[Qemu-devel] [v7 Patch 0/5]Qemu: Host pagecache setting from cmdline and monitor

[Supriya Kannery]

   Currently cache setting of a block device cannot be changed
without restarting a running VM. Following patchset is for
enabling dynamic change of cache setting for block devices
through qemu monitor and qmp. Code changes are based on 
patches from Christoph Hellwig and Prerna Saxena.

This patchset introduces 
a. monitor command 'block_set_hostcache' using which host 
   pagecache setting for a block device can be changed 
   dynamically while guest VM is running.
b. 'hostcache' - a new option for setting host cache 
   from qemu command -drive "hostcache=on/off".
c. BDRVReopenState, a generic structure which can be 
   extended by each of the block drivers to reopen 
   respective image files.
   Extension of this structure for raw-posix is done
   for now. I am working on to extend the same for 
   raw-win32  image files as well.

Note: 'Hostcache and 'cache' options cannot be used 
simultaneously from commandline.

v7:
 1. Added structure BDRVReopenState to support safe 
    reopening of image files.

v6:
 1. "block_set_hostcache" to replace "block_set" command

v5:
 1. Defined qerror class for incorrect command syntax.
 2. Changed error_report() calls to qerror_report()

v4:
    Added 'hostcache' option to '-drive' commandline option.

v3:
  1. Command "block_set" for changing various block params
  2. Enhanced info-block to display hostcache setting 
  3. Added qmp interfaces for setting and querying hostcache

v2:
  1. Support of dynamic cache change only for hostcache.
  2. Monitor command "hostcache_get" added to display cache setting
  3. Backed off the changes for display of cache setting in "info block"

v1:
     Dynamic cache change through monitor

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


New 'hostcache' option added to -drive:
 -drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n"
        ....
"       [,readonly=on|off][,hostcache=on|off]\n"

 qemu/block.c           |   119 ++++++++++++++++++++++++++++++++++++++-------
 qemu/block.h           |    2 +
 qemu/block/raw-posix.c |   67 ++++++++++++++++++++++++++++++++++++++++++++++
 qemu/block/raw.c       |   11 +++++++
 qemu/block_int.h       |   15 ++++++++++
 qemu/blockdev.c        |   39 +++++++++++++++++++++++++
 qemu/blockdev.h        |    2 +
 qemu/hmp-commands.hx   |   14 +++++++++
 qemu/qemu-common.h     |    1
 qemu/qemu-config.c     |    4 ++
 qemu/qemu-options.hx   |    2 -
 qemu/qerror.c          |    8 +++++
 qemu/qerror.h          |    6 ++++
 qemu/qmp-commands.hx   |   29 +++++++++++++++++++
 17 files changed, 306 insertions(+), 13 deletions(-)