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

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Message-ID: <Zh6KZ7ynHuOd0mgQ@gardel-login>
Date: Tue, 16 Apr 2024 16:25:43 +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, 16.04.24 08:22, Jens Axboe (axboe@...nel.dk) wrote:

> 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.

The text begins with:

    "This file documents the sysfs file block/<disk>/capability."

So it makes very clear this is about the sysfs interface.

Are you saying that sysfs of the block layer should be considered an
*internal* kernel API? That's a wild definition, if I may say so.

Lennart

--
Lennart Poettering, Berlin