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Date: Wed, 20 Jun 2012 14:18:38 -0400
From: Jeff Cody <jcody@redhat.com>
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Subject: Re: [Qemu-devel] [v1 Patch 3/10]Qemu: Cmd "block_set_hostcache" for
 dynamic cache change
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To: Supriya Kannery <supriyak@linux.vnet.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Shrinidhi Joshi <spjoshi31@gmail.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>, Christoph Hellwig <hch@lst.de>

On 06/15/2012 04:47 PM, Supriya Kannery wrote:
> New command "block_set_hostcache" added for dynamically changing 
> host pagecache setting of a block device.
> 
> Usage: 
>  block_set_hostcache  <device> <option>
>    <device> = block device
>    <option> = on/off
> 
> Example:
>  (qemu) block_set_hostcache ide0-hd0 off
> 
> Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>
> 
> ---
>  block.c         |   54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  block.h         |    2 ++
>  blockdev.c      |   26 ++++++++++++++++++++++++++
>  blockdev.h      |    2 ++
>  hmp-commands.hx |   14 ++++++++++++++
>  qmp-commands.hx |   27 +++++++++++++++++++++++++++
>  6 files changed, 125 insertions(+)
> 
> Index: qemu/block.c
> ===================================================================
> --- qemu.orig/block.c
> +++ qemu/block.c
> @@ -858,6 +858,35 @@ unlink_and_fail:
>      return ret;
>  }
>  
> +int bdrv_reopen(BlockDriverState *bs, int bdrv_flags)
> +{
> +    BlockDriver *drv = bs->drv;
> +    int ret = 0, open_flags;
> +
> +    /* Quiesce IO for the given block device */
> +    qemu_aio_flush();
> +    ret = bdrv_flush(bs);
> +    if (ret != 0) {
> +        qerror_report(QERR_DATA_SYNC_FAILED, bs->device_name);
> +        return ret;
> +    }
> +    open_flags = bs->open_flags;
> +    bdrv_close(bs);
> +
> +    ret = bdrv_open(bs, bs->filename, bdrv_flags, drv);
> +    if (ret < 0) {
> +        /* Reopen failed. Try to open with original flags */
> +        qerror_report(QERR_OPEN_FILE_FAILED, bs->filename);
> +        ret = bdrv_open(bs, bs->filename, open_flags, drv);
> +        if (ret < 0) {
> +            /* Reopen failed with orig and modified flags */
> +            abort();
> +        }
> +    }
> +
> +    return ret;
> +}
> +
>  void bdrv_close(BlockDriverState *bs)
>  {
>      bdrv_flush(bs);
> @@ -953,6 +982,34 @@ void bdrv_drain_all(void)
>      }
>  }
>  
> +int bdrv_change_hostcache(BlockDriverState *bs, bool enable)
> +{
> +    int bdrv_flags = bs->open_flags;
> +
> +    /* set hostcache flags (without changing WCE/flush bits) */
> +    if (enable) {
> +        bdrv_flags &= ~BDRV_O_NOCACHE;
> +    } else {
> +        bdrv_flags |= BDRV_O_NOCACHE;
> +    }
> +
> +    /* If no change in flags, no need to reopen */
> +    if (bdrv_flags == bs->open_flags) {
> +        printf("no need to change\n");
> +        return 0;
> +    }
> +
> +    if (bdrv_is_inserted(bs)) {
> +        /* Reopen file with changed set of flags */
> +        bdrv_flags &= ~BDRV_O_CACHE_WB;
> +        return bdrv_reopen(bs, bdrv_flags);
> +    } else {
> +        /* Save hostcache change for future use */
> +        bs->open_flags = bdrv_flags;
> +        return 0;
> +    }
> +}
> +
>  /* make a BlockDriverState anonymous by removing from bdrv_state list.
>     Also, NULL terminate the device_name to prevent double remove */
>  void bdrv_make_anon(BlockDriverState *bs)
> Index: qemu/block.h
> ===================================================================
> --- qemu.orig/block.h
> +++ qemu/block.h
> @@ -128,6 +128,7 @@ int bdrv_parse_cache_flags(const char *m
>  int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags);
>  int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
>                BlockDriver *drv);
> +int bdrv_reopen(BlockDriverState *bs, int bdrv_flags);
>  void bdrv_close(BlockDriverState *bs);
>  int bdrv_attach_dev(BlockDriverState *bs, void *dev);
>  void bdrv_attach_dev_nofail(BlockDriverState *bs, void *dev);
> @@ -177,6 +178,7 @@ int bdrv_commit_all(void);
>  int bdrv_change_backing_file(BlockDriverState *bs,
>      const char *backing_file, const char *backing_fmt);
>  void bdrv_register(BlockDriver *bdrv);
> +int bdrv_change_hostcache(BlockDriverState *bs, bool enable_host_cache);
>  
>  
>  typedef struct BdrvCheckResult {
> Index: qemu/blockdev.c
> ===================================================================
> --- qemu.orig/blockdev.c
> +++ qemu/blockdev.c
> @@ -1198,3 +1198,27 @@ BlockJobInfoList *qmp_query_block_jobs(E
>      bdrv_iterate(do_qmp_query_block_jobs_one, &prev);
>      return dummy.next;
>  }
> +
> +
> +/*
> + * Change host page cache setting while guest is running.
> +*/
> +void qmp_block_set_hostcache(const char *device, bool enable,
> +                             Error **errp)
> +{
> +    BlockDriverState *bs = NULL;
> +
> +    /* Validate device */
> +    bs = bdrv_find(device);
> +    if (!bs) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
> +        return;
> +    }
> +
> +    if (bdrv_change_hostcache(bs, enable)) {
> +        error_set(errp, QERR_HOSTCACHE_NOT_CHANGED, device);
> +    }
> +
> +    return;
> +}
> +
> Index: qemu/hmp-commands.hx
> ===================================================================
> --- qemu.orig/hmp-commands.hx
> +++ qemu/hmp-commands.hx
> @@ -808,7 +808,6 @@ ETEXI
>          .mhandler.cmd = hmp_migrate,
>      },
>  
> -
>  STEXI
>  @item migrate [-d] [-b] [-i] @var{uri}
>  @findex migrate
> @@ -1314,6 +1313,21 @@ client.  @var{keep} changes the password
>  ETEXI
>  
>      {
> +        .name       = "block_set_hostcache",
> +        .args_type  = "device:B,option:b",
> +        .params     = "device on|off",
> +        .help       = "Change setting of host pagecache",
> +        .mhandler.cmd = hmp_block_set_hostcache,
> +    },
> +
> +STEXI
> +@item block_set_hostcache @var{device} @var{option}
> +@findex block_set_hostcache
> +Change host pagecache setting of a block device while guest is running.
> +ETEXI
> +
> +
> +    {
>          .name       = "expire_password",
>          .args_type  = "protocol:s,time:s",
>          .params     = "protocol time",
> Index: qemu/qmp-commands.hx
> ===================================================================
> --- qemu.orig/qmp-commands.hx
> +++ qemu/qmp-commands.hx
> @@ -821,7 +821,31 @@ Example:
>  
>  EQMP
>  
> +
>      {
> +        .name       = "block_set_hostcache",
> +        .args_type  = "device:B,option:b",
> +        .mhandler.cmd_new = qmp_block_set_hostcache,

