Re: [PATCH RFC 33/41] fs: add file_is_pseudo()

[Alexander Mikhalitsyn <alex@xxxxxxxxxxxx>]

On Tue, 2026-11-10 at 10:14 +0100, Christian Brauner wrote:
> Add a helper to check whether a file is a regular file on a pseudo
> filesystem. Only regular files count. Device nodes on pseudo
> filesystems
> such as devpts, binderfs or the block devices on bdevfs are what they
> are.
> 
> Look at the inode that actually provides the data via d_real_inode().
> overlayfs accepts sysfs, cgroup2, debugfs, tracefs, configfs and
> securityfs as lower layers and reads of such an overlayfs file are
> served by the file on the pseudo filesystem. Checking the overlayfs
> inode would miss that.
> 
> No functional changes.
> 
> Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>

Reviewed-by: Alexander Mikhalitsyn <alex@xxxxxxxxxxxx>

> ---
>  include/linux/fs.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 99caef43ff3c..407ffb6342ec 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2553,6 +2553,18 @@ static inline const struct inode
> *file_user_inode(const struct file *f)
>       return file_inode(f);
>  }
>  
> +/*
> + * Regular files on pseudo filesystems are kernel interfaces and
> must not be
> + * used as storage. Look through stacking filesystems at the inode
> that
> + * provides the data.
> + */
> +static inline bool file_is_pseudo(const struct file *file)
> +{
> +     const struct inode *inode = d_real_inode(file-
> >f_path.dentry);
> +
> +     return S_ISREG(inode->i_mode) && (inode->i_sb->s_iflags &
> SB_I_PSEUDO);
> +}
> +
>  static inline struct file *file_clone_open(struct file *file)
>  {
>       return dentry_open(&file->f_path, file->f_flags, file-
> >f_cred);