Linux Virtualization - Mar 2012 - [PATCH] virtio-spec: clarify ro/rw bits and updating rule of virtio-net status field

This patch clarifies VIRTIO_NET_S_LINK_UP as a read-only bit and
VIRTIO_NET_S_ANNOUNCE as a read-writable bit. Also introduce the write 1 to
clear semantics for all read-writable bits of config status field. This could
help to reduce the config status field updating race between host and guest and
also simplify the implementation.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 virtio-0.9.4.lyx |   23 +++++++++++++++++++++--
 1 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/virtio-0.9.4.lyx b/virtio-0.9.4.lyx
index 6c7bab1..614ab55 100644
--- a/virtio-0.9.4.lyx
+++ b/virtio-0.9.4.lyx
@@ -58,6 +58,7 @@
 \html_be_strict false
 \author -608949062 "Rusty Russell,,," 
 \author 1531152142 "pbonzini" 
+\author 2090695081 "jason" 
 \end_header
 
 \begin_body
@@ -4013,7 +4014,21 @@ layout Two configuration fields are currently defined.
  The mac address field always exists (though is only valid if VIRTIO_NET_F_MAC
  is set), and the status field only exists if VIRTIO_NET_F_STATUS is set.
  Two bits are currently defined for the status field: VIRTIO_NET_S_LINK_UP
- and VIRTIO_NET_S_ANNOUNCE.
+ 
+\change_inserted 2090695081 1332220873
+(read-only) 
+\change_unchanged
+and VIRTIO_NET_S_ANNOUNCE
+\change_inserted 2090695081 1332220883
+ (read-writable)
+\change_unchanged
+.
+
+\change_inserted 2090695081 1332220901
+ Writing 1 to any read-writable bit of status filed would cause the bit
+ to be cleared.
+
+\change_unchanged
  
 \begin_inset listings
 inline false
@@ -4915,7 +4930,11 @@ Processing this notification involves:
 \end_layout
 
 \begin_layout Enumerate
-Clearing VIRTIO_NET_S_ANNOUNCE bit in the status field.
+Clearing VIRTIO_NET_S_ANNOUNCE bit in the status field
+\change_inserted 2090695081 1332220849
+ (by writing 1 to VIRTIO_NET_S_ANNOUNCE bit)
+\change_unchanged
+.
 \end_layout
 
 \begin_layout Enumerate

On Tue, 20 Mar 2012 14:20:21 +0800, Jason Wang <jasowang at redhat.com>
wrote:
> This patch clarifies VIRTIO_NET_S_LINK_UP as a read-only bit and
> VIRTIO_NET_S_ANNOUNCE as a read-writable bit. Also introduce the write 1 to
> clear semantics for all read-writable bits of config status field. This
could
> help to reduce the config status field updating race between host and guest
and
> also simplify the implementation.
> 
> Signed-off-by: Jason Wang <jasowang at redhat.com>
This approach assumes an active config field, which neither lguest nor
S/390 have.

Thanks,
Rusty.
-- 
  How could I marry someone with more hair than me?  http://baldalex.org