The QAPI commands need to go through the marshaller - this needs to be:
           .mhandler.cmd_new = qmp_marshal_input_block_set_hostcache,

(qmp_marshal_input_block_set_hostcache is automatically generated, and
it will call qmp_block_set_hostcache)

> +    },
> +
> +SQMP
> +block_set_hostcache
> +-------------------
> +
> +Change host pagecache setting of a block device
> +
> +Arguments:
> +
> +- "device": the device's ID, must be unique (json-string)
> +- "option": hostcache setting (json-bool)
> +
> +Example:
> +-> { "execute": "block_set_hostcache", "arguments": { "device": "ide0-hd0", "option": false } }
> +<- { "return": {} }
> +
> +EQMP
> +
> +	{
>          .name       = "balloon",
>          .args_type  = "value:M",
>          .mhandler.cmd_new = qmp_marshal_input_balloon,
> Index: qemu/qapi-schema.json
> ===================================================================
> --- qemu.orig/qapi-schema.json
> +++ qemu/qapi-schema.json
> @@ -1598,6 +1598,22 @@
>  { 'command': 'block_set_io_throttle',
>    'data': { 'device': 'str', 'bps': 'int', 'bps_rd': 'int', 'bps_wr': 'int',
>              'iops': 'int', 'iops_rd': 'int', 'iops_wr': 'int' } }
> +##
> +# @block_set_hostcache:
> +#
> +# Change host pagecache setting of a block device
> +#
> +# @device: name of the block device
> +#
> +# @option: hostcache setting (true/false)
> +#
> +# Returns: Nothing on success
> +#          If @device is not a valid block device, DeviceNotFound
> +#
> +# Since: 1.2
> +##
> +{ 'command': 'block_set_hostcache',
> +  'data': { 'device': 'str', 'option': 'bool' } }
>  
>  ##
>  # @block-stream:
> Index: qemu/hmp.c
> ===================================================================
> --- qemu.orig/hmp.c
> +++ qemu/hmp.c
> @@ -836,6 +836,15 @@ void hmp_block_set_io_throttle(Monitor *
>      hmp_handle_error(mon, &err);
>  }
>  
> +void hmp_block_set_hostcache(Monitor *mon, const QDict *qdict)
> +{
> +    Error *err = NULL;
> +
> +    qmp_block_set_hostcache(qdict_get_str(qdict, "device"),
> +                              qdict_get_bool(qdict, "option"), &err);
> +    hmp_handle_error(mon, &err);
> +}
> +
>  void hmp_block_stream(Monitor *mon, const QDict *qdict)
>  {
>      Error *error = NULL;
> Index: qemu/hmp.h
> ===================================================================
> --- qemu.orig/hmp.h
> +++ qemu/hmp.h
> @@ -64,5 +64,6 @@ void hmp_device_del(Monitor *mon, const 
>  void hmp_dump_guest_memory(Monitor *mon, const QDict *qdict);
>  void hmp_netdev_add(Monitor *mon, const QDict *qdict);
>  void hmp_netdev_del(Monitor *mon, const QDict *qdict);
> +void hmp_block_set_hostcache(Monitor *mon, const QDict *qdict);
>  
>  #endif
> 
>