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 <gust...@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

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