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

Jan Kara
2024-03-11T18:01:30Z

On Mon 11-03-24 15:39:39, 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.

No, "-o usrjquota" never worked and I'm inclined to keep refusing this
variant as IMHO it is confusing.

> > In any case, we need to document what we want:
> >
> > https://github.com/brauner/man-pages-md/blob/main/fsconfig.md
>
> What's the plan with these? It would be good if "man fsconfig" would
> finally work.

Yes, merging these into official manpages would be nice.

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR