[Xen-devel] [PATCH 2/2] argo: correctly report pending message length

[Nicholas Tsirakis <niko.tsirakis@xxxxxxxxx>]

When a message is requeue'd in Xen's internal queue, the queue
entry contains the length of the message so that Xen knows to
send a VIRQ to the respective domain when enough space frees up
in the ring. Due to a small bug, however, Xen doesn't populate
the length of the msg if a given write fails, so this length is
always reported as zero. This causes Xen to spurriously wake up
a domain even when the ring doesn't have enough space.

This patch makes sure that the msg len is properly reported by
populating it in the event of a write failure.

Signed-off-by: Nicholas Tsirakis <tsirakisn@xxxxxxxxxxxx>
---
 xen/common/argo.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/xen/common/argo.c b/xen/common/argo.c
index 2f874a570d..eb541829d6 100644
--- a/xen/common/argo.c
+++ b/xen/common/argo.c
@@ -2050,6 +2050,12 @@ sendv(struct domain *src_d, xen_argo_addr_t *src_addr,
         {
             int rc;
 
+            /*
+             * if ringbuf_insert fails, then len will never be populated.
+             * make sure to populate it here.
+             */
+            iov_count(iovs, niov, &len);
+
             argo_dprintk("argo_ringbuf_sendv failed, EAGAIN\n");
             /* requeue to issue a notification when space is there */
             rc = pending_requeue(dst_d, ring_info, src_id.domain_id, len);
-- 
2.17.1


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