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

Luis Henriques
2024-03-12T10:31:11Z

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> 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