Re: [RFC][PATCH 4/4] fs: factor out backing_file_mmap() helper

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On Thu, Dec 21, 2023 at 11:54:10AM +0200, Amir Goldstein wrote:
> Assert that the file object is allocated in a backing_file container
> so that file_user_path() could be used to display the user path and
> not the backing file's path in /proc/<pid>/maps.
> 
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
>  fs/backing-file.c            | 27 +++++++++++++++++++++++++++
>  fs/overlayfs/file.c          | 23 ++++++-----------------
>  include/linux/backing-file.h |  2 ++
>  3 files changed, 35 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/backing-file.c b/fs/backing-file.c
> index 46488de821a2..1ad8c252ec8d 100644
> --- a/fs/backing-file.c
> +++ b/fs/backing-file.c
> @@ -11,6 +11,7 @@
>  #include <linux/fs.h>
>  #include <linux/backing-file.h>
>  #include <linux/splice.h>
> +#include <linux/mm.h>
>  
>  #include "internal.h"
>  
> @@ -284,6 +285,32 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
>  }
>  EXPORT_SYMBOL_GPL(backing_file_splice_write);
>  
> +int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
> +		      struct backing_file_ctx *ctx)
> +{
> +	const struct cred *old_cred;
> +	int ret;
> +
> +	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||

Couldn't that WARN_ON_ONCE() be in every one of these helpers in this
series? IOW, when would you ever want to use a backing_file_*() helper
on a non-backing file?




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