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 extended to raw-posix, raw-win32 and vmdk block
drivers in this patchset. Once this is reviewed and finalised, I will
extend the implementation to other drivers like qcow2, qed etc..
* 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:
* memcpy is used to save driver state. Replace this with copying
individual fields of driver state (?)
* Extend this implementation to other block drivers.
* Build and verify raw-win32 driver changes in windows
Earlier discussions related to dynamic change of host pagecache can be found
at: http://lists.gnu.org/archive/html/qemu-devel/2011-11/msg01482.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 | 112 +++++++++++++++++++++++++++++++++++++++++++++----
qemu/block.h | 5 +
qemu/block/raw-posix.c | 74 ++++++++++++++++++++++++++++++++
qemu/block/raw-win32.c | 95 +++++++++++++++++++++++++++++++++++++++++
qemu/block/raw.c | 20 ++++++++
qemu/block/vmdk.c | 80 +++++++++++++++++++++++++++++++++--
qemu/block_int.h | 11 ++++
qemu/blockdev.c | 26 +++++++++++
qemu/blockdev.h | 2
qemu/hmp-commands.hx | 14 ++++++
qemu/hmp.c | 2
qemu/qapi-schema.json | 4 +
qemu/qemu-common.h | 1
qemu/qerror.c | 8 +++
qemu/qerror.h | 6 ++
qemu/qmp-commands.hx | 27 +++++++++++
18 files changed, 474 insertions(+), 13 deletions(-)
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