[PATCH MINI-OS v3 2/2] xenbus: workaround oxenstored short-write

[Wei Liu <wei.liu2@citrix.com>]

Oxenstored has a behaviour that it only writes a contiguous piece of
data. When it writes across ring boundary it will return a short-write
while there is still room. That leads to mini-os stalling when it sees
there is not enough data in the ring.

Given that oxenstored is the default xenstored implementation we think
it would be useful to workaround this for the benefit of running mini-os
(and unikernel based on it) on any Xen installation.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 xenbus/xenbus.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/xenbus/xenbus.c b/xenbus/xenbus.c
index 0ab387a..abf8b1b 100644
--- a/xenbus/xenbus.c
+++ b/xenbus/xenbus.c
@@ -205,8 +205,11 @@ static void xenbus_thread_func(void *ign)
             prod = xenstore_buf->rsp_prod;
             DEBUG("Rsp_cons %d, rsp_prod %d.\n", xenstore_buf->rsp_cons,
                     xenstore_buf->rsp_prod);
-            if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons < sizeof(msg))
+            if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons < sizeof(msg)) {
+                /* Work around oxenstored bug */
+                notify_remote_via_evtchn(start_info.store_evtchn);
                 break;
+            }
             rmb();
             memcpy_from_ring(xenstore_buf->rsp,
                     &msg,
@@ -217,8 +220,11 @@ static void xenbus_thread_func(void *ign)
                     xenstore_buf->rsp_prod - xenstore_buf->rsp_cons,
                     msg.req_id);
             if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons <
-                    sizeof(msg) + msg.len)
+                    sizeof(msg) + msg.len) {
+                /* Work around oxenstored bug */
+                notify_remote_via_evtchn(start_info.store_evtchn);
                 break;
+            }
 
             DEBUG("Message is good.\n");
 
-- 
2.1.4