Re: [PATCH v2 2/5] mm: Add file_offset_of_ helpers

Darrick J. Wong
2019-09-18T21:20:21Z

On Tue, Aug 20, 2019 at 05:30:36PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> The page_offset function is badly named for people reading the functions
> which call it. The natural meaning of a function with this name would
> be 'offset within a page', not 'page offset in bytes within a file'.
> Dave Chinner suggests file_offset_of_page() as a replacement function
> name and I'm also adding file_offset_of_next_page() as a helper for the
> large page work. Also add kernel-doc for these functions so they show
> up in the kernel API book.
>
> page_offset() is retained as a compatibility define for now.

No SOB?

Looks fine to me, and I appreciate the much less confusing name. I was
hoping for a page_offset conversion for fs/iomap/ (and not a treewide
change because yuck), but I guess that can be done if and when this
lands.

--D

> ---
> include/linux/pagemap.h | 25 ++++++++++++++++++++++---
> 1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 2728f20fbc49..84f341109710 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -436,14 +436,33 @@ static inline pgoff_t page_to_pgoff(struct page *page)
> return page_to_index(page);
> }
>
> -/*
> - * Return byte-offset into filesystem object for page.
> +/**
> + * file_offset_of_page - File offset of this page.
> + * @page: Page cache page.
> + *
> + * Context: Any context.
> + * Return: The offset of the first byte of this page.
> */
> -static inline loff_t page_offset(struct page *page)
> +static inline loff_t file_offset_of_page(struct page *page)
> {
> return ((loff_t)page->index) << PAGE_SHIFT;
> }
>
> +/* Legacy; please convert callers */
> +#define page_offset(page) file_offset_of_page(page)
> +
> +/**
> + * file_offset_of_next_page - File offset of the next page.
> + * @page: Page cache page.
> + *
> + * Context: Any context.
> + * Return: The offset of the first byte after this page.
> + */
> +static inline loff_t file_offset_of_next_page(struct page *page)
> +{
> + return ((loff_t)page->index + compound_nr(page)) << PAGE_SHIFT;
> +}
> +
> static inline loff_t page_file_offset(struct page *page)
> {
> return ((loff_t)page_index(page)) << PAGE_SHIFT;
> --
> 2.23.0.rc1
>