[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[PULL 64/91] vhost-user.rst: add clarifying language about protocol nego
From: |
Michael S. Tsirkin |
Subject: |
[PULL 64/91] vhost-user.rst: add clarifying language about protocol negotiation |
Date: |
Mon, 16 May 2022 06:39:19 -0400 |
From: Alex Bennée <alex.bennee@linaro.org>
Make the language about feature negotiation explicitly clear about the
handling of the VHOST_USER_F_PROTOCOL_FEATURES feature bit. Try and
avoid the sort of bug introduced in vhost.rs REPLY_ACK processing:
https://github.com/rust-vmm/vhost/pull/24
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Jiang Liu <gerry@linux.alibaba.com>
Message-Id: <20210226111619.21178-1-alex.bennee@linaro.org>
Message-Id: <20220321153037.3622127-8-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
docs/interop/vhost-user.rst | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 9159476678..73e710fe32 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -332,6 +332,18 @@ bit was dedicated for this purpose::
#define VHOST_USER_F_PROTOCOL_FEATURES 30
+Note that VHOST_USER_F_PROTOCOL_FEATURES is the UNUSED (30) feature
+bit defined in `VIRTIO 1.1 6.3 Legacy Interface: Reserved Feature Bits
+<https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-4130003>`_.
+VIRTIO devices do not advertise this feature bit and therefore VIRTIO
+drivers cannot negotiate it.
+
+This reserved feature bit was reused by the vhost-user protocol to add
+vhost-user protocol feature negotiation in a backwards compatible
+fashion. Old vhost-user master and slave implementations continue to
+work even though they are not aware of vhost-user protocol feature
+negotiation.
+
Ring states
-----------
@@ -890,7 +902,8 @@ Front-end message types
Get the protocol feature bitmask from the underlying vhost
implementation. Only legal if feature bit
``VHOST_USER_F_PROTOCOL_FEATURES`` is present in
- ``VHOST_USER_GET_FEATURES``.
+ ``VHOST_USER_GET_FEATURES``. It does not need to be acknowledged by
+ ``VHOST_USER_SET_FEATURES``.
.. Note::
Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must
@@ -906,7 +919,8 @@ Front-end message types
Enable protocol features in the underlying vhost implementation.
Only legal if feature bit ``VHOST_USER_F_PROTOCOL_FEATURES`` is present in
- ``VHOST_USER_GET_FEATURES``.
+ ``VHOST_USER_GET_FEATURES``. It does not need to be acknowledged by
+ ``VHOST_USER_SET_FEATURES``.
.. Note::
Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must support
--
MST
- [PULL 54/91] intel-iommu: block output address in interrupt address range, (continued)
- [PULL 54/91] intel-iommu: block output address in interrupt address range, Michael S. Tsirkin, 2022/05/16
- [PULL 55/91] intel-iommu: update root_scalable before switching as during post_load, Michael S. Tsirkin, 2022/05/16
- [PULL 56/91] intel-iommu: update iq_dw during post load, Michael S. Tsirkin, 2022/05/16
- [PULL 57/91] vhost_net: Print feature masks in hex, Michael S. Tsirkin, 2022/05/16
- [PULL 60/91] hw/virtio: add vhost_user_[read|write] trace points, Michael S. Tsirkin, 2022/05/16
- [PULL 58/91] hw/virtio: move virtio-pci.h into shared include space, Michael S. Tsirkin, 2022/05/16
- [PULL 62/91] docs: vhost-user: rewrite section on ring state machine, Michael S. Tsirkin, 2022/05/16
- [PULL 63/91] docs: vhost-user: replace master/slave with front-end/back-end, Michael S. Tsirkin, 2022/05/16
- [PULL 59/91] virtio-pci: add notification trace points, Michael S. Tsirkin, 2022/05/16
- [PULL 61/91] docs: vhost-user: clean up request/reply description, Michael S. Tsirkin, 2022/05/16
- [PULL 64/91] vhost-user.rst: add clarifying language about protocol negotiation,
Michael S. Tsirkin <=
- [PULL 65/91] libvhost-user: expose vu_request_to_string, Michael S. Tsirkin, 2022/05/16
- [PULL 66/91] docs/devel: start documenting writing VirtIO devices, Michael S. Tsirkin, 2022/05/16
- [PULL 67/91] include/hw: start documenting the vhost API, Michael S. Tsirkin, 2022/05/16
- [PULL 68/91] hw/virtio/vhost-user: don't suppress F_CONFIG when supported, Michael S. Tsirkin, 2022/05/16
- [PULL 69/91] virtio/vhost-user: dynamically assign VhostUserHostNotifiers, Michael S. Tsirkin, 2022/05/16
- [PULL 70/91] virtio: drop name parameter for virtio_init(), Michael S. Tsirkin, 2022/05/16
- [PULL 71/91] virtio: add vhost support for virtio devices, Michael S. Tsirkin, 2022/05/16
- [PULL 72/91] qmp: add QMP command x-query-virtio, Michael S. Tsirkin, 2022/05/16
- [PULL 73/91] qmp: add QMP command x-query-virtio-status, Michael S. Tsirkin, 2022/05/16
- [PULL 75/91] qmp: add QMP commands for virtio/vhost queue-status, Michael S. Tsirkin, 2022/05/16