linux-kernel - Re: [RFC 1/2] ovl: Define D_REAL_FILEDATA for d

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Date: Fri, 12 Apr 2024 21:05:00 +0300
From: Amir Goldstein <amir73il@...il.com>
To: Stefan Berger <stefanb@...ux.ibm.com>
Cc: linux-integrity@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, zohar@...ux.ibm.com, roberto.sassu@...wei.com, 
	miklos@...redi.hu
Subject: Re: [RFC 1/2] ovl: Define D_REAL_FILEDATA for d_real to return dentry
 with data

On Fri, Apr 12, 2024 at 5:01 PM Stefan Berger <stefanb@...ux.ibm.com> wrote:
>
> Define D_REAL_FILEDATA which is to be used as a parameter for d_real()
> to return the dentry that is holding the file data, which is either the

D_REAL_DATA already does that

> upper or the lower denry. The caller is expected to call d_real() again
> on the returned dentry to get to lower layers of a stacked filesystem,
> if available.
>
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
> ---
>  fs/overlayfs/super.c   | 6 ++++++
>  include/linux/dcache.h | 1 +
>  2 files changed, 7 insertions(+)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 06a231970cb5..f466ad89b005 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -36,6 +36,7 @@ static struct dentry *ovl_d_real(struct dentry *dentry, enum d_real_type type)
>         switch (type) {
>         case D_REAL_DATA:
>         case D_REAL_METADATA:
> +       case D_REAL_FILEDATA:
>                 break;
>         default:
>                 goto bug;
> @@ -47,6 +48,11 @@ static struct dentry *ovl_d_real(struct dentry *dentry, enum d_real_type type)
>         }
>
>         upper = ovl_dentry_upper(dentry);
> +       if (type == D_REAL_FILEDATA) {
> +               if (ovl_has_upperdata(d_inode(dentry)))
> +                       return upper;

This one is already the returned value for D_REAL_DATA

> +               return ovl_dentry_lower(dentry);

And this one is a wrong value, because the lower file's data is at
ovl_dentry_lowerdata(), which is what D_REAL_DATA
returns.

So it is not clear to me what it is that you tried to do here.

Thanks,
Amir.