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

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Message-ID: <875xxe2t56.fsf@brahms.olymp>
Date: Fri, 22 Mar 2024 15:17:09 +0000
From: Luis Henriques <luis.henriques@...ux.dev>
To: Christian Brauner <brauner@...nel.org>
Cc: Miklos Szeredi <miklos@...redi.hu>,  Jan Kara <jack@...e.cz>,  Theodore
 Ts'o <tytso@....edu>,  Andreas Dilger <adilger.kernel@...ger.ca>,
  Alexander Viro <viro@...iv.linux.org.uk>,  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 Tue, Mar 12, 2024 at 10:31:08AM +0000, Luis Henriques wrote:
>> 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
>
> This is now merged as of today and backported to at least util-linux
> 2.40 which is the current release.
> https://github.com/util-linux/util-linux/pull/2849
>
> If your distros ship 2.39 and won't upgrade to 2.40 for a while it might
> be worth cherry-picking that fix.

That's awesome, thanks a lot for pushing this.  I just gave it a try and
it looks good -- ext4/053 isn't failing any more with the next version.

Cheers,
-- 
Luis