From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from quartz.orcorp.ca ([184.70.90.242]) by bombadil.infradead.org with esmtps (Exim 4.87 #1 (Red Hat Linux)) id 1ciOd1-0006jG-6n for linux-mtd@lists.infradead.org; Mon, 27 Feb 2017 16:58:29 +0000 Date: Mon, 27 Feb 2017 09:56:18 -0700 From: Jason Gunthorpe To: Dan Williams Cc: Logan Gunthorpe , Greg Kroah-Hartman , Alexander Viro , Johannes Thumshirn , Jan Kara , Arnd Bergmann , Sajjan Vikas C , Dmitry Torokhov , Linus Walleij , Alexandre Courbot , Peter Huewe , Marcel Selhorst , Jarkko Sakkinen , Olof Johansson , Doug Ledford , Sean Hefty , Hal Rosenstock , Dmitry Vyukov , Haggai Eran , Parav Pandit , Leon Romanovsky , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Hans Verkuil , Mauro Carvalho Chehab , Artem Bityutskiy , Richard Weinberger , David Woodhouse , Brian Norris , Boris Brezillon , Marek Vasut , Cyrille Pitchen , Matt Porter , Alexandre Bounine , Andrew Morton , Joe Perches , Lorenzo Stoakes , Vladimir Zapolskiy , Alessandro Zummo , Alexandre Belloni , Boaz Harrosh , "James E.J. Bottomley" , "Martin K. Petersen" , Stephen Bates , Bjorn Helgaas , linux-pci@vger.kernel.org, linux-scsi , rtc-linux@googlegroups.com, linux-mtd@lists.infradead.org, "Linux-media@vger.kernel.org" , linux-iio@vger.kernel.org, linux-rdma@vger.kernel.org, linux-gpio@vger.kernel.org, linux-input@vger.kernel.org, "linux-nvdimm@lists.01.org" , linux-fsdevel , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2 01/16] chardev: add helper function to register char devs with a struct device 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-Disposition: inline In-Reply-To: List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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