Hi Alex, With this change, VHOST_USER_F_PROTOCOL_FEATURES bit will be set to backend for virtio block device (previously not).
From https://www.qemu.org/docs/master/interop/vhost-user.html spec: If VHOST_USER_F_PROTOCOL_FEATURES has not been negotiated, the ring starts directly in the enabled state. If VHOST_USER_F_PROTOCOL_FEATURES has been negotiated, the ring is initialized in a disabled state and is enabled by VHOST_USER_SET_VRING_ENABLE with parameter 1. Vhost-user-blk won't send out VHOST_USER_SET_VRING_ENABLE today. Backend gets VHOST_USER_F_PROTOCOL_FEATURES negotiated and can't get VHOST_USER_SET_VRING_ENABLE. VQs keep in disabled state. Can you check on this scenario? Thanks -----Original Message----- From: Qemu-devel <qemu-devel-bounces+yajunw=nvidia....@nongnu.org> On Behalf Of Alex Bennée Sent: Thursday, July 28, 2022 9:55 PM To: qemu-devel@nongnu.org Cc: m...@redhat.com; Alex Bennée <alex.ben...@linaro.org> Subject: [PATCH v2 1/4] hw/virtio: incorporate backend features in features External email: Use caution opening links or attachments There are some extra bits used over a vhost-user connection which are hidden from the device itself. We need to set them here to ensure we enable things like the protocol extensions. Currently net/vhost-user.c has it's own inscrutable way of persisting this data but it really should live in the core vhost_user code. Signed-off-by: Alex Bennée <alex.ben...@linaro.org> Message-Id: <20220726192150.2435175-7-alex.ben...@linaro.org> --- hw/virtio/vhost-user.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index 75b8df21a4..1936a44e82 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -1460,7 +1460,14 @@ static int vhost_user_set_features(struct vhost_dev *dev, */ bool log_enabled = features & (0x1ULL << VHOST_F_LOG_ALL); - return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features, + /* + * We need to include any extra backend only feature bits that + * might be needed by our device. Currently this includes the + * VHOST_USER_F_PROTOCOL_FEATURES bit for enabling protocol + * features. + */ + return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, + features | dev->backend_features, log_enabled); } -- 2.30.2
