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SubjectRe: [PATCH] scatterlist: Comment on pages for sg_set_page()
On Tue, Oct 01, 2019 at 11:32:50AM -0700, Alan Mikhak wrote:
> From: Alan Mikhak <alan.mikhak@sifive.com>
>
> Update the description of sg_set_page() to communicate current
> requirements for the page pointer parameter.
>
> Signed-off-by: Alan Mikhak <alan.mikhak@sifive.com>
> include/linux/scatterlist.h | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index 6eec50fb36c8..6dda865893aa 100644
> +++ b/include/linux/scatterlist.h
> @@ -112,6 +112,12 @@ static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
> * of the page pointer. See sg_page() for looking up the page belonging
> * to an sg entry.
> *
> + * Scatterlist currently expects the page parameter to be a pointer to
> + * a page that is backed by a page struct.
> + *
> + * Page pointers derived from addresses obtained from ioremap() are
> + * currently not supported since they require use of iomem safe memcpy.
> + *
> **/
> static inline void sg_set_page(struct scatterlist *sg, struct page *page,
> unsigned int len, unsigned int offset)

It seems a bit weird to have a comment explaining that 'struct page
*page' must actually be a valid pointer. Of course it must.

Computing a 'struct page *' to something that doesn't actually have a
struct page is simply a bug in whoever did that.

Code should never be interchanging ioremap results with the struct
page* world.

Jason

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