On Mon, Mar 21, 2022 at 03:30:36PM +0000, Alex Bennée wrote:
> Previously we would silently suppress VHOST_USER_PROTOCOL_F_CONFIG
> during the protocol negotiation if the QEMU stub hadn't implemented
> the vhost_dev_config_notifier. However this isn't the only way we can
> handle config messages, the existing vdc->get/set_config can do this
> as well.
Could you give an example where the problem is encountered please?
> Lightly re-factor the code to check for both potential methods and
> instead of silently squashing the feature error out. It is unlikely
> that a vhost-user backend expecting to handle CONFIG messages will
> behave correctly if they never get sent.
Hmm but are you sure? Most devices work mostly fine without CONFIG
messages, there's a chance a backend set this flag just in case
without much thought ...
> Fixes: 1c3e5a2617 ("vhost-user: back SET/GET_CONFIG requests with a protocol
> feature")
I'm not sure whether something is broken or this is a cleanup patch.
Fixes tag means "if you have 1c3e5a2617 you should pick this patch", so
cleanups don't need a fixes: tag.
> Cc: Maxime Coquelin <maxime.coque...@redhat.com>
> Cc: Michael S. Tsirkin <m...@redhat.com>
> Cc: Stefan Hajnoczi <stefa...@redhat.com>
> Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
>
> ---
> - we can't check for get_config/set_config as the stack squashed vdev
> - use vhost-user-state to transmit this
> ---
> include/hw/virtio/vhost-user.h | 1 +
> hw/scsi/vhost-user-scsi.c | 1 +
> hw/virtio/vhost-user.c | 46 ++++++++++++++++++++++++----------
> 3 files changed, 35 insertions(+), 13 deletions(-)
>
> diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
> index e44a41bb70..6e0e8a71a3 100644
> --- a/include/hw/virtio/vhost-user.h
> +++ b/include/hw/virtio/vhost-user.h
> @@ -22,6 +22,7 @@ typedef struct VhostUserState {
> CharBackend *chr;
> VhostUserHostNotifier notifier[VIRTIO_QUEUE_MAX];
> int memory_slots;
> + bool supports_config;
> } VhostUserState;
>
> bool vhost_user_init(VhostUserState *user, CharBackend *chr, Error **errp);
> diff --git a/hw/scsi/vhost-user-scsi.c b/hw/scsi/vhost-user-scsi.c
> index 1b2f7eed98..9be21d07ee 100644
> --- a/hw/scsi/vhost-user-scsi.c
> +++ b/hw/scsi/vhost-user-scsi.c
> @@ -121,6 +121,7 @@ static void vhost_user_scsi_realize(DeviceState *dev,
> Error **errp)
> vsc->dev.backend_features = 0;
> vqs = vsc->dev.vqs;
>
> + s->vhost_user.supports_config = true;
> ret = vhost_dev_init(&vsc->dev, &s->vhost_user,
> VHOST_BACKEND_TYPE_USER, 0, errp);
> if (ret < 0) {
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index b27b8c56e2..6ce082861b 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -1949,14 +1949,15 @@ static int
> vhost_user_postcopy_notifier(NotifierWithReturn *notifier,
> static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
> Error **errp)
> {
> - uint64_t features, protocol_features, ram_slots;
> + uint64_t features, ram_slots;
> struct vhost_user *u;
> + VhostUserState *vus = (VhostUserState *) opaque;
> int err;
>
> assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
>
> u = g_new0(struct vhost_user, 1);
> - u->user = opaque;
> + u->user = vus;
> u->dev = dev;
> dev->opaque = u;
>
> @@ -1967,6 +1968,10 @@ static int vhost_user_backend_init(struct vhost_dev
> *dev, void *opaque,
> }
>
> if (virtio_has_feature(features, VHOST_USER_F_PROTOCOL_FEATURES)) {
> + bool supports_f_config = vus->supports_config ||
> + (dev->config_ops && dev->config_ops->vhost_dev_config_notifier);
> + uint64_t protocol_features;
> +
> dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
>
> err = vhost_user_get_u64(dev, VHOST_USER_GET_PROTOCOL_FEATURES,
> @@ -1976,19 +1981,34 @@ static int vhost_user_backend_init(struct vhost_dev
> *dev, void *opaque,
> return -EPROTO;
> }
>
> - dev->protocol_features =
> - protocol_features & VHOST_USER_PROTOCOL_FEATURE_MASK;
> -
> - if (!dev->config_ops || !dev->config_ops->vhost_dev_config_notifier)
> {
> - /* Don't acknowledge CONFIG feature if device doesn't support it
> */
> - dev->protocol_features &= ~(1ULL <<
> VHOST_USER_PROTOCOL_F_CONFIG);
> - } else if (!(protocol_features &
> - (1ULL << VHOST_USER_PROTOCOL_F_CONFIG))) {
> - error_setg(errp, "Device expects VHOST_USER_PROTOCOL_F_CONFIG "
> - "but backend does not support it.");
> - return -EINVAL;
> + /*
> + * We will use all the protocol features we support - although
> + * we suppress F_CONFIG if we know QEMUs internal code can not
> support
> + * it.
> + */
> + protocol_features &= VHOST_USER_PROTOCOL_FEATURE_MASK;
> +
> + if (supports_f_config) {
> + if (!virtio_has_feature(protocol_features,
> + VHOST_USER_PROTOCOL_F_CONFIG)) {
> + error_setg(errp, "vhost-user device %s expecting "
> + "VHOST_USER_PROTOCOL_F_CONFIG but the vhost-user
> backend does "
> + "not support it.", dev->vdev->name);
> + return -EPROTO;
> + }
> + } else {
> + if (virtio_has_feature(protocol_features,
> + VHOST_USER_PROTOCOL_F_CONFIG)) {
> + warn_reportf_err(*errp, "vhost-user backend supports "
> + "VHOST_USER_PROTOCOL_F_CONFIG for "
> + "device %s but QEMU does not.",
> + dev->vdev->name);
> + protocol_features &= ~(1ULL << VHOST_USER_PROTOCOL_F_CONFIG);
> + }
> }
>
> + /* final set of protocol features */
> + dev->protocol_features = protocol_features;
> err = vhost_user_set_protocol_features(dev, dev->protocol_features);
> if (err < 0) {
> error_setg_errno(errp, EPROTO, "vhost_backend_init failed");
> --
> 2.30.2
