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From: Amir Goldstein <amir73il@gmail.com>
Date: Tue, 5 Sep 2017 11:55:47 +0300
Message-ID: <CAOQ4uxhv=GSxJjoJbM+qCazCC+VhmuHjDTYNfF0dmjG2tjSHTQ@mail.gmail.com>
Subject: Re: [PATCH 1/3] vfs: add flags to d_real()
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        overlayfs <linux-unionfs@vger.kernel.org>
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On Tue, Sep 5, 2017 at 10:46 AM, Miklos Szeredi <mszeredi@redhat.com> wrote:
> Add a separate flags argument (in addition to the open flags) to control
> the behavior of d_real().
>
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> ---
...
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
>
>  static struct dentry *ovl_d_real(struct dentry *dentry,
>                                  const struct inode *inode,
> -                                unsigned int open_flags)
> +                                unsigned int open_flags, unsigned int flags)
>  {
>         struct dentry *real;
>         int err;
> @@ -102,7 +102,7 @@ static struct dentry *ovl_d_real(struct dentry *dentry,
>                 goto bug;
>
>         /* Handle recursion */
> -       real = d_real(real, inode, open_flags);
> +       real = d_real(real, inode, open_flags, 0);
>

Shouldn't recursion pass on flags?
The answer is probably per flag.
The 2 currently proposed flags don't end up in recursion anyway,
although it is arguable that D_REAL_ALL should end up in recursion
because according to comment it should behave the same as
d_real for regular files.

For the purpose for which D_REAL_ALL was proposed (atime update)
the recursion case doesn't really matter.

Maybe a flag D_REAL_NORECURSE and then for
update_ovl_inode_times() use D_REAL_ALL|D_REAL_NORECURSE

Alternatively, update_ovl_inode_times() could use D_REAL_UPPER
and then we explicitly say that we don't care about lower mtime/ctime
modifications.

Amir.