Re: [RFC PATCH v5 02/26] vhost: Fix last queue index of devices with no cvq

[Juan Quintela]

Eugenio Pérez <eperezma@redhat.com> wrote:
> The -1 assumes that all devices with no cvq have an spare vq allocated
> for them, but with no offer of VIRTIO_NET_F_CTRL_VQ. This may not be the
> case, and the device may have a pair number of queues.
                                  ^^^^
even

I know, I know, I am Spanish myself O:-)

> To fix this, just resort to the lower even number of queues.

I don't understand what you try to achieve here.

> Fixes: 049eb15b5fc9 ("vhost: record the last virtqueue index for the
> virtio device")
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  hw/net/vhost_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index 0d888f29a6..edf56a597f 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -330,7 +330,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState 
> *ncs,
>      NetClientState *peer;
>  
>      if (!cvq) {
> -        last_index -= 1;
> +        last_index &= ~1ULL;
>      }

As far as I can see, that is a nop. last_index is defined as an int.

$ cat kk.c
#include <stdio.h>

int main(void)
{
        int i = 7;
        i &= -1ULL;
        printf("%d\n", i);
        i = 8;
        i &= -1ULL;
        printf("%d\n", i);
        i = 0;
        i &= -1ULL;
        printf("%d\n", i);
        i = -2;
        i &= -1ULL;
        printf("%d\n", i);
        return 0;
}
$ ./kk
7
8
0
-2