[dm-devel] [PATCH RFC 4/7] block: define blk_qc_t as uintptr_t

[Mike Snitzer]

On Wed, Dec 23 2020 at  6:26am -0500,
Jeffle Xu <jefflexu at linux.alibaba.com> wrote:

> To support iopoll for bio-based device, the returned cookie is actually
> a pointer to an implementation specific object, e.g. an object
> maintaining all split bios.
> 
> In such case, blk_qc_t should be large enough to contain one pointer,
> for which uintptr_t is used here. Since uintptr_t is actually an integer
> type in essence, there's no need of type casting in the original mq
> path, while type casting is indeed needed in bio-based routine.
> 
> Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>
> ---
>  include/linux/types.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/types.h b/include/linux/types.h
> index da5ca7e1bea9..f6301014a459 100644
> --- a/include/linux/types.h
> +++ b/include/linux/types.h
> @@ -126,7 +126,7 @@ typedef u64 sector_t;
>  typedef u64 blkcnt_t;
>  
>  /* cookie used for IO polling */
> -typedef unsigned int blk_qc_t;
> +typedef uintptr_t blk_qc_t;
>  
>  /*
>   * The type of an index into the pagecache.

I'd just fold this into patch 6.. not seeing benefit to having this be
separate.

Patch 6's header needs a lot more detail anyway so..