[libvirt] [PATCH v1 0/2] Fix environment-setting code.

[This patch is for discussion only: I have not proven that it fixes the bug] https://bugzilla.redhat.com/show_bug.cgi?id=859596 When libvirtd runs any command, it uses a simple strategy to set the environment for that command: (a) It creates a new, empty environment array. (b) It copies in a few known-good environment variables, including TMPDIR. (c) It appends environment variables specified by the user, eg. ones specified in <qemu:env>. Unfortunately this means if you try to set TMPDIR via a <qemu:env> XML directive, then it is appended to the list of environment variables which already includes TMPDIR. The qemu subprocess picks an environment variable (probably) first from the list, which is the TMPDIR that libvirtd had originally, not the TMPDIR that was specified by the user. This [possibly, not proven] leads to bug 859596, where we see qemu trying to create temporary files in a directory that no longer exists. The follow-up patches change libvirtd so that environment variables in the virCommandPtr array are replaced if they exist already. Rich.