Re: [Qemu-devel] [PATCH v2 1/5] range: add Range structure

[Hu Tao <hutao@cn.fujitsu.com>]

On Thu, May 30, 2013 at 02:07:16PM +0300, Michael S. Tsirkin wrote:
> Sometimes we need to pass ranges around, add a
> handy structure for this purpose.
> 
> Note: memory.c defines its own concept of AddrRange structure for
> working with 128 addresses.  It's necessary there for doing range math.
> This is not needed for most users: struct Range is
> much simpler, and is only used for passing the range around.
> 
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  include/qemu/range.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/include/qemu/range.h b/include/qemu/range.h
> index 3502372..b76cc0d 100644
> --- a/include/qemu/range.h
> +++ b/include/qemu/range.h
> @@ -1,6 +1,22 @@
>  #ifndef QEMU_RANGE_H
>  #define QEMU_RANGE_H
>  
> +#include <inttypes.h>
> +
> +/*
> + * Operations on 64 bit address ranges.
> + * Notes:
> + *   - ranges must not wrap around 0, but can include the last byte ~0x0LL.
> + *   - this can not represent a full 0 to ~0x0LL range.
> + */
> +
> +/* A structure representing a range of addresses. */
> +struct Range {
> +    uint64_t begin; /* First byte of the range, or 0 if empty. */

I don't understand, can't a range start from 0?

> +    uint64_t end;   /* 1 + the last byte. 0 if range empty or ends at ~0x0LL. */

How to tell from the two? Instead I suggest this be a length field,
whereas 0 means empty.

> +};
> +typedef struct Range Range;
> +
>  /* Get last byte of a range from offset + length.
>   * Undefined for ranges that wrap around 0. */
>  static inline uint64_t range_get_last(uint64_t offset, uint64_t len)
> -- 
> MST
>