nvmet: use flex_array_size and struct_size

In an effort to avoid open-coded arithmetic in the kernel [1], use the
flex_array_size() and struct_size() helpers instead of an open-coded
calculation.

[1] https://github.com/KSPP/linux/issues/160Signed-off-by: Len Baker <len.baker@gmx.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/multipath.c

@@ -562,7 +562,7 @@ static int nvme_parse_ana_log(struct nvme_ctrl *ctrl, void *data,
 			return -EINVAL;
 
 		nr_nsids = le32_to_cpu(desc->nnsids);
-		nsid_buf_size = nr_nsids * sizeof(__le32);
+		nsid_buf_size = flex_array_size(desc, nsids, nr_nsids);
 
 		if (WARN_ON_ONCE(desc->grpid == 0))
 			return -EINVAL;

drivers/nvme/target/admin-cmd.c

@@ -264,7 +264,7 @@ static u32 nvmet_format_ana_group(struct nvmet_req *req, u32 grpid,
 	desc->chgcnt = cpu_to_le64(nvmet_ana_chgcnt);
 	desc->state = req->port->ana_state[grpid];
 	memset(desc->rsvd17, 0, sizeof(desc->rsvd17));
-	return sizeof(struct nvme_ana_group_desc) + count * sizeof(__le32);
+	return struct_size(desc, nsids, count);
 }
 
 static void nvmet_execute_get_log_page_ana(struct nvmet_req *req)