Re: [Qemu-devel] [RFC 4/8] block: add block_backup QMP command

[Paolo Bonzini <pbonzini@redhat.com>]

Il 09/03/2013 23:22, Stefan Hajnoczi ha scritto:
> @block-backup
> 
> Start a point-in-time copy of a block device to a new destination.
> 
> @device:  the name of the device whose writes should be mirrored.
> 
> @target: the target of the new image. If the file exists, or if it
>          is a device, the existing file/device will be used as the new
>          destination.  If it does not exist, a new file will be created.
> 
> @format: #optional the format of the new destination, default is to
>          probe if @mode is 'existing', else the format of the source
> 
> @mode: #optional whether and how QEMU should create a new image, default is
>        'absolute-paths'.
> 
> @speed:  #optional the maximum speed, in bytes per second
> 
> Returns: nothing on success
>          If @device is not a valid block device, DeviceNotFound

Two features that would be nice to have:

1) a sync mode (full/top/none) like drive-mirror;

2) transaction support to start multiple backups live without stopping
the VM (for use cases that do not include migration)

Thanks,

Paolo

> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  blockdev.c       | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qapi-schema.json | 28 +++++++++++++++++
>  qmp-commands.hx  |  6 ++++
>  3 files changed, 126 insertions(+)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 0e67d06..95a72de 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1208,6 +1208,98 @@ void qmp_block_commit(const char *device,
>      drive_get_ref(drive_get_by_blockdev(bs));
>  }
>  
> +void qmp_block_backup(const char *device, const char *target,
> +                      bool has_format, const char *format,
> +                      bool has_mode, enum NewImageMode mode,
> +                      bool has_speed, int64_t speed,
> +                      Error **errp)
> +{
> +    BlockDriverState *bs;
> +    BlockDriverState *target_bs;
> +    BlockDriver *proto_drv;
> +    BlockDriver *drv = NULL;
> +    Error *local_err = NULL;
> +    int flags;
> +    uint64_t size;
> +    int ret;
> +
> +    if (!has_speed) {
> +        speed = 0;
> +    }
> +    if (!has_mode) {
> +        mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
> +    }
> +
> +    bs = bdrv_find(device);
> +    if (!bs) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
> +        return;
> +    }
> +
> +    if (!bdrv_is_inserted(bs)) {
> +        error_set(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
> +        return;
> +    }
> +
> +    if (!has_format) {
> +        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
> +    }
> +    if (format) {
> +        drv = bdrv_find_format(format);
> +        if (!drv) {
> +            error_set(errp, QERR_INVALID_BLOCK_FORMAT, format);
> +            return;
> +        }
> +    }
> +
> +    if (bdrv_in_use(bs)) {
> +        error_set(errp, QERR_DEVICE_IN_USE, device);
> +        return;
> +    }
> +
> +    flags = bs->open_flags | BDRV_O_RDWR;
> +
> +    proto_drv = bdrv_find_protocol(target);
> +    if (!proto_drv) {
> +        error_set(errp, QERR_INVALID_BLOCK_FORMAT, format);
> +        return;
> +    }
> +
> +    bdrv_get_geometry(bs, &size);
> +    size *= 512;
> +    if (mode != NEW_IMAGE_MODE_EXISTING) {
> +        assert(format && drv);
> +        bdrv_img_create(target, format,
> +                        NULL, NULL, NULL, size, flags, &local_err, false);
> +    }
> +
> +    if (error_is_set(&local_err)) {
> +        error_propagate(errp, local_err);
> +        return;
> +    }
> +
> +    target_bs = bdrv_new("");
> +    ret = bdrv_open(target_bs, target, flags, drv);
> +
> +    if (ret < 0) {
> +        bdrv_delete(target_bs);
> +        error_set(errp, QERR_OPEN_FILE_FAILED, target);
> +        return;
> +    }
> +
> +    backup_start(bs, target_bs, speed, block_job_cb, bs, &local_err);
> +    if (local_err != NULL) {
> +        bdrv_delete(target_bs);
> +        error_propagate(errp, local_err);
> +        return;
> +    }
> +
> +    /* Grab a reference so hotplug does not delete the BlockDriverState from
> +     * underneath us.
> +     */
> +    drive_get_ref(drive_get_by_blockdev(bs));
> +}
> +
>  #define DEFAULT_MIRROR_BUF_SIZE   (10 << 20)
>  
>  void qmp_drive_mirror(const char *device, const char *target,
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 6b64aec..1dbf7b5 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1716,6 +1716,34 @@
>              '*speed': 'int' } }
>  
>  ##
> +# @block-backup
> +#
> +# Start a point-in-time copy of a block device to a new destination.
> +#
> +# @device:  the name of the device whose writes should be mirrored.
> +#
> +# @target: the target of the new image. If the file exists, or if it
> +#          is a device, the existing file/device will be used as the new
> +#          destination.  If it does not exist, a new file will be created.
> +#
> +# @format: #optional the format of the new destination, default is to
> +#          probe if @mode is 'existing', else the format of the source
> +#
> +# @mode: #optional whether and how QEMU should create a new image, default is
> +#        'absolute-paths'.
> +#
> +# @speed:  #optional the maximum speed, in bytes per second
> +#
> +# Returns: nothing on success
> +#          If @device is not a valid block device, DeviceNotFound
> +#
> +# Since 1.5
> +##
> +{ 'command': 'block-backup',
> +  'data': { 'device': 'str', 'target': 'str', '*format': 'str',
> +            '*mode': 'NewImageMode', '*speed': 'int' } }
> +
> +##
>  # @drive-mirror
>  #
>  # Start mirroring a block device's writes to a new destination.
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 95022e2..bda8eb4 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -889,6 +889,12 @@ EQMP
>      },
>  
>      {
> +        .name       = "block-backup",
> +        .args_type  = "device:B,target:s,speed:i?,mode:s?,format:s?",
> +        .mhandler.cmd_new = qmp_marshal_input_block_backup,
> +    },
> +
> +    {
>          .name       = "block-job-set-speed",
>          .args_type  = "device:B,speed:o",
>          .mhandler.cmd_new = qmp_marshal_input_block_job_set_speed,
>