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From: mark.rutland@arm.com (Mark Rutland)
To: linux-arm-kernel@lists.infradead.org
Subject: [patch 2/7] dt: dtb version: document chosen/dtb-info node binding
Date: Fri, 20 Mar 2015 14:42:02 +0000	[thread overview]
Message-ID: <20150320144202.GH14766@leverpostej> (raw)
In-Reply-To: <550B3549.1030808@gmail.com>

> > You must be *absolutely* *sure* that you want to export this information,
> > and that you are absolutely happy with the consequences which would occur
> > should userspace then start using this information in a way which you did
> > not intend, which could very well block you from ever being able to change
> > the version number from a prescribed "this version number makes userspace
> > work" value.
> 
> I understand the concern you are expressing.  And I agree it is an issue to
> be concerned about and not dismissed.  But I also think that the concern is
> mis-characterizing the "DTB version".  To pick on the example in patch 0,
> an analogous Linux version is "#5" (not "4.0.0"):
> 
>    Linux version 4.0.0-rc4-dirty (frank at buildhost) (gcc version 4.6.x-google 20120106 (prerelease) (GCC) ) #5 SMP PREEMPT Wed Mar 18 20:04:48 PDT 2015
> 
> and the proposed DTB version is "#4":
> 
>    DTB version 4.0.0-rc4-dirty (frank at buildhost) (DTC 1.4.0-dirty) #4 Wed Mar 18 20:04:11 PDT 2015
> 
> I don't think the concern holds for "#5" and "#4".
> 
> I will concede that there is something unique in the proposed DTB version -
> the source code system commit version number (in this example "4.0.0-rc4-dirty"
> from git).

The problem that Russell is describing is that regardless of the origin
and intended purpose of the value, some consumer of the value will
decide that some arbitrary value means something special to them (even
if it does not), and when this changes thigns will break.

So in that respect, it doesn't matter where the value came from or what
you intend it to mean; it will almost certainly be abused. We try to
avoid introducing fragile interfaces like these.

Mark.

  reply	other threads:[~2015-03-20 14:42 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-19  3:29 [patch 0/7] dt: dtb version: add version info to dtb Frank Rowand
2015-03-19  3:31 ` [patch 1/7] dt: dtb version: consolidate documentation of chosen node bindings Frank Rowand
2015-03-19 13:40   ` Mark Rutland
2015-03-19  3:33 ` [patch 2/7] dt: dtb version: document chosen/dtb-info node binding Frank Rowand
2015-03-19 13:23   ` Rob Herring
2015-03-19 16:42     ` Frank Rowand
2015-03-19 18:41     ` Russell King - ARM Linux
2015-03-19 18:53       ` Mark Rutland
2015-03-19 19:01       ` Frank Rowand
2015-03-19 19:32         ` Russell King - ARM Linux
2015-03-19 20:44           ` Frank Rowand
2015-03-20 14:42             ` Mark Rutland [this message]
2015-03-19 13:49   ` Mark Rutland
2015-03-19 17:02     ` Frank Rowand
2015-03-19 17:23       ` Geert Uytterhoeven
2015-03-19 19:12       ` Mark Rutland
2015-03-19 21:27         ` Frank Rowand
2015-03-20 15:25           ` Mark Rutland
2015-03-19 17:37   ` Frank Rowand
2015-03-19  3:34 ` [patch 3/7] dt: dtb version: arm dts Makefile Frank Rowand
2015-03-19  3:36 ` [patch 4/7] dt: dtb version: kernel Makefile Frank Rowand
2015-03-19  3:38 ` [patch 5/7] dt: dtb version: kbuild scripts Frank Rowand
2015-03-19  3:39 ` [patch 6/7] dt: dtb version: dtsi files Frank Rowand
2015-03-19 18:46   ` Sascha Hauer
2015-03-19  3:41 ` [patch 7/7] dt: dtb version: report dtb info Frank Rowand
2015-03-19  8:12 ` [patch 0/7] dt: dtb version: add version info to dtb Gregory CLEMENT
2015-03-19 17:05   ` Frank Rowand
2015-03-20 13:46 ` Rob Herring
2015-03-20 19:14   ` Uwe Kleine-König

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