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Subject: Re: [RFC] Raising the UBI version
To: Boris Brezillon <boris.brezillon@free-electrons.com>
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 Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
From: Richard Weinberger <richard@nod.at>
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Date: Wed, 22 Jun 2016 15:54:34 +0200
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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?

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.

Thanks,
//richard