linux-kernel - Re: [PATCH 03/15] mm: Add file_offset_of

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Date:   Thu, 26 Sep 2019 17:02:11 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/15] mm: Add file_offset_of_ helpers

On Tue, Sep 24, 2019 at 05:52:02PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.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.

This should be trivial for coccinelle, right?

> ---
>  drivers/net/ethernet/ibm/ibmveth.c |  2 --
>  include/linux/pagemap.h            | 25 ++++++++++++++++++++++---
>  2 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
> index c5be4ebd8437..bf98aeaf9a45 100644
> --- a/drivers/net/ethernet/ibm/ibmveth.c
> +++ b/drivers/net/ethernet/ibm/ibmveth.c
> @@ -978,8 +978,6 @@ static int ibmveth_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
>  	return -EOPNOTSUPP;
>  }
>  
> -#define page_offset(v) ((unsigned long)(v) & ((1 << 12) - 1))
> -
>  static int ibmveth_send(struct ibmveth_adapter *adapter,
>  			union ibmveth_buf_desc *descs, unsigned long mss)
>  {
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 750770a2c685..103205494ea0 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -428,14 +428,33 @@ 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;

Wouldn't it be more readable as

	return file_offset_of_page(page) + page_size(page);

?

> +}
> +
>  static inline loff_t page_file_offset(struct page *page)
>  {
>  	return ((loff_t)page_index(page)) << PAGE_SHIFT;
> -- 
> 2.23.0
> 
> 

-- 
 Kirill A. Shutemov