[Qemu-devel] [v8 Patch 0/6]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. 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. 
b. a new option for setting host cache from qemu
   commandline option -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 drivers raw-posix 
   is done here.
d. 'hostcache and 'cache' options when used together,
   cache=xx will override hostcache=yy.

v8:
 1. Mandate implementation of all three reopen 
    related functions by block drivers.
 2. If 'cache=xx' and 'hostcache=yy' specified
    in cmdline, 'cache=' overrides 'hostcache='.
    

v7:
 1. Added structure BDRVReopenState to support safe 
    reopening of image files.
 2. Implemented reopen functions for raw-posix driver

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           |   79 +++++++++++++++++++++++++++++++++++++++--------
 qemu/block.h           |    3 ++
 qemu/block/raw-posix.c |   57 +++++++++++++++++++++++++++++++++++++++++
 qemu/block/raw.c       |   23 +++++++++++++++-
 qemu/block_int.h       |   16 +++++++++++
 qemu/blockdev.c        |    7 +++++
 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   |    4 ++
 14 files changed, 194 insertions(+), 16 deletions(-)
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