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References: <20210112220124.837960-1-christian.brauner@ubuntu.com> <20210112220124.837960-16-christian.brauner@ubuntu.com>
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From:   Jann Horn <jannh@google.com>
Date:   Tue, 19 Jan 2021 16:05:00 +0100
Message-ID: <CAG48ez3Ccr77+zH56YGimESf9jdy_xnQrebypn1TXEP3Q+xw=w@mail.gmail.com>
Subject: Re: [PATCH v5 15/42] fs: add file_user_ns() helper
To:     Christian Brauner <christian.brauner@ubuntu.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        John Johansen <john.johansen@canonical.com>,
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        Christoph Hellwig <hch@lst.de>
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On Wed, Jan 13, 2021 at 1:52 AM Christian Brauner
<christian.brauner@ubuntu.com> wrote:
> Add a simple helper to retrieve the user namespace associated with the
> vfsmount of a file. Christoph correctly points out that this makes
> codepaths (e.g. ioctls) way easier to follow that would otherwise
> dereference via mnt_user_ns(file->f_path.mnt).
>
> In order to make file_user_ns() static inline we'd need to include
> mount.h in either file.h or fs.h which seems undesirable so let's simply
> not force file_user_ns() to be inline.
[...]
> +struct user_namespace *file_user_ns(struct file *file)
> +{
> +       return mnt_user_ns(file->f_path.mnt);
> +}

That name is confusing to me, because when I think of "the userns of a
file", it's file->f_cred->user_ns. There are a bunch of places that
look at that, as you can see from grepping for "f_cred->user_ns".

If you really want this to be a separate helper, can you maybe give it
a clearer name? file_mnt_user_ns(), or something like that, idk.