linux-ext4 - Re: [PATCH v2 3/3] ovl: fix the parsing of empty string mount parameters

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Date: Tue, 12 Mar 2024 10:31:08 +0000
From: Luis Henriques <lhenriques@...e.de>
To: Christian Brauner <brauner@...nel.org>
Cc: Miklos Szeredi <miklos@...redi.hu>,  Theodore Ts'o <tytso@....edu>,
  Andreas Dilger <adilger.kernel@...ger.ca>,  Alexander Viro
 <viro@...iv.linux.org.uk>,  Jan Kara <jack@...e.cz>,  Amir Goldstein
 <amir73il@...il.com>,  linux-ext4@...r.kernel.org,
  linux-fsdevel@...r.kernel.org,  linux-unionfs@...r.kernel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] ovl: fix the parsing of empty string mount
 parameters

Christian Brauner <brauner@...nel.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@...nel.org> wrote:
>> 
>> > 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) = -1 EINVAL (Invalid argument)
>> >
>> > for both -o usrjquota and -o usrjquota=
>> 
>> For "-o usrjquota" this seems right.
>> 
>> For "-o usrjquota=" it doesn't.  Flags should never have that "=", so
>> this seems buggy in more than one ways.
>> 
>> > 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=" 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=" that it must
>> >     be passed as FSCONFIG_SET_STRING.
>> 
>> 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,
-- 
Luís