Re: [PATCH v11 05/13] copy-on-read: limit COR operations to base in COR driver
On 14.10.2020 15:01, Max Reitz wrote:
On 12.10.20 19:43, Andrey Shinkevich wrote:
> Limit COR operations by the base node in the backing chain when the
> overlay base node name is given. It will be useful for a block stream
> job when the COR-filter is applied. The overlay base 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(a)virtuozzo.com>
> ---
> block/copy-on-read.c | 39 +++++++++++++++++++++++++++++++++++++--
> 1 file changed, 37 insertions(+), 2 deletions(-)
>
> diff --git a/block/copy-on-read.c b/block/copy-on-read.c
> index c578b1b..dfbd6ad 100644
> --- a/block/copy-on-read.c
> +++ b/block/copy-on-read.c
> @@ -122,8 +122,43 @@ static int coroutine_fn cor_co_preadv_part(BlockDriverState
*bs,
> size_t qiov_offset,
> int flags)
> {
[...]
> + ret =
bdrv_is_allocated_above(bdrv_cow_bs(bs->file->bs),
> + state->base_overlay, true, offset,
> + n, &n);
> + if (ret) {
> + local_flags |= BDRV_REQ_COPY_ON_READ;
> + }
> + }
Furthermore, I just noticed – can the is_allocated functions not return
0 in @n, when @offset is a the EOF? Is that something to look out for?
(I’m not sure.)
Max
The check for EOF is managed earlier in the stream_run() for a
block-stream job. For other cases of using the COR-filter, the check for
EOF can be added to the cor_co_preadv_part().
I would be more than happy if we can escape the duplicated checking for
is_allocated in the block-stream. But how the stream_run() can stop
calling the blk_co_preadv() when EOF is reached if is_allocated removed
from it? May the cor_co_preadv_part() return EOF (or other error code)
to be handled by a caller if (ret == 0 && n == 0 && (flags &
BDRV_REQ_PREFETCH)?
Andrey