Re: [PATCH v2 02/33] mm: add kdoc comments for vma_start/last_pgoff()

On 26/07/10 09:16PM, 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.
> 
> We go to lengths to describe the edge cases that can be run into here.
> 
> No functional change intended.
> 
> Reviewed-by: Pedro Falcato <[email protected]>
> Reviewed-by: Gregory Price <[email protected]>
> Reviewed-by: Vlastimil Babka (SUSE) <[email protected]>
> Signed-off-by: Lorenzo Stoakes <[email protected]>

Reviewed-by: Liam R. Howlett (Oracle) <[email protected]>

> ---
>  include/linux/mm.h | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 09b06d8fea74..abac72785277 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4307,11 +4307,41 @@ 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 @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.
> + *
> + * If @vma is a MAP_PRIVATE file-backed mapping, then this returns the
> + * page offset within the file.
> + *
> + * Edge cases: nommu does not abide by these, MAP_PRIVATE-/dev/zero satisfies
> + * vma_is_anonymous() but has file-backed page offset, and MAP_PRIVATE-pfnmap
> + * regions have their page offset set to the first PFN in the range.
> + *
> + * Returns: The page offset of the start of @vma.
> + */
>  static inline pgoff_t vma_start_pgoff(const struct vm_area_struct *vma)
>  {
>  	return vma->vm_pgoff;
>  }
>  
> +/**
> + * vma_last_pgoff() - Get the page offset of the last page in @vma
> + * @vma: The VMA whose last page offset is required.
> + *
> + * This returns the last page offset contained within @vma.
> + *
> + * See the description of vma_start_pgoff() for a description of VMA page
> + * offsets.
> + *
> + * Returns: The last page offset of @vma.
> + */
>  static inline pgoff_t vma_last_pgoff(const struct vm_area_struct *vma)
>  {
>  	return vma_start_pgoff(vma) + vma_pages(vma) - 1;
> 
> -- 
> 2.55.0
>