Re: [Qemu-devel] [v8 Patch 0/6]Qemu: Host pagecache setting from cmdline and monitor

[Zhi Yong Wu <zwu.kernel@gmail.com>]

On Sun, Oct 30, 2011 at 6:33 PM, Supriya Kannery
<supriyak@linux.vnet.ibm.com> wrote:
> 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.
I got a bit confusion. Is it used to change host pagecache setting on
hyperviser or on guest?
This block device said by you is for guest, right?

> 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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> "txt" 13L, 574C
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-- 
Regards,

Zhi Yong Wu