Re: [PATCH v11 08/13] copy-on-read: add support for BDRV_REQ_PREFETCH to COR-filter

[Max Reitz]

On 12.10.20 19:43, Andrey Shinkevich wrote:
> Add support for the BDRV_REQ_PREFETCH flag to the supported_write_flags

s/write/read/

> of the COR-filter.
> 
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> ---
>  block/copy-on-read.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/block/copy-on-read.c b/block/copy-on-read.c
> index dfbd6ad..b136895 100644
> --- a/block/copy-on-read.c
> +++ b/block/copy-on-read.c
> @@ -50,6 +50,7 @@ static int cor_open(BlockDriverState *bs, QDict *options, 
> int flags,
>          return -EINVAL;
>      }
>  
> +    bs->supported_read_flags = BDRV_REQ_PREFETCH;
>      bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
>          (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);

Then we mustn’t let cor_co_preadv_part() pass the flag on to
bdrv_co_preadv_part() unless BDRV_REQ_COPY_ON_READ is set, too.  I
suspect the following patch is going to do that, but in the meantime the
code is wrong.

Perhaps just swap both patches?

And by the way, I’m also missing a patch that makes the block layer
evaluate supported_read_flags and e.g. strip BDRV_REQ_PREFETCH if it
isn’t supported, before it gets passed to such a block driver.

Max

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