Re: [PATCH v6 3/3] vhost: switch to arrays of feature bits

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Nov 28, 2025 at 10:39:57AM +0800, Jason Wang wrote:
> On Thu, Nov 27, 2025 at 2:40 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > The current interface where caller has to know in which 64 bit chunk
> > each bit is, is inelegant and fragile.
> > Let's simply use arrays of bits.
> > By using unroll macros text size grows only slightly.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  drivers/vhost/net.c   | 19 ++++++++++---------
> >  drivers/vhost/scsi.c  |  9 ++++++---
> >  drivers/vhost/test.c  |  6 +++++-
> >  drivers/vhost/vhost.h | 42 ++++++++++++++++++++++++++++++++++--------
> >  drivers/vhost/vsock.c | 10 ++++++----
> >  5 files changed, 61 insertions(+), 25 deletions(-)
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index d057ea55f5ad..f8ed39337f56 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -69,15 +69,15 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
> >
> >  #define VHOST_DMA_IS_DONE(len) ((__force u32)(len) >= (__force u32)VHOST_DMA_DONE_LEN)
> >
> > -static const u64 vhost_net_features[VIRTIO_FEATURES_U64S] = {
> > -       VHOST_FEATURES |
> > -       (1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
> > -       (1ULL << VIRTIO_NET_F_MRG_RXBUF) |
> > -       (1ULL << VIRTIO_F_ACCESS_PLATFORM) |
> > -       (1ULL << VIRTIO_F_RING_RESET) |
> > -       (1ULL << VIRTIO_F_IN_ORDER),
> > -       VIRTIO_BIT(VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) |
> > -       VIRTIO_BIT(VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO),
> > +static const int vhost_net_bits[] = {
> > +       VHOST_FEATURES,
> > +       VHOST_NET_F_VIRTIO_NET_HDR,
> > +       VIRTIO_NET_F_MRG_RXBUF,
> > +       VIRTIO_F_ACCESS_PLATFORM,
> > +       VIRTIO_F_RING_RESET,
> > +       VIRTIO_F_IN_ORDER,
> > +       VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO,
> > +       VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO
> >  };
> >
> >  enum {
> > @@ -1720,6 +1720,7 @@ static long vhost_net_set_owner(struct vhost_net *n)
> >  static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
> >                             unsigned long arg)
> >  {
> > +       const DEFINE_VHOST_FEATURES_ARRAY(vhost_net_features, vhost_net_bits);
> >         u64 all_features[VIRTIO_FEATURES_U64S];
> >         struct vhost_net *n = f->private_data;
> >         void __user *argp = (void __user *)arg;
> > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> > index 98e4f68f4e3c..f43c1fe9fad9 100644
> > --- a/drivers/vhost/scsi.c
> > +++ b/drivers/vhost/scsi.c
> > @@ -197,11 +197,14 @@ enum {
> >  };
> >
> >  /* Note: can't set VIRTIO_F_VERSION_1 yet, since that implies ANY_LAYOUT. */
> > -enum {
> > -       VHOST_SCSI_FEATURES = VHOST_FEATURES | (1ULL << VIRTIO_SCSI_F_HOTPLUG) |
> > -                                              (1ULL << VIRTIO_SCSI_F_T10_PI)
> > +static const int vhost_scsi_bits[] = {
> > +       VHOST_FEATURES,
> > +       VIRTIO_SCSI_F_HOTPLUG,
> > +       VIRTIO_SCSI_F_T10_PI
> >  };
> >
> > +#define VHOST_SCSI_FEATURES VHOST_FEATURES_U64(vhost_scsi_bits, 0)
> > +
> >  #define VHOST_SCSI_MAX_TARGET  256
> >  #define VHOST_SCSI_MAX_IO_VQ   1024
> >  #define VHOST_SCSI_MAX_EVENT   128
> > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
> > index 94cd09f36f59..f592b2f548e8 100644
> > --- a/drivers/vhost/test.c
> > +++ b/drivers/vhost/test.c
> > @@ -28,7 +28,11 @@
> >   */
> >  #define VHOST_TEST_PKT_WEIGHT 256
> >
> > -#define VHOST_TEST_FEATURES VHOST_FEATURES
> > +static const int vhost_test_bits[] = {
> > +       VHOST_FEATURES
> > +};
> > +
> > +#define VHOST_TEST_FEATURES VHOST_FEATURES_U64(vhost_test_features, 0)
> 
> Did you mean vhost_test_bits actually?
> 
> Thanks

indeed.