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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 95F87C433DF for ; Wed, 10 Jun 2020 14:52:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 682782078C for ; Wed, 10 Jun 2020 14:52:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="NTX/q4qG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726998AbgFJOwm (ORCPT ); Wed, 10 Jun 2020 10:52:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39034 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726956AbgFJOwm (ORCPT ); Wed, 10 Jun 2020 10:52:42 -0400 Received: from mail-vs1-xe42.google.com (mail-vs1-xe42.google.com [IPv6:2607:f8b0:4864:20::e42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 804F1C03E96F for ; Wed, 10 Jun 2020 07:52:42 -0700 (PDT) Received: by mail-vs1-xe42.google.com with SMTP id q2so1412885vsr.1 for ; Wed, 10 Jun 2020 07:52:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=L8rp+MArSRRSpQFZbpuYYbVfBKFL7AdnnK2tR2ekGzs=; b=NTX/q4qGHr9EjYtkkXB7Nj9DSl33xCzTiVxJhZzHrH3IcQIbJcROsY12VwdxliLX/V k2XNVmqHAz4QAOrCjP8zCyLPKS/dMfyUA++4zpCXnQaxNBvcoCnFmIQmLE9+WpCFKDNb WrM9FK8yuorcC9QeTKqkQZjQETjpEm2xC9x/81T1vvwe2pNOH+RDsxTZGQ0oJ0zGMTOH qY2g0ksDgrJubYc+x3EQaPgHLvOz8e5HCi0vjRdSmQz9cYacsSYRmqPxC1GKXD+yOiQ/ CsJ04GyO9ioleQX5OqMuXUlnYu5EmeHGb0UUfNEKE1D/bqZydCxa80kfRDxY9sJbSGbk J+0Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=L8rp+MArSRRSpQFZbpuYYbVfBKFL7AdnnK2tR2ekGzs=; b=aZ5aB3IljuPut7YUeopaRmTaXr0eNllFfUVMMhvq0mEReQ9PF5jrDJQiXACZrppniM eXlRpZ5FVstFIdbQJTMVqkc70tOiGiBbC4rPgdCIzml5ym4zqJmLWJqmRoex7f5ra6Yi qXMxauc3aGgJbNDALFcmr/ePX2kEN6Xld84PPLchw3eRRNPtcavsaRlMo5zBcQSRIdUI e1eck3+x7SvN7tuSCDTtCNerVeULXaO8n39k/CSDsgt6KUl7LgbC9MRQIzCFKU5BFdO7 upQt2ZnajSNhTqmxJh2zCHmC1qgjEQh5ajBGdS0nkWIQpHVPJJXwQ0Fi1eh+8rptwRwA 5b3A== X-Gm-Message-State: AOAM532aaA/tL2MWorvhS4DU6rhsBOtxSb5hYjyJIamR4tFItHv3DnXN j4Sq6TwfbTwCe7wbhCyKs3pILkEmr5w716ap5PsFZ28bHDUXbA== X-Google-Smtp-Source: ABdhPJw6aMJ9dyy4G/daFrXMNngDBFvzxNsGSUQNmxPAlbpy4epgww2/u+lBmaNyLn3UM7NX8xS/DrAfDxhNdVyKGtM= X-Received: by 2002:a67:db88:: with SMTP id f8mr2729187vsk.165.1591800761473; Wed, 10 Jun 2020 07:52:41 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Ulf Hansson Date: Wed, 10 Jun 2020 16:52:05 +0200 Message-ID: Subject: Re: Consistent block device references for root= cmdline To: Matthias Schiffer Cc: Al Viro , Jens Axboe , Sascha Hauer , "linux-mmc@vger.kernel.org" , linux-block , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, 10 Jun 2020 at 15:15, Matthias Schiffer wrote: > > Hello all, > > there have been numerous attempts to make the numbering of mmcblk > devices consistent, mostly by using aliases from the DTS ([1], [2], > [3]), but all have been (rightfully) rejected. Unless I have overlooked > a more recent development, no attempts for a different solution were > made. According to aliases attempts, I think those have failed, mainly because of two reasons. 1. Arguments stating that LABELs/UUIDs are variable alternatives. This isn't the case, which I think was also concluded from the several earlier discussions. 2. Patches that tried adding support for mmc aliases, were not correctly coded. More precisely, what needs to be addressed is that the mmc core also preserves the same ids to be set for the host class as the block device, mmc[n] must correspond to mmcblk[n]. > > As far as I can tell, the core of the issue seems to be the following: > > The existing solutions like LABELs and UUIDs are viable alternatives in > many cases, but in particular on embedded systems, this is not quite > sufficient: In addition to the problem that more knowledge about the > system to boot is required in the bootloader, this approach fails > completely when the same firmware image exists on multiple devices, for > example on an eMMC and an SD card - not an entirely uncommon situation > during the development of embedded systems. > > With udev, I can refer to a specific partition using a path like > /dev/disk/by-path/platform-2194000.usdhc-part2. In [4] it was proposed > to add a way to refer to a device path/phandle from the kernel command > line. Has there been any progress on this proposal? Lots of time during the years I have been approached, both publicly and offlist, about whether it would be possible to add support for "consistent" mmcblk devices. To me, I am fine with the aliases approach, as long as it gets implemented correctly. > > Kind regards, > Matthias > > > [1] https://patchwork.kernel.org/patch/8685711/ > [2] https://lore.kernel.org/patchwork/cover/674381/ > [3] https://www.spinics.net/lists/linux-mmc/msg26586.html > [4] https://www.spinics.net/lists/linux-mmc/msg26708.html > Kind regards Uffe