Re: [Qemu-devel] [PATCH 13/15] qapi: introduce drive-change (v2)

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri,  2 Sep 2011 12:34:56 -0500
Anthony Liguori <aliguori@us.ibm.com> wrote:

> A new QMP only command to change the blockdev associated with a block device.
> The semantics of change right now are just plain scary.  This command introduces
> sane semantics.  For more details, see the documentation in the schema file.
> 
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> ---
> v1 -> v2
>  - Rename command to drive-change (Kevin)
> ---
>  blockdev.c       |  108 +++++++++++++++++++++++++++++++++++++++++++++++++++---
>  qapi-schema.json |   30 +++++++++++++++
>  qmp-commands.hx  |    8 ++++
>  3 files changed, 140 insertions(+), 6 deletions(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 07eafce..cd338ed 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -688,12 +688,101 @@ void qmp_block_passwd(const char *device, const char *password, Error **err)
>      qmp_set_blockdev_password(device, password, err);
>  }
>  
> +static void qmp_bdrv_open_encrypted(BlockDriverState *bs, const char *filename,
> +                                    int bdrv_flags, BlockDriver *drv,
> +                                    const char *password, Error **errp)
> +{
> +    if (bdrv_open(bs, filename, bdrv_flags, drv) < 0) {
> +        error_set(errp, QERR_OPEN_FILE_FAILED, filename);
> +        return;
> +    }
> +
> +    if (bdrv_key_required(bs)) {
> +        if (password) {
> +            if (bdrv_set_key(bs, password) < 0) {
> +                error_set(errp, QERR_INVALID_PASSWORD);
> +            }
> +        } else {
> +            error_set(errp, QERR_DEVICE_ENCRYPTED, bdrv_get_device_name(bs),
> +                      bdrv_get_encrypted_filename(bs));
> +        }
> +    } else if (password) {
> +        error_set(errp, QERR_DEVICE_NOT_ENCRYPTED, bdrv_get_device_name(bs));
> +    }
> +}
> +
> +void qmp_drive_change(const char *device, const char *filename,
> +                      bool has_format, const char *format,
> +                      bool has_password, const char *password,
> +                      Error **errp)
> +{
> +    BlockDriverState *bs, *bs1;
> +    BlockDriver *drv = NULL;
> +    int bdrv_flags;
> +    Error *err = NULL;
> +    bool probed_raw = false;
> +
> +    bs = bdrv_find(device);
> +    if (!bs) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
> +        return;
> +    }
> +
> +    if (has_format) {
> +        drv = bdrv_find_whitelisted_format(format);
> +        if (!drv) {
> +            error_set(errp, QERR_INVALID_BLOCK_FORMAT, format);
> +            return;
> +        }
> +    }
> +
> +    bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
> +    bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
> +
> +    if (!has_password) {
> +        password = NULL;
> +    }
> +
> +    /* Try to open once with a temporary block device to make sure that
> +     * the disk isn't encrypted and we lack a key.  This also helps keep
> +     * this operation as a transaction.  That is, if we fail, we try very
> +     * hard to make sure that the state is the same as before the operation
> +     * was started.
> +     */
> +    bs1 = bdrv_new("");
> +    qmp_bdrv_open_encrypted(bs1, filename, bdrv_flags, drv, password, &err);
> +    if (!has_format && bs1->drv->unsafe_probe) {
> +        probed_raw = true;
> +    }
> +    bdrv_delete(bs1);
> +
> +    if (err) {
> +        error_propagate(errp, err);
> +        return;
> +    }
> +
> +    if (probed_raw) {
> +        /* We will not auto probe raw files. */
> +        error_set(errp, QERR_MISSING_PARAMETER, "format");
> +        return;
> +    }

This has to be noted in the documentation.

> +
> +    eject_device(bs, 0, &err);
> +    if (err) {
> +        error_propagate(errp, err);
> +        return;
> +    }

Hm. I'm not wondering if this command isn't actually overloading two
distinct operations: eject and insert. Maybe what we want here is drive-insert?

> +
> +    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, drv, password, errp);
> +}
> +
>  int do_change_block(Monitor *mon, const char *device,
>                      const char *filename, const char *fmt)
>  {
>      BlockDriverState *bs;
>      BlockDriver *drv = NULL;
>      int bdrv_flags;
> +    Error *err = NULL;
>  
>      bs = bdrv_find(device);
>      if (!bs) {
> @@ -707,16 +796,23 @@ int do_change_block(Monitor *mon, const char *device,
>              return -1;
>          }
>      }
> -    if (eject_device(bs, 0, NULL) < 0) {
> -        return -1;
> -    }
> +
>      bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
>      bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
> -    if (bdrv_open(bs, filename, bdrv_flags, drv) < 0) {
> -        qerror_report(QERR_OPEN_FILE_FAILED, filename);
> +
> +    eject_device(bs, 0, &err);
> +    if (err) {
> +        qerror_report_err(err);
> +        return -1;
> +    }
> +
> +    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, drv, NULL, &err);
> +    if (err) {
> +        qerror_report_err(err);
>          return -1;
>      }
> -    return monitor_read_bdrv_key_start(mon, bs, NULL, NULL);
> +
> +    return 0;
>  }
>  
>  int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 0c6c9b8..cbb5bf1 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -124,3 +124,33 @@
>  #         settings may change after executing this command.
>  ##
>  { 'command': 'change-vnc-listen', 'data': {'target': 'str'} }
> +
> +##
> +# @drive-change:
> +#
> +# This is the preferred interface for changing a block device.
> +#
> +# @device:   The block device name.
> +#
> +# @filename: The new filename for the block device.  This may contain options
> +#            encoded in a format specified by @format.
> +#
> +# @format:   #optional The format to use open the block device
> +#
> +# @password: #optional The password to use if the block device is encrypted
> +#
> +# Returns:  Nothing on success.
> +#          If @device is not a valid block device, DeviceNotFound
> +#          If @format is not a valid block format, InvalidBlockFormat
> +#          If @filename is encrypted and @password isn't supplied,
> +#            DeviceEncrypted.  The call should be repeated with @password
> +#            supplied.
> +#          If @format is not specified and @filename is a format that cannot
> +#            be safely probed, MissingParameter.
> +#          If @filename cannot be opened, OpenFileFailed
> +#
> +# Since: 1.0
> +##
> +{ 'command': 'drive-change',
> +  'data': {'device': 'str', 'filename': 'str', '*format': 'str',
> +           '*password': 'str'} }
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 5cab212..623f158 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -121,6 +121,14 @@ EQMP
>          .mhandler.cmd_new = do_change,
>      },
>  
> +    {
> +        .name       = "drive-change",
> +        .args_type  = "device:B,filename:F,format:s?password:s?",
> +        .params     = "device filename [format] [password]",
> +        .help       = "change a removable medium, optional format",
> +        .mhandler.cmd_new = qmp_marshal_input_drive_change,
> +    },
> +
>  SQMP
>  change
>  ------