Update xCAT bindings example, to prevent lsdef from gobbling stdin

[kcgthb]

lsdef consumes stdin by default, so we feed it /dev/null to avoid issues in read loops (useful in scripts!)
See xcat2/xcat-core#6024 for reference.

[martinetd]

I'd argue clustershell should not pass stdin to mapping commands in the first place?

diff --git a/lib/ClusterShell/NodeUtils.py b/lib/ClusterShell/NodeUtils.py
index f4a52f639743..ba8ebad4ec5b 100644
--- a/lib/ClusterShell/NodeUtils.py
+++ b/lib/ClusterShell/NodeUtils.py
@@ -44,7 +44,7 @@ import shlex
 import time
 
 from string import Template
-from subprocess import Popen, PIPE
+from subprocess import Popen, PIPE, DEVNULL
 
 try:
     basestring
@@ -202,8 +202,8 @@ class UpcallGroupSource(GroupSource):
         """
         cmdline = Template(self.upcalls[cmdtpl]).safe_substitute(args)
         self.logger.debug("EXEC '%s'", cmdline)
-        proc = Popen(cmdline, stdout=PIPE, shell=True, cwd=self.cfgdir,
-                     universal_newlines=True)
+        proc = Popen(cmdline, stdin=DEVNULL, stdout=PIPE, shell=True,
+                     cwd=self.cfgdir, universal_newlines=True)
         output = proc.communicate()[0].strip()
         self.logger.debug("READ '%s'", output)
         if proc.returncode != 0:

might want to check if we have more like that...

[thiell]

Very good point, why are we doing that?!

Maybe because subprocess.DEVNULL was only added in Python 3.3?

In clustershell 1.9.x we should just be careful to do it so it doesn't break the compat for py2.7 (I know, it's old, but it's nice to be able to upgrade older clusters)

[martinetd]

For 2.7 we apparently need to open devnull ourselves...
That's a bit ugly but not impossible?

# compat with python 2.7, import directly once deprecated
try:
    from subprocess import DEVNULL
except ImportError:
    DEVNULL = open(os.devnull, 'r')

[thiell]

Looks good to me, thank you! @degremont any opinion on this?

[degremont]

I'm fine with @martinetd proposal, that's the right thing to do here IMO.

[martinetd]

I can't push to kilian's tree so opened #581
#581

Note the other commit was already merged in #558, so there really only is the stdin bug fix in this PR and this can be closed.