From 9c233417e0bcf2837a619d7b21b42ed093dc8552 Mon Sep 17 00:00:00 2001
From: Iustin Pop <iustin@google.com>
Date: Wed, 19 Dec 2007 11:11:05 +0000
Subject: [PATCH] Make utils.RunCmd() deal with interleaved stdout/stderr
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Currently, RunCmd is written with the assumption that programs will have
a small stderr output, therefore we read the child's stdout (which can
be big, so we don't want to block the child) and then the stderr (which
is small, so it shouldn't block).
However, with the βgnt-cluster verify-disksβ command, we ourselves
generate heavy stderr, therefore we break the ganeti-watcher which runs
the verify-disks via utils.RunCmd.
This patch turns the RunCmd command into an poll-based one, which means
any kind of interleaved output by a child on stdout/stderr will be
handled correctly. Of course, since the output is buffered in memory,
there are other ways to break RunCmd(). But at least this should fix the
common case.
Reviewed-by: hansmi
---
lib/utils.py | 36 ++++++++++++++++++++++++++++++++++--
1 file changed, 34 insertions(+), 2 deletions(-)
diff --git a/lib/utils.py b/lib/utils.py
index a85ebb048..d5fe36ea9 100644
--- a/lib/utils.py
+++ b/lib/utils.py
@@ -36,6 +36,10 @@ import shutil
import errno
import pwd
import itertools
+import select
+import fcntl
+
+from cStringIO import StringIO
from ganeti import logger
from ganeti import errors
@@ -222,6 +226,7 @@ def RunCmd(cmd):
shell = True
env = os.environ.copy()
env["LC_ALL"] = "C"
+ poller = select.poll()
child = subprocess.Popen(cmd, shell=shell,
stderr=subprocess.PIPE,
stdout=subprocess.PIPE,
@@ -229,8 +234,35 @@ def RunCmd(cmd):
close_fds=True, env=env)
child.stdin.close()
- out = child.stdout.read()
- err = child.stderr.read()
+ poller.register(child.stdout, select.POLLIN)
+ poller.register(child.stderr, select.POLLIN)
+ out = StringIO()
+ err = StringIO()
+ fdmap = {
+ child.stdout.fileno(): (out, child.stdout),
+ child.stderr.fileno(): (err, child.stderr),
+ }
+ for fd in fdmap:
+ status = fcntl.fcntl(fd, fcntl.F_GETFL)
+ fcntl.fcntl(fd, fcntl.F_SETFL, status | os.O_NONBLOCK)
+
+ while fdmap:
+ for fd, event in poller.poll():
+ if event & select.POLLIN or event & select.POLLPRI:
+ data = fdmap[fd][1].read()
+ # no data from read signifies EOF (the same as POLLHUP)
+ if not data:
+ poller.unregister(fd)
+ del fdmap[fd]
+ continue
+ fdmap[fd][0].write(data)
+ if (event & select.POLLNVAL or event & select.POLLHUP or
+ event & select.POLLERR):
+ poller.unregister(fd)
+ del fdmap[fd]
+
+ out = out.getvalue()
+ err = err.getvalue()
status = child.wait()
if status >= 0:
--
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