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

[Stefano Garzarella]

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 <m...@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