[Qemu-devel] [v1 Patch 0/10]Qemu: Dynamic host pagecache change and image file reopen

[Supriya Kannery]

 For changing host pagecache setting of a running VM, it is
important to have a safe way of reopening its image file.

Following patchset introduces:
 * a generic way to reopen image files safely. 
        In this approach, before reopening an image, for each
    block driver, its state will be stashed. Incase preparation,
    (bdrv_reopen_prepare) for reopening returns success, the stashed 
    state will be cleared (bdrv_reopen_commit) and reopened state will 
    be used further. Incase preparation of reopening returns failure, 
    the state of the driver will be rolled back (bdrv_reopen_abort) 
    to the stashed state. This approach is implemented for raw-posix, 
    raw-win32, vmdk, qcow, qcow2 and qed block drivers.
  
 * qmp and hmp command 'block_set_hostcache' using which host 
   pagecache setting for a block device can be changed 
   when the VM is running.

 * BDRVReopenState, a generic structure which can be 
   extended by each of the block drivers to reopen 
   respective image files.

ToDo:
* Currently driver state is stashed by field-by-field copy.
  Optimise this by stashing only the required fields.
* Find out other drivers needing bdrv_reopen implementation.
* Do some more extensive testing, especially with drivers like
  floppy, cdrom etc..

Earlier discussions on RFC for dynamic change of host pagecache can be
 found at: http://lists.gnu.org/archive/html/qemu-devel/2012-01/msg04139.html

New block command added:
"block_set_hostcache"
    -- Sets hostcache parameter for block device  while guest is running.

Usage:
 block_set_hostcache  <device> <option>
   <device> = block device
   <option>  = on/off

 qemu/block.c           |  127 ++++++++++++++++++++++++++++++++--
 qemu/block.h           |    5 +
 qemu/block/qcow.c      |  108 +++++++++++++++++++++++++++++
 qemu/block/qcow2.c     |  177 +++++++++++++++++++++++++++++++++++++++++++++++++
 qemu/block/qed.c       |  103 ++++++++++++++++++++++++++++
 qemu/block/raw-posix.c |  123 ++++++++++++++++++++++++++++++++++
 qemu/block/raw-win32.c |   96 ++++++++++++++++++++++++++
 qemu/block/raw.c       |   20 +++++
 qemu/block/vmdk.c      |  103 ++++++++++++++++++++++++++++
 qemu/block_int.h       |   11 +++
 qemu/blockdev.c        |   24 ++++++
 qemu/hmp-commands.hx   |   16 ++++
 qemu/hmp.c             |   11 ++
 qemu/hmp.h             |    1
 qemu/qapi-schema.json  |   20 ++++-
 qemu/qemu-common.h     |    1
 qemu/qerror.c          |    8 ++
 qemu/qerror.h          |    6 +
 qemu/qmp-commands.hx   |   24 ++++++
 19 files changed, 971 insertions(+), 13 deletions(-)