[PATCH] ACPICA: utids: Use struct_size() helper

["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 acpi_pnp_device_id_list {
	...
        struct acpi_pnp_device_id ids[1];       /* ID array */
};

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

So, replace the following form:

sizeof(struct acpi_pnp_device_id_list) + ((count - 1) * sizeof(struct acpi_pnp_device_id))

with:

struct_size(cid_list, ids, count - 1)

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
Notice that checkpatch reports the following warning:

WARNING: line over 80 characters
#54: FILE: drivers/acpi/acpica/utids.c:265:
+	cid_list_size = struct_size(cid_list, ids, count - 1) + string_area_size;

The line above is 81-character long. So, I think we should be fine
with that, instead of split it into two lines.

Thanks

 Gustavo

 drivers/acpi/acpica/utids.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/acpica/utids.c b/drivers/acpi/acpica/utids.c
index e805abdd95b8..737aa6a8f362 100644
--- a/drivers/acpi/acpica/utids.c
+++ b/drivers/acpi/acpica/utids.c
@@ -202,7 +202,7 @@ acpi_ut_execute_CID(struct acpi_namespace_node *device_node,
 	char *next_id_string;
 	u32 string_area_size;
 	u32 length;
-	u32 cid_list_size;
+	size_t cid_list_size;
 	acpi_status status;
 	u32 count;
 	u32 i;
@@ -262,10 +262,7 @@ acpi_ut_execute_CID(struct acpi_namespace_node *device_node,
 	 * 2) Size of the CID PNP_DEVICE_ID array +
 	 * 3) Size of the actual CID strings
 	 */
-	cid_list_size = sizeof(struct acpi_pnp_device_id_list) +
-	    ((count - 1) * sizeof(struct acpi_pnp_device_id)) +
-	    string_area_size;
-
+	cid_list_size = struct_size(cid_list, ids, count - 1) + string_area_size;
 	cid_list = ACPI_ALLOCATE_ZEROED(cid_list_size);
 	if (!cid_list) {
 		status = AE_NO_MEMORY;
-- 
2.21.0