[PATCH v3 00/18] libxl: domain save/restore: run in a separate process

[Ian Jackson <ian.jackson@eu.citrix.com>]

This is v4 of my series to asyncify save/restore.  All comments have
been addressed.

I have retested this with HVM (RHEL) and PV guests, for both localhost
migration and save/restore.  RHEL seems to have some unreliability
which occurs with the baseline too.  I was not able to test stub dms
at all because when trying to boot my RHEL guest with a stub dm the dm
domain immediately crashed.  (I discovered that my previous tests had
occasionally not been using all of the new code.)

In the list below "A" indicates a patch which has been acked
sufficiently to go in (assuming its dependencies were to go in too).
"*" indicates a new patch in v4 and "+" indicates a patch with
nontrivial changes from v3.

Preparatory fixes:

   A libxc: xc_domain_restore, make toolstack_restore const-correct
 *   libxc: Do not segfault if (e.g.) switch_qemu_logdirty fails

Preparatory reshuffling:

   A libxl: domain save: rename variables etc.
   A libxl: domain restore: reshuffle, preparing for ao
 +   libxl: domain save: API changes for asynchrony

The meat:

 +   libxl: domain save/restore: run in a separate process

Some more fixups:

   A libxl: rename libxl_dom:save_helper to physmap_path
   A libxl: provide libxl__xs_*_checked and libxl__xs_transaction_*
 + A libxl: wait for qemu to acknowledge logdirty command

Asyncify writing of qemu save file, too:

   A libxl: datacopier: provide "prefix data" facility
   A libxl: prepare for asynchronous writing of qemu save file
   A libxl: Make libxl__domain_save_device_model asynchronous

Fix gc_opt handling:

   A libxl: Add a gc to libxl_get_cpu_topology
   A libxl: Do not pass NULL as gc_opt; introduce NOGC
   A libxl: Get compiler to warn about gc_opt==NULL

Work on essentially-unrelated bugs:

   A xl: Handle return value from libxl_domain_suspend correctly
   A libxl: do not leak dms->saved_state
   A libxl: do not leak spawned middle children
   A libxl: do not leak an event struct on ignored ao progress
     libxl: further fixups re LIBXL_DOMAIN_TYPE
     libxl: DO NOT APPLY enforce prohibition on internal

Thanks,
Ian.