Linux Virtualization - Jun 2019 - [PATCH] scsi: virtio_scsi: Use struct_size() helper

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 virtio_scsi {
	...
        struct virtio_scsi_vq req_vqs[];
};

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(*vscsi) + sizeof(vscsi->req_vqs[0]) * num_queues

with:

struct_size(vscsi, req_vqs, num_queues)

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>
---
 drivers/scsi/virtio_scsi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 13f1b3b9923a..ed4f79bffc73 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -795,7 +795,7 @@ static int virtscsi_probe(struct virtio_device *vdev)
 	num_targets = virtscsi_config_get(vdev, max_target) + 1;
 
 	shost = scsi_host_alloc(&virtscsi_host_template,
-		sizeof(*vscsi) + sizeof(vscsi->req_vqs[0]) * num_queues);
+				struct_size(vscsi, req_vqs, num_queues));
 	if (!shost)
 		return -ENOMEM;
 
-- 
2.21.0

On Wed, Jun 19, 2019 at 02:28:33PM -0500, Gustavo A. R. Silva
wrote:
> 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 virtio_scsi {
> 	...
>         struct virtio_scsi_vq req_vqs[];
> };
> 
> 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(*vscsi) + sizeof(vscsi->req_vqs[0]) * num_queues
> 
> with:
> 
> struct_size(vscsi, req_vqs, num_queues)
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>
> ---
>  drivers/scsi/virtio_scsi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>
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Gustavo,
> 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:
Applied to 5.4/scsi-queue, thanks!

-- 
Martin K. Petersen	Oracle Linux Engineering

On Thu, Jul 11, 2019 at 08:18:54PM -0400, Martin K. Petersen
wrote:
> 
> Gustavo,
> 
> > 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:
> 
> Applied to 5.4/scsi-queue, thanks!
Oh I put it in the virtio tree already.
Can't hurt I guess :)
> -- 
> Martin K. Petersen	Oracle Linux Engineering