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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Thu, 5 May 2022 20:34:06 +0300
Message-ID: <CAOQ4uxjkJ37Nzke4YN_se4ztr-yZgm6SK_LhmBQ-ckWutOwWrQ@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] fanotify: define struct members to hold response
 decision context
To:     Jan Kara <jack@suse.cz>
Cc:     Richard Guy Briggs <rgb@redhat.com>,
        Paul Moore <paul@paul-moore.com>,
        Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Eric Paris <eparis@parisplace.org>,
        Steve Grubb <sgrubb@redhat.com>
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> One open question I have is what should the kernel do with 'info_type' in
> response it does not understand (in the future when there are possibly more
> different info types). It could just skip it because this should be just
> additional info for introspection (the only mandatory part is in
> fanotify_response, however it could surprise userspace that passed info is
> just getting ignored. To solve this we would have to somewhere report
> supported info types (maybe in fanotify fdinfo in proc). I guess we'll
> cross that bridge when we get to it.
>
> Amir, what do you think?

Regardless if and how we provide a way to enumerate supported info types,
I would prefer to reject (EINVAL) unknown info types.

We can provide a command FAN_RESPONSE_TEST to write a test response with
FAN_NOFD and some extra info so the program can test if certain info
types are supported.

Thanks,
Amir.