Re: [PATCH 1/2] QSLIST: add atomic replace operation

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Aug 24, 2020 at 12:31:20PM +0800, wanghonghao wrote:
> Replace a queue with another atomicly. It's useful when we need to transfer
> queues between threads.
> 
> Signed-off-by: wanghonghao <wanghonghao@bytedance.com>
> ---
>  include/qemu/queue.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/qemu/queue.h b/include/qemu/queue.h
> index 456a5b01ee..a3ff544193 100644
> --- a/include/qemu/queue.h
> +++ b/include/qemu/queue.h
> @@ -226,6 +226,10 @@ struct {                                                                \
>          (dest)->slh_first = atomic_xchg(&(src)->slh_first, NULL);        \
>  } while (/*CONSTCOND*/0)
>  
> +#define QSLIST_REPLACE_ATOMIC(dest, src) do {                                 \
> +        (src)->slh_first = atomic_xchg(&(dest)->slh_first, (src)->slh_first); \
> +} while (/*CONSTCOND*/0)

This is atomic for dest but not src.

Maybe the name should make this clear: QSLIST_REPLACE_ATOMIC_DEST().

Please also add a doc comment mentioning that the modification to src is
not atomic.

Stefan

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