From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [RFC PATCH v1 5/7] media: v4l2: introduce two IOCTLs for face detection Date: Tue, 6 Dec 2011 14:41:25 +0000 Message-ID: <201112061441.25822.arnd@arndb.de> References: <1322817178-8931-1-git-send-email-ming.lei@canonical.com> <201112061255.56136.arnd@arndb.de> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Ming Lei Cc: linux-arm-kernel@lists.infradead.org, Mauro Carvalho Chehab , Tony Lindgren , Greg KH , linux-kernel@vger.kernel.org, Sylwester Nawrocki , Alan Cox , linux-omap@vger.kernel.org List-Id: linux-omap@vger.kernel.org On Tuesday 06 December 2011, Ming Lei wrote: > > Using an array added to the end of the v4l2_fd_result structure > > rather than a pointer would really make this easier IMHO. > > I have tried to do this, but video_usercopy needs a few changes > to handle array args if no indirect pointer is passed to kernel. Ah, I see. Or you would have to encode the array size into the ioctl command, which is also ugly in a different way. > I am not sure if media guys are happy to accept the changes, :-) Maybe Mauro can comment on which solution he prefers then, given the choice between: 1. adding another handler in drivers/media/video/v4l2-compat-ioctl32.c 2. passing a pointer that is casted to __u64 in user space an back in the kernel 3. extending video_usercopy in some way to make this work, preferably in a generic way. 4. using a variable command number like #define VIDIOC_G_FD_RESULT(num) _IOC(_IOC_READ|_IOC_WRITE,'V', 95, \ sizeof(struct v4l2_fd_result) + (num) * sizeof(struct v4l2_fd_detection) 5. requiring the interface to be simplified to return only a single struct v4l2_fd_detection at a time I agree that none of these are nice. My preferred option would be last one, but I don't know how performance critical the interface is or if it would cause any races that you want to avoid. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Tue, 6 Dec 2011 14:41:25 +0000 Subject: [RFC PATCH v1 5/7] media: v4l2: introduce two IOCTLs for face detection In-Reply-To: References: <1322817178-8931-1-git-send-email-ming.lei@canonical.com> <201112061255.56136.arnd@arndb.de> Message-ID: <201112061441.25822.arnd@arndb.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tuesday 06 December 2011, Ming Lei wrote: > > Using an array added to the end of the v4l2_fd_result structure > > rather than a pointer would really make this easier IMHO. > > I have tried to do this, but video_usercopy needs a few changes > to handle array args if no indirect pointer is passed to kernel. Ah, I see. Or you would have to encode the array size into the ioctl command, which is also ugly in a different way. > I am not sure if media guys are happy to accept the changes, :-) Maybe Mauro can comment on which solution he prefers then, given the choice between: 1. adding another handler in drivers/media/video/v4l2-compat-ioctl32.c 2. passing a pointer that is casted to __u64 in user space an back in the kernel 3. extending video_usercopy in some way to make this work, preferably in a generic way. 4. using a variable command number like #define VIDIOC_G_FD_RESULT(num) _IOC(_IOC_READ|_IOC_WRITE,'V', 95, \ sizeof(struct v4l2_fd_result) + (num) * sizeof(struct v4l2_fd_detection) 5. requiring the interface to be simplified to return only a single struct v4l2_fd_detection at a time I agree that none of these are nice. My preferred option would be last one, but I don't know how performance critical the interface is or if it would cause any races that you want to avoid. Arnd