bitbake: server/process: Show last 60 lines of the log if the server didn't start

We're seeing issues where the server doesn't start with no logs as to why. Allow
the server to print the last 60 log lines just in case this shows us something useful
about what is failing.

(Bitbake rev: 1351978585b76262cb104f3d609d79c184ee5d2b)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/process.py

@@ -414,22 +414,28 @@ class BitBakeServer(object):
                 logstart_re = re.compile(self.start_log_format % ('([0-9]+)', '([0-9-]+ [0-9:.]+)'))
                 started = False
                 lines = []
+                lastlines = []
                 with open(logfile, "r") as f:
                     for line in f:
                         if started:
                             lines.append(line)
                         else:
+                            lastlines.append(line)
                             res = logstart_re.match(line.rstrip())
                             if res:
                                 ldatetime = datetime.datetime.strptime(res.group(2), self.start_log_datetime_format)
                                 if ldatetime >= startdatetime:
                                     started = True
                                     lines.append(line)
+                        if len(lastlines) > 60:
+                            lastlines = lastlines[-60:]
                 if lines:
                     if len(lines) > 60:
                         bb.error("Last 60 lines of server log for this session (%s):\n%s" % (logfile, "".join(lines[-60:])))
                     else:
                         bb.error("Server log for this session (%s):\n%s" % (logfile, "".join(lines)))
+                elif lastlines:
+                        bb.error("Server didn't start, last 60 loglines (%s):\n%s" % (logfile, "".join(lastlines)))
             else:
                 bb.error("%s doesn't exist" % logfile)