Re: [PATCH v2 13/15] vsock/virtio: reorder fields to reduce padding

Stefano Garzarella
2026-01-08T14:11:59Z

On Mon, Jan 05, 2026 at 03:23:41AM -0500, Michael S. Tsirkin wrote:
>Reorder struct virtio_vsock fields to place the DMA buffer (event_list)
>last. This eliminates the padding from aligning the struct size on
>ARCH_DMA_MINALIGN.
>
>Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>---
> net/vmw_vsock/virtio_transport.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>index ef983c36cb66..964d25e11858 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -60,9 +60,7 @@ struct virtio_vsock {
> */
> struct mutex event_lock;
> bool event_run;
>- __dma_from_device_group_begin();
>- struct virtio_vsock_event event_list[8];
>- __dma_from_device_group_end();
>+
> u32 guest_cid;
> bool seqpacket_allow;
>
>@@ -76,6 +74,10 @@ struct virtio_vsock {
> */
> struct scatterlist *out_sgs[MAX_SKB_FRAGS + 1];
> struct scatterlist out_bufs[MAX_SKB_FRAGS + 1];
>+

IIUC we would like to have these fields always on the bottom of this
struct, so would be better to add a comment here to make sure we will
not add other fields in the future after this?

Maybe we should also add a comment about the `event_lock` requirement we
have in the section above.

Thanks,
Stefano

>+ __dma_from_device_group_begin();
>+ struct virtio_vsock_event event_list[8];
>+ __dma_from_device_group_end();
> };
>
> static u32 virtio_transport_get_local_cid(void)
>--
>MST
>