[PATCH] mm/hmm: constify hmm_devmem_page_get_drvdata() parameter

[PATCH] mm/hmm: constify hmm_devmem_page_get_drvdata() parameter

[Jérôme Glisse]

From: Ralph Campbell <rcampbell@nvidia.com>

Constify pointer parameter to avoid issue when use from code that
only has const struct page pointer to use in the first place.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: JA(C)rA'me Glisse <jglisse@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 include/linux/hmm.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 96e6997..325017a 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -471,9 +471,9 @@ static inline void hmm_devmem_page_set_drvdata(struct page *page,
  * @page: pointer to struct page
  * Return: driver data value
  */
-static inline unsigned long hmm_devmem_page_get_drvdata(struct page *page)
+static inline unsigned long hmm_devmem_page_get_drvdata(const struct page *page)
 {
-	unsigned long *drvdata = (unsigned long *)&page->pgmap;
+	const unsigned long *drvdata = (const unsigned long *)&page->pgmap;
 
 	return drvdata[1];
 }
-- 
2.4.11

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Re: [PATCH] mm/hmm: constify hmm_devmem_page_get_drvdata() parameter

[Andrew Morton]

On Mon,  2 Oct 2017 15:32:54 -0400 Jérôme Glisse <jglisse@redhat.com> wrote:

> From: Ralph Campbell <rcampbell@nvidia.com>
> 
> Constify pointer parameter to avoid issue when use from code that
> only has const struct page pointer to use in the first place.

That's rather vague.  Does such calling code exist in the kernel?  This
affects the which-kernel-gets-patched decision.

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Re: [PATCH] mm/hmm: constify hmm_devmem_page_get_drvdata() parameter

[Jerome Glisse]

On Mon, Oct 02, 2017 at 02:40:42PM -0700, Andrew Morton wrote:
> On Mon,  2 Oct 2017 15:32:54 -0400 Jerome Glisse <jglisse@redhat.com> wrote:
> 
> > From: Ralph Campbell <rcampbell@nvidia.com>
> > 
> > Constify pointer parameter to avoid issue when use from code that
> > only has const struct page pointer to use in the first place.
> 
> That's rather vague.  Does such calling code exist in the kernel?  This
> affects the which-kernel-gets-patched decision.

This is use by device driver, no driver upstream yet so it does not
affect anybody upstream yet.

Jerome

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RE: [PATCH] mm/hmm: constify hmm_devmem_page_get_drvdata() parameter

[Ralph Campbell]

The use case is when called by struct hmm_devmem_ops.fault() which passes a const struct page * pointer and hmm_devmem_page_get_drvdata() is called to get the private data.
Since HMM was only recently added, it only affects kernels after September 8, 2017.

> -----Original Message-----
> From: Andrew Morton [mailto:akpm@linux-foundation.org]
> Sent: Monday, October 2, 2017 2:41 PM
> To: Jérôme Glisse <jglisse@redhat.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org; Ralph Campbell
> <rcampbell@nvidia.com>
> Subject: Re: [PATCH] mm/hmm: constify hmm_devmem_page_get_drvdata()
> parameter
> 
> On Mon,  2 Oct 2017 15:32:54 -0400 Jérôme Glisse <jglisse@redhat.com>
> wrote:
> 
> > From: Ralph Campbell <rcampbell@nvidia.com>
> >
> > Constify pointer parameter to avoid issue when use from code that only
> > has const struct page pointer to use in the first place.
> 
> That's rather vague.  Does such calling code exist in the kernel?  This affects the
> which-kernel-gets-patched decision.

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