[qemu-xen staging] iotests.py: QemuIoInteractive: print output on failure

[patchbot@xxxxxxx]

commit 1f4b774a6444575b86f27b17d3d01e4f41df6581
Author:     Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
AuthorDate: Wed Jul 1 13:53:28 2020 +0300
Commit:     Eric Blake <eblake@xxxxxxxxxx>
CommitDate: Mon Jul 13 09:01:01 2020 -0500

    iotests.py: QemuIoInteractive: print output on failure
    
    Make it simpler to debug when qemu-io fails due to wrong arguments or
    environment.
    
    Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
    Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
    Message-Id: <20200701105331.121670-3-vsementsov@xxxxxxxxxxxxx>
    Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
---
 tests/qemu-iotests/iotests.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 109fb3884a..2a08fea3c9 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -217,7 +217,13 @@ class QemuIoInteractive:
                                    stdout=subprocess.PIPE,
                                    stderr=subprocess.STDOUT,
                                    universal_newlines=True)
-        assert self._p.stdout.read(9) == 'qemu-io> '
+        out = self._p.stdout.read(9)
+        if out != 'qemu-io> ':
+            # Most probably qemu-io just failed to start.
+            # Let's collect the whole output and exit.
+            out += self._p.stdout.read()
+            self._p.wait(timeout=1)
+            raise ValueError(out)
 
     def close(self):
         self._p.communicate('q\n')
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#staging