Re: [PATCH v10 5/9] copy-on-read: limit guest COR activity to base in COR driver

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

29.09.2020 15:38, Andrey Shinkevich wrote:
> Limit the guest's COR operations by the base node in the backing chain
> when the base node name is given. It will be useful for a block stream
> job when the COR-filter is applied.
> 
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> ---
>   block/copy-on-read.c | 38 ++++++++++++++++++++++++++++++++++++--
>   1 file changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/block/copy-on-read.c b/block/copy-on-read.c
> index e04092f..f53f7e0 100644
> --- a/block/copy-on-read.c
> +++ b/block/copy-on-read.c
> @@ -121,8 +121,42 @@ static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs,
>                                              size_t qiov_offset,
>                                              int flags)
>   {
> -    return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
> -                               flags | BDRV_REQ_COPY_ON_READ);
> +    int64_t n = 0;
> +    int64_t size = offset + bytes;
> +    int local_flags;
> +    int ret;
> +    BDRVStateCOR *state = bs->opaque;
> +
> +    if (!state->base_bs) {
> +        return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
> +                                   flags | BDRV_REQ_COPY_ON_READ);
> +    }
> +
> +    while (offset < size) {
> +        local_flags = flags;
> +
> +        /* In case of failure, try to copy-on-read anyway */

But you add the flag only in case of success.. On any failure of furhter is*allocated calls we should set the flag.

> +        ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
> +        if (!ret) {
> +            ret = bdrv_is_allocated_above(bdrv_cow_bs(bs->file->bs),
> +                                          state->base_bs, false, offset, n, &n);
> +            if (ret > 0) {
> +                local_flags |= BDRV_REQ_COPY_ON_READ;
> +            }
> +        }
> +
> +        ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
> +                                  local_flags);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +
> +        offset += n;
> +        qiov_offset += n;
> +        bytes -= n;
> +    }
> +
> +    return 0;
>   }
>   
>   
> 


-- 
Best regards,
Vladimir