[Qemu-devel] [PATCH 1/2] virtio-9p: print error message and exit instead of BUG_ON()

[Greg Kurz]

Calling assert() really makes sense when hitting a genuine bug, which calls
for a fix in QEMU. However, when something goes wrong because the guest
sends a malformed message, it is better to write down a more meaningul
error message and exit.

Signed-off-by: Greg Kurz <address@hidden>
---
 hw/9pfs/virtio-9p-device.c |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
index 009b43f6d045..67059182645a 100644
--- a/hw/9pfs/virtio-9p-device.c
+++ b/hw/9pfs/virtio-9p-device.c
@@ -19,6 +19,7 @@
 #include "coth.h"
 #include "hw/virtio/virtio-access.h"
 #include "qemu/iov.h"
+#include "qemu/error-report.h"
 
 void virtio_9p_push_and_notify(V9fsPDU *pdu)
 {
@@ -35,6 +36,11 @@ void virtio_9p_push_and_notify(V9fsPDU *pdu)
     virtio_notify(VIRTIO_DEVICE(v), v->vq);
 }
 
+static void virtio_9p_error(const char *msg)
+{
+    error_report("The virtio-9p driver in the guest has an issue: %s", msg);
+}
+
 static void handle_9p_output(VirtIODevice *vdev, VirtQueue *vq)
 {
     V9fsVirtioState *v = (V9fsVirtioState *)vdev;
@@ -56,13 +62,23 @@ static void handle_9p_output(VirtIODevice *vdev, VirtQueue 
*vq)
             break;
         }
 
-        BUG_ON(elem->out_num == 0 || elem->in_num == 0);
+        if (elem->out_num == 0) {
+            virtio_9p_error("missing VirtFS request's header");
+            exit(1);
+        }
+        if (elem->in_num == 0) {
+            virtio_9p_error("missing VirtFS reply's header");
+            exit(1);
+        }
         QEMU_BUILD_BUG_ON(sizeof out != 7);
 
         v->elems[pdu->idx] = elem;
         len = iov_to_buf(elem->out_sg, elem->out_num, 0,
                          &out, sizeof out);
-        BUG_ON(len != sizeof out);
+        if (len != sizeof out) {
+            virtio_9p_error("malformed VirtFS request");
+            exit(1);
+        }
 
         pdu->size = le32_to_cpu(out.size_le);