Xen devel - Dec 2006 - [PATCH] Improve XendCheckpoint''s forkHelper error handling

# HG changeset patch
# User Brendan Cully <brendan@cs.ubc.ca>
# Date 1166060750 28800
# Node ID f2e7504c6693b80c98bb0b5368f3f7a4e5021333
# Parent  147608edc24993eaff17fd57709c77b8e2fee6b2
Improve XendCheckpoint''s forkHelper error handling.

When inputHandler raises an exception, close stdin and stdout in the
child before attempting to close stderr, which is held open by a
separate thread. Without this patch, exceptions raised by device
migration caused xend to hang on child.childerr.close().

Signed-off-by: Brendan Cully <brendan@cs.ubc.ca>

diff -r 147608edc249 -r f2e7504c6693 tools/python/xen/xend/XendCheckpoint.py
--- a/tools/python/xen/xend/XendCheckpoint.py	Wed Dec 13 17:42:38 2006 -0800
+++ b/tools/python/xen/xend/XendCheckpoint.py	Wed Dec 13 17:45:50 2006 -0800
@@ -224,18 +224,17 @@ def forkHelper(cmd, fd, inputHandler, cl
                     log.debug(''%s'', line)
                     inputHandler(line, child.tochild)
 
-            thread.join()
-
         except IOError, exn:
             raise XendError(''Error reading from child process for %s:
%s'' %
                             (cmd, exn))
     finally:
         child.fromchild.close()
-        child.childerr.close()
         if not closeToChild:
             child.tochild.close()
-
-    status = child.wait()
+        thread.join()
+        child.childerr.close()
+        status = child.wait()
+
     if status >> 8 == 127:
         raise XendError("%s failed: popen failed" % string.join(cmd))
     elif status != 0:

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On Wednesday, 13 December 2006 at 17:46, Brendan Cully
wrote:
> # HG changeset patch
> # User Brendan Cully <brendan@cs.ubc.ca>
> # Date 1166060750 28800
> # Node ID f2e7504c6693b80c98bb0b5368f3f7a4e5021333
> # Parent  147608edc24993eaff17fd57709c77b8e2fee6b2
> Improve XendCheckpoint''s forkHelper error handling.
> 
> When inputHandler raises an exception, close stdin and stdout in the
> child before attempting to close stderr, which is held open by a
> separate thread. Without this patch, exceptions raised by device
> migration caused xend to hang on child.childerr.close().
> 
> Signed-off-by: Brendan Cully <brendan@cs.ubc.ca>
*bump*

it''s pretty easy to wedge xend without this patch. Just have
migrateDevices return an error code, eg by running an
external-device-migrate script that returns 1.

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On Wed, Dec 13, 2006 at 05:46:12PM -0700, Brendan Cully wrote:
> # HG changeset patch
> # User Brendan Cully <brendan@cs.ubc.ca>
> # Date 1166060750 28800
> # Node ID f2e7504c6693b80c98bb0b5368f3f7a4e5021333
> # Parent  147608edc24993eaff17fd57709c77b8e2fee6b2
> Improve XendCheckpoint''s forkHelper error handling.
> 
> When inputHandler raises an exception, close stdin and stdout in the
> child before attempting to close stderr, which is held open by a
> separate thread. Without this patch, exceptions raised by device
> migration caused xend to hang on child.childerr.close().
> 
> Signed-off-by: Brendan Cully <brendan@cs.ubc.ca>
Applied, thanks Brendan, and sorry about the delay.

Ewan.

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