[libvirt] [PATCHv4 0/2] qemu: eliminate "Ignoring open failure" (virFileOpenAs)

[Laine Stump]

I believe this version addresses all the issues Eric raised in his
review of V3, *except* those that we agreed should be left for a later patch.

Patch 2/2 is unchanged all the way since v1.

Patch 1/2 has the following changes from V3:

* The "last ditch attempt to open the file in the parent process after
  failing with fork+setuid is done only if VIR_FILE_OPEN_NOFORK is
  false (meaning that it wasn't already tried). fchmod/fchown is then
  performed if necessary.

* fchmod is only attempted after checking the file's current
  permissions and seeing that they don't match what is desired.

* fchown and fchmod stuff is moved into a helper function that's
  called from 3 places.

* fixed typos, added command about uid & gid no longer being "-1"

Items *NOT* addressed:

* eliminate log messages in child process
* figure out how to have qemuOpenFile call virFileOpenAs just once
* switch from use of waitpid to virPidWait() (and use of
  virPidAbort() to cause the child to terminate when an error is
  encountered while waiting for an fd from the child.
* figure out when it is appropriate to unlink the file on failure.
* move virFileOpenAs (and several other functions) to virfile.c