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

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Date: Tue, 16 Apr 2024 16:18:14 +0200
From: Lennart Poettering <mzxreary@...inter.de>
To: Jens Axboe <axboe@...nel.dk>
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 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.

Lennart