Re: [PATCH] nvmet-fc: use zero-sized array and struct_size() in kzalloc()

From: James Smart
Date: Fri Mar 08 2019 - 14:15:41 EST

On 2/23/2019 10:51 AM, Gustavo A. R. Silva wrote:
Update the code to use a zero-sized array instead of a pointer in
structure nvmet_fc_tgt_queue and use struct_size() in kzalloc().

Notice that 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 foo {
int stuff;
struct boo entry[];

instance = kzalloc(sizeof(struct foo) + sizeof(struct boo) * 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, entry, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
drivers/nvme/target/fc.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/target/fc.c b/drivers/nvme/target/fc.c
index 1e9654f04c60..23baec38f97e 100644
--- a/drivers/nvme/target/fc.c
+++ b/drivers/nvme/target/fc.c
@@ -128,12 +128,12 @@ struct nvmet_fc_tgt_queue {
struct nvmet_cq nvme_cq;
struct nvmet_sq nvme_sq;
struct nvmet_fc_tgt_assoc *assoc;
- struct nvmet_fc_fcp_iod *fod; /* array of fcp_iods */
struct list_head fod_list;
struct list_head pending_cmd_list;
struct list_head avail_defer_list;
struct workqueue_struct *work_q;
struct kref ref;
+ struct nvmet_fc_fcp_iod fod[]; /* array of fcp_iods */
} __aligned(sizeof(unsigned long long));
struct nvmet_fc_tgt_assoc {
@@ -588,9 +588,7 @@ nvmet_fc_alloc_target_queue(struct nvmet_fc_tgt_assoc *assoc,
if (qid > NVMET_NR_QUEUES)
return NULL;
- queue = kzalloc((sizeof(*queue) +
- (sizeof(struct nvmet_fc_fcp_iod) * sqsize)),
+ queue = kzalloc(struct_size(queue, fod, sqsize), GFP_KERNEL);
if (!queue)
return NULL;
@@ -603,7 +601,6 @@ nvmet_fc_alloc_target_queue(struct nvmet_fc_tgt_assoc *assoc,
if (!queue->work_q)
goto out_a_put;
- queue->fod = (struct nvmet_fc_fcp_iod *)&queue[1];
queue->qid = qid;
queue->sqsize = sqsize;
queue->assoc = assoc;

Reviewed-by:Â James Smart <>

I guess this is a better style.

-- james