Raise an exception if an error appears on the pipes to our children, and make

sure that the child's pipes are closed even under that exception.  Move the
handling of POLLHUP to the end of the loop, so that we guarantee to read any
remaining data from the child if POLLHUP and POLLIN appear at the same time.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

tools/python/xen/xend/XendCheckpoint.py

@@ -116,6 +116,7 @@ def restore(xd, fd):
 
     assert dominfo.store_channel
     assert dominfo.console_channel
+    assert dominfo.getDomainPath()
 
     try:
         l = read_exact(fd, sizeof_unsigned_long,
@@ -138,6 +139,11 @@ def restore(xd, fd):
             if m:
                 store_mfn = int(m.group(2))
                 dominfo.setStoreRef(store_mfn)
+                log.debug("IntroduceDomain %d %d %d %s",
+                          dominfo.getDomid(),
+                          store_mfn,
+                          dominfo.store_channel.port1,
+                          dominfo.getDomainPath())
                 IntroduceDomain(dominfo.getDomid(),
                                 store_mfn,
                                 dominfo.store_channel.port1,
@@ -161,34 +167,40 @@ def forkHelper(cmd, fd, inputHandler, closeToChild):
     if closeToChild:
         child.tochild.close()
 
-    fds = [child.fromchild.fileno(),
-           child.childerr.fileno()]
-    p = select.poll()
-    map(p.register, fds)
-    while len(fds) > 0:
-        r = p.poll()
-        for (fd, event) in r:
-            if event & select.POLLHUP or event & select.POLLERR:
-                fds.remove(fd)
-                p.unregister(fd)
-                continue
-            if not event & select.POLLIN:
-                continue
-            if fd == child.childerr.fileno():
-                lasterr = child.childerr.readline().rstrip()
-                log.error('%s', lasterr)
-            else:
-                l = child.fromchild.readline().rstrip()
-                while l:
-                    log.debug('%s', l)
-                    inputHandler(l, child.tochild)
-                    try:
+    try:
+        fds = [child.fromchild.fileno(),
+               child.childerr.fileno()]
+        p = select.poll()
+        map(p.register, fds)
+        while len(fds) > 0:
+            r = p.poll()
+            for (fd, event) in r:
+                if event & select.POLLIN:
+                    if fd == child.childerr.fileno():
+                        lasterr = child.childerr.readline().rstrip()
+                        log.error('%s', lasterr)
+                    else:
                         l = child.fromchild.readline().rstrip()
-                    except:
-                        l = None
+                        while l:
+                            log.debug('%s', l)
+                            inputHandler(l, child.tochild)
+                            try:
+                                l = child.fromchild.readline().rstrip()
+                            except:
+                                l = None
 
-    child.fromchild.close()
-    child.childerr.close()
+                if event & select.POLLERR:
+                    raise XendError('Error reading from child process for %s',
+                                    cmd)
+
+                if event & select.POLLHUP:
+                    fds.remove(fd)
+                    p.unregister(fd)
+    finally:
+        child.fromchild.close()
+        child.childerr.close()
+        if not closeToChild:
+            child.tochild.close()
 
     if child.wait() >> 8 == 127:
         lasterr = "popen failed"