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 38CE5C41514 for ; Thu, 25 Jul 2019 18:08:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F35E22BE8 for ; Thu, 25 Jul 2019 18:08:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726215AbfGYSIr (ORCPT ); Thu, 25 Jul 2019 14:08:47 -0400 Received: from ale.deltatee.com ([207.54.116.67]:40804 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727619AbfGYSIn (ORCPT ); Thu, 25 Jul 2019 14:08:43 -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 1hqiAH-0002J3-9h; Thu, 25 Jul 2019 12:08:30 -0600 To: Matthew Wilcox Cc: Greg Kroah-Hartman , 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> <682ff89f-04e0-7a94-5aeb-895ac65ee7c9@deltatee.com> <20190725175834.GB30641@bombadil.infradead.org> From: Logan Gunthorpe Message-ID: <4bfbeaa7-9b81-b802-4cb6-ca141eb1a0c9@deltatee.com> Date: Thu, 25 Jul 2019 12:08:27 -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: <20190725175834.GB30641@bombadil.infradead.org> 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, willy@infradead.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 11:58 a.m., Matthew Wilcox wrote: > On Thu, Jul 25, 2019 at 11:53:20AM -0600, Logan Gunthorpe wrote: >> >> >> 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. > > But you're not really trying to go from a string to a chardev. You're > trying to go from a nvmet_subsys to a chardev. Isn't there a better > way to link the two somewhere else? > > (I must confess that once I would have known the answer to this, but > the NVMe subsystem has grown ridiculously complex and I can no longer > fit it in my head) Well the nvmet_subsys isn't related to the nvme_ctrl (and thus char dev) at all. An nvmet_subsys is created via configfs and the user has to specify an NVMe controller for it to use (by writting a string to a config attribute). The best handle the user has is a path to the controller's cdev (/dev/nvmeX) so the fabrics code has to be able to lookup the corresponding struct nvme_ctrl from the path. This is directly analogous to the way NVMe-of works today: it uses blkdev_get_by_path() to translate a user provided path to a struct block_device. The only difference here is that, for passthru, we need a nvme_ctrl, not a block device. Logan