[RFC PATCH 0/2] libxl: support common cases without block script

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

This series in an attempt to speed up the domain start by removing slow block
script from the picture. The current RFC covers the simplest possible case only
- target being a block device directly. This case does not require locking at
all. Further version will cover also setting up a loop device.

This, compared to the default block script, saves about 0.5s of domain start
time, per disk. Similar speedup can be achieved with a trivial lock-less script
too. But for file-based disks, it won't be that simple with a script - setting
up a loop device lock-less is tricky and ability to keep an FD open and call
different ioctls on it greatly helps. Furthermore reusing the same loop device
for the same file can be done significantly better with a cache (which can be
stored in the libxl hosting process - like xl devd, or libvirt).

This surely isn't the only option to improve disk setup time, but is a very
atractive one. Few questions:
1. Is it acceptable approach at all?
2. Is empty 'script' parameter value going to fly? Unfortunately, NULL is
   already taken as "use default".

Marek Marczykowski-Górecki (2):
  libxl: rename 'error' label to 'out' as it is used for success too
  libxl: allow to skip block script completely

 docs/man/xl-disk-configuration.5.pod.in |  4 ++-
 tools/libs/light/libxl_disk.c           |  7 ++-
 tools/libs/light/libxl_linux.c          | 68 ++++++++++++++++++++++++--
 3 files changed, 74 insertions(+), 5 deletions(-)

base-commit: bea65a212c0581520203b6ad0d07615693f42f73
-- 
git-series 0.9.1