Re: [Qemu-block] [Qemu-devel] [PATCH] block/rbd: add .bdrv_reopen_prepare() stub

[Jason Dillaman]

On Tue, May 17, 2016 at 6:03 AM, Sebastian Färber <address@hidden> wrote:
> Hi Kevin,
>
>> A correct reopen implementation must consider all options and flags that
>> .bdrv_open() looked at.
>>
>> The options are okay, as both "filename" and "password-secret" aren't
>> things that we want to allow a reopen to change. However, in the flags
>> BDRV_O_NOCACHE makes a difference:
>>
>>     if (flags & BDRV_O_NOCACHE) {
>>         rados_conf_set(s->cluster, "rbd_cache", "false");
>>     } else {
>>         rados_conf_set(s->cluster, "rbd_cache", "true");
>>     }
>>
>> A reopen must either update the setting, or if it can't (e.g. because
>> librbd doesn't support it) any attempt to change the flag must fail.
>
> Thanks for the feedback.
> As far as i can tell it's not possible to update the cache settings
> without reconnecting. I've added a check in the following patch.
> Would be great if someone who knows the internals of ceph/rbd could
> have a look as well.

Correct, you cannot currently dynamically enable nor disable the
cache.  You would need to close the image and re-open it to change the
cache settings.

> Sebastian
>
> -- >8 --
> Subject: [PATCH] block/rbd: add .bdrv_reopen_prepare() stub
>
> Add support for reopen() by adding the .bdrv_reopen_prepare() stub
>
> Signed-off-by: Sebastian Färber <address@hidden>
> ---
>  block/rbd.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 5bc5b32..8ecf096 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -577,6 +577,19 @@ failed_opts:
>      return r;
>  }
>
> +/* Note that this will not re-establish a connection with the Ceph cluster
> +   - it is effectively a NOP.  */
> +static int qemu_rbd_reopen_prepare(BDRVReopenState *state,
> +                                   BlockReopenQueue *queue, Error **errp)
> +{
> +    if (state->flags & BDRV_O_NOCACHE &&
> +        ((state->bs->open_flags & BDRV_O_NOCACHE) == 0)) {
> +        error_setg(errp, "Cannot turn off rbd_cache during reopen");
> +        return -EINVAL;
> +    }
> +    return 0;
> +}
> +
>  static void qemu_rbd_close(BlockDriverState *bs)
>  {
>      BDRVRBDState *s = bs->opaque;
> @@ -976,6 +989,7 @@ static BlockDriver bdrv_rbd = {
>      .instance_size      = sizeof(BDRVRBDState),
>      .bdrv_needs_filename = true,
>      .bdrv_file_open     = qemu_rbd_open,
> +    .bdrv_reopen_prepare = qemu_rbd_reopen_prepare,
>      .bdrv_close         = qemu_rbd_close,
>      .bdrv_create        = qemu_rbd_create,
>      .bdrv_has_zero_init = bdrv_has_zero_init_1,
> --
> 1.8.3.1
>
>



-- 
Jason