From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53FA4C76190 for ; Thu, 25 Jul 2019 17:53:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38F4E229F3 for ; Thu, 25 Jul 2019 17:53:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730084AbfGYRxk (ORCPT ); Thu, 25 Jul 2019 13:53:40 -0400 Received: from ale.deltatee.com ([207.54.116.67]:40494 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730082AbfGYRxk (ORCPT ); Thu, 25 Jul 2019 13:53:40 -0400 Received: from s01061831bf6ec98c.cg.shawcable.net ([68.147.80.180] helo=[192.168.6.132]) by ale.deltatee.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1hqhvg-0001pD-6S; Thu, 25 Jul 2019 11:53:25 -0600 To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, Christoph Hellwig , Sagi Grimberg , Keith Busch , Jens Axboe , Chaitanya Kulkarni , Max Gurtovoy , Stephen Bates , Alexander Viro References: <20190725172335.6825-1-logang@deltatee.com> <20190725172335.6825-3-logang@deltatee.com> <20190725174032.GA27818@kroah.com> From: Logan Gunthorpe Message-ID: <682ff89f-04e0-7a94-5aeb-895ac65ee7c9@deltatee.com> Date: Thu, 25 Jul 2019 11:53:20 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190725174032.GA27818@kroah.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 68.147.80.180 X-SA-Exim-Rcpt-To: viro@zeniv.linux.org.uk, sbates@raithlin.com, maxg@mellanox.com, Chaitanya.Kulkarni@wdc.com, axboe@fb.com, kbusch@kernel.org, sagi@grimberg.me, hch@lst.de, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v6 02/16] chardev: introduce cdev_get_by_path() X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2019-07-25 11:40 a.m., Greg Kroah-Hartman wrote: > On Thu, Jul 25, 2019 at 11:23:21AM -0600, Logan Gunthorpe wrote: >> cdev_get_by_path() attempts to retrieve a struct cdev from >> a path name. It is analagous to blkdev_get_by_path(). >> >> This will be necessary to create a nvme_ctrl_get_by_path()to >> support NVMe-OF passthru. > > Ick, why? Why would a cdev have a "pathname"? So we can go from "/dev/nvme0" (which points to a char device) to its struct cdev and eventually it's struct nvme_ctrl. Doing it this way also allows supporting symlinks that might be created by udev rules. This is very similar to blkdev_get_by_path() that lets regular NVMe-OF obtain the struct block_device from a path. I didn't think this would be all that controversial. > What is "NVMe-OF passthru"? Why does a char device node have anything > to do with NVMe? NVME-OF passthru is support for NVME over fabrics to directly target a regular NVMe controller and thus export an entire NVMe device to a remote system. We need to be able to tell the kernel which controller to use and IMO a path to the device file is the best way as it allows us to support symlinks created by udev. > We have way too many ways to abuse cdevs today, my long-term-wish has > always been to clean this interface up to make it more sane and unified, > and get rid of the "outliers" (all created at the time for a good > reason, that's not the problem.) But to add "just one more" seems > really odd to me. Well it doesn't seem all that much like an outlier to me. Logan