Re: [PATCH v2 6/7] block/copy-before-write: implement cbw-timeout option

[Hanna Reitz]

On 01.04.22 11:19, Vladimir Sementsov-Ogievskiy wrote:
> In some scenarios, when copy-before-write operations lasts too long
> time, it's better to cancel it.
>
> Most useful would be to use the new option together with
> on-cbw-error=break-snapshot: this way if cbw operation takes too long
> time we'll just cancel backup process but do not disturb the guest too
> much.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
> ---
>   block/copy-before-write.c | 6 +++++-
>   qapi/block-core.json      | 5 ++++-
>   2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/block/copy-before-write.c b/block/copy-before-write.c
> index 7ef3f9f4c1..0ea5506f77 100644
> --- a/block/copy-before-write.c
> +++ b/block/copy-before-write.c
> @@ -42,6 +42,7 @@ typedef struct BDRVCopyBeforeWriteState {
>       BlockCopyState *bcs;
>       BdrvChild *target;
>       OnCbwError on_cbw_error;
> +    uint32_t cbw_timeout_ns;
>   
>       /*
>        * @lock: protects access to @access_bitmap, @done_bitmap and
> @@ -107,7 +108,7 @@ static coroutine_fn int 
> cbw_do_copy_before_write(BlockDriverState *bs,
>       off = QEMU_ALIGN_DOWN(offset, cluster_size);
>       end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
>   
> -    ret = block_copy(s->bcs, off, end - off, true, 0);
> +    ret = block_copy(s->bcs, off, end - off, true, s->cbw_timeout_ns);
>       if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) {
>           return ret;
>       }
> @@ -412,6 +413,7 @@ static BlockdevOptionsCbw *cbw_parse_options(QDict 
> *options, Error **errp)
>        */
>       qdict_extract_subqdict(options, NULL, "bitmap");
>       qdict_del(options, "on-cbw-error");
> +    qdict_del(options, "cbw-timeout");
>   
>   out:
>       visit_free(v);
> @@ -455,6 +457,8 @@ static int cbw_open(BlockDriverState *bs, QDict *options, 
> int flags,
>       }
>       s->on_cbw_error = opts->has_on_cbw_error ? opts->on_cbw_error :
>               ON_CBW_ERROR_BREAK_GUEST_WRITE;
> +    s->cbw_timeout_ns = opts->has_cbw_timeout ?
> +        opts->cbw_timeout * NANOSECONDS_PER_SECOND : 0;
>   
>       bs->total_sectors = bs->file->bs->total_sectors;
>       bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 3f08025114..e077506e0f 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -4207,12 +4207,15 @@
>   # @on-cbw-error: Behavior on failure of copy-before-write operation.
>   #                Default is @break-guest-write. (Since 7.0)
>   #
> +# @cbw-timeout: Zero means no limit. Non-zero sets the timeout in seconds
> +#               for copy-before-write operation. Default 0. (Since 7.0)

*7.1, but:

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

> +#
>   # Since: 6.2
>   ##
>   { 'struct': 'BlockdevOptionsCbw',
>     'base': 'BlockdevOptionsGenericFormat',
>     'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap',
> -            '*on-cbw-error': 'OnCbwError' } }
> +            '*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32' } }
>   
>   ##
>   # @BlockdevOptions: