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]> --- 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
