doc: add virtio LSC note

Virtio PMD already has supported link status change(lsc), but VM which
must be created by qemu 2.7.0 and above can support it when vhost
user disconnects, since the capability to detect vhost user disconnection
is introduced in qemu 2.7.0. The patch updates doc to let user know that.

Signed-off-by: Zhiyong Yang <zhiyong.yang@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>

diff --git a/doc/guides/nics/virtio.rst b/doc/guides/nics/virtio.rst
index 4d6a837..af82f86 100644 (file)
--- a/doc/guides/nics/virtio.rst
+++ b/doc/guides/nics/virtio.rst
@@ -291,6 +291,13 @@ interrupt, Rx interrupts, and Tx interrupts. Config interrupt is used for
 notification of device configuration changes, especially link status (lsc).
 Interrupt mode is translated into Rx interrupts in the context of DPDK.
 
+.. Note::
+
+   Virtio PMD already has support for receiving lsc from qemu when the link
+   status changes, especially when vhost user disconnects. However, it fails
+   to do that if the VM is created by qemu 2.6.2 or below, since the
+   capability to detect vhost user disconnection is introduced in qemu 2.7.0.
+
 Prerequisites for Rx interrupts
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~