Re: [PATCH 02/30] mm: add kdoc comments for vma_start/last_pgoff()

[David Hildenbrand (Arm)]

On 6/29/26 14:23, Lorenzo Stoakes wrote:
> Describe what vma_start_pgoff() and vma_last_pgoff() actually provide in
> detail.
> 
> This is in order that we can differentiate this between functions that will
> be added in a subsequent patch which provide a different page offset.
> 
> No functional change intended.
> 
> Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
> ---
>  include/linux/mm.h | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 059144435729..2f00c75e66bd 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4278,11 +4278,37 @@ static inline unsigned long vma_pages(const struct vm_area_struct *vma)
>  	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
>  }
>  
> +/**
> + * vma_start_pgoff() - Get the page offset of the start of @vma
> + * @vma: The VMA whose page offset is required.
> + *
> + * If the VMA is file-backed, this is the page offset into the file.
> + *
> + * If the VMA is anonymous, this is the virtual page offset of the start of the
> + * VMA - if unfaulted, then vma->vm_start >> PAGE_SHIFT, if faulted then the
> + * virtual page offset at the time of first fault.
> + *
> + * Note that if @vma is a MAP_PRIVATE file-backed mapping, then this returns the
> + * file offset.

There is the ugly case of @vma being a MAP_PRIVATE PFNMAP mapping, where it
returns something different.

(remap_pfn_range_prepare_vma() -> vma->vm_pgoff set to PFN)

-- 
Cheers,

David