Re: [libvirt] [PATCH 1/3] Add a function to the security driver API that sets the label of an open fd.

A need was found to set the SELinux context label on an open fd (a pipe, as a matter of fact). This patch adds a function to the security driver API that will set the label on an open fd to secdef.label. For all drivers other than the SELinux driver, it's a NOP. For the SElinux driver, it calls fsetfilecon(). If the return is a failure, it only returns error up to the caller if 1) the desired label is different from the existing label, 2) the destination fd is of a type that supports setting the selinux context, and 3) selinux is in enforcing mode. Otherwise it will return success. This follows the pattern of the existing function SELinuxSetFilecon().