[Xen-devel] [PATCH] XenBus: Don't wait for producer to fill the ring if the ring

[Anshul Makkar <anshul.makkar@xxxxxxxxxx>]

    The condition to check for if there is space in the ring buffer
    also becomes true if the buffer is full, thus consumer waits for
    the producer to fill the buffer eventhough it is already full.

    To resolve the situation, check if the buffer is full and then
    break from the loop.
    e.g case: prod = 1272, cons = 248.

    Signed-off-by: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
---
 tools/firmware/hvmloader/xenbus.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/firmware/hvmloader/xenbus.c 
b/tools/firmware/hvmloader/xenbus.c
index 448157d..f8fd730 100644
--- a/tools/firmware/hvmloader/xenbus.c
+++ b/tools/firmware/hvmloader/xenbus.c
@@ -141,7 +141,18 @@ static void ring_read(char *data, uint32_t len)
         /* Don't overrun the producer pointer */
         while ( (part = MASK_XENSTORE_IDX(rings->rsp_prod -
                                           rings->rsp_cons)) == 0 )
+        {
+            /* don't wait for producer to fill the ring if it is already full.
+             * Condition happens when you write string > 1K into the ring.
+             * eg case prod=1272 cons=248.
+             */
+            if ( !(XENSTORE_RING_SIZE - (rings->rsp_prod - rings->rsp_cons)) )
+            {
+                part = XENSTORE_RING_SIZE;
+                break;
+            }
             ring_wait();
+        }
         /* Don't overrun the end of the ring */
         if ( part > (XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(rings->rsp_cons)) )
             part = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(rings->rsp_cons);
-- 
2.7.4


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