CA-287928: Use logger for upstream QEMU logging

QEMU's stdout and stderr are connected to a forkexecd child proccess
which is responsible for logging to syslog. This forkexecd child does
not remain running when using qemu-trad since it logs to syslog via its
privileged half. Since the forkexecd child is fairly heavyweight,
replace it with "logger" which does the same thing but uses
substantially less memory.

Unfortunately, to have the logs prefixed with QEMU's pid implies
starting QEMU before logger which requires a fair amount of code
refactoring in the wrapper so that QEMU is started as a subprocess and
logger is exec()ed rather than exec()ing QEMU directly.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>

scripts/qemu-wrapper

@@ -21,7 +21,7 @@ import errno
 import stat
 import pwd
 import grp
-from subprocess import call
+import subprocess
 import ctypes
 import ctypes.util
 import os
@@ -136,10 +136,34 @@ def close_fds():
     for i in open_fds:
         os.close(i)
 
-def main(argv):
-    f = sys.stdout
+def prepare_exec():
+    """Set up the execution environment for QEMU."""
 
-    f.write("Arguments: %s\n" % " ".join(argv[1:]))
+    if cgroup_slice is not None:
+        # Move to nominated cgroup slice
+        print "Moving to cgroup slice '%s'" % cgroup_slice
+        try:
+            # Note the default slice uses /sys/fs/cgroup/cpu/tasks but
+            # other.slice uses /sys/fs/cgroup/cpu/other.slice/tasks.
+            g = open("/sys/fs/cgroup/cpu/%s/tasks" % cgroup_slice, 'w')
+            g.write(str(os.getpid()))
+            g.close()
+        except IOError, e:
+            print "Warning: writing pid to '%s' tasks file: %s" \
+                % (cgroup_slice, e)
+
+    core_dump_limit = enable_core_dumps()
+    print "core dump limit: %d" % core_dump_limit
+
+    restrict_fsize()
+
+    unshare(CLONE_NEWNET | CLONE_NEWNS | CLONE_NEWIPC)
+
+    sys.stdout.flush()
+    sys.stderr.flush()
+
+def main(argv):
+    print "Arguments: %s" % " ".join(argv[1:])
 
     for n in range(len(argv)):
         if argv[n] == "-xen-domid":
@@ -240,7 +264,7 @@ def main(argv):
         if p == "-loadvm":
             loadvm_path = qemu_args[n+1]
             if qemu_trad_image.is_trad_image(loadvm_path):
-                f.write("QEMU Traditional image detected. Upgrading...\n")
+                print "QEMU Traditional image detected. Upgrading..."
 
                 loadvm_file = open(loadvm_path, "rb")
                 incoming_file = tempfile.TemporaryFile()
@@ -294,10 +318,11 @@ def main(argv):
 
     xenstore_write("/libxl/%d/dm-version" % domid, "qemu_xen")
 
-    f.write("Exec: %s %s\n" % (qemu_dm, " ".join(qemu_args)))
+    print "Exec: %s %s" % (qemu_dm, " ".join(qemu_args))
 
     clipboardd = '/opt/xensource/libexec/xs-clipboardd'
-    call([clipboardd, "-d", str(domid), "-s", str(s2.fileno())], preexec_fn = lambda : (close_fds()))
+    subprocess.call([clipboardd, "-d", str(domid), "-s", str(s2.fileno())],
+                    preexec_fn=close_fds)
 
     s2.close()
 
@@ -309,31 +334,25 @@ def main(argv):
        qemu_env["LD_PRELOAD"] = "/usr/lib64/libjemalloc.so.1:" + qemu_env["LD_PRELOAD"]
     qemu_env["MALLOC_CONF"] = "narenas:1,tcache:false,lg_dirty_mult:22"
 
-    core_dump_limit = enable_core_dumps()
-    f.write("core dump limit: %d\n" % core_dump_limit)
+    sys.stdout.flush()
+    sys.stderr.flush()
 
-    pid = os.getpid()
-    xenstore_write("/local/domain/%d/qemu-pid" % domid, "%d" % pid)
+    qemu = subprocess.Popen(qemu_args, executable=qemu_dm, env=qemu_env,
+                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
+                            preexec_fn=prepare_exec)
 
-    if cgroup_slice is not None:
-        # Move to nominated cgroup slice
-        f.write("Moving to cgroup slice '%s'\n" % cgroup_slice)
-        try:
-            # Note the default slice uses /sys/fs/cgroup/cpu/tasks but
-            # other.slice uses /sys/fs/cgroup/cpu/other.slice/tasks.
-            g = open("/sys/fs/cgroup/cpu/%s/tasks" % cgroup_slice, 'w')
-            g.write(str(pid))
-            g.close()
-        except IOError, e:
-            print "Warning: writing pid to '%s' tasks file: %s" \
-                % (cgroup_slice, e)
+    xenstore_write("/local/domain/%d/qemu-pid" % domid, "%d" % qemu.pid)
 
-    restrict_fsize()
+    # Redirect output from QEMU to logger
+    os.dup2(qemu.stdout.fileno(), 0)
+    qemu.stdout.close()
 
-    unshare(CLONE_NEWNET | CLONE_NEWNS | CLONE_NEWIPC)
+    # Close all unneeded fds
+    open_fds.extend([1, 2])
+    close_fds()
 
-    f.flush()
-    os.execve(qemu_dm, qemu_args, qemu_env)
+    os.execvp('logger', ['logger', '-p', 'daemon.info', '-t',
+                         'qemu-dm-%d[%d]' % (domid, qemu.pid)])
 
 if __name__ == '__main__':
     raise SystemExit(main(sys.argv))