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From: Luis Henriques <lhenriques@suse.de>
To: Christian Brauner <brauner@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>,  Theodore Ts'o <tytso@mit.edu>,
  Andreas Dilger <adilger.kernel@dilger.ca>,  Alexander Viro
 <viro@zeniv.linux.org.uk>,  Jan Kara <jack@suse.cz>,  Amir Goldstein
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  linux-fsdevel@vger.kernel.org,  linux-unionfs@vger.kernel.org,
  linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] ovl: fix the parsing of empty string mount
 parameters
In-Reply-To: <20240312-orten-erbsen-2105c134762e@brauner> (Christian Brauner's
	message of "Tue, 12 Mar 2024 09:47:52 +0100")
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Date: Tue, 12 Mar 2024 10:31:08 +0000
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Christian Brauner <brauner@kernel.org> writes:

> On Mon, Mar 11, 2024 at 03:39:39PM +0100, Miklos Szeredi wrote:
>> On Mon, 11 Mar 2024 at 14:25, Christian Brauner <brauner@kernel.org> wro=
te:
>>=20
>> > Yeah, so with that I do agree. But have you read my reply to the other
>> > thread? I'd like to hear your thoughs on that. The problem is that
>> > mount(8) currently does:
>> >
>> > fsconfig(3, FSCONFIG_SET_FLAG, "usrjquota", NULL, 0) =3D -1 EINVAL (In=
valid argument)
>> >
>> > for both -o usrjquota and -o usrjquota=3D
>>=20
>> For "-o usrjquota" this seems right.
>>=20
>> For "-o usrjquota=3D" it doesn't.  Flags should never have that "=3D", so
>> this seems buggy in more than one ways.
>>=20
>> > So we need a clear contract with userspace or the in-kernel solution
>> > proposed here. I see the following options:
>> >
>> > (1) Userspace must know that mount options such as "usrjquota" that can
>> >     have no value must be specified as "usrjquota=3D" when passed to
>> >     mount(8). This in turn means we need to tell Karel to update
>> >     mount(8) to recognize this and infer from "usrjquota=3D" that it m=
ust
>> >     be passed as FSCONFIG_SET_STRING.
>>=20
>> Yes, this is what I'm thinking.  Of course this only works if there
>> are no backward compatibility issues, if "-o usrjquota" worked in the
>> past and some systems out there relied on this, then this is not
>> sufficient.
>
> Ok, I spoke to Karel and filed:
>
> https://github.com/util-linux/util-linux/issues/2837
>
> So this should get sorted soon.

OK, so I if I understand it correctly I can drop all these changes as
there's nothing else to be done from the kernel, right?

(I'll still send out a patch to move the fsparam_string_empty() helper to
a generic header.)

And thanks everyone for your reviews.

Cheers,
--=20
Lu=C3=ADs