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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 03822C76191 for ; Thu, 25 Jul 2019 18:10:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0740218F0 for ; Thu, 25 Jul 2019 18:10:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564078250; bh=x+ORaQJeKgS3j+rdkVUxb78f2fEXbMS5Q2oS/qDLRjw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=oT0lZZWXJT75lrKmvVLpvsysfOhhS3kLtf7hMNYp7aXRdk4LeuxqDfkcSG6GK+pgJ LllJXwQdpqbJCk69e/druKWmvVk6646OwKA/ZQ1k6v4CgHt4tvBs3YvZxeKEdD2QA9 w5CD0fq8RjnBoefo7biPFl04UZB8f/l43m9ySKuw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726808AbfGYSKp (ORCPT ); Thu, 25 Jul 2019 14:10:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:53442 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726722AbfGYSKo (ORCPT ); Thu, 25 Jul 2019 14:10:44 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3B9FB218F0; Thu, 25 Jul 2019 18:10:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564078243; bh=x+ORaQJeKgS3j+rdkVUxb78f2fEXbMS5Q2oS/qDLRjw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=k2WeOieaFmoBq89MT9udtoPLN34+nsgmch91w02bA4td9R4/cEQgRmb7lZhWMKW1A l5E5M61NIfcaDSZmsX37Wv5yAHX5Z7sMH2djshb0kxmJJL84DUzaGilW0Pbc17ey6w pJsVMG1J1e8yqgwBOfIg8z9YWW7vfgCEpiGsOkWQ= Date: Thu, 25 Jul 2019 20:10:41 +0200 From: Greg Kroah-Hartman To: Logan Gunthorpe 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 Subject: Re: [PATCH v6 02/16] chardev: introduce cdev_get_by_path() Message-ID: <20190725181041.GB32305@kroah.com> References: <20190725172335.6825-1-logang@deltatee.com> <20190725172335.6825-3-logang@deltatee.com> <20190725174032.GA27818@kroah.com> <682ff89f-04e0-7a94-5aeb-895ac65ee7c9@deltatee.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <682ff89f-04e0-7a94-5aeb-895ac65ee7c9@deltatee.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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. > > 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. open() in userspace handles symlinks just fine, what crazy interface passes a string to try to find a char device node that is not open()? And why do you need a char device at all anyway? Is this just the "normal" nvme controller's character device node? > > 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. Everyone is special, just like everyone else :) Seriously, as no one else has ever needed this, you are an outlier. thanks, greg k-h