On Wed, Dec 06, 2023 at 05:41:43PM +0100, Stefano Garzarella wrote:
> After backporting commit 581512a6dc93 ("vsock/virtio: MSG_ZEROCOPY
> flag support") in CentOS Stream 9, CI reported the following error:
>
> In file included from ./include/linux/kernel.h:17,
> from ./include/linux/list.h:9,
> from ./include/linux/preempt.h:11,
> from ./include/linux/spinlock.h:56,
> from net/vmw_vsock/virtio_transport_common.c:9:
> net/vmw_vsock/virtio_transport_common.c: In function ???virtio_transport_can_zcopy???:
> ./include/linux/minmax.h:20:35: error: comparison of distinct pointer types lacks a cast [-Werror]
> 20 | (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
> | ^~
> ./include/linux/minmax.h:26:18: note: in expansion of macro ???__typecheck???
> 26 | (__typecheck(x, y) && __no_side_effects(x, y))
> | ^~~~~~~~~~~
> ./include/linux/minmax.h:36:31: note: in expansion of macro ???__safe_cmp???
> 36 | __builtin_choose_expr(__safe_cmp(x, y), \
> | ^~~~~~~~~~
> ./include/linux/minmax.h:45:25: note: in expansion of macro ???__careful_cmp???
> 45 | #define min(x, y) __careful_cmp(x, y, <)
> | ^~~~~~~~~~~~~
> net/vmw_vsock/virtio_transport_common.c:63:37: note: in expansion of macro ???min???
> 63 | int pages_to_send = min(pages_in_iov, MAX_SKB_FRAGS);
>
> We could solve it by using min_t(), but this operation seems entirely
> unnecessary, because we also pass MAX_SKB_FRAGS to iov_iter_npages(),
> which performs almost the same check, returning at most MAX_SKB_FRAGS
> elements. So, let's eliminate this unnecessary comparison.
>
> Fixes: 581512a6dc93 ("vsock/virtio: MSG_ZEROCOPY flag support")
> Cc: avkrasnov@xxxxxxxxxxxxxxxxx
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> ---
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> net/vmw_vsock/virtio_transport_common.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index f6dc896bf44c..c8e162c9d1df 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -59,8 +59,7 @@ static bool virtio_transport_can_zcopy(const struct virtio_transport *t_ops,
> t_ops = virtio_transport_get_ops(info->vsk);
>
> if (t_ops->can_msgzerocopy) {
> - int pages_in_iov = iov_iter_npages(iov_iter, MAX_SKB_FRAGS);
> - int pages_to_send = min(pages_in_iov, MAX_SKB_FRAGS);
> + int pages_to_send = iov_iter_npages(iov_iter, MAX_SKB_FRAGS);
>
> /* +1 is for packet header. */
> return t_ops->can_msgzerocopy(pages_to_send + 1);
> --
> 2.43.0
