[PATCH] testsuite: Improve VM output check for login prompt

[Uladzimir Bely <ubely@ilbers.de>]

VM output is read by chunks and " login:" string is looked up in
the every chunk. This may fail in case this string is splitted by
two consecutive chunks.

Improve this by looking up in a bigger data buffer instead of
current chunk.

Signed-off-by: Uladzimir Bely <ubely@ilbers.de>
---
 testsuite/cibuilder.py | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/testsuite/cibuilder.py b/testsuite/cibuilder.py
index 002a368b..fa30c2f5 100755
--- a/testsuite/cibuilder.py
+++ b/testsuite/cibuilder.py
@@ -487,17 +487,20 @@ BBPATH .= ":${LAYERDIR}"\
         poller.register(p1.stdout, select.POLLIN)
         poller.register(p1.stderr, select.POLLIN)
 
+        # Databuf of size enough to keep two data chunks + checked string
+        databuf = bytearray(b'')
+        databuf_size = 1024 * 2 + len(login_prompt)
+
         while time.time() < timeout and p1.poll() is None:
             events = poller.poll(1000 * (timeout - time.time()))
             for fd, event in events:
                 if event != select.POLLIN:
                     continue
                 if fd == p1.stdout.fileno():
-                    # Wait for the complete string if it is read in chunks
-                    # like "i", "sar", " login:"
-                    time.sleep(0.01)
                     data = os.read(fd, 1024)
-                    if login_prompt in data:
+                    shift = max(0, len(data) + len(databuf) - databuf_size)
+                    databuf = databuf[shift:] + bytearray(data)
+                    if login_prompt in databuf:
                         self.log.info('Got login prompt')
                         return 0
                 if fd == p1.stderr.fileno():
-- 
2.20.1