[RFC 01/16] io_uring: add helper calculating region byte size

[Pavel Begunkov <asml.silence@gmail.com>]

There has been type related issues with region size calculation, add an
utility helper function that returns the size and handles type
conversions right.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/memmap.c | 4 ++--
 io_uring/memmap.h | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/io_uring/memmap.c b/io_uring/memmap.c
index ce8118434c5a..b329cee8d6e8 100644
--- a/io_uring/memmap.c
+++ b/io_uring/memmap.c
@@ -135,7 +135,7 @@ static int io_region_pin_pages(struct io_ring_ctx *ctx,
 				struct io_mapped_region *mr,
 				struct io_uring_region_desc *reg)
 {
-	unsigned long size = (size_t)mr->nr_pages << PAGE_SHIFT;
+	size_t size = io_region_size(mr);
 	struct page **pages;
 	int nr_pages;
 
@@ -156,7 +156,7 @@ static int io_region_allocate_pages(struct io_ring_ctx *ctx,
 				    unsigned long mmap_offset)
 {
 	gfp_t gfp = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN;
-	size_t size = (size_t) mr->nr_pages << PAGE_SHIFT;
+	size_t size = io_region_size(mr);
 	unsigned long nr_allocated;
 	struct page **pages;
 
diff --git a/io_uring/memmap.h b/io_uring/memmap.h
index f9e94458c01f..d4b8b6363a7d 100644
--- a/io_uring/memmap.h
+++ b/io_uring/memmap.h
@@ -43,4 +43,9 @@ static inline void io_region_publish(struct io_ring_ctx *ctx,
 	*dst_region = *src_region;
 }
 
+static inline size_t io_region_size(struct io_mapped_region *mr)
+{
+	return (size_t)mr->nr_pages << PAGE_SHIFT;
+}
+
 #endif
-- 
2.49.0