[PATCH] libnvdimm, region: Use struct_size() in kzalloc()

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct nd_region {
	...
        struct nd_mapping mapping[0];
};

instance = kzalloc(sizeof(struct nd_region) + sizeof(struct nd_mapping) *
                          count, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kzalloc(struct_size(instance, mapping, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/nvdimm/region_devs.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index b4ef7d9ff22e..88becc87e234 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -1027,10 +1027,9 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus,
 		}
 		region_buf = ndbr;
 	} else {
-		nd_region = kzalloc(sizeof(struct nd_region)
-				+ sizeof(struct nd_mapping)
-				* ndr_desc->num_mappings,
-				GFP_KERNEL);
+		nd_region = kzalloc(struct_size(nd_region, mapping,
+						ndr_desc->num_mappings),
+				    GFP_KERNEL);
 		region_buf = nd_region;
 	}
 
-- 
2.21.0