC6008@ziepe.ca> From: Arnd Bergmann Date: Mon, 24 Sep 2018 23:17:01 +0200 Message-ID: Subject: Re: [PATCH v2 05/17] compat_ioctl: move more drivers to generic_compat_ioctl_ptrarg To: Jason Gunthorpe Cc: Darren Hart , Al Viro , Linux FS-devel Mailing List , gregkh , David Miller , driverdevel , Linux Kernel Mailing List , qat-linux@intel.com, "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" , Linux Media Mailing List , dri-devel , linaro-mm-sig@lists.linaro.org, amd-gfx@lists.freedesktop.org, "open list:HID CORE LAYER" , linux-iio@vger.kernel.org, linux-rdma , linux-nvdimm@lists.01.org, linux-nvme@lists.infradead.org, linux-pci , Platform Driver , linux-remoteproc@vger.kernel.org, sparclinux , linux-scsi , USB list , linux-fbdev@vger.kernel.org, linuxppc-dev , linux-btrfs , ceph-devel , linux-wireless , Networking Content-Type: text/plain; charset="UTF-8" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Sep 24, 2018 at 10:35 PM Jason Gunthorpe wrote: > On Mon, Sep 24, 2018 at 10:18:52PM +0200, Arnd Bergmann wrote: > > On Tue, Sep 18, 2018 at 7:59 PM Jason Gunthorpe wrote: > > > On Tue, Sep 18, 2018 at 10:51:08AM -0700, Darren Hart wrote: > > > > On Fri, Sep 14, 2018 at 09:57:48PM +0100, Al Viro wrote: > > > > > On Fri, Sep 14, 2018 at 01:35:06PM -0700, Darren Hart wrote: > > We already do this inside of some subsystems, notably drivers/media/, > > and it simplifies the implementation of the ioctl handler function > > significantly. We obviously cannot do this in general, both because of > > traditional drivers that have 16-bit command codes (drivers/tty and others) > > and also because of drivers that by accident defined the commands > > incorrectly and use the wrong type or the wrong direction in the > > definition. > > That could work well, but the first idea could be done globally and > mechanically, while this would require very careful per-driver > investigation. > > Particularly if the core code has worse performance.. ie due to > kmalloc calls or something. > > I think it would make more sense to start by having the core do the > case to __user and then add another entry point to have the core do > the copy_from_user, and so on. Having six separate callback pointers to implement a single system call seems a bit excessive though. Arnd