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

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Date: Tue, 9 Apr 2024 08:09:57 +0200
From: Hannes Reinecke <hare@...e.de>
To: Keith Busch <kbusch@...nel.org>, 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 4/9/24 00:41, Keith Busch wrote:
> 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.
> 
I'll side with Keith. Our management tools use 'ext_range' to find
if a device is partitionable, and we've done that since the very
beginning of sysfs.

Cheers,

Hannes