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(-)
