execute does not support file for stdin

[Edward Hope-Morley]

processutils.execute() does not support PIPEing stdout of one command to stdin of another using a file. Currently, only passing var as stdin is suppored which means that all data must be held in memory. If the first process generates a large amount of data this will have an undesirable effect and this approach is discouraged in the Python docs:

http://docs.python.org/2/library/subprocess.html#popen-constructor

I would like to add an alternative method to the standard processutils.execute() that allows something like:

p1 = Popen(cmd1, stdout=subprocess.PIPE)
p2 = Popen(cmd2, stdin=p1.stdout, stdout=subprocess.PIPE)
p1.stdout.close()
out = p2.communicate()[0]

as recommended in the docs.

[Thierry Carrez (ttx)]

That code belongs to Oslo and is synced into Cinder, so that would have to be implemented there.