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Subject: Re: [Qemu-devel] [v2 Patch 8/9]block: Cmd "block_set_hostcache" for
 dynamic cache change
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To: 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 08/01/2012 02:44 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>
> 
> ---
> Index: qemu/block.c
> ===================================================================
> --- qemu.orig/block.c
> +++ qemu/block.c
> @@ -970,6 +970,30 @@ void bdrv_close_all(void)
>      }
>  }
>  
> +void bdrv_change_hostcache(BlockDriverState *bs, bool enable, Error **errp)
> +{
> +    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) {
> +        if (bdrv_is_inserted(bs)) {
> +            /* Reopen file with changed set of flags */
> +            bdrv_flags &= ~BDRV_O_CACHE_WB;
> +            bdrv_reopen(bs, bdrv_flags, errp);
> +        } else {
> +            /* Save hostcache change for future use */
> +            bs->open_flags = bdrv_flags;
> +        }
> +    }
> +}
> +

BDRV_O_CACHE_WB is cleared here, and it never gets set again. Is that
intentional?


>  /*
>   * Wait for pending requests to complete across all BlockDriverStates
>   *
> Index: qemu/blockdev.c
> ===================================================================
> --- qemu.orig/blockdev.c
> +++ qemu/blockdev.c
> @@ -1191,3 +1191,22 @@ 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;
> +    }
> +
> +    bdrv_change_hostcache(bs, enable, errp);
> +    return;
> +}
> Index: qemu/hmp-commands.hx
> ===================================================================
> --- qemu.orig/hmp-commands.hx
> +++ qemu/hmp-commands.hx
> @@ -1344,6 +1344,21 @@ passed since 1970, i.e. unix epoch.
>  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       = "info",
>          .args_type  = "item:s?",
>          .params     = "[subcommand]",
> Index: qemu/qmp-commands.hx
> ===================================================================
> --- qemu.orig/qmp-commands.hx
> +++ qemu/qmp-commands.hx
> @@ -987,6 +987,30 @@ Example:
>  EQMP
>  
>      {
> +        .name       = "block_set_hostcache",
> +        .args_type  = "device:B,option:b",
> +        .mhandler.cmd_new = qmp_marshal_input_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       = "set_password",
>          .args_type  = "protocol:s,password:s,connected:s?",
>          .mhandler.cmd_new = qmp_marshal_input_set_password,
> Index: qemu/qapi-schema.json
> ===================================================================
> --- qemu.orig/qapi-schema.json
> +++ qemu/qapi-schema.json
> @@ -1604,6 +1604,23 @@
>              '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:
>  #
>  # Copy data from a backing file into a block device.
> Index: qemu/hmp.c
> ===================================================================
> --- qemu.orig/hmp.c
> +++ qemu/hmp.c
> @@ -837,6 +837,15 @@ 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
> @@ -66,5 +66,6 @@ void hmp_netdev_add(Monitor *mon, const 
>  void hmp_netdev_del(Monitor *mon, const QDict *qdict);
>  void hmp_getfd(Monitor *mon, const QDict *qdict);
>  void hmp_closefd(Monitor *mon, const QDict *qdict);
> +void hmp_block_set_hostcache(Monitor *mon, const QDict *qdict);
>  
>  #endif
> Index: qemu/block.h
> ===================================================================
> --- qemu.orig/block.h
> +++ qemu/block.h
> @@ -187,6 +187,7 @@ 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);
> +void bdrv_change_hostcache(BlockDriverState *bs, bool enable, Error **errp);
>  
>  
>  typedef struct BdrvCheckResult {
> 
>