linux-kernel - Re: API break, sysfs "capability" file

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Date: Mon, 8 Apr 2024 16:41:08 -0600
From: Keith Busch <kbusch@...nel.org>
To: Lennart Poettering <mzxreary@...inter.de>
Cc: Linux regressions mailing list <regressions@...ts.linux.dev>,
	Christoph Hellwig <hch@....de>, linux-block@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: API break, sysfs "capability" file

On Mon, Apr 08, 2024 at 10:23:49PM +0200, Lennart Poettering wrote:
> Not sure how this is salvageable. This is just seriously fucked
> up. What now?
>
> It has been proposed to use the "range_ext" sysfs attr instead as a
> hint if partition scanning is available or not. But it's entirely
> undocumented. Is this something that will remain stable? (I mean,
> whether something is documented or not apparently has no effect on the
> stability of an API anyway, so I guess it's equally shaky as the
> capability sysattr? Is any of the block device sysfs interfaces
> actually stable or can they change any time?)

The "ext_range" attribute does look like an appropriate proxy for the
attribute, but indeed, it's not well documented.

Looking at the history of the documentation you had been relying on, it
appears that was submitted with good intentions (9243c6f3e012a92d), but
it itself changed values, acknowledging the instability of this
interface.

So what to do? If documentation is all that's preventing "ext_range"
from replacing you're previous usage, then let's add it in the
Documentation/ABI/stable/sysfs-block. It's been there since 2008, so
that seems like a reliable attribute to put there.