linux-kernel - [RFC] mm/gup.c: Use gup_flags as parameter instead of passing write flag

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Date:   Tue, 19 May 2020 01:28:23 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Souptick Joarder <jrdr.linux@...il.com>
Subject: [RFC] mm/gup.c: Use gup_flags as parameter instead of passing write flag

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@...il.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