Re: [PATCH v3 2/7] block/copy-before-write: add on-cbw-error open parameter

[Hanna Reitz]

On 06.04.22 20:07, Vladimir Sementsov-Ogievskiy wrote:
> Currently, behavior on copy-before-write operation failure is simple:
> report error to the guest.
>
> Let's implement alternative behavior: break the whole copy-before-write
> process (and corresponding backup job or NBD client) but keep guest
> working. It's needed if we consider guest stability as more important.
>
> The realisation is simple: on copy-before-write failure we set
> s->snapshot_ret and continue guest operations. s->snapshot_ret being
> set will lead to all further snapshot API requests. Note that all
> in-flight snapshot-API requests may still success: we do wait for them
> on BREAK_SNAPSHOT-failure path in cbw_do_copy_before_write().
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
> ---
>   qapi/block-core.json      | 25 ++++++++++++++++++++++++-
>   block/copy-before-write.c | 32 ++++++++++++++++++++++++++++++--
>   2 files changed, 54 insertions(+), 3 deletions(-)
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index beeb91952a..085f1666af 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json

[...]

> @@ -4184,11 +4203,15 @@
>   #          modifications (or removing) of specified bitmap doesn't
>   #          influence the filter. (Since 7.0)
>   #
> +# @on-cbw-error: Behavior on failure of copy-before-write operation.
> +#                Default is @break-guest-write. (Since 7.0)

With *7.1:

Reviewed-by: Hanna Reitz <hreitz@redhat.com>

> +#
>   # Since: 6.2
>   ##
>   { 'struct': 'BlockdevOptionsCbw',
>     'base': 'BlockdevOptionsGenericFormat',
> -  'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap' } }
> +  'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap',
> +            '*on-cbw-error': 'OnCbwError' } }
>   
>   ##
>   # @BlockdevOptions: