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Subject[RFC] mm/gup.c: Use gup_flags as parameter instead of passing write flag
Date
The idea is to get rid of write parameter. Instead caller will pass
FOLL_WRITE to __get_user_pages_fast(). This will not change any
functionality of the API. Once it is upstream all the callers will
be changed to pass FOLL_WRITE.

Updated the documentation of the API.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
---
include/linux/mm.h | 4 ++--
mm/gup.c | 18 +++++++++++-------
2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5a32342..15dd594 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1816,8 +1816,8 @@ extern int mprotect_fixup(struct vm_area_struct *vma,
/*
* doesn't attempt to fault and will return short.
*/
-int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
- struct page **pages);
+int __get_user_pages_fast(unsigned long start, int nr_pages,
+ unsigned int gup_flags, struct page **pages);
/*
* per-process(per-mm_struct) statistics.
*/
diff --git a/mm/gup.c b/mm/gup.c
index 87a6a59..a8f869e 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2666,7 +2666,14 @@ static bool gup_fast_permitted(unsigned long start, unsigned long end)
}
#endif

-/*
+/**
+ * __get_user_pages_fast() - pin user pages in memory
+ * @start: starting user address
+ * @nr_pages: number of pages from start to pin
+ * @gup_flags: flags modifying pin behaviour
+ * @pages: array that receives pointers to the pages pinned.
+ * Should be at least nr_pages long.
+ *
* Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
* the regular GUP.
* Note a difference with get_user_pages_fast: this always returns the
@@ -2675,8 +2682,8 @@ static bool gup_fast_permitted(unsigned long start, unsigned long end)
* If the architecture does not support this function, simply return with no
* pages pinned.
*/
-int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
- struct page **pages)
+int __get_user_pages_fast(unsigned long start, int nr_pages,
+ unsigned int gup_flags, struct page **pages)
{
unsigned long len, end;
unsigned long flags;
@@ -2685,10 +2692,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
* Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
* because gup fast is always a "pin with a +1 page refcount" request.
*/
- unsigned int gup_flags = FOLL_GET;
-
- if (write)
- gup_flags |= FOLL_WRITE;
+ gup_flags |= FOLL_GET;

start = untagged_addr(start) & PAGE_MASK;
len = (unsigned long) nr_pages << PAGE_SHIFT;
--
1.9.1
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