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

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Date: Tue, 16 Apr 2024 08:22:54 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Lennart Poettering <mzxreary@...inter.de>
Cc: Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...nel.org>,
 Linux regressions mailing list <regressions@...ts.linux.dev>,
 linux-block@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: API break, sysfs "capability" file

On 4/16/24 8:18 AM, Lennart Poettering wrote:
> On Di, 09.04.24 09:17, Jens Axboe (axboe@...nel.dk) wrote:
> 
>> On 4/9/24 8:15 AM, Christoph Hellwig wrote:
>>> On Tue, Apr 09, 2024 at 10:19:09AM +0200, Lennart Poettering wrote:
>>>> All I am looking for is a very simple test that returns me a boolean:
>>>> is there kernel-level partition scanning enabled on this device or
>>>> not.
>>>
>>> And we can add a trivial sysfs attribute for that.
>>
>> And I think we should. I don't know what was being smoked adding a sysfs
>> interface that exposed internal flag values - and honestly what was
>> being smoked to rely on that, but I think it's fair to say that the
>> majority of the fuckup here is on the kernel side.
> 
> Yeah, it's a shitty interface, the kernel is rich in that. But it was
> excessively well documented, better in fact than almost all other
> kernel interfaces:
> 
> ? https://www.kernel.org/doc/html/v5.16/block/capability.html ?
> 
> If you document something on so much detail in the API docs, how do
> you expect this *not* to be relied on by userspace.

This is _internal_ documentation, not user ABI documentation. The fact
that it's talking about internal flag values should make that clear,
though I can definitely see how that's just badly exposed along with
other things that document things that users/admins could care about.

-- 
Jens Axboe