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Date: Wed, 22 Jun 2016 16:01:18 +0200
From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Richard Weinberger <richard@nod.at>
Cc: "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>, Artem
 Bityutskiy <dedekind1@gmail.com>, Alexander Kaplan <alex@nextthing.co>,
 Brian Norris <computersforpeace@gmail.com>, Ezequiel Garcia
 <ezequiel@vanguardiasur.com.ar>
Subject: Re: [RFC] Raising the UBI version
Message-ID: <20160622160118.28a4339a@bbrezillon>
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On Wed, 22 Jun 2016 15:54:34 +0200
Richard Weinberger <richard@nod.at> wrote:

> Am 22.06.2016 um 14:43 schrieb Boris Brezillon:
> > Why do we need to hardcode /sys/class/ubi/version to 1? We just need to
> > update the mtd-utils to support version 2. Am I missing something?  
> 
> We don't want to break existing userspace.
> Why should ubimkvol or ubiattach fail on a system with SLC NAND and
> CONFIG_MTD_UBI_CONSOLIDATE=y?

But version won't be set to 2 in this case. If it's an SLC NAND we
don't need to use UBI version 2, do we.

> 
> Especially since existing tools *will* work with CONFIG_MTD_UBI_CONSOLIDATE=y.
> Rasing /sys/class/ubi/version and breaking existing tools is only acceptable
> when we change all UBI ioctl() and sysfs files in a way such that version 1
> userspace cannot work. Which is not the case here.
> 
> This is a nice example why version numbers is bad and feature flags should be used.
> Currently UBI mixes the implementation version and the on-flash version.
> We're changing only the on-flash version. The user visible ABI stays and will only
> get extended.

Correct. So /sys/class/ubi/version is representing the user-space ABI
version, right? Maybe we should expose the on-flash version in a
different file then.