From dcb10c000cdd4d14f5ac4f07b04fb666494ef4a8 Mon Sep 17 00:00:00 2001 From: Michael S. Tsirkin Date: Wed, 23 Sep 2015 12:19:56 +0800 Subject: vhost-user: add protocol feature negotiation Support a separate bitmask for vhost-user protocol features, and messages to get/set protocol features. Invoke them at init. No features are defined yet. [ leverage vhost_user_call for request handling -- Yuanhan Liu ] Signed-off-by: Michael S. Tsirkin Signed-off-by: Yuanhan Liu Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin Signed-off-by: Yuanhan Liu Reviewed-by: Marcel Apfelbaum Tested-by: Marcel Apfelbaum --- docs/specs/vhost-user.txt | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'docs') diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt index 650bb18186..70da3b197e 100644 --- a/docs/specs/vhost-user.txt +++ b/docs/specs/vhost-user.txt @@ -113,6 +113,7 @@ message replies. Most of the requests don't require replies. Here is a list of the ones that do: * VHOST_GET_FEATURES + * VHOST_GET_PROTOCOL_FEATURES * VHOST_GET_VRING_BASE There are several messages that the master sends with file descriptors passed @@ -127,6 +128,13 @@ in the ancillary data: If Master is unable to send the full message or receives a wrong reply it will close the connection. An optional reconnection mechanism can be implemented. +Any protocol extensions are gated by protocol feature bits, +which allows full backwards compatibility on both master +and slave. +As older slaves don't support negotiating protocol features, +a feature bit was dedicated for this purpose: +#define VHOST_USER_F_PROTOCOL_FEATURES 30 + Message types ------------- @@ -138,6 +146,8 @@ Message types Slave payload: u64 Get from the underlying vhost implementation the features bitmask. + Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for + VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES. * VHOST_USER_SET_FEATURES @@ -146,6 +156,33 @@ Message types Master payload: u64 Enable features in the underlying vhost implementation using a bitmask. + Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for + VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES. + + * VHOST_USER_GET_PROTOCOL_FEATURES + + Id: 15 + Equivalent ioctl: VHOST_GET_FEATURES + Master payload: N/A + Slave payload: u64 + + 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. + Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support + this message even before VHOST_USER_SET_FEATURES was called. + + * VHOST_USER_SET_PROTOCOL_FEATURES + + Id: 16 + Ioctl: VHOST_SET_FEATURES + Master payload: u64 + + 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. + Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support + this message even before VHOST_USER_SET_FEATURES was called. * VHOST_USER_SET_OWNER -- cgit v1.2.3-55-g7522