1 files changed, 18 insertions, 0 deletions
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 364c7cb446..e88bb50f13 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -630,6 +630,24 @@ static void coroutine_fn pdu_complete(V9fsPDU *pdu, ssize_t len)
     V9fsState *s = pdu->s;
     int ret;
 
+    /*
+     * The 9p spec requires that successfully cancelled pdus receive no reply.
+     * Sending a reply would confuse clients because they would
+     * assume that any EINTR is the actual result of the operation,
+     * rather than a consequence of the cancellation. However, if
+     * the operation completed (succesfully or with an error other
+     * than caused be cancellation), we do send out that reply, both
+     * for efficiency and to avoid confusing the rest of the state machine
+     * that assumes passing a non-error here will mean a successful
+     * transmission of the reply.
+     */
+    bool discard = pdu->cancelled && len == -EINTR;
+    if (discard) {
+        trace_v9fs_rcancel(pdu->tag, pdu->id);
+        pdu->size = 0;
+        goto out_notify;
+    }
+
     if (len < 0) {
         int err = -len;
         len = 7;