Re: [PATCH v12 07/14] copy-on-read: limit COR operations to bottom node

[Vladimir Sementsov-Ogievskiy]

22.10.2020 21:13, Andrey Shinkevich wrote:
> Limit COR operations to the bottom node (inclusively) in the backing
> chain when the bottom node name is given. It will be useful for a block
> stream job when the COR-filter is applied. The bottom node is passed as
> the base itself may change due to concurrent commit jobs on the same
> backing chain.
>
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> ---
>   block/copy-on-read.c | 42 ++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/block/copy-on-read.c b/block/copy-on-read.c
> index 3d8e4db..8178a91 100644
> --- a/block/copy-on-read.c
> +++ b/block/copy-on-read.c
> @@ -123,8 +123,46 @@ 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;

no need to initialize n actually.

> +    int local_flags;
> +    int ret;
> +    BDRVStateCOR *state = bs->opaque;
> +
> +    if (!state->bottom_bs) {
> +        return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
> +                                   flags | BDRV_REQ_COPY_ON_READ);
> +    }
> +
> +    while (bytes) {
> +        local_flags = flags;
> +
> +        /* In case of failure, try to copy-on-read anyway */
> +        ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
> +        if (!ret || ret < 0) {

simper: if (ret <= 0) {

> +            ret = 
> bdrv_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
> +                                          state->bottom_bs, true, offset,
> +                                          n, &n);
> +            if (ret == 1 || ret < 0) {
> +                local_flags |= BDRV_REQ_COPY_ON_READ;
> +            }
> +            /* Finish earlier if the end of a backing file has been reached */
> +            if (ret == 0 && n == 0) {

"n == 0" should be enough

> +                break;
> +            }
> +        }
> +
> +        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;
>   }
>   

My remarks are minor, so:
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

And yes, I still think that this is good to be merged with two previous patches.


--
Best regards,
Vladimir