From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH v2 01/16] chardev: add helper function to register char devs with a struct device Date: Mon, 27 Feb 2017 09:56:18 -0700 Message-ID: <20170227165618.GE5891@obsidianresearch.com> References: <1488091097-12328-1-git-send-email-logang@deltatee.com> <1488091097-12328-2-git-send-email-logang@deltatee.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: Dan Williams Cc: Alessandro Zummo , Jan Kara , linux-iio-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linus Walleij , Jarkko Sakkinen , Alexandre Bounine , Alexandre Belloni , Peter Meerwald-Stadler , linux-scsi , Peter Huewe , Parav Pandit , Sean Hefty , Alexandre Courbot , Lars-Peter Clausen , "James E.J. Bottomley" , rtc-linux-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, Leon Romanovsky , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Richard Weinberger , Marek Vasut , Doug Ledford , Hans Verkuil , Matt List-Id: linux-gpio@vger.kernel.org On Sun, Feb 26, 2017 at 10:21:25AM -0800, Dan Williams wrote: > > + * cdev_device_add() adds the char device represented by @cdev to the system, > > + * just as cdev_add does. It then adds @dev to the system using device_add > > + * The dev_t for the char device will be taken from the struct device which > > + * needs to be initialized first. This helper function correctly takes a > > + * reference to the parent device so the parent will not get released until > > + * all references to the cdev are released. > > + * > > + * This function should be used whenever the struct cdev and the > > + * struct device are members of the same structure whose lifetime is > > + * managed by the struct device. > > + */ > > Perhaps add a note here that userspace may have invoked file > operations between cdev_add() and a failing device_add(), so > additional cleanup beyond put_device() (like mmap invalidation) might > be needed. That can be a later follow-on patch. Yes please, that is way too subtle. Suggest: NOTE: Callers must assume that userspace was able to open the cdev and can call cdev fops callbacks at any time, even if this function fails. I would also add a note to cdev_device_del: NOTE: This guarantees that associated sysfs callbacks are not running or runnable, however any open cdevs will remain and their fops remain callable even after this returns. Since I have seen a lot of confusion on that point as well.. Jason