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libvhost-user: advertise vring features

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libvhost-user implements several vring features without advertising
them. There is no way for the vhost-user master to detect support for
these features.

Things more or less work today because QEMU assumes the vhost-user
backend always implements certain feature bits like
VIRTIO_RING_F_EVENT_IDX. This is not documented anywhere.

This patch explicitly advertises features implemented in libvhost-user
so that the vhost-user master does not need to make undocumented
assumptions.

Feature bits that libvhost-user now advertises can be removed from
vhost-user-blk.c. Devices should not be responsible for advertising
vring feature bits, that is libvhost-user's job.

Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20200529161338.456017-1-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2020-05-29 17:13:38 +01:00 committed by Michael S. Tsirkin
parent b650d5f4b1
commit a9a5c473d2
2 changed files with 11 additions and 3 deletions
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10
contrib/libvhost-user/libvhost-user.c
View file

@ -498,6 +498,16 @@ static bool
vu_get_features_exec(VuDev *dev, VhostUserMsg *vmsg)
{
vmsg->payload.u64 =
/*
* The following VIRTIO feature bits are supported by our virtqueue
* implementation:
*/
1ULL << VIRTIO_F_NOTIFY_ON_EMPTY |
1ULL << VIRTIO_RING_F_INDIRECT_DESC |
1ULL << VIRTIO_RING_F_EVENT_IDX |
1ULL << VIRTIO_F_VERSION_1 |
/* vhost-user feature bits */
1ULL << VHOST_F_LOG_ALL |
1ULL << VHOST_USER_F_PROTOCOL_FEATURES;

4
contrib/vhost-user-blk/vhost-user-blk.c
View file

@ -382,9 +382,7 @@ vub_get_features(VuDev *dev)
1ull << VIRTIO_BLK_F_DISCARD |
1ull << VIRTIO_BLK_F_WRITE_ZEROES |
#endif
1ull << VIRTIO_BLK_F_CONFIG_WCE |
1ull << VIRTIO_F_VERSION_1 |
1ull << VHOST_USER_F_PROTOCOL_FEATURES;
1ull << VIRTIO_BLK_F_CONFIG_WCE;
if (vdev_blk->enable_ro) {
features |= 1ull << VIRTIO_BLK_F_RO;